Alain Varray
email: alain.varray@umontpellier.fr

Improving Health Status Through Physical Activity for Individuals with Chronic Pulmonary Diseases: Theory to Practice

The aim of this paper is to show how pertinent pathophysiological bases have been built for physical activity prescription for individuals with obstructive pulmonary disease (asthma and chronic obstructive pulmonary disease). The pathophysiological bases were constructed by taking into account exercise mismatching, which was analysed in terms of both short-and long-term impact on disease outcome. Specific exercise adaptations based on a keen understanding of the underlying physiological processes provided the key to an adapted intervention with well-defined exercise program aims. The results that were achieved are striking, and one might conclude that sometimes exercise is simply the best way to improve the general well-being of individuals with chronic disease. Since this is a major concern for health professionals and chronically ill individuals, physical activity offers a means to rise to this challenge.

 Physical Activity, Chronic Disease and HealthThe interaction between exercise and health is now evident, and the amount of scientific information amassed on this topic is considerable. We have numerous examples in the literature of regular exercise being a powerful means to counter functional deterioration due to sedentary living. Most of the time, this concept is applied to healthy individuals, but the issue becomes much more complicated when exercise is proposed for individuals with chronic disease, especially when the disease implies a sharp reduction in exercise tolerance. The use of physical activity in chronic disease states is quite recent. Originally, the intention was to disprove the long-held conviction that physical activity is contraindicated in chronic disease states. This first step was essentially driven by a humanistic concern and we owe much to the work of several pioneers [START_REF] Bar-Or | Pediatric Sports Medicine for the Practitioner[END_REF][START_REF] Shephard | Training and the respiratory system: therapy for asthma and other obstructive lung diseases[END_REF]Shephard, , 1884)). We are currently undergoing a tremendous shift in thinking, and exercise prescription is increasingly viewed as an efficient means to manage disease. This change is truly surprising because, in cases of chronic disease states, physical activity is never intuitively accepted. [START_REF] Bar-Or | Pediatric Sports Medicine for the Practitioner[END_REF] was one of the first scientists to model the dynamic between a chronic disease state and subsequent functional deterioration (Figure 1). With chronic illness, the habitual level of activity is often decreased and the resulting deconditioning reinforces hypoactivity. For a long time, this vicious circle of hypoactivity was only considered as deleterious for "normal" individuals. Today, however, we have indisputable evidence of the aggravating consequences of hypoactivity on the disease process itself. We thus might logically assume that acceptance of physical activity is a given. Unfortunately, however, this is not the case because in chronic disease states, a strange paradox occurs: From a longterm perspective, the positive effects of physical activity have been supported by a number of studies (ACCP AACVPR Pulmonary Rehabilitation Guidelines Panel, 1997;[START_REF] Bak | Insulin receptor function and glycogen synthase activity in skeletal muscle biopsies from patients with insulindependent diabetes mellitus: effects of physical training[END_REF][START_REF] Varray | Importance of physical exercise training in asthmatics[END_REF]) but because of short-term fears experienced by the patients during exercise, physical activity will often be avoided and the long-term effects are thus never attained (see some typical examples in Table 1). The main challenge today is therefore to determine how this paradox can be resolved. In our experience, a powerful solution is suggested by a careful response to the following questions:

-why should exercise training be proposed? In other words, we need to know the specific goals to be achieved in a very precise pathology; Physical Activity, Chronic Disease and Health We ask these three questions because experience has taught us that we cannot consider implementing any physical activity program without first defining its pathophysiological bases. These bases must be built from precise knowledge of the physiological exercise impairments encountered in specific pathological states, and by a thorough analysis of their short-or long-term consequences for the individuals.

Thus, the aim of this paper is to examine the issues that have limited the acceptance of physical activity by drawing on our experience with children and adults with pulmonary diseases. The second aim is to demonstrate how improved knowledge of exercise adaptations has resulted in some specific justifications for physical activity and a more relevant understanding of final activity aims. Last, we will present how applied research has provided data showing the efficacy of physical activity adapted to individuals with respiratory illness.

Bronchial asthma: from exercise adaptations to pathophysiological justification of exercise training

Asthma is defined as a "clinical syndrome characterized by reversible obstruction to airflow and increased bronchial responsiveness to a variety of stimuli both allergic and environmental" [START_REF] Mannino | Chronic obstructive pulmonary disease surveillance--United States, 1971-2000[END_REF]. Asthma is a very common disease and, unfortunately, despite improvements in disease management, its prevalence and severity are rising in industrial countries [START_REF] Basagana | Socioeconomic status and asthma prevalence in young adults: the European Community Respiratory Health Survey[END_REF][START_REF] Rees | ABC of asthma. Prevalence[END_REF]. Consistent with its definition, asthma is characterized by an abnormal bronchial responsiveness to various stimuli, among them exercise. For many years, exercise was contraindicated because of a particular manifestation of the disease called exercise-induced asthma (EIA). The typical expression of EIA is a drop in respiratory function, which can be maximal within the first 15 minutes following intense exercise, and during which the subject wheezes and feels dyspnea. For many years, EIA was considered as an exacerbation of asthma directly attributed to Physical Activity, Chronic Disease and Health exercise. The studies on EIA led to two major findings: 1) EIA is not due to exercise but to hyperventilation [START_REF] Bundgaard | The importance of ventilation in exercise-induced asthma[END_REF] and 2) the pathophysiological pathways of EIA are not the same as in a classical asthma attack since bronchial hyperosmolarity is still considered to be mainly implicated [START_REF] Anderson | The mechanism of exercise-induced asthma is[END_REF]. As a consequence, the name "exercise-induced bronchospasm" (EIB) is now preferred because of its higher pathophysiological relevance. The link between exercise hyperventilation and physical fitness is so important that we must first fully understand the exercise cardiorespiratory adaptations in terms of exercise tolerance, sensitivity to EIB, and the role played by asthma severity in the adjustment to exercise, in order to conclude on the relevant pathophysiological bases for APA in asthma. Today, despite some controversy in the literature due to a lack of direct control groups, we have evidence that both anaerobic [START_REF] Counil | Anaerobic fitness in children with asthma: adaptation to maximal intermittent short exercise[END_REF][START_REF] Counil | Wingate test performance in children with asthma: aerobic or anaerobic limitation[END_REF] and aerobic fitness [START_REF] Clark | Assessment of work performance in asthma for determination of cardiorespiratory fitness and training capacity[END_REF][START_REF] Freeman | The effect of endurance running training on asthmatic adults[END_REF][START_REF] Varray | Cardiac role in exercise limitation in asthmatic subjects with special reference to disease severity[END_REF] are appreciably lower in individuals with asthma. From a pathophysiological point of view, the decreased aerobic fitness is troublesome. Moreover, hypoactivity cannot entirely explain these differences in comparison with normal populations, since in some studies the asthmatics were normally active. In contrast, we have shown that altered aerobic fitness is linked to the degree of airway obstruction (Varray, Mercier, Ramonatxo, & Prefaut, 1989) and is mainly explained by low cardiac output [START_REF] Varray | Cardiac role in exercise limitation in asthmatic subjects with special reference to disease severity[END_REF]. The consequences of these limitations must be taken into account because low aerobic fitness in childhood can have a deep impact on functional capacity and the risk of an abnormally sedentary lifestyle is high. In asthmatic individuals, this risk is reinforced because of the breathlessness experienced during exercise, which leads naturally to negative attitudes toward exercise.

Another exercise misadaptation in asthmatics is an obvious excessive hyperventilation for a given workload [START_REF] Chryssanthopoulos | An assessment of cardiorespiratory adjustments of asthmatic adults to exercise[END_REF]. With our improved understanding of EIB pathophysiology, we now know that any increase in minute ventilation is a potent stimulus to EIB, whatever the exact nature of the underlying mechanism [Hyperosmolarity due to respiratory water loss [START_REF] Sheppard | Respiratory water loss as a stimulus to exerciseinduced bronchoconstriction[END_REF] or associated vascular events [START_REF] Ichinose | A neurokinin 1-receptor antagonist improves exercise-induced airway narrowing in asthmatic patients[END_REF][START_REF] Mcfadden | Hypothesis: exercise-induced asthma as a vascular phenomenon[END_REF]]. Fortunately, asthmatics can reduce this risk by a specific exercise adaptation: exercise-induced bronchodilation [START_REF] Haas | Effect of aerobic training on forced expiratory airflow in exercising asthmatic humans[END_REF]Haas, Pineda, 6 Physical Activity, Chronic Disease and Health this "protective" reaction occurs only if aerobic fitness is good enough. Thus, the need to improve physical fitness is all the more important, and the presence of EIB can no longer be used to justify the avoidance of physical activity. Indeed, with a sedentary lifestyle, aerobic fitness will progressively decrease and the exercise bronchodilation will disappear, resulting in an even lower exercise tolerance with regard to EIB.

A less well known result is that hyperventilation is linked to decreased cardiac output due to heartlung interactions. Indeed, a strong relationship has been obtained between submaximal stroke volume and level of hyperventilation during an incremental exercise in asthmatics [START_REF] Varray | Cardiac role in exercise limitation in asthmatic subjects with special reference to disease severity[END_REF]. This phenomenon can be explained by abnormal end expiratory lung volume with important consequences for cardiac efficiency [START_REF] Babb | Effect of mild-tomoderate airflow limitation on exercise capacity[END_REF][START_REF] Varray | Cardiac role in exercise limitation in asthmatic subjects with special reference to disease severity[END_REF]. Again, the negative impact of hyperventilation levels must be underlined in addition to the previous effects on EIB risk.

In summary, the main hurdle to exercise in asthmatics is always EIB, especially when asthma is severe. However, an understanding of the specific asthmatic exercise adaptations provides convincing arguments for the use of exercise training as a means to improve patients' well-being and quality of life. By understanding these adaptations, appropriate pathophysiological aims for adapted physical activity can be defined, as these aims are very closely based on the concrete impairments encountered in asthma. The first aim is to improve aerobic fitness, because this is a very powerful means to counter the functional deterioration that leads to an inactive lifestyle and its subsequent problems, and to improve the exercise bronchodilation in order to reduce EIB risk. The second and probably the more important goal is to reduce excessive hyperventilation to reduce: 1) the unpleasant feeling of breathlessness during exercise that is at the root of the negative attitudes toward exercise, 2) the potent risk of EIB, and 3) the cardiovascular alteration mediated by excessive ventilation requirement.

Last, because asthma severity plays an important role in impaired exercise adaptation, the physical activity intensities must be carefully individualized to the true exercise capacity of each asthmatic [START_REF] Varray | Importance of physical exercise training in asthmatics[END_REF]. This is the only way to ensure efficient training procedures and to reach the above pathophysiological goals.

Chronic Obstructive Pulmonary Disease (COPD): from lung to muscle Physical Activity, Chronic Disease and Health COPD is defined as a "preventable and treatable disease state characterised by airflow limitation that is not fully reversible. The airflow limitation is usually progressive and is associated with an abnormal inflammatory response of the lungs to noxious particles or gases, primarily caused by cigarette smoking " (Celli & MacNee, 2004, p. 933). COPD is a leading cause of morbidity and mortality worldwide, and the social and economic burden is both substantial and increasing. Despite a systematic underestimation (the disease is difficult to identify until it becomes clinically apparent), COPD is increasingly prevalent and fatal [START_REF] Mannino | Chronic obstructive pulmonary disease surveillance--United States, 1971-2000[END_REF]. Two studies project that mortality due to COPD will rise from 6 th place in 1990 to 3 rd place in 2020 [START_REF] Murray | Alternative projections of mortality and disability by cause 1990-2020: Global Burden of Disease Study[END_REF][START_REF] Stang | The prevalence of COPD: using smoking rates to estimate disease frequency in the general population[END_REF]. From a clinical point of view, COPD is characterized by a progressive and permanent airflow limitation due to bronchial obstruction. At the last stage of the disease, respiratory failure can occur, which then requires long-term oxygen therapy. The major symptom of the disease is dyspnea, which can be experienced during any daily activity (walking, getting dressed, eating, and so on). The obvious consequences will be a sharp drop in the quality of life and poor social interactions [START_REF] Scharloo | Physical and psychological correlates of functioning in patients with chronic obstructive pulmonary disease[END_REF], abnormal levels of depression [START_REF] Kunik | Surprisingly high prevalence of anxiety and depression in chronic breathing disorders[END_REF][START_REF] Mikkelsen | Anxiety and depression in patients with chronic obstructive pulmonary disease (COPD). A review[END_REF]Wagena, Arrindell, Wouters, & can Schayck, 2005), and a clear exercise intolerance (Carter, Holiday, Stocks, & Teip, 2003;[START_REF] Oga | Exercise capacity deterioration in patients with COPD: longitudinal evaluation over 5 years[END_REF][START_REF] Prefaut | Pathophysiological bases of exercise training in patients with chronic obstructive lung disease[END_REF]. Originally, physical training for individuals with COPD was thought to be without justification for two main reasons. The first was directly linked to the presence of dyspnea even in resting conditions: any exercise was assumed to be detrimental because of dyspnea worsening. The second was more closely related to the fact that COPD is an obstructive disease: it was widely believed (no longer the case) that the only way to improve patients was to increase lung function, which is not possible with exercise training. Thus, exercise training was considered to be really difficult to manage or even absolutely irrelevant.

Fortunately, over the past ten years, the many studies on the COPD/exercise interface have completely modified our concept of the disease. Among the major changes, COPD is no longer considered an isolated respiratory disease, but as a systemic disease with the lung as a starting point.

The systemic repercussions of the disease have thus been increasingly studied [START_REF] Agusti | Systemic effects of chronic obstructive pulmonary disease[END_REF], and it now seems evident that exercise tolerance is not directly linked to the severity of bronchial obstruction, but is mainly affected by peripheral factors, among which muscle function plays a central Physical Activity, Chronic Disease and Health role. For example, it is well known that muscle dysfunction occurs during exercise even without a problem in oxygen supply (Gosselin et al., 2003;[START_REF] Maltais | Metabolic and hemodynamic responses of lower limb during exercise in patients with COPD[END_REF][START_REF] Maltais | Effects of oxygen on lower limb blood flow and O2 uptake during exercise in COPD[END_REF][START_REF] Simon | Limitation of lower limb VO(2) during cycling exercise in COPD patients[END_REF]. The implication of muscle function in COPD exercise tolerance, quality of life and survival rates is probably one of the most striking discoveries of the research into the disease and its management. The data are quite recent, and their importance is well summarized by the amazing title of one editorial published in a leading review in the field: "COPD as a muscle disease" [START_REF] Reid | COPD as a muscle disease[END_REF].

As a consequence, the focus on the unique link between lung function and exercise tolerance has become irrelevant. On the contrary, if dyspnea can be related to impaired muscle function, exercise training becomes a powerful tool for decreasing exercise dyspnea because of its known effect on the ventilatory requirement. The major challenge of the last few years has thus been to prove that muscle function abnormalities can be responsible for excessive dyspnea.

COPD muscle presents both quantitative and qualitative abnormalities. The muscle mass is sharply reduced [START_REF] Baarends | Peak exercise response in relation to tissue depletion in patients with chronic obstructive pulmonary disease[END_REF]. The fiber typology is also modified in comparison with that of non-COPD individuals, with an important reduction in oxidative fibers (type I) and an increased proportion of fast fatiguing glycolytic fibers (type IIb) [START_REF] Whittom | Histochemical and morphological characteristics of the vastus lateralis muscle in patients with chronic obstructive pulmonary disease[END_REF]. The enzymatic equipment is characterized by the decreased activity of several oxidative enzymes such as citrate synthetase, 3-hydroxyacyl CoA dehydrogenase [START_REF] Maltais | Oxidative capacity of the skeletal muscle and lactic acid kinetics during exercise in normal subjects and in patients with COPD[END_REF] and the preserved activity of glycolytic enzymes like lactate dehydrogenase (LDH) and phosphofructokinase (PFK). Because of the above, several consequences are easy to understand: maximal force will be decreased [START_REF] Gosselink | Peripheral muscle weakness contributes to exercise limitation in COPD[END_REF], as will muscle endurance, even in localized exercise-that is, even without reaching the subject's ventilatory limits [START_REF] Serres | Impaired skeletal muscle endurance related to physical inactivity and altered lung function in COPD patients[END_REF].

Cardiorespiratory fitness is sharply reduced [START_REF] Serres | Impaired skeletal muscle endurance related to physical inactivity and altered lung function in COPD patients[END_REF][START_REF] Vallet | Intérêt du réentraînement à l'effort individualisé, au niveau du seuil ventilatoire, au cours de la bronchopneumopathie chronique obstructive de sévérité modérée[END_REF]) and significant muscle dysfunction occurs during the onset of incremental exercise characterized by a drop in muscle excitability (Gosselin et al., 2003). More qualitatively, excessive anaerobic contribution is exhibited by COPD patients from the beginning of any general [START_REF] Maltais | Metabolic and hemodynamic responses of lower limb during exercise in patients with COPD[END_REF] or localized exercise [START_REF] Wuyam | Metabolism and aerobic capacity of skeletal muscle in chronic respiratory failure related to chronic obstructive pulmonary disease[END_REF]. It is worth noting that in both types of exercise, this anaerobic contribution occurs prior to any impairment in the muscle oxygen supply. Because of an excessive anaerobic contribution for a given exercise intensity, lactic acid production will lead to excessive H + concentration in the muscle and then in the blood. The intervention of the buffering Physical Activity, Chronic Disease and Health system (NaHCO3 -) will rapidly produce excessive CO 2 . A short time later, when the buffering system is exceeded, metabolic acidosis occurs [START_REF] Maltais | Metabolic and hemodynamic responses of lower limb during exercise in patients with COPD[END_REF]. Both CO 2 production and acidosis (via carotid body stimulation) are potent stimuli of respiratory centers. These findings describe the direct link between muscle dysfunction and dyspnea, despite the apparent independence between respiratory impairment and muscle structure, since excessive hyperventilation for a given exercise intensity will increase dyspnea in COPD. In addition, an understanding of the metabolic pathways provides insight into why dyspnea may progressively increase, even with stable disease, because of deconditioning effects on muscle function. This has been described by the concept of the dyspnea spiral [see Figure 2 ( [START_REF] Prefaut | Pathophysiological bases of exercise training in patients with chronic obstructive lung disease[END_REF]], which assumes that dyspnea in COPD is first experienced at maximal exercise intensity. As a consequence, spontaneous activity will be decreased to avoid any situation in which dyspnea might reoccur. The deconditioning effects will be a decreased aerobic participation in ATP synthesis during exercise, counteracted by increased anaerobic involvement. The respiratory centers will be more stimulated by extra CO 2 production and/or acidosis and the dyspnea will increasingly be felt for lower exercise intensities, independently of any disease worsening. The same causes will produce comparable effects, and daily physical activity will progressively be reduced, with worsening effects on muscle function and anaerobic metabolism contribution for a given exercise level, and exacerbation of dyspnea for lower and lower exercise intensities. Thus, dyspnea is no longer considered as a unique manifestation of the respiratory impairment due to COPD, but is instead seen as an interface between the prime pathology (bronchial obstruction) and a true secondary pathology typified by muscle dysfunction. The use of exercise training is thus more relevant than it was thought to be in the past. Moreover, this insight into the relationship between muscle dysfunction and dyspnea is an illustration of one of the pathophysiological bases for retraining programs in COPD: we need to improve muscle function, and especially its aerobic capacity, to be able to lower ventilatory center drive and thus to reduce dyspnea by decreased anaerobic contribution for any given exercise level, even if the severity of the pathology remains (unfortunately) unchanged. The impact of these bases is tremendous, because they provide a striking opportunity to combat the major symptom of the disease.

Thanks to physical activity prescription based on solid pathophysiological understanding, hope of an improved quality of life can now be offered to individuals with chronic illnesses. Physical Activity, Chronic Disease and Health It is important to note that the exact factors that cause skeletal muscle dysfunction in COPD are for the most part unknown. Although it seems evident that a sedentary lifestyle plays an important role (Goris, Vermeeren, Wouters, Schols, & Weserterp, 2003;[START_REF] Pitta | Characteristics of physical activities in daily life in chronic obstructive pulmonary disease[END_REF], there are several reasons to think that inactivity, albeit an important element, is not the only factor responsible for this dysfunction, especially the finding that training programs fail to totally normalize this dysfunction (Troosters, Casaburi, Gooselink, & Decramer, 2005). Several studies have provided strong arguments in favor of systemic inflammation as a mechanism for the development of muscle weakness and muscle apoptosis [START_REF] Debigare | Catabolic/anabolic balance and muscle wasting in patients with COPD[END_REF][START_REF] Spruit | Muscle force during an acute exacerbation in hospitalised patients with COPD and its relationship with CXCL8 and IGF-I[END_REF]. Recently, muscle oxidative stress was described during rest and exercise in COPD [START_REF] Heunks | Xanthine oxidase is involved in exercise-induced oxidative stress in chronic obstructive pulmonary disease[END_REF], even during localized exercise (Couillard, Keochlin, Cristol, Varray, & Prefaut, 2002;[START_REF] Couillard | Exercise-induced quadriceps oxidative stress and peripheral muscle dysfunction in patients with chronic obstructive pulmonary disease[END_REF]. The consequences of oxidative stress on lipid membrane and proteins are numerous and are strongly implicated in exercise intolerance [START_REF] Koechlin | Does oxidative stress alter quadriceps endurance in chronic obstructive pulmonary disease?[END_REF]. Another potential factor is related to the angiotensin-converting enzyme genotype in COPD, which would explain the large difference in quadriceps force [START_REF] Hopkinson | Angiotensin converting enzyme genotype and strength in chronic obstructive pulmonary disease[END_REF] and endurance [START_REF] Gosker | ACE Gene Polymorphism in COPD[END_REF] in COPD individuals. Irrespective of the exact underlying mechanisms that lead to muscle alterations, the above pathophysiological bases are relevant because the adapted training programs aim to reverse skeletal muscle dysfunction and its consequences on dyspnea and exercise intolerance.

As for asthmatics, the individualization of retraining intensities is of prime importance to ensure that excessive dyspnea feelings are prevented and that exercise will thus be well tolerated. To avoid this problem, we chose to promote and validate a training intensity at the ventilatory threshold [VTh, [START_REF] Beaver | A new method for detecting anaerobic threshold by gas exchange[END_REF]] since it represents an individual parameter of cardiorespiratory fitness and characterizes the maximal exercise intensity prior to an exponential rise in ventilation (Figure 3) that is an efficient intensity without causing major dyspnea feelings (Varray & Prefaut, 1995).

The effects of retraining programs on individuals with obstructive pulmonary disease

As we have seen above, and even if the underlying reasons are quite different in asthma and COPD, the major aim of training programs is to counter the excessive ventilation requirement by developing greater aerobic fitness. This aim is based on precise pathophysiological analysis. Because this Physical Activity, Chronic Disease and Health objective and the efficacy of training effects are similar in asthmatics and COPD patients, we will present the effects of physical activity in both patient groups in the same part.

Although few general reviews have been published on the overall effects of physical activity in asthmatics [START_REF] Ram | Physical training for asthma[END_REF][START_REF] Welsh | Effects of physical conditioning on children and adolescents with asthma[END_REF], the impact on different asthma symptoms or their consequences have long been known and confirmed in more recent studies. The main consequences are fewer and less severe asthmatic attacks [START_REF] Petersen | Effects of a physical fitness program upon asthmatic boys[END_REF], fewer wheezing days, fewer days requiring medication, and decreased hospitalizations and school absenteeism [START_REF] Huang | The effect of swimming in asthmatic children--participants in a swimming program in the city of Baltimore[END_REF][START_REF] Szentagothai | Physical exercise program for children with bronchial asthma[END_REF][START_REF] Wardell | A swimming program for children with asthma. Does it improve their quality of life?[END_REF]. The effects on EIB risk remain debatable, since some studies have described a decrease in the frequency and degree of EIB after training, and others have not [START_REF] Welsh | Effects of physical conditioning on children and adolescents with asthma[END_REF]. The underlying reasons for the discrepancies are probably differences in training regimen, as the reduction in EIB is strongly supported by cardiorespiratory effects (presented further).

In contrast, the amount of work carried out on the training effects on COPD is so great that several reviews, meta-analyses and publications on "evidence-based medicine" have been published (ACCP AACVPR Pulmonary Rehabilitation Guidelines Panel, 1997;BTS Statement, 2001;[START_REF] Chavannes | Effects of physical activity in mild to moderate COPD: a systematic review[END_REF][START_REF] Lacasse | Pulmonary rehabilitation for chronic obstructive pulmonary disease (Cochrane Review)[END_REF][START_REF] Lacasse | Meta-analysis of respiratory rehabilitation in chronic obstructive pulmonary disease[END_REF][START_REF] Troosters | Pulmonary rehabilitation in chronic obstructive pulmonary disease[END_REF]. The literature devoted to evidence-based medicine rates the strength of evidence according to three different levels:

-grade A: evidence from well designed, well conducted, controlled trials with statistically significant results. This grade is the highest and characterizes the proven efficacy of a treatment; -grade B: evidence from observational studies or controlled trials with less consistent results. This grade indicates that a technique is efficient but acknowledges a remaining lack of certainty; -grade C: expert opinion supports the guideline recommendations though the available research does not have consistent results and controlled trials are lacking.

According to this classification, pulmonary rehabilitation based on retraining programs is currently the only technique accorded a grade A for its effectiveness in improving the breathlessness, Physical Activity, Chronic Disease and Health depression and anxiety associated with COPD; the number and duration of hospitalizations; the health-related quality of life; and -to an amazing degree -the exercise tolerance (that is, increased exercise capacity and decreased breathlessness for any given exercise intensity (ACCP AACVPR Pulmonary Rehabilitation Guidelines Panel, 1997;[START_REF] Fabbri | Global Strategy for the Diagnosis, Management and Prevention of COPD: 2003 update[END_REF]. In addition, pulmonary rehabilitation has received a grade B for improved survival rate Among these general effects, the central one is obviously the substantial increase in exercise tolerance, which is the exact response expected from a training program built on pathophysiological bases. By using individualized training programs, it is possible to induce better aerobic fitness ( 2 O V ! max and VTh) in asthmatics [START_REF] Ahmaidi | Cardiorespiratory fitness evaluation by the shuttle test in asthmatic subjects during aerobic training[END_REF][START_REF] Varray | Individualized aerobic and high intensity training for asthmatic children in an exercise readaptation program. Is training always helpful for better adaptation to exercise[END_REF] and patients with COPD, although with a lower magnitude in this population [START_REF] Vallet | Intérêt du réentraînement à l'effort individualisé, au niveau du seuil ventilatoire, au cours de la bronchopneumopathie chronique obstructive de sévérité modérée[END_REF]. The improvement in VTh means that the ventilatory requirement is lowered at submaximal intensities, since the moment of an exponential increase in ventilation is delayed. In addition, several studies have shown ventilatory savings in asthmatics for any exercise intensity [START_REF] Hallstrand | Aerobic conditioning in mild asthma decreases the hyperpnea of exercise and improves exercise and ventilatory capacity[END_REF][START_REF] Varray | Individualized training reduces excessive exercise hyperventilation in asthmatics[END_REF] and in COPD patients for heavy exercise workloads [START_REF] Vallet | Comparison of two training programmes in chronic airway limitation patients: standardized versus individualized protocols[END_REF]. As mentioned in the pathophysiological section, these results are of prime importance, since the dyspnea will be reduced for any given exercise intensity and thus the dyspnea feeling is lessened. More specifically, in asthmatics, this represents a decreased risk of EIB and the possibility of reduced heart-lung interactions. Another very interesting finding is that after training, the breathing pattern is modified with a systematic decrease in breathing frequency for a given ventilation level in both populations. This means that alveolar ventilation will be higher for a given ventilatory flow, reflecting a decrease in dynamic hyperinflation in asthmatics [START_REF] Ramazanoglu | Cardiorespiratory response to physical conditioning in children with bronchial asthma[END_REF] and COPD patients [START_REF] Porszasz | Exercise training decreases ventilatory requirements and exerciseinduced hyperinflation at submaximal intensities in patients with COPD[END_REF]. Thus by changing the breathing pattern, the main ventilatory effects are maximized.

Because of a strong muscle dysfunction in COPD, the literature reports several attempts to provide evidence that skeletal muscle may be more efficient during exercise. By using the model of localized exercise, it has been shown that training can induce important changes in muscle function, and especially higher critical power, which means that more intense exercise can be performed without fatigue [START_REF] Serres | Improved skeletal muscle performance after individualized exercise training in patients with chronic obstructive pulmonary disease[END_REF]. In addition, quadriceps endurance after Physical Activity, Chronic Disease and Health training can be increased up to 250% of its pre-training value. The muscle impairment characterized by an early drop in muscle excitability can also be corrected by individualized training [Figure 4 (Gosselin, et al., 2003)].

More recently, decreased oxidative stress was described after training [START_REF] Mercken | Rehabilitation Decreases Exercise-induced Oxidative Stress in Chronic Obstructive Pulmonary Disease[END_REF], especially training in submaximal exercise conditions. The underlying mechanisms are unclear, and it is still unknown whether this decrease is attributable to a more efficient oxidative metabolism or an increased capacity of endogenous antioxidative systems. Physical Activity, Chronic Disease and Health

Conclusion

Because of the effectiveness of retraining programs that have been developed from pathophysiological bases, the overall quality of life of individuals with obstructions can be sharply improved. This is illustrated by better functional status despite the chronicity of the disease. However, it is important to bear in mind that training is not always efficient and close monitoring of physical activity is essential. Indeed, one comparative work showed that with the use of non-individualized intensities-that is, standardized intensities for all individuals-the training program failed to decrease the ventilation or the anaerobic requirement, as was expected [Figure 5 [START_REF] Vallet | Comparison of two training programmes in chronic airway limitation patients: standardized versus individualized protocols[END_REF]].

This indicates that 1) physical activity prescription requires an attentive and knowledgeable approach, 2) the professional expertise of physical education teachers specializing in adapted physical activity is indispensable, and 3) training intensities must be defined by taking into account the triad of "pathology-exercise adaptations-training effects".

Last but not least, since functional improvement is always possible irrespective of the disease severity [START_REF] Vogiatzis | Physiological response to moderate exercise workloads in a pulmonary rehabilitation program in patients with varying degrees of airflow obstruction[END_REF], hope can now be offered to individuals with chronic diseases: a better quality of life starting today. Physical Activity, Chronic Disease and Health Physical Activity, Chronic Disease and Health Table 1 Example of paradox between chronic physical activity effects and short term fears during exercise

Disease

Chronic effects of physical activity Fear linked with physical activity Asthma Improved exercise-induced bronchodilation [START_REF] Haas | Effect of aerobic training on forced expiratory airflow in exercising asthmatic humans[END_REF][START_REF] Haas | Effects of physical fitness on expiratory airflow in exercising asthmatic people[END_REF] Decreased risk of exercise-induced bronchospasm by less exercise-induced hyperventilation [START_REF] Varray | Individualized training reduces excessive exercise hyperventilation in asthmatics[END_REF] Exercise-induced bronchospasm attack COPD Decreased exercise hyperventilation for a given work load [START_REF] Vallet | Comparison of two training programmes in chronic airway limitation patients: standardized versus individualized protocols[END_REF] Decreased dyspnea with sharp quality of life improvement [START_REF] Lacasse | Meta-analysis of respiratory rehabilitation in chronic obstructive pulmonary disease[END_REF] Dyspnea worsening

Type I diabetes mellitus

Better metabolic control, less hyperglycemia, increased glucose tolerance [START_REF] Bak | Insulin receptor function and glycogen synthase activity in skeletal muscle biopsies from patients with insulindependent diabetes mellitus: effects of physical training[END_REF][START_REF] Mosher | Aerobic circuit exercise training: effect on adolescents with well-controlled insulindependent diabetes mellitus[END_REF] Problem of hypo-or hyperglycemia during exercise [START_REF] Nordfeldt | Fear and other disturbances of severe hypoglycaemia in children and adolescents with type 1 diabetes mellitus[END_REF] Physical Activity, Chronic Disease and Health Figure 1. The vicious circle of hypoactivity illustrating how a chronic disease state can lead to functional deterioration [from [START_REF] Bar-Or | Pediatric Sports Medicine for the Practitioner[END_REF]]. Today, evidence indicates that functional deterioration has a major impact on symptoms of the chronic disease state. Physical Activity, Chronic Disease and Health training in COPD. Data taken from Gosselin and co-workers (Gosselin, Lambert et al., 2003;Gosselin, Matecki et al., 2003). After training, muscle excitability can be maintained throughout exercise and recovery, as in healthy subjects. involvement for a given exercise intensity. In the group trained at 50% of heart rate reserve, training induced no effects [START_REF] Vallet | Comparison of two training programmes in chronic airway limitation patients: standardized versus individualized protocols[END_REF].

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  how should training be carried out? The procedural problems are always delicate and must be dealt with according to the stated aims defined for the specific pathology and the classical effects of training; -what type of results can be expected by training? Again, it is impossible to give a relevant answer without a clear definition of the training goals.

Figure 2 .

 2 Figure 2. Dyspnea spiral leading to dyspnea worsening, irrespective of the progression of disease severity.

Figure 3 .

 3 Figure 3. Ventilatory kinetics [ventilation and respiratory equivalent for oxygen (

Figure 4 .

 4 Figure 4. Changes in M-wave amplitudes according to the level of activity and after individualizedtraining in COPD. Data taken from Gosselin and co-workers(Gosselin, Lambert et al., 2003; Gosselin, Matecki et al., 2003). After training, muscle excitability can be maintained throughout exercise and recovery, as in healthy subjects.

  after training Physical Activity, Chronic Disease and Health

Figure 5 .

 5 Figure 5. Differences in training effects on ventilation and index of anaerobic metabolisminvolvement for a given exercise intensity. In the group trained at 50% of heart rate reserve, training induced no effects[START_REF] Vallet | Comparison of two training programmes in chronic airway limitation patients: standardized versus individualized protocols[END_REF].

Axen, Gaudino, &[START_REF] Haas | Effects of physical fitness on expiratory airflow in exercising asthmatic people[END_REF], which can reach 30% of pre-exercise values. The only problem is that


G Ninot

D Delignières

A Varray

Stability of physical self: Examining the role of chronic obstructive pulmonary disease Stabilité physique et estime de soi : examen du rôle de la maladie bronchopneumopathie chronique obstructive

Keywords: Variability, Self-esteem, Physical self, Dynamics, Chronic respiratory disease, Depression Résumé Variabilité, Estime de soi, Soi physique, Dynamique, Bronchopneumopathie chronique obstructive, Dépression

This observational study compared global self-esteem and physical self scores and their stability over a three-week period in patients with chronic obstructive pulmonary disease (COPD) and healthy adults, through the analysis of day-to-day time series. Two groups were formed: a COPD group of 27 patients with stable and moderate COPD, and a control group of 31 "healthy" adults. The results showed lower mean scores over the study period for global self-esteem, physical self-worth, and each of the physical self subdomains in COPD patients as compared with the "healthy" group. Moreover, the results showed less stability in global self-esteem, physical self-worth, and the physical self subdomains over the same period in these patients. Our principal findings support the assertion of Kernis and colleagues that unstable global self-esteem and physical self reflects a certain vulnerability to endogenous and exogenous events.

Everyday life is full of events that can affect the way we feel about ourselves and our bodies [START_REF] Greenier | Individual differences in reactivity to daily events: examining the roles of stability and level of self-esteem[END_REF]. These events, from endogenous or exogenous origin, create individual differences in level of self-esteem or physical self [START_REF] Marsh | Top-down, bottom-up, and horizontal models: the direction of causality in multidimensional, hierarchical self-concept models[END_REF] and perhaps in stability [START_REF] Greenier | Individual differences in reactivity to daily events: examining the roles of stability and level of self-esteem[END_REF][START_REF] Kernis | The interactive roles of stability and level of self-esteem: Research and theory[END_REF][START_REF] Nezlek | Day-to-day relationships among self-concept clarity, self-esteem, daily events, and moods[END_REF][START_REF] Nowak | Society of self: the emergence of collective properties in self-structure[END_REF]. Adults with high self-esteem are generally characterized by high levels of sociability, impulsivity [START_REF] Eysenck | On the dual nature of extraversion[END_REF], emotional stability [START_REF] Francis | Coopersmith's model of self-esteem: bias toward the stable extravert?[END_REF] and resilience to stress [START_REF] Wylie | Measures of self-concept[END_REF]. Inversely, people with low self-esteem often present depressive episodes [START_REF] Butler | A comparison of self-esteem liability and low trait self-esteem as vulnerability factors for depression[END_REF][START_REF] Baumeister | Self-esteem: The puzzle of low self-regard[END_REF]. They report more negative emotions, are more sensitive to negative events [START_REF] Dutton | Global self-esteem and specific self-views as determinants of people's reactions to success and failure[END_REF][START_REF] Epstein | Coping ability, negative self-evaluation, and overgeneralization: Experiment and theory[END_REF], and are more concerned by and with social evaluation [START_REF] Baumgardner | To know oneself is to like oneself: self-certainty and self-affect[END_REF]. The low self-esteem is typically reported in chronic obstructive pulmonary disease (COPD) patients [START_REF] Engström | Functional status and well being in chronic obstructive pulmonary disease with regard to clinical parameters and smoking: a descriptive and comparative study[END_REF][START_REF] Kersten | Changes in self-concept during pulmonary rehabilitation[END_REF], who face a number of stresses, including increasing functional limitations and subsequent dependency on others, changes in body image and sexual performance, and the threat of death [START_REF] Toshima | Does rehabilitation reduce depression in patients with chronic obstructive pulmonary disease?[END_REF]. They experience anxiety, especially about dyspnoea episodes [START_REF] Hynninen | Psychological characteristics of patients with chronic obstructive pulmonary disease: a review[END_REF][START_REF] Maurer | Anxiety and depression in COPD: Current understanding, unanswered questions, and research needs[END_REF]. COPD patients have low self-efficacy [START_REF] Kaplan | Psychosocial issues in the rehabilitation of patients with chronic obstructive pulmonary disease[END_REF] and depression syndromes that have been reported to be as high as 42% in patients with moderate to severe COPD [START_REF] Light | Prevalence of depression and anxiety in patients with COPD: relationship to funtional capacity[END_REF][START_REF] Mcsweeny | Life quality of patients with chronic obstructive pulmonary disease[END_REF][START_REF] Kunik | Surprisingly high prevalence of anxiety and depression in chronic breathing disorders[END_REF].

Recent research has emphasized the inherent fluctuations of self-esteem [START_REF] Nezlek | Day-to-day relationships among self-concept clarity, self-esteem, daily events, and moods[END_REF][START_REF] Nowak | Society of self: the emergence of collective properties in self-structure[END_REF][START_REF] Thewissen | Fluctuations in Self-Esteem and Paranoia in the Context of Daily Life[END_REF] and physical self [START_REF] Amorose | Intraindividual variability of self-evaluations in the physical domain: prevalence, consequences, and antecedents[END_REF][START_REF] Ninot | A psychometric tool for the assessment of the dynamics of the physical self[END_REF]. For healthy adults, these perceived dimensions consistently exhibit either noisy fluctuations around a reference value [START_REF] Marsh | Top-down, bottom-up, and horizontal models: the direction of causality in multidimensional, hierarchical self-concept models[END_REF], short-term fluctuations, from none to considerable [START_REF] Kernis | Measuring self-esteem in context: The importance of stability of self-esteem in psychological functioning[END_REF] or a slowly varying mean over daily events and across situations [START_REF] Ninot | A psychometric tool for the assessment of the dynamics of the physical self[END_REF][START_REF] Ninot | The dynamics of self-esteem in adults over a six-month period: An exploratory study[END_REF]. Stability in these dimensions creates stable behaviors and psychological reactions [START_REF] Mccrae | The stability of personality: Observations and evaluations[END_REF][START_REF] Mortimer | Persistence and change in development: The multidimensional self-concept[END_REF]. Stable self-perceptions reflect self-consistency with the development of feelings of unity, independence, predictability and control [START_REF] Epstein | The stability of behaviour: on predicting most of the people much of the time[END_REF]. Inversely, individuals with unstable self-esteem often experience anger and hostility [START_REF] Kernis | Stability of self-esteem as a moderator of the relation between level of self-esteem and depression[END_REF]. Unstable self-esteem also reveals interesting information about depression [START_REF] Greenier | Individual differences in reactivity to daily events: examining the roles of stability and level of self-esteem[END_REF][START_REF] Kernis | Stability of self-esteem as a moderator of the relation between level of self-esteem and depression[END_REF][START_REF] Oosterwegel | The relation of self-esteem variability to emotion variability, mood, personality traits, and depressive tendencies[END_REF] and paranoia [START_REF] Thewissen | Fluctuations in Self-Esteem and Paranoia in the Context of Daily Life[END_REF]. Patients with COPD can experience unpredictable exacerbations such as increased dyspnoea, wheezing, cough, sputum production [START_REF] Madison | Chronic obstructive pulmonary disease[END_REF]. These symptoms, particularly dyspnoea, may interfere with the maintenance of stable auto-evaluative patterns and significantly raise anxiety [START_REF] Borak | Psychological status of COPD patients on long term oxygen therapy[END_REF][START_REF] Karajgi | The prevalence of anxiety disorders in patients with chronic obstructive pulmonary disease[END_REF][START_REF] Withers | Anxiety and depression in severe chronic obstructive pulmonary disease: the effects of pulmonary rehabilitation[END_REF]. No study, however, has yet to investigate the stability of global self-esteem or physical self in patients with COPD.

The purpose of the present study was to compare the level and stability of self-esteem and physical self in patients with COPD and healthy adults over a three-week period through the analysis of day-to-day time series. We suspect that the irregular symptoms of a chronic respiratory disease powerfully influence the stability of these perceived dimensions over time. We supposed that the mean scores of global self-esteem and physical self and stability indices would be lower in COPD patients than in healthy adults.

Method

Participants

Fifty-eight adults assigned to two groups participated in this study (Table 1). The first group comprised 27 patients with stable and moderate COPD (from 46 to 74 years old). The other group served as control and was composed of 31 adults (from 48 to 73 years old). The control group was used to determine whether the perceived dimensions in "healthy" adults exhibit lower fluctuations (standard deviation and range), and higher levels as compared with those of COPD patients. Patients with moderate COPD were consecutively recruited from three regional hospitals where they had just benefited from their first exercise test. Inclusion criteria were as follows: a post-bronchodilator forced expiratory volume in one second (FEV1)/forced vital capacity (FVC) < 0.7 and an FEV1 30-79% predicted, no indication for home oxygen therapy, and no exacerbation or hospitalization in the previous two months. The study was approved by the medical ethics committees of all three hospitals. Healthy subjects were consecutively recruited during conference of health primary prevention. None of them had pharmacologically treated psychiatric disorders or acute medical illnesses and none were facing major negative life events that would have affected psychological function over the three-week period. All subjects gave informed written consent to participate. This instrument was proven to reproduce the hierarchical structure of the corresponding multi-item inventories using correlations and partial correlations, factor analysis and confirmatory factor analysis [START_REF] Fox | The Physical Self Perception Profile: Development and preliminary validation[END_REF][START_REF] Ninot | L'évaluation de l'estime de soi dans le domaine corporel[END_REF], as well as for its external validity [START_REF] Fox | The Physical Self Perception Profile: Development and preliminary validation[END_REF].

Measures

To assess day-to-day dynamics, the instrument needed to be short (quick assessment to maintain motivation), easy to complete (single sheet of paper, weekly journal, software), sensitive (for example, visual analog scale), reliable (consistent with other measuring instruments) and valid (predictive, concurrent). A single-item provides an adequate measure of global self-esteem because most adults are schematic for self-esteem [START_REF] Robins | Measuring global selfesteem: construct validation of a single-item measure and the Rosenberg self-esteem scale[END_REF], and physical self [START_REF] Ninot | A psychometric tool for the assessment of the dynamics of the physical self[END_REF]. Thus, these perceived dimensions are likely to be repeatedly activated in a wide range of situations and become chronically accessible by adulthood [START_REF] Robins | Measuring global selfesteem: construct validation of a single-item measure and the Rosenberg self-esteem scale[END_REF]. The Physical Self Inventory-6 (PSI-6; [START_REF] Ninot | A psychometric tool for the assessment of the dynamics of the physical self[END_REF], which measures global self-esteem, physical self-worth and four physical subdomains (physical condition, sport competence, physical strength and attractive body) with one item per dimension, has acceptable psychometric properties (Table 2). The participants responded to this inventory using a visual analog scale (a single 10-cm horizontal line without formal indications is drawn under each item) that ranged from "not at all" (measured 0.0 cm) to "absolutely" (measured 10.0 cm). [START_REF] Ninot | A psychometric tool for the assessment of the dynamics of the physical self[END_REF] validated this tool specifically designed to allow repeated administration and reveal variability in self-esteem and physical self. This instrument was proven to reproduce the hierarchical structure of the corresponding multi-item inventories using correlations and partial correlations, factor analysis and confirmatory factor analysis [START_REF] Fox | The Physical Self Perception Profile: Development and preliminary validation[END_REF][START_REF] Ninot | L'évaluation de l'estime de soi dans le domaine corporel[END_REF], as well as for its external validity [START_REF] Fox | The Physical Self Perception Profile: Development and preliminary validation[END_REF]. For the COPD group, a specific item about dyspnoea was added with the same response mode, from 0.0 for "no breathlessness" to 10.0 for "maximal breathlessness". They were also requested to draw a mark on the center of a second 10-cm horizontal visual analog scale. This additive item was designated to estimate the measurement error, which corresponded to the difference between the true value of the center of the line (i.e., 5 cm) and the value of the response mark.

Procedure

Each participant completed an inventory on a single page of a personal notepad twice a day between 7:00 and 9:00 (AM and PM) over a three-week period. Each page included the six items of the PSI-6, plus the dyspnoea item for the COPD group, presented in random order. Individual time series were then composed of 42 observations per dimension. The participants based their responses on how they felt at the moment they were completing each form. They assessed their immediate, contextually based feelings of self-perception. They were not allowed to consult their previous responses.

Statistical analyses

Three dependent variables were computed for each individual time series: the mean value, the standard deviation and the range (defined as the difference between the highest and lowest values of the time series). Multivariate analyses of variance (MANOVAs) were used to test the global Group (2) effect on the PSI-6 dimensions. When MANOVAs were significant, univariate analyses of variance (ANOVA) were performed to determine which dimensions were significantly affected. The dyspnoea item for the COPD group was treated separately by analysis of the Pearson's correlations between this item and the six dimensions of the inventory.

Results

Mean values

There were no significant differences between the two groups on age (p = .26), height (p = .46) and weight (p = .13) using t-test, and gender using Chi 2 statistic (p = .90). The MANOVA revealed a significant Group effect on the mean values of perceived PSI-6 dimensions (Wilks' Lambda = 0.44, R/Rao = 10.82, p < .0001). Subsequent univariate analyses showed that the Group effect was significant for all dimensions and not for the measure error item (Table 3). The results showed that COPD patients scored significantly lower than the "healthy" group on the six perceived dimensions.

The mean correlations between dyspnoea and the PSI-6 dimensions for the 26 COPD patients were, respectively:

• global self-esteem: -0.09; • physical self-worth: -0.17; • physical condition: -0.18; • sport competence: -0.19; • attractive body: -0.14; • physical strength: -0.21.

As a global illustration of these results (random selection), an individual physical self-worth series from each of the two groups is plotted in Fig. 1. The Fig. 2 shows time series of global self-esteem, perceived physical condition and dyspnoea of one COPD patient and Pearson's correlation coefficients between these time series.

Standard deviation

The MANOVA showed a significant overall Group effect on the PSI-6 dimensions (Wilks' Lambda = 0.65, R/Rao = 4.47, p = .001). Univariate analyses showed that all dimensions contributed significantly to the overall effect (Table 4). The tests evidenced that the time series of the COPD patients were significantly more varied than those of the "healthy" group for all perceived dimensions.

Range

The MANOVA revealed a significant overall Group effect (Wilks' Lambda = 0.64, R/Rao = 4.82, p < .001). Univariate ANOVAs showed that all dimensions contributed to this overall effect (Table 5). The tests indicated that the COPD patients had a wider response range than the "healthy" group for all perceived dimensions.

Discussion

This study showed lower mean scores for global self-esteem, physical self-worth and each of the physical self subdomains over a period of three weeks in patients with moderate COPD as compared with "healthy" adults. Moreover, the patients showed less stability in scores for global self-esteem, physical self-worth, and the subdomains, over the same period. As in previous studies [START_REF] Kersten | Changes in self-concept during pulmonary rehabilitation[END_REF][START_REF] Moullec | An innovative maintenance follow-up program after a first inpatient pulmonary rehabilitation[END_REF] and reviews [START_REF] Hynninen | Psychological characteristics of patients with chronic obstructive pulmonary disease: a review[END_REF][START_REF] Maurer | Anxiety and depression in COPD: Current understanding, unanswered questions, and research needs[END_REF], these results support the hypothesis that individuals with moderate COPD present lower global self-esteem than "healthy" adults over time, as well as lower scores for physical self-worth and its subdomains.

COPD negatively affects the entire perception system related to physical abilities. This negative effect is classically observed in disabled persons living in an ordinary environment [START_REF] Sherrill | Disability, identity and involvement in sport and exercise[END_REF]. The low level of perceived physical ability in the COPD group indicated that the patients recognized their deteriorated health status, due to chronic lack of energy, repeated symptom exacerbation, and probably the poor prognosis for this incurable disease. The higher correlations between dyspnoea and the physical ability subdomains, as compared with global self-esteem, support this explanation. They raise important questions about the psychological mechanisms that operate in the hierarchical structure between physical self and global self-esteem once a patient has fully understood his or her diagnosis (and the longterm prognosis). The knowledge and psychological integration of the biopsychosocial consequences of COPD could increase self-depreciation. COPD is usually caused by tobacco smoking [START_REF] Calverley | COPD: early detection and intervention[END_REF][START_REF] Madison | Chronic obstructive pulmonary disease[END_REF]. When it is diagnosed, the implications are unmistakable -the individual's own behavior has to a great extent caused the disease -and this may lead to feelings of guilt. Moreover, comparing the present physical status with memories of satisfying physical capacities of few years previous and the status of healthy peers further decreases global self-esteem. A low perception of physical abilities affects global self-esteem by overgeneralization [START_REF] Kernis | Self-esteem and reactions to failure: The mediating role of overgeneralization[END_REF].

The results showed that global self-esteem, physical selfworth and the physical subdomains were less stable in moderate COPD patients than in same-age "healthy" adults: these dimensions exhibited higher fluctuations (standard deviation and range) in the COPD patients, indicating that they resist, less effectively to several endogenous and exogenous constraints. In other words, the patients seemed to be more sensitive to their health status and environmental change. Many patients with COPD find it difficult to cope with the distressing symptom of breathlessness [START_REF] Ries | Effects of pulmonary rehabilitation on physiologic and psychosocial outcomes in patients with chronic obstructive pulmonary disease[END_REF]. They are subjected to other unpredictable, frightening and disabling symptoms that make it hard to feel in control of their lives. Many patients develop a lack of confidence in their ability to avoid breathing difficulties while participating in certain activities, however minimal the physical demands of the activity may be [START_REF] Wigal | The COPD Self-Efficacy Scale[END_REF]. Over time, a vicious circle of physical deconditioning caused by activity restriction [START_REF] Young | Rehabilitation of patients with pulmonary disease[END_REF], and, as our study indicates, "psychological" deconditioning related to exercise, thus results in the patients no longer knowing the exact limits of their physical abilities. They then begin to increasingly rely on passive coping mechanisms, which may explain why overall behavior is slowed down with depression or anxiety [START_REF] Dantchev | The measurement of retardation in depression[END_REF]. Further studies are needed to determine whether the heightened instability of global selfesteem and physical self in moderate COPD patients follow a specific dynamics. [START_REF] Greenier | Individual differences in reactivity to daily events: examining the roles of stability and level of self-esteem[END_REF] stated that instability in these dimensions has "psychological" meaning: it both promotes and is a product of the fragility of feelings of self-worth. This statement could contribute to explain why anxiety, health status and depression increase the risk for hospital re-admission in COPD patients [START_REF] Maurer | Anxiety and depression in COPD: Current understanding, unanswered questions, and research needs[END_REF].

We can also suggest that the instability of physical self could depict the importance attributed by COPD to body domain, as a consequence of physical symptoms. It could support the assumption of [START_REF] Kernis | There's more to self-esteem than whether it is high or low: The importance of stability of self-esteem[END_REF], who suggested that the more importance people place on physical competence as determinants of overall self-worth, the more these feelings of self-worth fluctuate.

A limitation must be mentioned. Single-item measuring certain psychological dimensions can provide an acceptable balance between practical needs and psychometric concerns [START_REF] Robins | Measuring global selfesteem: construct validation of a single-item measure and the Rosenberg self-esteem scale[END_REF]. Single-item self-report scales are not necessary relevant for assessing all kinds of psychological dimensions. For example, it is unlikely that a single-item would be valid for a multifaceted and psychodynamically complex structure. According to [START_REF] Robins | Measuring global selfesteem: construct validation of a single-item measure and the Rosenberg self-esteem scale[END_REF], a single self-report item may be adequate when the construct is highly schematized for most individuals. Most adults are schematic for global selfesteem and physical self because such dimensions are likely to be activated in a wide range of situations and, therefore, likely to be chronically accessible to adulthood [START_REF] Robins | Measuring global selfesteem: construct validation of a single-item measure and the Rosenberg self-esteem scale[END_REF]. Nevertheless, further studies are needed to determine the signal/noise ratio and the validity of a single-item measure.

In conclusion, this three-week study highlighted lower mean score of global self-esteem and physical self, and greater instability in these scores, in patients with moderate COPD as compared with "healthy" adults. The findings support the assertion that unstable global self-esteem or physical self reflects a certain vulnerability to the impact of the impact of COPD and its characteristics [START_REF] Kernis | There's more to self-esteem than whether it is high or low: The importance of stability of self-esteem[END_REF][START_REF] Greenier | Individual differences in reactivity to daily events: examining the roles of stability and level of self-esteem[END_REF][START_REF] Nezlek | Day-to-day relationships between self-awareness, daily events, and anxiety[END_REF][START_REF] Maurer | Anxiety and depression in COPD: Current understanding, unanswered questions, and research needs[END_REF]. Combined with the lower scores, the greater fluctuation in scoring by COPD patients indicated that their global self-esteem and physical self, considered as a complex system, did not cope efficiently with several endogenous and exogenous constraints. These two characteristics of self-esteem and physical self should be routinely measured and taken into account for part of the patient's treatment plan is to decrease anxiety or depressive symptoms [START_REF] Ries | Effects of pulmonary rehabilitation on physiologic and psychosocial outcomes in patients with chronic obstructive pulmonary disease[END_REF]. Researches are needed to determine the influence of other domain of competence on global self-esteem and to examine the relation between physical self and perceived health status, and between self-esteem and well being or quality of life.

Fluctuations across multiple assessments of daily selfperceptions reflect meaningful psychological processes [START_REF] Greenier | Individual differences in reactivity to daily events: examining the roles of stability and level of self-esteem[END_REF][START_REF] Nowak | Society of self: the emergence of collective properties in self-structure[END_REF]. Further studies are needed to discover the principles that govern the emergence of order in complex systems such as self-esteem over time.

Fig. 1 .

 1 Fig. 1. Changes in physical self-worth in two participants over a three-week period (two measures per day).

Fig. 2 .

 2 Fig.2. Changes in Global Self-Esteem (GSE), perceived Physical Condition (PC) and dyspnoea in one chronic obstructive pulmonary disease (COPD) patient over a three-week period (Pearson's correlation coefficient between GSE and Dyspneoa, -0.54; between PC and dyspnoea, -0.60; between GSE and PC, 0.78).

Table 1

 1 Characteristics of participants.

	Variable	COPD	Healthy
	N	27	31
	Gender (W/M)	10/17	11/20
	Age (M ± S.D.)	63.0 ± 7.3	65.1 ± 7.1
	FEV 1 % (M ± S.D.)	54.0 ± 12.0#	-
	FEV 1 /FVC% (M ± S.D.)	61.3 ± 15.1¤	-
	Weight (kg) (M ± S.D.)	72.4 ± 12.6	68.0 ± 8.9
	Height (cm) (M ± S.D.)	166.4 ± 5.3	168.4 ± 4.1
	Note: FEV1: forced expiratory volume in 1 s; FVC: forced volume capacity; #:
	min = 30% and max = 74%; ¤: min = 30% and max = 81%.

Table 2

 2 Items of the Physical Self Inventory[START_REF] Ninot | A psychometric tool for the assessment of the dynamics of the physical self[END_REF].

	Category	Item
	Global self-esteem	You have a good opinion of yourself
	Physical self-worth	Physically, you are proud of who you are and
		what you can do
	Physical condition	You should do well in an endurance test
	Physical strength	When you come upon situations requiring
		strength, you are among the first to step forward
	Sport competence	You think you are good in all sports
	Attractive body	You think that you have a body pleasant to look
		at

Table 3

 3 Means of Global Self-Esteem (GSE), Physical Self-Worth (PSW), Physical Condition (PC), Sport Competence (SC), Attractive Body (AB), Physical Strength (PS) and Measure Error (ME) over a three-week period (referring between-persons).

		COPD		Healthy
		M	S.D.	M	S.D.	F(1,2)	p
	GSE	4.69	1.94	7.13	1.47	28.01	<0.000
	PSW	3.93	1.70	6.88	1.50	46.56	<0.000
	PC	3.48	1.67	6.51	1.53	49.09	<0.000
	SC	3.60	1.73	6.27	2.04	27.12	<0.000
	AB	4.27	2.05	6.92	1.61	29.47	<0.000
	PS	3.43	1.73	6.78	1.57	56.43	<0.000
	ME	5.01	0.08	5.03	0.13	0.46	0.41
	COPD: chronic obstructive pulmonary disease.

Table 5 Ranges

 5

		COPD		Healthy
		M	S.D.	M	S.D.	F(1,2)	p
	GSE	4.23	1.75	2.45	1.14	20.57	<0.001
	PSW	4.27	1.75	2.44	1.21	21.53	<0.001
	PC	4.08	2.08	2.78	1.64	6.86	0.011
	SC	4.25	2.02	2.48	1.49	14.03	<0.001
	AB	3.88	1.83	2.34	1.49	10.96	0.002
	PS	3.84	1.61	2.55	1.29	10.95	0.002
	ME	0.62	0.22	0.55	0.18	1.80	0.185
	COPD: chronic obstructive pulmonary disease.

of Global Self-Esteem (GSE), Physical Self-Worth (PSW), Physical Condition (PC), Sport Competence (SC), Attractive Body (AB), Physical Strength (PS) and Measure Error (ME) over a three-week period (referring within-persons).


A Submerged Freeze Microgripper for Micromanipulations

Beatriz López Walle, Michaël Gauthier, and Nicolas Chaillet Abstract-Efficient, reliable and flexible handling is still very challenging in micromanipulation and micro-assembly. In this paper, we propose an original thermally actuated gripper based on the use of ice to manipulate submerged artificial micro-objects sized under 100 µm. Manipulating in liquid surroundings can indeed be more interesting than in dry conditions. A comparative analysis on the impact of dry and liquid media on surface forces, contact forces and hydrodynamic forces shortly given first shows it. Concerning the use of ice for micromanipulation, cryogenic grippers are a flexible solution. Nevertheless, as they currently work in air, water must be provided by an external device and capillary force occurs during the release. Our submerged freeze microgripper takes advantages of the aqueous surroundings for the handling process as explained. The thermal principle, based on the Peltier effect, the characteristics of the microgripper prototype and the first micromanipulation tests are also presented. To control and optimize the heat exchanges in the developed gripper, a static thermal model using electrical analogy has been developed and validated for the Peltier elements and a 3D heat sink of the gripper. Further work will focus on the dynamic equivalent electric model.

I. INTRODUCTION

The increasing complexity of the microsystems requires different and new micromanipulation processes and micro-assembly technologies and methods [START_REF] Van Brussel | Assembly of microsystems[END_REF]. A main approach in this domain is the robotic assembly which seems relevant for a small production batch [START_REF] Dechev | Microassembly of 3-d microstructures using a compliant, passive microgripper[END_REF], [START_REF] Udeshi | Assembly sequence planning for automated micro assembly[END_REF]. Current manipulation strategies do not allow sufficient reliability and flexibility for micro-objects of which typical dimension is below 100 µm. When the dimension of the objects falls under this size, surface forces permanently influences the interactions between the object and its surroundings [START_REF] Savia | Simulating adhesion forces between arbitrarily shaped objects in micro/nanohandling operations[END_REF]. Their impact perturbs especially the release of the micro-object.

Surface forces, contact forces and hydrodynamic forces strongly depend on environmental parameters [START_REF] Zhou | Ambient environment effects in micro/nano handling[END_REF]. An original way to reduce adhesion perturbations consists in performing micromanipulation tasks being totally submerged in a liquid medium.

Van der Waals forces are proportional to Hamaker constant, which reduces in liquid medium [START_REF] Israelachvili | Intermolecular and surfaces forces[END_REF]. In liquid, double layer, solvation and steric forces have also to be considered. These forces, modelled by the XDLVO theory blopez@ens2m.fr [START_REF] Xu | The role of hydrophobic interactions in coagulation[END_REF], [START_REF] Xu | A study of hydrophobic coagulation[END_REF], are normally repulsive and consequently reduce the effect of attractive van der Waals forces.

Electrostatic forces are also greatly reduced in water: the dielectric constant is higher and the electric conductivity is better in water than in air.

The capillary force between a gripper and an object often induced in air by ambient humidity totally disappears in a liquid medium.

The pull-off force, which represents the necessary force to break the contact between two objects, is proportional to the surface energy between these two objects, and decreases when objects are submerged [START_REF] Israelachvili | Intermolecular and surfaces forces[END_REF].

Finally hydrodynamic force limits the maximal velocity of the micro-object, decreasing their loss rate. However, the maximum velocity of the microgripper endeffectors has also to be limited to avoid disturbances.

[9], [START_REF] Gauthier | Forces analyses for micromanipulations in dry and liquid media[END_REF] gives a detailed comparative analysis of these forces in liquid and dry surroundings. Considering thus the reduction of surface and contact forces, and the limitation of micro-objects loss caused by the hydrodynamic forces, liquid medium is a promising approach to perform micro-assembly.

Though the adhesion effects are reduced, they do not disappear and could always perturb release phases. Consequently, original micromanipulation strategies have to be proposed to guarantee reliable and repeatable micromanipulation tasks. In this paper, we propose a new freeze microgripper to manipulate micro-objects in a submerged medium.

Existing cryogenic grippers work in air, as presented in [START_REF] Liu | Freeze tweezer to manipulate mini/micro objects[END_REF]- [START_REF] Seliger | Hydroadhesive gripping by using peltier effect[END_REF], using adhesive properties of ice for handling. In this case, water must be provided by an external device and capillary force can appear during the release because water does not evaporate completely. They have to combine thus additive release strategies as the use of adhesive surface to place and detach manipulated objects. The gripped objects are typically, bigger than 200 µm. The miniaturization of these grippers is limited by the release difficulties.

In the submerged freeze gripper proposed in this paper, capillary force does not influence the handling procedure. Consequently, it can be extended to smaller objects below 100 µm. Main applications are micro-assembly of optical, mechanical, electrical and even biological microcomponents. Cryogenic grippers do not cause damages to object surfaces, provide high holding forces without introducing additional stress, and their handling abilities are almost independent of objects shape and material properties (low thermal conductive objects are nevertheless recommended).

The proposed handling strategy for submerged micromanipulations is presented in Fig. 1. In the first step, the gripper approaches to the object without touching it. In the second step, an ice microdrop is generated covering just a small part of the object or completely. After this, the object can be picked and positioned. Finally, in the last step, the ice droplet is thawed and the object is liberated without adhesion perturbations. Inserting micro-objects into the water tank, recuperating them, and drying them must be analysed yet.

The thermal validation has been previously modelled with the finite elements software (FEM) COMSOL Multiphysics 3.2. Results are detailed in [START_REF] López-Walle | Submerged freeze gripper to manipulate micro-objects[END_REF]. This paper is structured in two main sections. Section II describes the principle of the submerged freeze gripper, the characteristics of the experimental device, and its first tests. Section III deals with the thermal modelling of the device using an equivalent electrical model.

II. EXPERIMENTAL DEVICE

A first prototype of the submerged freeze gripper has been developed. The whole system principle based on the Peltier effect, its physical characteristics and a manipulation test are described in this section.

A. Principle of the Submerged Freeze Gripper

The basic idea is to grip a micro-object using an ice droplet formed and controlled in an aqueous medium, then to manipulate the micro-object, and finally to release it through a controlled ice thawing. To carry out this sequence a specific microgripper was developed. The necessary cooling and heating energy to actuate the microgripper is obtained by two thermoelectrics Peltier modules. Classically a Peltier module is the association of bismuth-telluride p and n-doped semiconductors connected electrically in series and thermally in parallel. A Peltier module gives an electrical current-proportional generation or absorption of heat when current flows through it. The direction of the heat flow depends on the direction of the current. The difference of temperatures caused by the heat transfer imposes two faces: a cold face, and a hot face. The hot face is associated to a heat sink which dissipates the heat flux. The submerged freeze system is composed of two Peltier modules stages and a forced convection system, as illustrated in Fig. 2. The first module, named MicroPelt (µP ), provides the cooling energy to generate the ice droplet on the end-effector, which is directly attached to its cold side. The freezing process increases the temperature of the MicroPelt's hot face. The convection is thus so important than the whole system (liquid, gripper and Peltier micromodule) could warm up. That is why a second Peltier module, called MiniPeltier (mP ), is also used to actively decrease the temperature on the MicroPelt's heat sink. To optimize the performance of the MiniPeltier, the temperature of its hot face must be constant. This temperature is so maintained at the ambient temperature by forced convection using a liquid cooling system. The liquid cooling system can not be used directly on the MicroPelt's hot face because of its small size (720 µm × 1420 µm). In addition, its maximal cooling capacity is not enough to freezing the end-effector from ambient temperature.

The MiniPeltier and the cooling liquid system stay in air to dissipate heat outside water. The end-effector and the MicroPelt are completely submerged and electrically insulated .

B. Physical and Technical Characteristics

The first prototype of the submerged freeze gripper (without the end-effector) is shown in Fig. 3. The dimensions of the MicroPelt (from Infineon Technologies AG) are: 720 × 720 × 428 µm 3 . Its heat sink is fixed, on one side, to the MicroPelt's hot face, and on the other side, to the MiniPeltier's cold face. The dimensions of the MiniPeltier (Melcor FC0.6-18-05) are: 6.2 × 6.2 × 2.4 mm 3 . Its hot face is fixed to the copper liquid heat sink of the cooling liquid system.

A specific PCB has been fabricated to make the electrical connections of the Peltier modules. Because of the very small dimensions at stake, microbonding technology were used for its connection to the MicroPelt.

C. First Experimentations

First experimentations using the prototype described above in water surroundings were performed. The objectives were to validate the good working of this new system and its reliability. For these tests, the end-effector was not included. The active part was then the Micro-Pelt's cold face; manipulated objects corresponds thus to its dimensions. However, the handling principle to manipulate micro-objects under 100 µm is verified in [START_REF] López-Walle | Submerged freeze gripper to manipulate micro-objects[END_REF].

Fig. 4 describes the tele-manipulation of a silicon object whose dimensions are: 600 × 600 × 100 µm 3 . The micromanipulation has been performed in 30 s. This time can be optimize automating micromanipulations. A precooling phase is necessary to decrease the temperature of the MicroPelt's heat sink. During this phase, only the current in the MiniPeltier (i mP ) is applied and set constant at 0.9 A (Fig. 4a). When the temperature is about 0.5 o C (this temperature is sufficiently close to 0 o C but it prevents the heat sink to freeze), the MicroPelt is approached to the micro-object and its current (i µP ) is turned on at 0.5 A. The cooling energy generates the ice droplet (4 µl) which involves part of the object in 3 s (Fig. 4b). The freeze gripper can thus displace it towards a new position (Fig. 4c). To release it, the MicroPelt's current is inverted at -0.3 A. The ice droplet thaws in 7 s and melts with the medium, liberating the microobject without adhesion perturbations (Fig. 4d). In fact, contrary to the cryogenics gripper in air, capillary forces do not perturb the release because the object and the MicroPelt are submerged. The same experiment was successfully repeated several times. The submerged freeze principle seems a promising approach to manipulate micro-objects. Further manipulations will be dedicated to objects sized under 100 µm.

To maximize the cooling energy to the end-effector and optimize the cycle time, it is necessary to control the cold temperature of both Peltier elements, the MicroPelt and the MiniPeltier, via their electrical currents. The definition of the control strategy requires a model of the thermal exchanges in the whole system. Next section deals with the static modelling of both Peltier elements and a heat sink by electrical analogy.

III. ELECTRICAL MODEL

Thermal modelling and control is a crucial part of the design of the submerged freeze system. An equivalent electrical model, so-called thermal network, represents a relatively simple, but powerful tool for simulating the real system [START_REF] Holman | Heat transfer[END_REF]. It notably allows to easily connect several thermal subsystems together. Classical electrical models correspond in general to planar thermal systems. Consequently, they can not be applied to our 3D device. For all these reasons, and considering the complexity of heat transfers on the submerged freeze gripper, we propose to build up its proper thermal network. This section reminds first the bases of the electrical analogy for thermal systems; then, the Peltier module's electrical modelling is presented; and finally, we propose the model of a 3D heat sink. This paper focus on the description of the steady state models of our microgripper.

A. Bases of Electrical Analogy for 1D Thermal Problem

An equivalent electrical model usually facilitates and simplifies the analysis of a thermal problem. Used relationship between thermal and electrical systems are summarized in table II. Fig. 5 illustrates the heat transfer in a multilayer wall and its equivalent electrical circuit. It corresponds to the typical example for the application of this concept. In this case, heat convection takes place between the lateral surfaces and the external fluids, and heat conduction takes place in the layers. Convection thermal resistance R conv is a function of the convective heat transfer coefficient h and the lateral surface S of the wall:

R conv = 1/hS, ( 1
)
while conduction thermal resistance R cond is obtained according to the thickness e of the layer, its thermal conductivity k, and the lateral surface S: R cond = e/kS.

(2)

Then, the steady state model of this multilayer wall can be obtained in connecting in series the electrical resistances, as shown in Fig. 5. This thermal network is valid for e L.

B. Thermal Network for a Peltier Module

Peltier modules are active elements of the submerged freeze microgripper. As described above, they are controlled by electrical current. The cooling capacity Q c of a Peltier module is related to its Peltier coefficient α, its electrical resistance R, its thermal conductivity coefficient k P , the electrical current supplied i, and the temperature of its cold and hot face, T c and T h respectively. The heat flow Q h of the hot face can be obtained by symmetries. They can be written as:

Q c = -αT c i + Ri 2 /2 + k P (T h -T c ) (3)
Q h = αT h i + Ri 2 /2 -k P (T h -T c ) (4)
The thermal network for a Peltier module is described by [START_REF] Seliger | Hydroadhesive gripping by using peltier effect[END_REF]. The steady state thermal network based on ( 3) and ( 4) is described in Fig. 6. Peltier effect is represented by current source P S = αT c i; Joule effect is modelled by current sources P J/2 = Ri 2 /2; and the conductivity coefficient is analogous to the thermal resistance term, R th = 1/k P . Fig. 6. Thermal network for a Peltier element [START_REF] Seliger | Hydroadhesive gripping by using peltier effect[END_REF] In order to validate the performance of the MiniPeltier, we compared its net cooling, i.e. T h -T c , obtained with the electrical model with experimental measurements. According to Fig. 6, net cooling is written as:

T h -T c = R th Q c + P S -P J/2 . ( 5
)
All the parameters are provided by the MiniPeltier's handbook. Temperatures have been measured using a microthermocouple on each face (cold face and hot face) of the MiniPeltier. Fig. 7 shows electrical modelled and experimental results and is composed of successive steady-state situations when the electrical current is ranged from 0 to 1.1 A. Despite the fact that the electrical model does not take into account other sources of heat loss, like connections or junctions, which impact increases with the electrical current, the model seems statisfactory.

C. Thermal Network for a 3D Thermal Problem

In addition to the Peltier modules, the submerged freeze gripper consists also on passive elements, like the end-effector and the heat sinks. Then the global thermal behaviour of the gripper involves a combination of conduction and convection effects. As shown in Fig. 8, the heat flux Q takes place between the two lateral temperatures T 1 and T 2 , and heat convection Q h occurs from all other surfaces in contact with the external fluid whose temperature is T ext . This configuration is quite different from the typical example illustrated in Fig. 5. In order to obtain the equivalent electrical model for these passive elements, we establish the relationship between the heat flux, and the convection and conduction terms as:

Q 1 = T 1 -T ext R v + T 1 -T 2 R c , (6)
where Q 1 is the heat flux on the left lateral surface, R c is the thermal conduction resistance, and R v is the thermal convection resistance.

The heat flux in the right lateral surface Q 2 can be obtained by symmetry of the heat flux Q 1 in (6):

Q 2 = T 2 -T ext R v + T 2 -T 1 R c . (7)
Equations ( 6) and ( 7) implies the thermal network of the Fig. 9. The calculation of the resistances required the determination of the heat flux Q(x). The heat balance for the volume given in Fig. 8 gives:

Q(x) = Q(x + dx) + dQ h . (8)
The conduction through the element is:

Q(x) = -kS dT dx , (9)
and the convection to the environment is:

dQ h = -hP dx(T (x) -T ext ), (10)
where P = 2a + 2b is the perimeter, and S = ab is the section. Parameters a, b and l, defined in Fig. 8, corresponds on height, width and length respectively.

Considering ( 8), [START_REF] Gauthier | Comparison between micro-objects manipulations in dry and liquid mediums[END_REF], and [START_REF] Gauthier | Forces analyses for micromanipulations in dry and liquid media[END_REF], the temperature T (x) of the element verifies:

L 2 d 2 T (x) dx 2 -T (x) = -T ext , (11)
where: L = kS/hP .

After solving [START_REF] Liu | Freeze tweezer to manipulate mini/micro objects[END_REF] to obtain the temperature T (x), and introducing the solution in [START_REF] Gauthier | Comparison between micro-objects manipulations in dry and liquid mediums[END_REF], the heat flux expression can be determined as:

Q(x) = - kS L (T 1 -T ext ) sinh(x/L) + cosh(x/L) sinh(l/L) (1 -cosh(l/L)) + (T 2 -T 1 ) cosh(x/L) sinh(l/L) . (13)
For x = 0, the heat flux Q(x) becomes Q 1 , given by:

Q 1 = -kS (T 1 -T ext ) (1 -cosh(l/L)) + (T 2 -T 1 )
Lsinh(l/L) .

(

) 14
Associating ( 6) and ( 14), the thermal resistances R c and R v can be written as:

R c = Lsinh(l/L) kS , (15)
R v = Lsinh(l/L) kS(cosh(l/L) -1) . ( 16
)
Both expressions can be also written as:

R c = l kS sinh(l/L) (l/L) ≈ l kS 1 + (l/L) 2 6 , (17)
R v = 2 P lh (l/L)sinh(l/L) 2(cosh(l/L) -1) ≈ 2 P lh 1 + (l/L) 2 6 . (18)
Consequently, for small ratio l/L verifying the inequality:

δ = (l/L) 2 6 1, (19)
the convection and conduction resistances can be simplified as:

R c0 = l/kS, (20) R v0 = 2/P lh. (21)
To validate the thermal network, the left lateral heat Q 1 and the right lateral heat Q 2 for different geometries have been calculated in water and air, using three different models: the analytical model applying (13); a finite element (FEM) calculation simulated with COMSOL Multiphysics 3.2; and the thermal network in Fig. 9. The experimental validation of the whole system will be presented in a next work.

The comparison of the values for several cases is presented in Table III. Let us note that the criterion δ defined in (19) represents the relevance of the thermal network. The first case for each medium (water and air) corresponds to the MicroPelt's heat sink geometry. The results obtained comparing either analytical or FEM calculation with the static thermal network allow us to validate it.

A whole system thermal network could then estimate properly heat processes, analyse clearly the parameters and finally is of great help for the design and optimization of the submerged freeze microgripper. Further works will focus on dynamic modelling, characterization of the parameters involved in the whole thermal network and its experimental validation.

IV. CONCLUSIONS AND FUTURE WORKS

An innovative handling strategy to manipulate microobjects whose typical size is under 100 µm has been developed and successfully tested. A comparative analysis of the interaction of dry and liquid media on surface forces, contact forces, and hydrodynamic forces have shown the interest of submerged artificial micro-objects manipulations. This approach permits new micromanipulation strategies adapted to the aqueous medium. A freeze gripper for such medium is proposed: an ice droplet is generated at the active part of the end-effector to pick up the object; to release it, the ice is thawed without having influence of the capillary force. During first experimentations the advantages of the liquid medium were exhibited: adhesion perturbations reduce considerably. The submerged freeze gripper is thus a promising approach to execute reliable and flexible micromanipulation and micro-assembly tasks.

To control and optimize the heat exchanges involved in the handling process and its cycle time, an equivalent electrical model is proposed. The thermal network for a Peltier module has been presented and compared to the MiniPeltier's experimental results. A new thermal network for a 3D heat sink has been also developed and compared to an analytical model and a FEM model. In all cases, the equivalent electrical model in steady state seems sufficiently accurate.

Dynamic thermal modelling is currently under development. This model will allow us in the next step to control the temperature and thickness of the ice microdrop.

Fig. 1 .

 1 Fig. 1. Handling strategy: (1) the micro-gripper approaches, (2) an ice droplet is generated and catch the object, (3) the object is manipulated, (4) the ice thaws and the object is liberated

Fig. 2 .

 2 Fig. 2. Submerged freeze microgripper principle

Fig. 3 .

 3 Fig. 3. Experimental freeze gripper

Fig. 4 .

 4 Fig. 4. Micromanipulation of a 600 × 600 × 100 µm 3 silicon object with the submerged freeze gripper

Fig. 5 .

 5 Fig. 5. Multilayer wall and its equivalent electric circuit

Fig. 7 .

 7 Fig. 7. Comparison between the electrical modelled net cooling and the experimental net cooling

Fig. 8 .

 8 Fig. 8. Thermal schema of passive elements

Fig. 9 .

 9 Fig. 9. Equivalent electric model for passive elements

TABLE I

 I Temperature at the Hot Face of the MiniPeltier

	Current i mP (A)	0	0.39	0.79 1.10
	Temperature T hmP ( o C)	21.3 21.5	22.0 22.4

TABLE II

 II Thermal and Electrical Analogy

	Thermal system	Equivalent electrical system
	Heat flux Q	Current i
	Temperature difference ∆T	Voltage difference ∆V
	Thermal resistance R th	Resistance R

TABLE III

 III Comparison of Heat Flux Q 1 and Q 2

	Geometry	δ (19)	Model	Q 1	Q 2
	(mm)			(W)	(W)
		Comparison in air
	a = 2	0.040 < 1	Analytical	-0.023 1.025
	b = 7		FEM	-0.025 1.029
	l = 22		Electrical	-0.014 1.056
	a = 50	0.001 < 1	Analytical	560	598
	b = 300		FEM	559	600
	l = 20		Electrical	561	599
		Comparison in water
	a = 2	0.403 < 1	Analytical	-3.89	5.07
	b = 7		FEM	-3.90	5.09
	l = 22		Electrical	-4.56	6.13
	a = 50	0.012 < 1	Analytical	395	770
	b = 300		FEM	382	779
	l = 20		Electrical	401	779

This work is supported by the PRONOMIA project granted by the ANR French National Research Agency Authors are with Lab.