M.D Artur Fedorowski
email: artur.fedorowski@med.lu.se

Bo Hedblad

Olle Melander

Early postural blood pressure response and cause-specific mortality among middleaged adults

Keywords: orthostatic hypotension, baroreflex, blood pressure, injuries, neurodegenerative diseases, cerebrovascular disease OH, orthostatic hypotension MPP, Malmö Preventive Project CVD, cardiovascular disease BMI, body-mass index SBP, systolic blood pressure DBP, diastolic blood pressure ICD, International Classification of Diseases IHD, ischaemic heart disease COPD, chronic obstructive pulmonary disease

Orthostatic hypotension (OH) is associated with increased total mortality but contribution of specific death causes has not been thoroughly explored. In this prospective study, authors followed up 32 068 individuals without baseline history of cancer or cardiovascular disease (69% men; mean age, 46 yrs; range, 26 to 61 yrs) over a period of 24 yrs. Hazard ratios (HRs) for total and cause-specific mortality associated with presence of OH and by quartiles of postural systolic blood pressure response (∆SBP)

were assessed using multivariate adjusted Cox regression model. A total of 7145 deaths (22.3%, 9.4 deaths/1000 person-yrs) occurred during follow-up. Those with OH (n=1943) had higher risk of death due to injury (HR, 1.86; 1.36-2.54) and neurological disease (HR, 2.19;. Analogically, risk of death caused by injury and neurological disease increased across the quartiles of ∆SBP from hyper-(Q1 SBP , +8.5±4.7 mmHg) to hypotensive response (Q4 SBP , -13.7±5.7 mmHg; HR, 1.29; 0.99-1.69, and 1.82; 1.19-2.80, respectively) as did also risk of death due to respiratory disease (Q4 SBP vs. Q1 SBP : HR, 1.48; 1.11-1.97). In contrast, risk curve for cerebrovascular death was U-shaped with nadir in the mildly hypotensive 3 rd quartile of ∆SBP (-5.0±0.1 mmHg, Q3 SBP vs.Q1 SBP ; HR, 0.74, 0.54-1.02; p for linear trend = 0.016). Additionally, cardiovascular mortality was increased among 5 805 rescreened participants (mean age, 53 yrs; 9.8% OH positive: HR, 1.54; 1.24-1.89, and Q4 SBP vs. Q1 SBP : 1.27; 1.02-1.57, respectively). In summary, increased mortality predicted by blood pressure fall on standing is associated with injuries, neurodegenerative, and respiratory diseases, as well as with cardiovascular disease in older adults. Moreover, both increase and pronounced decrease of SBP during early orthostasis indicate higher risk of cerebrovascular death.

INTRODUCTION

Orthostatic hypotension (OH), a relatively common manifestation of autonomic dysfunction [START_REF] Goldstein | Dysautonomias: clinical disorders of the autonomic nervous system[END_REF][START_REF] Goldstein | Neurogenic orthostatic hypotension: a pathophysiological approach[END_REF][START_REF] Mansoor | Orthostatic hypotension due to autonomic disorders in the hypertension clinic[END_REF], has been linked to increased mortality in general population [START_REF] Masaki | Orthostatic hypotension predicts mortality in elderly men: the Honolulu Heart Program[END_REF][START_REF] Luukinen | Prognosis of diastolic and systolic orthostatic hypotension in older persons[END_REF][START_REF] Rose | Orthostatic hypotension predicts mortality in middle-aged adults: the Atherosclerosis Risk In Communities (ARIC) Study[END_REF][START_REF] Verwoert | Orthostatic hypotension and risk of cardiovascular disease in elderly people: the Rotterdam study[END_REF][START_REF] Fedorowski | Orthostatic hypotension predicts all-cause mortality and coronary events in middle-aged individuals (The Malmo Preventive Project)[END_REF].

Although it seems indisputable that OH is associated with higher all-cause mortality, specific causes of death have been only partially studied. In particular, Rose et al. noticed that OH predicted both higher cardiovascular and non-cardiovascular mortality, but not cancer-related one [START_REF] Rose | Orthostatic hypotension predicts mortality in middle-aged adults: the Atherosclerosis Risk In Communities (ARIC) Study[END_REF]. However, other causes of the two-fold increased mortality were not explored. In parallel, authors reported that younger (< 42 yrs) compared to older individuals with OH demonstrated a higher all-cause mortality risk, but the risk of incident coronary event and stroke was not increased in this subset of population [START_REF] Fedorowski | Orthostatic hypotension predicts all-cause mortality and coronary events in middle-aged individuals (The Malmo Preventive Project)[END_REF].

Previous epidemiological studies concentrated mainly upon OH as a pronounced and well-defined variant of the hypotensive postural blood pressure response [START_REF] Benvenuto | Morbidity and mortality of orthostatic hypotension: implications for management of cardiovascular disease[END_REF]. Meanwhile, it is still unknown which mortality pattern is followed by other types of orthostatic responses: mildly hypotensive, neutral and hypertensive. Consequently, authors decided to study specific causes of death among those with and without OH, as well as in the subsets of different postural blood pressure responses within a large middle-aged Swedish population.

METHODS

Study population

The Malmö Preventive Project (MPP) is a population-based prospective cohort study in the city of Malmö, in southern Sweden [START_REF] Trell | Community-based preventive medical department for individual risk factor assessment and intervention in an urban population[END_REF]. The primary aim of the project was to invite large strata of the adult population to screening for cardiovascular disease (CVD). A total of 33,346 [START_REF] Allen | Risk factors for ischaemic stroke[END_REF]444 men and 10,902 women; mean age, 45 yrs; range, 26 to 61 yrs) inhabitants of Malmö, born between 1921 and 1948, were examined between 1974 and 1992. The overall attendance rate was 71% (range for examined age cohorts, 64 to 78%) [START_REF] Nilsson | Prevention of cardiovascular disease and diabetes: lessons from the Malmo Preventive Project[END_REF]. In the present study we excluded 549 participants because of missing blood pressure values, eight outliers (difference between systolic or diastolic blood pressure in supine and standing position of more than 80 mmHg), and all individuals with baseline history of CVD (myocardial infarction or stroke, n=159) or cancer (n=562). Thus, the study population consisted of 32,068 individuals (22,130 men and 9,938 women). An overall study design is presented in Fig. 1.

Baseline examination

The mailed invitation contained instructions to abstain from food, alcohol and tobacco for 12 h prior to the examination, which was performed by trained nurses in the morning.

Participants were, however, allowed to drink water ad libitum. Blood pressure was measured using the auscultatory method with a mercury sphygmomanometer and an appropriately sized cuff placed around the right arm supported at the level of the heart.

The first blood pressure reading was taken twice after 10 min rest in the supine position.

Then, the participants were asked to stand up and the second blood pressure measurement was taken twice in the standing position between one and three minutes of standing. The mean value of two readings was recorded for each position and rounded to nearest 5 mmHg. The body-mass index (BMI) was calculated as weight in kg divided by height squared in meters. Blood samples were collected from the antecubital vain and analyzed by standard methods at the Department of Clinical Chemistry, Malmö University Hospital. At the end, the participants were asked to fill in a self-administered questionnaire focused on personal and familiar history of CVD, hypertension, diabetes, cancer, smoking habits, and lifestyle patterns. The following questions were relevant to the history of myocardial infarction, stroke, and cancer, if the answer was yes: "Have you ever been hospitalized for myocardial infarction/stroke?" or "Have you ever had/do you have cancer?" Antihypertensive treatment was defined as a positive answer to the following question: "Do you take medication for high blood pressure?", but data on particular types of antihypertensive agents were not collected. Those who confirmed regular or occasional current smoking were classified as smokers. Alcohol intake was dichotomized by drinking behavior (problematic, non-problematic), and socioeconomic status was divided into low (manual worker) and high (non-manual worker) according to previously applied method [START_REF] Hedblad | Obesity and myocardial infarction--vulnerability related to occupational level and marital status. A 23-year follow-up of an urban male Swedish population[END_REF]. A detailed description of recruitment and screening procedures may be found elsewhere [START_REF] Trell | Community-based preventive medical department for individual risk factor assessment and intervention in an urban population[END_REF][START_REF] Berglund | Long-term outcome of the Malmo preventive project: mortality and cardiovascular morbidity[END_REF]. The health service authority of Malmö approved and funded the screening program. All participants gave informed consent.

Definitions of clinical characteristics

OH was defined according to the international consensus criteria as a decrease in systolic blood pressure (SBP) ≥20 mm Hg and/or decrease in diastolic blood pressure (DBP) ≥10 mm Hg within three minutes of standing [START_REF]The definition of orthostatic hypotension, pure autonomic failure, and multiple system atrophy[END_REF]. Orthostatic (postural) SBP response (ΔSBP) was defined as standing SBPsupine SBP.

Diabetes was defined as fasting plasma glucose ≥ 7.0 mmol/L, or current pharmacological treatment of diabetes, or self-reported history of diabetes [START_REF] Alberti | Definition, diagnosis and classification of diabetes mellitus and its complications. Part 1: diagnosis and classification of diabetes mellitus provisional report of a WHO consultation[END_REF].

Retrieval of end-points

All study participants were followed from the baseline examination until the death, emigration from Sweden, or 31 December 2006. Authors applied linkage of the unique 10-digit personal identification number with the Swedish National Cause of Death Register. The primary diagnosis retrieved from the register was considered valid for the specific cause of death as applied in previous studies [START_REF] Berglund | Long-term outcome of the Malmo preventive project: mortality and cardiovascular morbidity[END_REF][START_REF] Seshasai | Diabetes mellitus, fasting glucose, and risk of cause-specific death[END_REF]. The International Classification of Diseases (ICD)-8 codes were converted to ICD-9 codes, if applicable.The causes of deaths were classified into CVD (ICD-9 codes 390 to 459, ICD-10; I00 to I99), cancer (ICD-9 codes 140 to 239, ICD-10; C00 to C99), injury (ICD-9 codes 800 to 999, ICD-10; V, W, X, Y), respiratory diseases (ICD-9 codes 460 to 519, ICD-10; J), digestive system diseases (ICD-9 codes 520 to 579, ICD-10; K), neurological diseases (ICD-9 codes 320 to 389, ICD-10; G, H), and other causes of death. Death due to ischemic heart disease was defined as 410 to 414 or I20 to I22 according to ICD-9 and ICD-10, whereas death due to cerebrovascular disease as 430 to 438, or I60 to I69, respectively.

Those who emigrated from Sweden before 31 December 2006, and had been event-free at the time of emigration (n=624, 1.9%), were censored at the date of emigration. The mean follow-up time was 23.5 6.2 yrs.

Statistical analysis

The relationship between OH, quartiles of ∆SBP and all-cause mortality was assessed by the Kaplan-Meier method and the log-rank test. The hazards risks for total and causespecific mortality according to OH status, or, alternatively, by quartiles of ∆SBP were investigated using Cox proportional hazards models. The proportional hazards assumption was assessed graphically in a univariate model. Two Cox regression models were applied: a basic Model 1 adjusted for age and gender, and a more comprehensive Model 2 adjusted additionally for traditional risk factors for OH and mortality: BMI, SBP, resting heart rate, antihypertensive treatment, diabetes, total cholesterol and current smoking [START_REF] Fedorowski | Orthostatic hypotension predicts all-cause mortality and coronary events in middle-aged individuals (The Malmo Preventive Project)[END_REF]. In Model 2, authors excluded individuals with missing data on BMI (n=5) and total cholesterol (n=58). In additional adjustment, alcohol intake and socioeconomic status were entered into the Model 2, and analyses were repeated. Those with the unspecified socioeconomic status were excluded (n=2 512), of these 10.4% were OH positive. Finally, authors performed Cox regression analysis according to Model 1 and 2 on a subset of MPP cohort (n=6 109), which was rescreened after approximately six years from baseline, including orthostatic BP measurements (Fig. 1).

Potential interactions between OH and age or gender on cause-specific mortality were evaluated by including interaction terms in the multivariate model. All analyses were performed using SPSS statistical software version 17.0 for Windows (SPSS Inc., Chicago, IL). All tests were two-sided whereby p<0.05 was considered statistically significant for non-interaction terms, and p<0.10 for interaction terms.

RESULTS

Out of 32 068 individuals included in the present study, 1 943 (6.1%) met the diagnostic criteria of OH at baseline, whereas 570 among 5 805 participants (9.8%) were found to have OH during rescreening program. The baseline characteristics of MPP cohort and the rescreened subset of study population according to OH status were published previously. [START_REF] Fedorowski | Orthostatic hypotension predicts all-cause mortality and coronary events in middle-aged individuals (The Malmo Preventive Project)[END_REF][START_REF] Fedorowski | Consequences of orthostatic blood pressure variability in middle-aged men (The Malmo Preventive Project)[END_REF] As can be seen in Table 1, nearly one third of study participants (Q2 SBP , n=10,123) demonstrated a neutral orthostatic SBP response (i.e. no difference between supine and standing SBP), which resulted in a disproportional partition of study sample into quartiles. Those with hypotensive response (Q4 SBP ) were older, had higher SBP and DBP, and higher proportions of women, patients with diabetes and of those receiving antihypertensive treatment. Figure 2 illustrates the cumulative all-cause mortality during follow-up by quartiles of ∆SBP. The Kaplan-Meier curves for the total mortality by OH status corresponded to authors' previous publication [START_REF] Fedorowski | Orthostatic hypotension predicts all-cause mortality and coronary events in middle-aged individuals (The Malmo Preventive Project)[END_REF] and were not shown (log-rank test, p<0.001 for both). As can be seen in Table 2, total mortality and mortality rate were higher among those with as compared to those without OH (14.1 vs. 9.1 deaths per 1,000 person-yrs). A similar trend was observed across the quartiles of ∆SBP (Q1 SBP vs. Q4 SBP : 8.1 vs. 12.3 deaths per 1,000 person-yrs). As shown in Table 3, OH was predictive of four specific causes of death in the Cox regression analysis according to Model 1: CVD, injuries, respiratory and neurological diseases. However, after further adjustment for traditional risk factors (Model 2), only death due to injury and neurological disease (in 16/20 cases diagnosed as neurodegenerative disease) were predicted by OH. There were two potential interactions between OH and age: on death due to cancer (p=0.001) and neurological disease (p=0.082). In a subgroup analysis authors found that cancer-related mortality was significantly increased in the youngest stratum of study population (<42 yrs, n= 9,357; HR, 1.66; 95% CI: 1.03-2.69, p=0.039), whereas risk of death due to neurological disease was highest among the oldest study participants (>48 yrs, n= 11,830; HR, 2.87, 95% CI: 1.64-5.08, p<0.001). There was no potential interaction between OH and gender.

The main mortality trends found among those with OH were confirmed by stratification of study participants according to quartiles of postural BP response. As presented in Table 4, subset of population characterized by a pronounced hypotensive response (Q4 SBP, -13.7±5.7 mmHg) had highest total mortality (HR, 1.12; 95%CI: 1.05-1.20). Risk of death caused by both injury and neurological disease increased across the quartiles of ∆SBP, being for the latter and for Q4 SBP similar to that observed among OH positive individuals (HR, 1.82; 95%CI: 1.19-2.80 vs. 2.19; 1.37-3.48, respectively). In contrast, those with hypertensive BP response (Q1 SBP , +8.5±4.7 mmHg) had significantly lower risk of death due to respiratory disease (mainly represented by chronic obstructive pulmonary disease) as compared to the other quartiles of ∆SBP (Q4 SBP vs. Q1 SBP : HR, 1.48; 95%CI: 1.11-1.97). Moreover, authors noted a U-shaped risk curve for cerebrovascular death with a nadir in the 3 rd quartile of ∆SBP (Q3 SBP , -5.0±0.1 mmHg; HR, 0.74; 95%CI: 0.54-1.02; p for linear trend = 0.016). There was one potential interaction between quartiles of ∆SBP and age: on cancer-related mortality (p=0.031). In a subgroup analysis, the pronounced hypotensive response was predictive of cancerrelated mortality within the middle age stratum (42-48 yrs, n=10 881, Q4 SBP vs. Q1 SBP : HR, 1.25; 95%CI: 1.04-1.49; p for linear trend 0.067), whereas among youngest study participants (<42 yrs) the highest risk was observed in the 3 rd but not 4 th quartile (Q3 SBP vs. Q1 SBP : HR, 1.23; 95%CI: 0.91-1.67, and Q4 SBP vs. Q1 SBP : HR, 0.96; 95%CI: 0.67-1.39; p for linear trend 0.69).

Additional adjustments for socioeconomic status and alcohol intake did not change the main results and only slightly attenuated mortality risk associated with OH (injuries, HR:

1.74; 95%CI: 1.20-2.53; neurological, 2.00, 1.18-3.36), and Q4 SBP (injuries, HR: 1.21; 95%CI: 0.89-1.64; neurological, 1.68; 1.05-2.69, respiratory, 1.46; 1.05-2.04).

As shown in Table 5, results obtained from the subsidiary analysis on the rescreened subset of MPP cohort were essentially consistent with the main findings. However, the relative mortality risk conferred by presence of hypotensive response at rescreening (i.e.

OH positive or Q4 SBP ) was in general higher than that at baseline, both for all and specific causes of death. Furthermore, the hypotensive response at rescreening independently predicted higher cardiovascular mortality, in contrast to the baseline status (OH positive, HR, 1.54; 95%CI: 1.24-1.89; p<0.001, and Q4 SBP vs. Q1 SBP : HR, 1.27; 95%CI: 1.02-1.57, p for linear trend =0.021, respectively).

DISCUSSION

Orthostatic haemodynamic impairment is generally regarded as a troublesome clinical condition, especially in elderly, chronically ill, neurological, and polymorbid patients [START_REF] Gupta | Orthostatic hypotension in the elderly: diagnosis and treatment[END_REF][START_REF] Low | Management of neurogenic orthostatic hypotension: an update[END_REF][START_REF] Maule | Orthostatic hypotension: evaluation and treatment[END_REF], and surprisingly little is known about its prevalence and consequences in general population. In particular, association between OH and the cause-specific mortality remains largely unexplored. To our knowledge, this is the first study to report that injuries and neurological diseases may be etiologically related to the increased mortality among middle-aged individuals with often asymptomatic OH. Moreover, a statistical evidence could be also demonstrated for respiratory diseases (for the quartile with the most pronounced hypotensive SBP response) and cancer (in younger individuals aged <48 yrs). The main findings are discussed below in regard to specific diagnostic categories:

Cardiovascular disease

The association between prevalent OH and long-term mortality due to CVD (or ischemic heart disease only), reported previously by other authors in the ARIC cohort [START_REF] Rose | Orthostatic hypotension predicts mortality in middle-aged adults: the Atherosclerosis Risk In Communities (ARIC) Study[END_REF], was remarkably attenuated after adjustment for conventional risk factors. These results were most probably an effect of a strong correlation between OH and CV risk factors, which in turn predict increased mortality mediated by CVD. Except for total cholesterol, all other covariates entered into the more comprehensive model are known to be independent determinants of both OH [START_REF] Fedorowski | Orthostatic hypotension predicts all-cause mortality and coronary events in middle-aged individuals (The Malmo Preventive Project)[END_REF] and cardiovascular morbidity, such as myocardial infarction and stroke [START_REF] Khot | Prevalence of conventional risk factors in patients with coronary heart disease[END_REF][START_REF] Allen | Risk factors for ischaemic stroke[END_REF]. Taking into account conventional risk factors might thus efficiently explain why individuals with OH were prematurely affected by CVD and died. However, in the rescreened subset of study population, characterized by similar mean age as that in the ARIC cohort (53 vs. 54 yrs) the hypotensive orthostatic response was independently predictive of cardiovascular mortality. Consequently, presence of impaired orthostatic BP response in a more advanced age may be a stronger cardiovascular risk factor than the same phenomenon among relatively younger individuals.

Another important finding in this diagnostic group was a trend toward U-shaped curve for quartiles of ∆SBP and cerebrovascular mortality, in concordance with previous reports [START_REF] Kario | Ucurve relationship between orthostatic blood pressure change and silent cerebrovascular disease in elderly hypertensives: orthostatic hypertension as a new cardiovascular risk factor[END_REF][START_REF] Yatsuya | Postural changes in blood pressure and incidence of ischemic stroke subtypes: the ARIC study[END_REF]. Thus, a neutral or a slightly hypotensive SBP response during orthostatic challenge may play a protective role against cerebrovascular lesion.

Injuries

One of the most consistent findings in this study was the relationship between OH and injury-related deaths. Haemodynamic impairment during orthostasis is a well-known risk factor of traumatic falls among neurologically-ill and elderly patients [START_REF] Goldstein | Neurogenic orthostatic hypotension: a pathophysiological approach[END_REF][START_REF] Chang | Incidence, risk factors and consequences of falling injuries among the community-dwelling elderly in Shihpai, Taiwan[END_REF]. The mean age of the studied population was, however, only about 45 yrs. We propose that some of injuries were provoked by a temporary impairment of the cerebral circulation when the haemodynamic reserve between minimal BP needed for maintenance of cerebral perfusion (usually SBP ≥ 60-70 mm Hg) [START_REF] Van Beek | Cerebral autoregulation: an overview of current concepts and methodology with special focus on the elderly[END_REF] and the actual value of BP was compressed by the orthostatic drop. Some patients with asymptomatic impairment of orthostatic BP regulation may not be aware of the problem until the first episode of sudden onset dizziness or syncope occurs. Interestingly, the best predictor of injury-related death was the standard OH definition, which suggests that the magnitude of BP fall is a crucial factor behind this association.

Neurological diseases

Neurological etiology was found to be another factor associated with increased mortality in individuals with OH and a pronounced postural decrease of SBP (Q4 SBP ). This finding is not at all surprising taking into account a strong etiological relationship between OH and neurodegenerative diseases, such as Parkinson's disease and primary autonomic failure [START_REF] Freeman | Clinical practice. Neurogenic orthostatic hypotension[END_REF]. Thus, in some participants, subclinical neurodegenerative process may have already been present at baseline and the orthostatic challenge was sensitive enough to detect the accompanying autonomic dysfunction. Notably, the risk of fatal neurological disease was higher among older participants (>48 yrs), and in the rescreened subset of cohort, confirming that postural BP drop is more often related to neurogenic OH with advancing older [START_REF] Low | Prevalence of orthostatic hypotension[END_REF].

Respiratory diseases

Association between postural BP response and mortality due to a respiratory disease (mainly chronic obstructive pulmonary disease, COPD) was a surprising finding. We know that smoking is associated with OH [START_REF] Fedorowski | Orthostatic hypotension predicts all-cause mortality and coronary events in middle-aged individuals (The Malmo Preventive Project)[END_REF]. However, after adjustment for current smoking the predictive role of postural SBP and MAP response remained statistically significant. These results suggest that autonomic dysfunction is associated with a higher risk of developing terminal lung disease. Among the proposed predictors of increased mortality in COPD there are no parameters that can be directly linked to OH or autonomic dysfunction [START_REF] Puhan | Expansion of the prognostic assessment of patients with chronic obstructive pulmonary disease: the updated BODE index and the ADO index[END_REF]. On the other hand, some authors claim that spirometry alone is not a good predictor of mortality in COPD, and other parameters, such as low BMI, dyspnoea, and exercise capacity are often included in the mortality risk score systems [START_REF] Celli | Predictors of Survival in COPD: more than just the FEV1[END_REF]. Interestingly, low BMI is also an independent determinant of OH [START_REF] Fedorowski | Orthostatic hypotension predicts all-cause mortality and coronary events in middle-aged individuals (The Malmo Preventive Project)[END_REF]. Moreover, in patients with COPD, cardiac autonomic dysfunction (reduced heart rate variability) was found to be correlated with lower BMI, reduced level of physical activity in daily life, and impairment of respiratory and peripheral muscle condition [START_REF] Camillo | Heart rate variability and disease characteristics in patients with COPD[END_REF]. In orthostatic blood pressure dysregulation a similar pattern has been observed: a sympathetic hyperactivity associated with reduced variability of the parasympathetic nervous system [START_REF] Sato | Autonomic function in adolescents with orthostatic dysregulation measured by heart rate variability[END_REF]. Thus, the common pathway for the orthostatic blood pressure drop and increased risk of respiratory-related mortality might be a chronically altered autonomic function signaled by lower BMI, worse exercise tolerance, and more subtle markers, such as reduced heart rate variability. Unfortunately, given the available cohort data, authors were not able to confirm this hypothesis.

Cancer

The relevance of the association between cancer-related mortality and hypotensive BP response in younger adults is unclear and might suggest that haemodynamic postural impairment (and subclinical autonomic disorders), if acting long enough, can favor carcinogenesis through unspecified biologically active substances, whose plasma or tissue activity is altered by a chronically increased sympathetic tonus and reduced parasympathetic reactivity. However, such hypothesis would require further studies to be confirmed.

Strengths and limitations of the study

Strength of this study lies in a large number and similar ethnic background of the studied cohort, long follow-up, and access to an end-point register with a high case ascertainment. The main limitation is the fact that standing blood pressure was recorded between the 1 st and 3 rd minute after assuming an upright position and we may have, therefore, missed those with initial (<1 min) [START_REF] Wieling | Initial orthostatic hypotension: review of a forgotten condition[END_REF] and delayed (>3 min) orthostatic hypotension [START_REF] Gibbons | Delayed orthostatic hypotension: a frequent cause of orthostatic intolerance[END_REF]. Moreover, OH was assessed in the whole cohort only once between baseline and end-point.

Conclusions

Among middle-aged individuals the increased risk of mortality independently conferred by impairment of orthostatic blood pressure regulation is associated with injuries, neurodegenerative, and respiratory diseases. Furthermore, both increase and pronounced decrease of systolic blood pressure during early orthostasis indicate a higher risk of death due to cerebrovascular disease, whereas blood pressure decrease on standing in the advanced age seems to be also an independent predictor of higher cardiovascular mortality.

Causes of Death

Hazard Ratio

Figure 1 .

 1 Figure 1. Overall Study Design.

Figure 2 .

 2 Figure 2. Cumulative All-Cause Mortality During Follow-up According to Quartiles of

Table 1 .

 1 Baseline Characteristics of Participants of the Malmö Preventive ProjectAccording to Quartiles of Postural Systolic Blood Pressure Response.

	Characteristics	All	1st	2nd	3rd	4th
		n=32 068	Quartile	Quartile	Quartile	Quartile
			(Q1 SBP )	(Q2 SBP )	(Q3 SBP )	(Q4 SBP )
			n= 9 543	n=10 123	n= 5 917	n= 6 485
	Postural SBP response	-1.2±8.7	+8.5±4.7	0.0±0.1	-5.0±0.1	-13.7±5.7
	(mmHg)
	Age (yrs)	45.5±7.4	44.0±7.4	45.1±7.5	46.1±7.1	47.8±7.0
	Gender (male, %)	69.0	75.8	70.0	64.8	61.2
	BMI (kg/m 2 )	24.6±3.6	24.5±3.4	24.6±3.6	24.6±3.7	24.6±3.8
	Current smoker (%)	44.8	45.1	44.4	45.1	44.7
	Supine SBP (mmHg)	126.3	122.6	125.5	126.3	133.2
		±15.5	±14.3	±14.6	±14.4	±17.1
	Supine DBP (mmHg)	84.3±9.6	83.6±9.6	84.1±9.4	84.0±9.3	86.0±10.1
	Heart rate (beats/min)	67.5±9.8	66.9±9.7	67.2±9.7	67.8±9.5	68.5±10.1
	Antihypertensive	5.2	3.6	4.7	4.7	8.9
	treatment (%)
	Diabetes (%)	4.6	3.9	4.4	4.6	6.1
	Total cholesterol	5.7±1.1	5.6±1.1	5.6±1.1	5.7±1.1	5.8±1.1
	(mmol/L)
	Problematic drinking	21.6	23.6	22.3	20.1	19.1
	behavior (%)

Table 2 .

 2 All-Cause Mortality in Relation to Presence or Absence of Orthostatic Hypotension (OH) and Quartiles of Orthostatic Systolic Blood Pressure Response (∆SBP) Among 32 068 Participants of the Malmö Preventive Project.

	Subgroups according	Number of	Total mortality	No of deaths/1000
	to OH status	individuals at risk	(%)	person-yrs
	All	32 068	7 145 (22.3)	9.4
	OH negative	30 125	6 540 (21.7)	9.1
	OH positive	1 943	605 (31.1)	14.1
	1 st Quartile of ∆SBP	9 543	1 886 (19.8)	8.1
	2 nd Quartile of ∆SBP	10 123	2 154 (21.3)	8.9
	3 rd Quartile of ∆SBP	5 917	1 299 (22.0)	9.3
	4 th Quartile of ∆SBP	6 485	1 806 (27.8)	12.3

Table 3 .

 3 Association Between Orthostatic Hypotension (OH) and Specific Causes of Death Among 32 068 Participants of the Malmö Preventive Project. Model 1: adjusted for age and gender; Model 2: adjusted for age, gender, body mass index, systolic blood pressure, resting heart rate, antihypertensive treatment, diabetes, total cholesterol, and current smoking. IHD, ischaemic heart disease.

	Causes of Death	Model 1	Model 2
	No of deaths	Hazard Ratio	Hazard Ratio
	OH neg/pos	[95% CI]	[95% CI]
	All causes	1.30	1.11
	6 540/605	[1.19-1.41]	[1.02-1.21]
		P<0.001	P=0.018
	Cancer	1.08	1.01
	2 524/198	[0.93-1.25]	[0.87-1.17]
		P=0.32	P=0.93
	Cardiovascular	1.36	1.02
	2 394/244	[1.19-1.56]	[0.89-1.17]
		P<0.001	P=0.78
	IHD	1.40	1.03
	1 571/161	[1.19-1.65]	[0.87-1.22]
		P<0.001	P=0.74
	Cerebrovascular	1.02	0.79
	376/31	[0.71-1.48]	[0.54-1.16]
		P=0.91	P=0.23
	Injuries	1.88	1.88
	418/46	[1.39-2.56]	[1.37-2.57]

Table 5

 5 Association between Orthostatic Hypotension, Quartiles of Systolic Blood Pressure Response (ΔSBP) and Cause-Specific Mortality Among 5 805 Participants of the Rescreening Program within Malmö Preventive Project.

ACKNOWLEDGMENTS

This work was supported by grants from the Swedish Medical Research Council, the Swedish Heart and Lung Foundation, the Medical Faculty of Lund University, Skåne University Hospital, the Albert Påhlsson Research Foundation, the Crafoord Foundation, the Ernhold Lundströms Research Foundation, the Region Skåne, the Hulda and Conrad Mossfelt Foundation, the King Gustaf V and Queen Victoria Foundation, the Wallenberg Foundation, and the Lennart Hanssons Memorial Fund.


PhD Luna C Muñoz
email: lmunoz@uclan.ac.uk

PhD Vilmante Pakalniskiene

PhD Paul J Frick

Parental Monitoring 1 Running head: PARENTING AND YOUTH BEHAVIOR BY CALLOUS-UNEMOTIONAL TRAITS Parental Monitoring and Youth Behavior Problems: Moderation by Callous-Unemotional Traits Over Time

Keywords: Parenting, Callous-unemotional traits, Delinquency, Problem behaviors

Background and Objectives: Prior research suggests that parents' monitoring behaviors are related to the conduct problems of children but not to the conduct problems of children with callous-unemotional traits. However, these studies have been cross-sectional. The present short-term longitudinal study investigates the bidirectional influences of parental monitoring Parental Monitoring 2 and youth problem behaviors, while also examining the potential moderating influence of callous-unemotional traits.

Methods:

We assessed adolescents (Mean age=14.5 years; SD =1.8) and parents at two time points. Youths reported their callous-unemotional traits and delinquency, while parents reported their child's conduct problems, and their parenting behaviors to track and control their child's activities.

Results:

We found support for a child-driven change in parents' monitoring behaviors over time. Specifically, children with high callous-unemotional traits had parents who reduced their monitoring behaviors over time, and their different types of monitoring behaviors were less synchronous over time. Also, parents of youths with high callous-unemotional traits showed a trend toward not being stable in their surveillance efforts over time. Moreover, greater behavioral control for youths high on callous-unemotional traits did not lead to parents' greater knowledge about their youths. In fact, having less knowledge was related to decreases in parental control, when youths were high on callous-unemotional traits.

Conclusions: The present study supports the importance of personality in shaping how parents actively monitor their children.

Parental Monitoring and Youth Behavior Problems: Moderation by Callous-Unemotional

Traits Over Time Problem behaviors may be influenced by parental efforts to know where their children are, but this may be truer for some youths than others. For example, problem behaviors have been less strongly related to parenting when they co-occur with callous-unemotional (CU) traits [START_REF] Edens | Psychopathic features moderate the relationship between harsh and inconsistent parental discipline and adolescent antisocial behavior[END_REF][START_REF] Oxford | Callous-unemotional traits moderate the relation between ineffective parenting and child externalizing problems: A partial replication and extension[END_REF][START_REF] Hipwell | Callous-unemotional behaviors in young girls: Shared and unique effects relative to conduct problems[END_REF][START_REF] Wootton | Ineffective parenting and childhood conduct problems: The moderating role of callous-unemotional traits[END_REF]. The suggestion has been that youths with CU traits (i.e., lack of guilt; low empathy; constricted emotions) have high levels of conduct problems, regardless of their parents' monitoring [START_REF] Wootton | Ineffective parenting and childhood conduct problems: The moderating role of callous-unemotional traits[END_REF][START_REF] Oxford | Callous-unemotional traits moderate the relation between ineffective parenting and child externalizing problems: A partial replication and extension[END_REF]. Thus, etiological factors separate from parental monitoring seem to play a more important role in the development of conduct problems for these youths [START_REF] Wootton | Ineffective parenting and childhood conduct problems: The moderating role of callous-unemotional traits[END_REF].

However, research has made a distinction between monitoring efforts and knowledge, and many of the assessments being used assess what parents know about their children (i.e., knowledge) rather than actions (i.e., monitoring) to gain knowledge [START_REF] Stattin | Parental monitoring: A reinterpretation[END_REF][START_REF] Kerr | What parents know, how they know it, and several forms of adolescent adjustment: Further support for a reinterpretation of monitoring[END_REF]. Indeed, much parental monitoring research has simply assessed whether parents know their children's whereabouts and peer activities. For example, questions included in the Wootton and colleagues [START_REF] Wootton | Ineffective parenting and childhood conduct problems: The moderating role of callous-unemotional traits[END_REF] study asked about whether the child hung out with peers that were unknown to the parent. However, this question does not assess what led to the lack of knowledge.

Children may be unsupervised, because they sneak out, disobey their parents' demands, or because parents have been lax; the former two are part of the child's behavior. Other items ask about the child telling the parent where she/he is going, which measures the child's willingness to disclose information and not what the parent does [START_REF] Stattin | Parental monitoring: A reinterpretation[END_REF][START_REF] Kerr | What parents know, how they know it, and several forms of adolescent adjustment: Further support for a reinterpretation of monitoring[END_REF]. Thus, to truly understand the associations between parental monitoring efforts and child behavior problems, it is important to assess parents' knowledge separate from monitoring (e.g., using behavioral control and soliciting youths for information). Treatment for children with conduct problems often rely on research showing that parents' actions (i.e., what parents do) affect behavior. This issue is particularly important when a possibility exists that this differs for youths with high levels of CU traits who may influence parental behavior to a greater degree than other children. Specifically, research supports the contention that parental behavior is often a reaction to problem behaviors in the child, as much as it is a cause of behavior problems [START_REF] Huh | Does problem behavior elicit poor parenting?: A prospective study of adolescent girls[END_REF][START_REF] Kerr | Children's influence on family dynamics: The neglected side of family relationships[END_REF]. Longitudinal research has shown that conduct problems often lead to parents loosening control over their children [START_REF] Kerr | Children's influence on family dynamics: The neglected side of family relationships[END_REF][START_REF] Huh | Does problem behavior elicit poor parenting?: A prospective study of adolescent girls[END_REF][START_REF] Fanti | Toward a transactional model of parent-adolescent relationship quality and adolescent psychological adjustment[END_REF][START_REF] Burke | Reciprocal relationships between parenting behavior and disruptive psychopathology from childhood through adolescence[END_REF][START_REF] Stice | A longitudinal examination of the reciprocal relations between perceived parenting and adolescents' substance use and externalizing behaviors[END_REF][START_REF] Kerr | Parents react to adolescent problem behaviors by worrying more and monitoring less. What can parents do? New insights into the role of parents in adolescent problem behaviors[END_REF]. For example, greater delinquency has been found to lead to parents being less controlling and less supportive [START_REF] Kerr | Children's influence on family dynamics: The neglected side of family relationships[END_REF]. Therefore, youth behaviors may affect the way parents react. However, parents' reactions to children with CU traits have rarely been studied, and less frequently in a longitudinal study. Thus, the direction of effect is unclear from these studies.

Based on the research showing that problem behaviors can affect parenting, we argue for another possibility other than simply conceptualizing parents as the contributors to problem behaviors, depending on the level of CU traits. Thus, it is possible that youth behaviors may change parents' monitoring, and this may depend on the level of CU traits.

When children are cold and emotionally closed, parents may have less knowledge and monitor less often [START_REF] Kerr | Parents react to adolescent problem behaviors by worrying more and monitoring less. What can parents do? New insights into the role of parents in adolescent problem behaviors[END_REF]. Also, other studies have shown that youths' manipulative and secretive actions at home were predictive of parents' reactions [START_REF] Kerr | Children's influence on family dynamics: The neglected side of family relationships[END_REF]. The combination of coldness, manipulativeness, and delinquency may increase the reaction parents have. Indeed, children high on CU traits have parents who report a high level of distress over these traits [13]. Thus, prior cross-sectional findings can be re-conceptualized as showing that problem behaviors could contribute to poor parental monitoring, and this could vary depending on the level of CU traits.

Prior cross-sectional studies [START_REF] Wootton | Ineffective parenting and childhood conduct problems: The moderating role of callous-unemotional traits[END_REF][START_REF] Edens | Psychopathic features moderate the relationship between harsh and inconsistent parental discipline and adolescent antisocial behavior[END_REF][START_REF] Hipwell | Callous-unemotional behaviors in young girls: Shared and unique effects relative to conduct problems[END_REF] have suggested parental monitoring, along with other parenting measures, is more strongly associated with behavior problems in children low on CU traits. Longitudinal research is needed to support this suggestion. Moreover, existing research has not considered the opposite direction of effect (i.e., child behaviors affecting monitoring) as an explanation for the findings [START_REF] Wootton | Ineffective parenting and childhood conduct problems: The moderating role of callous-unemotional traits[END_REF][START_REF] Edens | Psychopathic features moderate the relationship between harsh and inconsistent parental discipline and adolescent antisocial behavior[END_REF][START_REF] Hipwell | Callous-unemotional behaviors in young girls: Shared and unique effects relative to conduct problems[END_REF]. That is, it may be that children's behavior affects parenting in a different manner for children high and low on CU traits.

Further, prior research has not assessed parents' monitoring actions, such as solicitation of information and behavioral control, when they have CU traits. We focused on these parenting behaviors, because a recent meta-analysis has found a strong effect for poor monitoring on adolescent's antisocial behavior [START_REF] Hoeve | The relationship between parenting and delinquency: A meta-analysis[END_REF].

To address these limitations, we assessed delinquent and conduct problem behaviors and parental monitoring and knowledge at two time points (with one year lag) using both parent and youth reports. Rather than relying on cross-sectional data [START_REF] Oxford | Callous-unemotional traits moderate the relation between ineffective parenting and child externalizing problems: A partial replication and extension[END_REF][START_REF] Wootton | Ineffective parenting and childhood conduct problems: The moderating role of callous-unemotional traits[END_REF], the cross-lagged design used in the present study allowed us to test the effect of problem behavior on parental monitoring and parental knowledge over time, using some of the same measures that have been used in past research (i.e., the Alabama Parenting Questionnaire) [START_REF] Oxford | Callous-unemotional traits moderate the relation between ineffective parenting and child externalizing problems: A partial replication and extension[END_REF][START_REF] Wootton | Ineffective parenting and childhood conduct problems: The moderating role of callous-unemotional traits[END_REF] as well as newer measures of monitoring. Also, this design allowed us to test the effect of monitoring and knowledge on problem behavior over time. Finally, the moderation of these effects by CU traits was tested.

Two structural equation models were tested: one with delinquency and one with conduct problems as outcome variables. These analyses tested two main hypotheses. First, we tested whether changes in parenting were predicted by the problem behaviors of youths who Parental Monitoring 5 were high versus low in CU traits, which would indicate a reduction in parental monitoring due to a combination of problem behavior and a lack of caring and remorse over these actions. Thus, parents were expected to react to a closed, antisocial child with less solicitation and control over time. Second, parenting behaviors were expected to have a stronger effect on problem behaviors, but this was predicted to be only in those low on CU traits.

Method

Participants

A two-step stratified random sampling procedure was employed to recruit participants.

In the first step, approximately 4,000 parents of children in the 3 rd , 4 th , 6 th , and 7 th grades of two school systems in a moderate sized city in the southeastern United States received announcements about the study. The two school systems were chosen because one served the immediate urban area and the second served the surrounding region that was predominantly suburban and rural. Those parents who agreed to have their child participate in the study completed informed consent forms and screening questionnaires used to assess the presence of DSM-IV symptoms [START_REF]Diagnostic and statistical manual of mental disorders[END_REF] and CU traits [16,see 17 for a detailed description of the sample].

The sample of 1,136 participating children was divided into four groups based on combined parent and teacher ratings of conduct problem symptoms and callous-unemotional (CU) traits [START_REF] Frick | Psychopathic traits and conduct problems in community and clinic-referred samples of children: Further development of the psychopathy screening device[END_REF]. Next, 25 children out of each of four groups (high and low on conduct problems and high and low on CU traits), ensuring that about half of each group came from the younger and older cohorts. These four groups were first blocked according to gender, ethnicity, and socioeconomic status and participants were selected through a stratified random sampling procedure to ensure that the four groups matched the group from which they were sampled on the three stratification variables. This sample of 100 children and their parents were reassessed at approximately yearly intervals for the next four years as part of a larger study of children at risk for antisocial and aggressive behavior [START_REF] Frick | Callousunemotional traits and developmental pathways to severe conduct problems[END_REF][START_REF] Frick | Callousunemotional traits in predicting the severity and stability of conduct problems and delinquency[END_REF]. For the present study, all data were taken from the final two waves of assessment. We did not utilize the original cut-offs which were used to form groups because they were done two years prior to the current assessment. As reported in Muñoz and Frick [17], there was no selective attrition over the course of the study. Also, attrition did not differ by CU traits or antisocial behavior [17]. Our decision to use the final two waves was due to our need to include questionnaires about monitoring, which were included at these two waves only. The average length of time between these two waves was 13.38 (SD= 2.82) months. Of the 100 children, 91 children (47 boys and 44 girls) participated in at least one of the waves of data collection reported in this paper. Our final sample included 75 parents and reported in the current manuscript (when the children were in the 6th, 7th, 9th, and 10th grades) was 14.5 (SD= 1.8) years.

Callous-Unemotional Traits. The callous-unemotional dimension of the Antisocial

Process Screening Device [START_REF] Frick | The antisocial process screening device[END_REF] was used. Each of the six items were scored either 0 (Not at all true), 1 (Sometimes true), or 2 (Definitely true). Consistent with past research [17], the internal consistency for the CU dimension (0.61 and 0.53 at Times 1 and 2, respectively) was modest. Despite the low internal consistency, the self-report version of the APSD has been shown to designate a more severe, chronic, and violent juvenile offender [START_REF] Caputo | Family violence and juvenile sex offending: Potential mediating roles of psychopathic traits and negative attitudes toward women[END_REF][START_REF] Kruh | Historical and personality correlates to the violence patterns of juveniles tried as adults[END_REF], and the CU dimension has shown acceptable stability over time [17]. Thus, despite the modest internal consistency, there is evidence to support the stability and construct validity of the scale.

Youth-Reported Delinquency. The Self-Report of Delinquency Scale [START_REF] Elliott | Reconciling race and class differences in self-reported and official estimates of delinquency[END_REF] assesses the child's self-report of 36 illegal juvenile acts. Consistent with past uses of the scale [START_REF] Krueger | Personality traits are linked to crime among men and women: Evidence from a birth cohort[END_REF], a composite measure was created by summing the number of delinquent acts committed (with a possible range of 0 to 33). Youth-reported delinquency was used since parents may be unaware of behaviors that occur outside the home. This composite had coefficient alphas of 0.83 and 0.85 at the two assessment points.

Parent-Reported Conduct Problems. The Behavioral Assessment System for

Children-Parent Rating Scale [START_REF] Reynolds | Behavior assessment system for children[END_REF] is a standardized measure of child adjustment based on parent report that has normative data for children ages 4 to 18. Behaviors are rated on a fourpoint scale of frequency from Never to Always. The Conduct Problems scale includes behaviors, such as cheats in school and gets into trouble; thus, parents report on problem behaviors that they would be able to observe in the home or obtain knowledge about from the school. In a nationwide normative sample, coefficient alpha reliabilities for the Conduct Problems scale ranged from .64 to .75 [START_REF] Reynolds | Behavior assessment system for children[END_REF]. The internal consistency for this scale (α = .66 at Time 1 and α = .76 at Time 2) was adequate in the current sample.

Parental Knowledge. The Alabama Parenting Questionnaire [START_REF] Shelton | Assessment of parenting practices in families of elementary school-age children[END_REF] includes 42 items which assess five parenting constructs. For this study, we used the 10 parent-reported items assessing Poor Monitoring/Supervision (e.g., "Your child goes out without a set time to be home" and "Your child is out with friends you do not know"), which we call "parental knowledge". Items on the global report form are rated on a 5-point frequency scale indicating (1) "never" to (5) "always". This scale has shown differential relations with children's conduct problems based on high and low CU traits [START_REF] Oxford | Callous-unemotional traits moderate the relation between ineffective parenting and child externalizing problems: A partial replication and extension[END_REF][START_REF] Wootton | Ineffective parenting and childhood conduct problems: The moderating role of callous-unemotional traits[END_REF]. The internal consistency Parental Monitoring 7 for this scale (α = .74 at Time 1 and α = .78 at Time 2) was good. This scale was reverse scored so that higher scores indicated greater knowledge.

Parental Monitoring. Research shows that monitoring should be based on parents' actions [START_REF] Kerr | What parents know, how they know it, and several forms of adolescent adjustment: Further support for a reinterpretation of monitoring[END_REF][START_REF] Stattin | Parental monitoring: A reinterpretation[END_REF]. The parenting questionnaire created by Stattin and Kerr includes scales regarding parents' solicitation, parental control, and child's disclosure. These measures have been validated in Swedish and US samples [e.g., [START_REF] Kerr | What parents know, how they know it, and several forms of adolescent adjustment: Further support for a reinterpretation of monitoring[END_REF][START_REF] Stattin | Parental monitoring: A reinterpretation[END_REF][START_REF] Crouter | How do parents learn about adolescents' experiences? Implications for parental knowledge and adolescent risky behavior[END_REF]. The measures included were regarding parents monitoring attempts, such as control and solicitation. Items asked parents to rate, on a five-point frequency scale, indicating (1) "yes, always" to (5) "no, never".

Parental control and solicitation were each comprised of five items such as, "Does your child have to ask you first, before he/ she can make Saturday night plans with friends?" (indicating control) and "Do you usually ask your child to tell you about what happens during free time? (who he/ she meets out on the town, leisure activities, etc)" (indicating solicitation). The internal consistency for control (α = .72 at Time 1 and α = .78 at Time 2) and solicitation (α = .62 at Time 1 and α = .67 at Time 2) were acceptable in the current sample. These scales were again reverse scored so that higher scores indicated greater control and solicitation.

Data Analysis

To examine relations between parents' behaviors and youth behavior, we tested crosslagged panel design model with Mplus 5.0 [START_REF] Muthén | Mplus user's guide[END_REF]. For analyses we used full information maximum likelihood (FIML) because we used raw data as the input file for the program and some of the data were missing. The full information maximum likelihood techniques provide less biased estimates than listwise or pairwise deletion [START_REF] Schafer | Missing data: Our view of the state of the art[END_REF], and are used even when data are not missing at random [START_REF] Little | Statistical analysis with missing values[END_REF]. Proportions of missing data are examined by a covariance "coverage" provided by Mplus. The minimum coverage is recommended at .10 [START_REF] Muthén | Mplus user's guide[END_REF]. In this study, the coverage in the models ranged from .74 to .93.

Cross-lagged panel design models were tested in this study and the conceptual model is presented in Figure 1. We tested two models: one model included delinquency and parenting, while another model included conduct problems (instead of delinquency) and parenting. In both models, all the variables measured at the same time were correlated (see Table 1 for descriptives and zero-order correlations). A person-centered approach to analysis was chosen, recognizing that using cut-scores on continuous dimensions can reduce the power to detect significant associations. Although significant debate exists as to whether psychopathy scores should be conceptualized as taxonic [31] or along a continuum [START_REF] Murrie | Youth with psychopathy features are not a discrete class: A taxometric analysis[END_REF], we wanted a practical way to translate results into unambiguous implications for subgroups of individuals with conduct problems. Thus, we used multiple group analyses to examine the possible moderating effects of CU traits. A median split on the youths' report of CU traits was performed to investigate the effects at low and high levels of CU traits. The median split was used, given that the current sample recruitment overrepresented children high on conduct problems and high on CU traits. This procedure resulted in relatively equal numbers of boys and girls in the two groups, and no differences in age between the groups were evident.

Results

Full Sample

In the full sample, we tested whether youth problem behaviors, such as youth reported delinquency or parents' reported conduct problems, predicted parent-reported parenting, after controlling for the stability of parenting over time. We also tested the reverse: whether parenting predicted youth problem behavior after controlling for the stability of problem behavior. The directions of effects were tested in the cross-lagged panel design model presented in Figure 1. Table 1 notes the correlations among the main study variables. First, we tested the model using youth self reported delinquency as the outcome. This model is a fully saturated model. Standardized estimates of all cross-paths are presented in Table 2.

Second, we tested the effect of parent-reported youth conduct problems as the outcome measure. This second model is also a fully saturated model. Standardized estimates of all cross-paths are presented in the second column of Table 2.

First, across both models youth problem behavior (standardized autoregressive coefficients of .73 and .80 for delinquency and conduct problems, respectively) showed relatively high rates of stability, whereas parenting (coefficients ranging from .49 to .71) showed moderate to high rates of stability. Second, the only predictive relationship between parenting dimensions, as indicated by significant cross-paths, suggests that higher parental control predicted more parental knowledge over time. This significant cross path was found for the model using delinquency and the model using conduct problems as the measure of youth problem behavior.

The cross-paths predicting problem behaviors from parenting and predicting parenting from problem behaviors are the ones most directly related to the main study questions. For parenting predicting later youth problem behavior (controlling for initial levels of problem behavior), parental solicitation predicted decreases in conduct problems one year later and parental knowledge predicted decreases in delinquency one year later. In the prediction of parenting, youth delinquent behaviors predicted a decrease in parents' control over time.

Testing the Effect of Callous-Unemotional Traits on the Two Models

The next set of study questions focused on the potential moderating role of CU traits on the bidirectional effects between parenting and behavior problems. These questions were addressed using a multigroup analysis. There are two common ways to approach multigroup analyses. First, one can constrain all paths to be equal and compare the differences in chisquare and then free one path at a time. Second, one can specify all the paths on the model to be free and then constrain one path at a time to be equal between groups. One then evaluates the effect of the equality constraint by examining the chi-square difference test (i.e., chisquare of the new model minus the old-saturated model). The latter approach was used in these analyses. We tested the effect of having equality constraints on all the paths (one at a time) for both groups in both initial models. Chi-square difference tests suggest some similarities between youth with low and high CU traits; however, there are also several significant differences. Results from the multigroup analyses are presented in Table 3.

Chi-square difference tests suggest that delinquency was significantly more stable over time for youth with low CU traits than for youth with high CU traits ( 2 = 8.79, df = 1). Specifically, both groups increased their delinquency over time, but the high CU group evinced a sharper increase, as shown by their lower stability coefficient in the model. There was a trend for parental control to show more stability over time for youths low on CU traits than for youths high on these traits in the model with youth delinquency only ( 2 = 2.96, df = 1). Also, higher parental control predicted increases in knowledge ( 2 = 6.37, df = 1 in the model with youth delinquency and 2 = 5.46, df = 1 in the model with youth conduct problems) and parents' solicitation predicted increases in parental control over time ( 2 = 3.74, df = 1 in the model with youth delinquency and 2 = 4.57, df = 1 in the model with youth conduct problems), but these associations were only found for youth low on CU traits in both models. Thus, for children low on CU traits, parents who demand to know where their children are and give children set times to be home acquire more knowledge over time. Also for children low on CU traits, using one form of monitoring (i.e., solicitation) was related to increases in another form of monitoring (i.e., control).

Interestingly, there was a very different association between parental knowledge and parental control for those low and high on CU traits ( 2 = 6.11, df = 1 in the model with youth delinquency and 2 = 8.66, df = 1 in the model with youth conduct problems).

Specifically, having less knowledge led to increases in control over time for youths low on CU traits, while having less knowledge led to decreases in control for youths high on CU traits.

Parental Monitoring 10

There was no coefficient that reached significance for parenting predicting youth problem behavior. Further, there was only a tendency for delinquency to predict decreases in parental control for youths high on CU traits ( 2 = 3.09, df = 1). Thus, parents might respond to youth delinquency by reducing their control and this was limited to those youths who are most likely to engage in delinquency.

Discussion

This study is unique in investigating the moderating effects of CU traits on parental monitoring over time. Results indicated that youth behaviors influenced parents' reactions, and this was moderated by CU traits. The results of the present study suggest that parents may respond differently when their children's behaviors are accompanied by a lack of remorse. Children with high CU traits had parents who reduced their monitoring and supervision behaviors over time, and their behaviors were less linked to other monitoring and supervision efforts over time. Prior cross-sectional studies did not allow for the testing of bidirectional associations between parental monitoring behaviors and behavior problems for youths low and high on CU traits. Thus, whereas parenting has been more strongly related to conduct problems in those without CU traits, this study is unique in prospectively testing whether the opposite effects (i.e., child-driven effects on parenting behaviors) may be stronger or weaker based on the level of CU traits in the child [START_REF] Larsson | Callous-unemotional traits and antisocial behavior: Genetic, environmental, and early parenting characteristics[END_REF].

Although parenting was not more strongly related to problem behavior in youths low on CU traits, parenting was more stable and predicted other parenting behaviors more strongly in youths low on CU traits. For parents with youths who were low on CU traits, their behavioral control informed them of their child's activities (i.e., was related to increases in knowledge) over time, which is consistent with prior research on youths in general [e.g., 34]. While parenting efforts have been found to lead to knowledge in prior research [START_REF] Soenens | Parenting and adolescent problem behavior: An integrated model with adolescent self-disclosure and perceived parental knowledge as intervening variables[END_REF],

other research suggests that only the child's self-disclosure predicts knowledge and parenting efforts make little contribution to knowledge [START_REF] Kerr | What parents know, how they know it, and several forms of adolescent adjustment: Further support for a reinterpretation of monitoring[END_REF]. Considering CU traits as a moderator may account for these differences in findings. That is, parents may be more successful in gaining knowledge from youths with low CU traits who are willing to answer parents' questions. For youths high on CU traits, parents may have to rely more on what the youth decides to disclose. Indeed, youths with CU traits are possibly less likely to freely give information to their parents [START_REF] Tilton-Weaver | Open up or close down: How do parental reactions affect youth information management?[END_REF], and parents might be responding to this closed behavior by reducing their monitoring attempts.

Parental Monitoring 11

Moreover, our findings suggest that for parents of youths who were low on CU traits, knowledge was negatively related to control over time. It may be that the more parents know, the less they need to control their child. Further, their monitoring activities seem to work in concert, with solicitation and control being used together more often and control techniques being used more consistently over time. Alternatively, for youths high on CU traits, parents who have poor knowledge of their child's activities attempt to control them even less. Thus, these parents reduce control when they do not have information. Youths with CU traits are possibly least likely to freely give information to their parents, and parents might respond to this closed behavior by reducing their monitoring attempts with their growing experience with a cold child and adolescent. Thus, a child that is closed off from parents may elicit the same from their parents. Indeed, children who are warm and open tend be monitored more over time, while the reverse is true for children who are cold and closed [START_REF] Kerr | Parents react to adolescent problem behaviors by worrying more and monitoring less. What can parents do? New insights into the role of parents in adolescent problem behaviors[END_REF]. Also, parents may notice that what they do to gain knowledge is ineffective and may respond by backing off. This reaction would be consistent with research showing that children with CU traits are resistant to punishment efforts by parents [START_REF] Dadds | Punishment insensitivity and parenting: Temperament and learning as interacting risks for antisocial behavior[END_REF]. There was a trend for parents to control less over time when their children displayed high levels of CU traits. Parents have been found to disengage in their parenting efforts over time when their children display problem behaviors [e.g., [START_REF] Dishion | Premature adolescent autonomy: Parent disengagement and deviant peer process in the amplification of problem behaviour[END_REF][START_REF] Stice | A longitudinal examination of the reciprocal relations between perceived parenting and adolescents' substance use and externalizing behaviors[END_REF][START_REF] Kerr | Children's influence on family dynamics: The neglected side of family relationships[END_REF]. Thus, parents may recognize when their youths are resistant to discipline and surveillance and then respond by limiting their control attempts.

The present findings must be interpreted in light of several limitations. We had a small sample and the children were selected to overrepresent those with conduct problems.

For this reason, these results need replication in a larger sample of unselected youth to assess whether these findings generalize to a general sample. Indeed, our limited sample size prevented us from examining gender differences over the one-year period. Also, the present study included only a one-year follow-up assessment, and further research should look at these processes over longer periods of time. With relation to parenting, the knowledge measure we used was originally designed to measure monitoring and supervision, but included many items reflecting knowledge rather than parents' behaviors. Thus, we included it because it has been used in other research and we included newer measures which focus on parenting actions to supervise their children. However, in the future, it may be fruitful to examine the relation between scales of the Alabama Parenting Questionnaire and other parenting measures. Finally, since we do not have a measure of parents' own CU traits, we cannot test whether the behavior of parents with children with high levels of CU traits is a result of their own personality traits. However, the results of the present study are not

inconsistent with the idea of a gene-environment correlation, whereby aversive child predispositions elicit poor parenting behaviors that in turn lead to delinquency or conduct problems [START_REF] Larsson | Callous-unemotional traits and antisocial behavior: Genetic, environmental, and early parenting characteristics[END_REF]. Indeed, we found a trend toward delinquency reducing parental control when children were high on CU traits.

The present findings may be useful in considering interventions for severe problem behaviors that often occur with CU traits. Prevention efforts may need to target the early relationship between parent and child [START_REF] Gao | Early maternal and paternal bonding, childhood physical abuse and adult psychopathic personality[END_REF], since what parents do in adolescence seems to matter less. In sum, the present study and other recent findings support the greater importance of personality than knowledge or active monitoring [START_REF] Eaton | Parental monitoring, personality, and delinquency: Further support for a reconceptualization of monitoring[END_REF]. Cold, closed, and antisocial personalities expressed by youths may underlie poor knowledge, and their parents seem unable to coordinate their monitoring behaviors to gain better knowledge about their children's activities and friends.

Figure 1 .

 1 Figure 1. Conceptual model of parents' reactions and youths' problem behavior.

Table 1 .

 1 Descriptive statistics and concurrent correlations among study measures.

		Time 1	Time 2
		M (SD)	M (SD)	1	2	3	4	5	6
	1. Callous-Unemotional Traits	3.05 (1.87)	3.01 (1.81)	-	.22*	.23*	-.11	-.24*	.10
	2. Delinquency YR	1.20 (2.32)	1.48 (2.71)	.25*	-	.22*	-.34**	-.09	-.19
	3. Conduct Problems PR	1.62 (2.57)	2.03 (3.00)	.26*	.23*	-	.00	.04	.10
	4. Parental Knowledge	16.04 (4.42)	17.21 (4.91)	-.05	-.30**	-.04	-	.27*	.41***
	5. Parental Solicitation	7.09 (2.72)	6.59 (2.67)	-.01	-.01	-.11	.46***	-	.34**
	6. Parental Control	15.26 (4.53)	16.75 (5.21)	.02	-.34**	-.01	.52*** .39***	-

Note: * p< .05; **p<.01; *** p< .001; Time 1 is listed above the diagonal and Time 2 is below.

Table 2 .

 2 Standardized estimates of all the paths from both models for the full sample.

	Model with
	Youth delinquency	Youth conduct
	YR	problems PR

***p < .001; **p < .01; *p < .05; †p < .10 Note. YR: youth report; PR: parent report

Table 3 .

 3 Standardized estimates of all the paths from both models for the adolescents who are low and high on callous-unemotional (CU) traits

				Model with
			Youth delinquency	Youth conduct
			YR	problems PR
			Low CU	High CU	Low CU	High
			traits	traits	traits	CU
						traits
	Autoregressive Coefficients:
	Youth problem behavior T1	.89***	.41**	.73***	.87***
	Youth problem behavior T2
	Parents' solicitation T1		.43***	.49***	.42***	.48***
	Parents' solicitation T2
	Parents' knowledge T1		.54***	.76***	.55***	.81***
	Parents' knowledge T2
	Parents' control T1	Parents'	.75***	.41**	.77***	.50***
	control T2
	Parenting Predicting Other
	Parenting:
	Parents' solicitation T1		.06	.11	.06	.07
	Parents' knowledge T2
	Parents' solicitation T1		.30***	.07	.30***	.06
	Parents' control T2
	Parents' control T1	Parents'	.11	.22	.09	.23
	solicitation T2
	Parents' control T1	Parents'	.39***	-.05	.40***	-.01
	knowledge T2
	Parents' knowledge T1		.17	.04	.17	.08
	Parents' solicitation T2
	Parents' knowledge T1		-.22*	.20	-.21*	.35*
	Parents' control T2

***p < .001; **p < .01; *p < .05; †p < .10 Note. YR: youth report; PR: parent report.


Gerardus Läslo

Evers
email: evers@knmi.nl

Johannes Schweitzer
email: johannes@norsar.no

L G Evers

A climatology of infrasound detections in northern Norway at the experimental ARCI array

Keywords: Infrasound, Array, Signal detection, Source identification, Acoustic propagation lightning, meteors, oceanic waves, earthquakes, 58 severe weather, volcanoes, and sprites. Among

The study of infrasound is experiencing 1 a renaissance in recent years since it was chosen 2 as a verification technique for the Comprehen-3 sive Nuclear-Test-Ban Treaty. Currently, 60 infra-4 sound arrays are being installed to monitor the 5 atmosphere for nuclear tests as part of the Inter-6 national Monitoring System (IMS). The number 7 of non-IMS arrays also increases worldwide. The 8 experimental ARCES infrasound array (ARCI) is 9 an example of such an initiative. The detectabil-10 ity of infrasound differs for each array and is a 11 function of the array location and configuration, 12 the state of the atmosphere, and the presence of 13 natural and anthropogenic sources. In this study, 14 a year of infrasound data is analyzed as recorded 15 by ARCI.

Introduction

Infrasound was first discovered after the violent eruption of the Krakatoa, Indonesia, in 1883. Low-frequency pressure waves were observed at traditional barographs. These appeared to have traveled with the sound speed and up to four passages where noticed at some instruments (Symons 1888). The first microbarometer recordings date from 1908 when a comet, or asteroid, exploded over Siberia in Russia, the so-called Tunguska event (Whipple 1930). The societal and scientific interest in infrasound increased during World War I, e.g., Whipple (1939), and later on in the nuclear testing era [START_REF] Posey | Estimation of nuclear explosion energies from microbarograph records[END_REF]. With the The propagation of infrasound through the highly dynamic atmosphere plays an important role in source identification. Infrasound travels up to thermospheric altitudes of 120 km and experiences refractions due to an increase in wind and/or temperature as a function of altitude. If the gradients in the propagation velocity are strong enough, infrasound will be sent back to the Earth's surface [START_REF] Drob | The global mor-558 phology of infrasound propagation[END_REF]. There are three regions in the atmosphere where such gradients might exist. These are of importance in long-range sound propagation, i.e., over distances larger than 150 km. The regions are marked by (1) a strong jet stream at 10 km altitude, near the tropopause; (2) the combined effect of wind and temperature at the stratopause, around 50 km altitude; and (3) the temperature increase in the thermosphere from 100 km and upward. The aim of this study is to identify the sources around the ARCES array and to build up a climatology of station-specific detections. Each infrasound array has its own detection capabilities as its configuration, the atmospheric conditions, and source characteristics are highly variable as function of geographical location and time. Special attention will be paid to the low-frequency band of 0.1 to 1.0 Hz which is of utmost importance for the verification of the CTBT as small-sized nuclear tests (around 1 kT TNT) are expected to generate infrasound of 0.1 to 0.2 Hz [START_REF] Evers | Listening to sounds from an exploding meteor and oceanic waves[END_REF].

It is also this band in which the almost continuous background noise of microbaroms is present that peak around 0.2 Hz [START_REF] Posmentier | A theory of microbaroms[END_REF]).

The ARCES infrasound array

A three-element experimental infrasound array was established at ARCES in March 2008, which will be abbreviated as ARCI [START_REF] Roth | Setup of an experimental infrasound deployment within the ARCES array[END_REF].

The purpose of the installation is to gain experience with the simultaneous recording of infrasonic and seismological data. The detections of coherent infrasonic signals trav-133 eling over the array can be achieved by evaluating 134 the Fisher (F) ratio. The F detector has been 135 described in both the time (

Detections in the low-frequency band

Figure 5 shows the results of the previously described processing approach for ARCI data in the low-frequency band between 0.1 and 1.0 Hz. The lower frame shows the maximum Fisher ratio for each bin. This value is related to the squared signal-to-noise ratio (SNR) on the traces (see axis on the right). The middle and top frames show the resolved apparent sound speed and backazimuth. Color coded are the number of detections within an hour, where five or more detections are denoted by red. Here, only detections with a SNR larger than 1.0 are plotted, which equals a Fisher ratio of four and higher. Such a detection from this figure that events from the west are more easily detected in winter as the stratospheric winds are favorable for such propagation. Events from the east are better detected in summer, but some show up in wintertime. The detections of sources which are not affected by the direction of the polar vortex probably find their origin close to the array, i.e., at distances less than 150 km, where tropospheric propagation is still dominant.

U N C O R R E C T E D P R O O F JrnlID 10950_ArtID 9237_Proof# 1 -

Consequences for the low-frequency band

In Fig. 5, the wind direction at 50 km altitude is superimposed on the resolved backazimuths, for the low frequency band. Clearly, the detection of coherent infrasound is guided by the stratospheric wind. In winter, microbarom energy from the Northern Atlantic Ocean is recorded. As the winds turn around the equinox, microbarom energy from the east is being detected.

As can been seen in Fig. 6, an abrupt change in the winds and temperature occurred in the winter of 2009, between late January and early February. Such changes are related to a major sudden stratospheric warming (SSW; [START_REF] Holton | An introduction to dynamic meteorology[END_REF]). The temperature increases by 50 • C in the stratosphere, in only a couple of days, and the polar vortex changes its direction. The major SSW also had its effect on the infrasound detections (see also Fig. 5). Suddenly, microbaroms from the east are detected because of the change in direction of the polar vortex, which is unusual in winter [START_REF] Evers | Infrasonic signature of the 2009 major sudden stratospheric warming[END_REF].

Variability in the boundary layer

The state of the boundary layer above the array can cause de-correlation of the signals. A turbulent atmosphere affects the signal coherency which leads to a decrease of the detection capability. The summer boundary layer is far more turbulent than the winter one. Heating of the boundary layer due to solar radiation generates a high degree of mixing. This effect is also visible on a daily scale where the nighttime boundary layer stabilizes as the influence of solar radiation decreases. [START_REF] Posmentier | A theory of microbaroms[END_REF]. To accurately predict the generation of microbaroms, the directional spectra of oceanic waves should be evaluated to identify the almost oppositely traveling waves and their periods [START_REF] Kedar | The origin of deep ocean microseisms in the North Atlantic Ocean[END_REF]). Here, it is assumed that the waves are interacting near the maximum of the squared multiplication of the wave height and frequency. This allows for an efficient calculation, to get an indication of the source activity (Evers Ocean, from 12-hourly oceanic wave models provided by the ECMWF. The source intensity, I S , is also estimated. The observed backazimuths of the infrasound and direction of microbarom activity coincide throughout the seasons. The detection of microbaroms is also clearly related to the direction of the stratospheric winds [START_REF] Garcés | On using ocean swells for continuous infrasonic measurements of winds and temperature in the lower, middle, and upper atmosphere[END_REF][START_REF] Pichon | On using infrasound from interacting ocean swells for global continuous measurements of winds and temperature in the stratosphere[END_REF]. During the SSW which occurred in the winter of 2009, there is a sudden change in resolved backazimuths. Microbarom energy from the Pacific Ocean is detected, during Seismic data from the ARCES array (see Fig. 1) are processed to detect energy from microseism. The processing sequence is as follows:

-Band-pass filter with a third-order Butterworth filter with corner frequencies of 0.1 and 0.4 Hz.

-Decimate the data with a factor of 8, from a 40-to 5-Hz sampling rate.

-Split the data in a window of 20 s.

-Apply a frequency-wavenumber analysis, between 0.15 and 0.25 Hz, by moving this window with 6 s.

-Calculate a beam and measure the maximum amplitude in the window.

The array response of ARCES for a 0.2-Hz planar wave is given in Fig. 2. At such low frequencies, the main lob is quite broad but its maximum can still be determined with enough accuracy for this study, since only a rough estimate (±5 • ) of the backazimuth is sufficient. The detections of microseism at ARCES are shown in Fig. 9. A total of 6.4 million coherent seismic arrivals are detected between 0.15 and 0.25 Hz. This number is band. These seasonal changes are also partly visible in the high-frequency band. In winter, the sources to the west are detected while preference is given to sources in the east during summer. The state of the boundary layer, or turbulence and low-level winds, partly determines the signal coherency. In summer, there is a daily variation caused by the influence of solar radiation. A more stable boundary layer during nighttime leads to less coherency loss.

In addition, microbarom activity has been estimated by evaluating the ocean wave height and period. ARCI is sensitive to microbaroms from the Atlantic Ocean in winter. Microbarom energy from the east is detected during summer. This anisotropic behavior was also identified during a period of only a couple of days, related to a SSW. A sudden change was noted from the detection of microbarom energy from the Atlantic Ocean to those from the Pacific Ocean.

The importance of taking into account both the characteristics of the medium and the source is illustrated by comparing Figs. 5 and8. The detections move from west (270 • ) to northwest (330 • ) during March and April 2008. It follows from Fig. 8 that the sources, microbaroms in the Atlantic Ocean, are occurring with a more or less stable backazimuth between 270 • and 300 • . The stratospheric wind, on other hand, is varying from southwest to north during this period. Therefore, this change in the resolved backazimuths should be attributed to the wind which enables the detection of an unknown source to the south of ARCI.

Another change is visible, in Fig. 8, between October 2008 and April 2009. The resolved backazimuths tend to move somewhat from the northwest to the west. The cause should be related to the source, as the wind shows no evidence for such translation. Whether this change relates to the southward movement of sea ice during winter remains to be investigated. It is hypothesized that the sea ice blocks the northward propagation of oceanic waves. Consequently, the generation of microbaroms is limited up to a certain longitude. This is also indicated by the microseism detections. The source seems limited in its northward propagation during winter (see Fig. 10).

The seasonal variations in microbarom detections also follow from the comparison with the

Fig. 1

 1 Fig.1The location of the ARCES seismic array and positions of the seismometers (gray dots). The temporary array ARCI is configured with three microbarometers (red

  Figure 1 shows the location and configuration of ARCI. The instruments are microbarometers of type Martec MB2005 which have a flat frequency response to pressure in the range of 0.01 to 27 Hz. Infrasound measurements are affected by noise due to wind.Therefore, a spatial filter is applied at each instrument which essentially integrates the pressure field. Doing so, pressure fluctuations with a small coherency length, like those of tens of centimeters associated with wind noise, are partly canceled out. The infrasonic waves of interest remain undisturbed because of their much larger coherency length of tens to hundreds of meters. Such analog filters can consist of a pipe array with discrete inlets or porous hoses[START_REF] Hedlin | Evaluation of rosette infrasonic noise-reducing spatial filters[END_REF]. The latter approach is applied at ARCI with four soaker hoses, each with a length of 12 m, connected to the MB2005. For one of the three sites, the hoses are additionally centered in a drainage pipe. Environmental restrictions at the ARCES array prevent the installation of larger pipe arrays that require fencing. The applied noise reduction should be considered as minimal. The atmospheric pressure changes around ARCI are sampled at a rate of 129

Fig. 2

 2 Fig. 2 The array response of ARCI to a 0.2-and 1.0-Hz planar wave (left two frames). The black circle represent an apparent velocity of 340 m/s. The array response of

Fig. 3 Fig. 4 Fig.

 34 Fig.3Results from the array processing of ARCI data in the high-frequency band of 1.0 to 7.0 Hz. The histograms shows the time of occurrence of infrasound events, betweenMarch 13, 2008 and May 14, 2009. Light blue colors indicate events with an signal-to-noise ratio (SNR) larger

Figure

  Figure6shows the wind and temperature near 268

  287 4.2.1 Consequences for the high-frequency band 288 For the high-frequency band, a distinction is made 289 between summer and winter in Fig. 4. It follows 290

Figure 7 Fig. 6 Fig. 7

 767 Figure7shows the signal coherency, by means of the Fisher ratio, for July and October 2008

  Figure8shows the backazimuths in the direction 380

Fig. 8 Fig. 9

 89 Fig. 8 An estimate of the microbarom activity in the Atlantic (black dots) and Pacific Ocean (green dots). The dots give the directions, i.e., backazimuths, to the Atlantic and Pacific maxima. The retrieved directions, in the lower

Fig. 10

 10 Fig. 10 The occurrence of microseism at the ARCES array. Detections are contoured as function of time and backazimuth. The detections are averaged per hour and one or more detections are indicated by red colors

-Split the data in segments of 256 samples,

which equals a bin of 12.8 s.

-Evaluate the Fisher ratio for each beam in

each bin (with 50% overlapping bins).

-Extract the slowness value, i.e., the backaz-170 imuth and apparent sound speed, at the maxi-171 mum Fisher ratio, for each bin.