Adam Scheinherr
email: scheinherr@irphe.univ-mrs.fr

Lucie Bailly

Olivier Boiron

Aude Lagier

Thierry Legou

Marine Pichelin

Georges Caillibotte

Antoine Giovanni

Realistic glottal motion and airflow rate during human breathing

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

Inhaled therapies play a major role in the treatment of lung diseases like asthma or chronic obstructive pulmonary diseases. Basic advantage of aerosol therapy lies in the direct delivery of high local concentrations of the drug to the site of action [START_REF] Khilnani | Non-invasive ventilation in chronic obstructive pulmonary[END_REF].H o w e v e r , characteristics of inhaled particles, airways morphology, carrier gas and flow properties can largely influence the transport mechanisms and treatment efficiency [START_REF] Finlay | The mechanics of inhaled pharmaceutical aerosols[END_REF][START_REF] Grgic | Regional aerosol deposition and flow measurements in an idealized mouth and throat[END_REF][START_REF] Sandeau | CFD simulation of particle deposition in a reconstructed human oral extrathoracic airway for air and helium-oxygen mixtures[END_REF][START_REF] Kleinstreuer | Airflow and particle transport in the human respiratory system[END_REF]. Particularly, the upper airways (UA) anatomic arrangement can act as an unwanted filter, which limits the amount of drug delivered to the lungs. Recent clinical experiments have been conducted to quantify the distribution of radiolabeled aerosols in the human airways using combined single photon emission computed tomography (SPECT) and X-ray computer tomography (CT) [START_REF] Fleming | The use of combined single photon emission computed tomography and x-ray computed tomography to assess the fate of inhaled aerosol[END_REF][START_REF] Conway | Controlled, parametric, individualized, 2-D and 3-D imaging measurements of aerosol deposition in the respiratory tract of healthy human subjects for model validation[END_REF]. It was shown that particle deposition in extra-thoracic region can reach as much as 40% of the inhaled mass in the worst cases.

More specifically, within the larynx, the glottis (the space between vocal folds) narrows the airways to a minimal transition crosssection. Therefore its geometrical variations can affect breathing flow resistance [START_REF] Jackson | Glottal aperture during panting with voluntary limitation of tidal volume[END_REF][START_REF] Baier | Relationships among glottis opening, respiratory flow, and upper airway resistance in humans[END_REF][START_REF] Brancatisano | Respiratory movements of the vocal cords[END_REF][START_REF] Chen | Determination of glottic opening fluctuation by a new method based on nasopharyngoscopy[END_REF]. This anatomical singularity yields to a complex jet-like glottal airflow, important recirculation zones and a locally turbulent behavior [START_REF] Martonen | Fluid dynamics of the human larynx and upper tracheobronchial airways[END_REF][START_REF] Katz | Three-dimensional computational study of inspiratory aerosol flow through the larynx: the effect of glottal aperture modulation[END_REF][START_REF] Katz | A numerical study of particle motion within the human larynx and trachea[END_REF][START_REF] Renotte | Numerical 3D analysis of oscillatory flow in the time-varying laryngeal channel[END_REF][START_REF] Gemci | A CFD study of the throat during aerosol drug delivery using heliox and air[END_REF][START_REF] Brouns | Tracheal stenosis: a flow dynamics study[END_REF][START_REF] Brouns | Influence of glottic aperture on the tracheal flow[END_REF][START_REF] Lin | Characteristics of the turbulent laryngeal jet and its effect on airflow in the human intra-thoracic airways[END_REF], which can be determinant on particle deposition by inertial impaction [START_REF] Grgic | Regional aerosol deposition and flow measurements in an idealized mouth and throat[END_REF][START_REF] Xi | Effects of the laryngeal jet on nano-and microparticle transport and deposition in an approximate model of the upper tracheobronchial airways[END_REF][START_REF] Heenan | An investigation of the relationship between the flow field and regional deposition in realistic extra-thoracic airways[END_REF]. Regarding the glottal geometry's impact on the tracheal flow during breathing, a devoted description has been given by Brouns et al. [START_REF] Brouns | Influence of glottic aperture on the tracheal flow[END_REF][START_REF] Lin | Characteristics of the turbulent laryngeal jet and its effect on airflow in the human intra-thoracic airways[END_REF]. This numerical study demonstrates the effect of the glottal size and shape on the overall fluid dynamics behavior, using a 3D idealized model of upper airways comprising a static glottis of parametrical aperture. This typical flow alteration can yield to the rise of the tracheal deposition of nano-and micrometer particles by factors ranging from 2 to 10 [START_REF] Xi | Effects of the laryngeal jet on nano-and microparticle transport and deposition in an approximate model of the upper tracheobronchial airways[END_REF].H o w e v e r , a sp o i n t e do u ti nB r o u n se ta l . [START_REF] Brouns | Influence of glottic aperture on the tracheal flow[END_REF], there is a current need for rendering the design of future upper airway models even more realistic, including glottal shape, area and kinematics in correlation with a given inlet inhalation flow rate. Thus, the knowledge of realistic glottal motion during human breathing will enable to further assess the filtration efficiency of the upper airways.

In this context, the purpose of the present study is to determine the glottal motion during several oral breathing tasks, and to investigate the correlation between this motion and the measured breathing flow rates. The first in vivo observation of the glottal motion dates back to the 19th century, with Garcia's laryngeal mirror [START_REF] Henrich | Mirroring the voice from Garcia to the present day: some insights into singing voice registers[END_REF]. Since the 1980s, advances in the medical equipment have allowed a refined exploration of the vocal-fold dynamics using laryngoscopy [START_REF] Baier | Relationships among glottis opening, respiratory flow, and upper airway resistance in humans[END_REF][START_REF] Brancatisano | Respiratory movements of the vocal cords[END_REF], high-speed cinematography [START_REF] Bailly | Vocal fold and ventricular fold vibration in perioddoubling phonation: physiological description and aerodynamic modelings[END_REF][START_REF] Childers | Electroglottography, speech, and ultra-high speed cinematography[END_REF], videokymography [START_REF] Švec | Videokymography: A new high-speed method for the examination of vocal-fold vibrations[END_REF], electroglottography [START_REF] Rothenberg | A multichannel electroglottograph[END_REF] or photoglottography [START_REF] Honda | Glottal-opening and airflow pattern during production of voiceless fricatives: a new non-invasive instrumentation[END_REF]. These experimental techniques were extensively used to characterize the vocal-fold vibrations during human phonation (e.g. see a review by Ziethe et al. [START_REF] Ziethe | Clinical analysis methods of voice disorders[END_REF]). By contrast, however, the glottal variations during different human breathing regimes have been barely investigated so far. Despite a few reference studies [START_REF] Baier | Relationships among glottis opening, respiratory flow, and upper airway resistance in humans[END_REF][START_REF] Brancatisano | Respiratory movements of the vocal cords[END_REF][START_REF] England | Influence of human vocal cord movements on airflow and resistance during eupnea[END_REF], the relationship between the glottal area and the inhaled airflow rate is still poorly understood. In the present work, a clinical database comprising 8 breathing tasks recorded on 20 healthy subjects is presented. The physiological mechanisms of the respiratory cycles were observed using videorecording of laryngofiberscopic examinations, and synchronized oral airflow measurements. A quantitative characterization of glottal motion was derived from the processing of the recorded laryngeal images. The impact of the glottal motion on flow parameters is discussed as a function of breathing task and subject gender.

Materials and methods

The recording sessions took place at the Otolaryngology Department of the La Timone Adults Hospital (APHM, Marseille, France). In the following, the "realistic glottal motion" is defined by the 2D timevariations of the space area separating both free edges of the vocal folds, as observed in vivo on their superior transversal plane.

In vivo recordings

Subjects

From 20 healthy volunteers (10 females Fi, and 10 males Mi, i Є [01, 02, … , 10]) were obtained informed consents for the study. All subjects were non-smokers, without any professional sportive activity, any previous laryngeal or respiratory disorders, aging between 22 and 28 years. Table 1 lists the subject's age and body mass index (BMI).

Breathing tasks and database

Each subject was asked to produce eight 30s-tasks of slow or rapid breathing, described as follows:

Slow breathing tasks-below 20 cycles.min -1 :

(i) Eup f :taskoffreeeupnea (quiet breathing) (ii) Repetition of Eup f (iii) Eup 15 :taskofeupnea with a controlled breathing frequency at 15 cycles.min -1 . (iv) Hyper f :t a s ko ff r e ehyperpnea (deep breathing with maximal respiratory volume)

Rapid breathing tasks: above 20 cycles.min -1 :

(v) Tachyp 30 :t a s ko ftachypnea with a controlled breathing frequency at 30 cycles.min -1 . (vi) Tachyp 60 :t a s ko ftachypnea with a controlled breathing frequency at 60 cycles.min -1 . (vii) Tachyp 90 :t a s ko ftachypnea with a controlled breathing frequency at 90 cycles.min -1 .

Specific inhalation task:

(viii) Aerosol: task mimicking the breathing gesture typically performed when using a dry powder inhaler to deliver medication (quick and deep inspiration followed by slow expiration).

For all tasks, the subject's nose was closed to ensure that the subject breathed only through his mouth. Note that both tasks of free eupnea (Eup f ) were intentionally presented to the subject as a phase of acquisition trials. This aimed to prepare him before the recording of the controlled tasks, which were described as the target of the study. Thereby, by reducing the effect of a motor control focused on the respiration, tasks (i) and (ii) were acquired in condition of spontaneous breathing. By contrast, the other tasks corresponded to cases of controlled breathing, for which the subjects were asked to synchronize their breathing frequency with a metronome projected on an instruction computer. These tasks intended to explore the extent of glottal motion and breathing capacity in specific respiratory contexts. In the end, 18 volunteers only (9 females and 9 males) successfully performed the entire protocol, thus yielding to a database comprising 144 sequences of 30s.

Measurements

All measurements were done in the seated posture. The glottis was observed using a flexible nasofiberscope equipped with a PAL camera (Storz endovision XL 202800) and a continuous cold light source. Laryngeal images were captured at a frequency of 25 Hz (768 × 288 pixels). The airflow rate was simultaneously registered by means of a pneumotachograph placed at the mouth, the EVA2 TM system (S.Q.Lab, www.sglab.fr) [START_REF] Ghio | Evaluation of the acoustic and aerodynamic constraints of a pneumotachograph for speech and voice studies[END_REF]. It consists of a two-grid flowmeter characterized by a small dead volume, specific linearized response for the inhaled and exhaled flow, and an accuracy of 1 cm 3 s -1 .T h e sampling frequency of the flow rate signal was 6250 Hz. A trigger generated by an acquisition tool developed in NI LabWindows TM /CVI was used to synchronize the recordings of laryngeal images and flow rate signal. Note that for several subjects, a local anesthetic (Lidocaine Aguettant 5%) was sprayed in the naris before the fiberscope introduction, so as to provide a better comfort during the invasive examination. Ambient temperature T a [K] was also measured.

Data processing

All data was processed using Matlab ® . Any point in the upper airways was located by the (x, y, z) coordinates as introduced in Fig. 1.

Airflow rate

Within each recorded 30s-sequence, every respiratory cycle was detected on the airflow signal, Q, using a zero-tracking method. Conventionally, positive and negative flow rate values correspond to inspiration and expiration, respectively. A BTPS correction (Body Temperature Pressure Saturated) was applied to convert the flow measured at ambient conditions to the thermodynamic conditions expected within the extrathoracic region [START_REF] Juroszek | Air features in spirometric transducers[END_REF]. For each sequence, the 2, column #6). Each corrected sequence was averaged into one mean flow rate

Q (t) = 1 N • N • j=1 Q (t + jT t ) [L.min -1 ],
where N°stands for the number of breathing cycles with average period T t [s]asillustratedinFig. 1a.

Glottal motion detection

This procedure was limited to the analysis of two major tasks, Eup 15 and Tachyp 30 , altogether representing slow and rapid breathing tasks respectively. At first, breathing cycles, with hidden glottis aperture (by epiglottis or arytenoid cartilages) were removed from the video processing. Finally, about 126 (252) respiratory cycles out of 149 (291) were associated to task Eup 15 (Tachyp 30 ). For these retained sequences, the glottal motion was extracted from each laryngoscopic image k taken at shot-instant t k as follows: (i) correction of

x-a n dy-motions of the fiberscope and focus on a region of interest using a customized cross-correlation technique; (ii) smoothing of the resized image using a Gaussian bandpass filtering; (iii) detection of the glottal area A g (t k ) contours applying a geodesic active contourbased method [START_REF] Caselles | Geodesic active contours[END_REF], as shown in Fig. 1c; (iv) determination of anteroposterior diameter AP g (t k ) (see Fig. 1d): at first 2 points were detected on left and right vocal-fold contour to identify the left and right glottal border lines; then, from the intersection of those border lines was derived a centerline; at last AP g was defined by the 2 cross points of the centerline with the vocal-fold contour; (v) determination of glottal width d g (t k ) (see Fig. 1d), as a perpendicular line to AP g at its mid-level; (vi) correction of vertical movement of the larynx and zmotion of the fiberscope by assuming AP g as a geometrical invariant during breathing [START_REF] Higenbottam | Narrowing of glottis opening in humans associated with experimentally induced bronchoconstriction[END_REF]; (vii) finally, conversion of the measured data from pixels to millimeters, assuming AP g = 22.1 mm for males and 17.6 mm for females [START_REF] Eckel | Morphometry of the larynx in horizontal sections[END_REF]. Note that the relevance of these latter values was preliminary checked using other means of clinical investi-gation allowing an easier spatial calibration, such as the high resolution computed tomographic scans recorded by Fleming et al. [START_REF] Fleming | The use of combined single photon emission computed tomography and x-ray computed tomography to assess the fate of inhaled aerosol[END_REF].I n particular, a typical value of 22 mm was confirmed by this technique inthecaseofamaleadult.

Methodology accuracy

The measurement of the distance between the camera extremity and the glottal plane would enable direct dimensions conversion from pixels to millimeters. However, touching the glottal plane was not allowed as it could cause laryngospasm. Therefore, we chose the hypothesis of AP g being a geometrical invariant [START_REF] Higenbottam | Narrowing of glottis opening in humans associated with experimentally induced bronchoconstriction[END_REF] as an alternative to convert our pixels measurements. This assumption was previously applied by several authors [START_REF] Brancatisano | Respiratory movements of the vocal cords[END_REF][START_REF] Hurbis | Laryngeal changes during exercise and exercise-induced asthma[END_REF][START_REF] Beaty | Laryngeal motion during exercise[END_REF]. The accuracy of the protocol was tested by recording a printed glottal image while simulating motions of the camera along x-, y-and z-directions. The glottal dimensions were detected with an average error smaller than 5%. Nevertheless, depending on the recorded laryngoscopic image quality (e.g. variable light contrast), the maximal error reached by the detection procedure was assessed at 10%.

RESULTS

In the followings, if X is a function of time t, X max refers to the maximum value of X over duration t.

Airflow-rate pattern

For each task and gender of the database, Table 2 summarizes the measured primary respiratory variables T t [s], mean inspiration airflow rate peak Q max I [L.min -1 ] and inspired volume V I [L]. Derived ratios T t /T I (T I [s] being the mean inspiration period, see Fig. 1a),

Q max I /Q max E (Q max E [L.min -1
] being the mean expiration airflow rate peak), and the BTPS correction factor C c are also reported, as well as the number of processed breathing cycles N°. Figs. 2 and3 present the corresponding normalized mean flow-rates Q/Q max I as a function of ωt [rad], where ω is the pulsation of the average cycle defined as ω = 2π /T t . The flow-rates obtained for the slow breathing tasks (i) to

General features

For each case, the measured airflow pattern was confronted to the sinusoidal evolution sin(ωt ), commonly used as an idealized breathing pattern [START_REF] Sandeau | CFD simulation of particle deposition in a reconstructed human oral extrathoracic airway for air and helium-oxygen mixtures[END_REF][START_REF] Honda | Glottal-opening and airflow pattern during production of voiceless fricatives: a new non-invasive instrumentation[END_REF].Forslow and rapid breathing tasks, Fig. 2 shows that the quasi-sinusoidal approximation can be a priori usable as a whole. Yet, several discrepancies can be highlighted. First, the Euclidean distance between measurements and this harmonic signal (noted ε i [-] at instant t i ) is smaller for male than female subjects (ε = 5.4 versus 6.9, mean value over breathing cycle). Furthermore, the approximation is closer to measurements during inspiration (ε = 5.0) than during expiration phase (ε = 7.3). Note that smallest distances ε i were found during inspiratory phases of tasks Eup f , Tachyp 30 , Tachyp 60

and Tachyp 90 (ε ∼ = 3.8), whereas largest ε i were found for the Aerosol task (9.1 and 17.1 for inspiration and expiration, respectively). Now, whatever the task, a phase difference in maximal flow rate occurrences has been measured between sinusoid and realistic patterns. We found a phase angle smaller for male subjects than female ( ). Thus, the sinusoidal hypothesis is no more valuable in case of specific inhalation task (Fig. 3).

Breathing frequency

From T t in Table 2 can be deduced that spontaneous slow breathing (Eup f ) was achieved at a mean frequency of 20 cycles.min -1 for males and 15 cycles.min -1 for females. The measured frequencies of tasks Eup 15, Tachyp [START_REF] Ghio | Evaluation of the acoustic and aerodynamic constraints of a pneumotachograph for speech and voice studies[END_REF] and Tachyp 60 correspond to the target values, which validates the protocol for this range of breathing rates. Note that the target value chosen for task Tachyp 90 (90 cycles.min -1 )was excessively high for most of the subjects, who worked out with a breathing frequency around 80 cycles.min -1 instead. All the tasks were performed so that in average T t /T I > 2, thereby yielding to an inspiratory duration shorter than the expiratory one, as found in previous studies made on healthy subjects [START_REF] Benchetrit | Breathing pattern in humans: diversity and individuality[END_REF]. In particular, in Proctor &Hardy [START_REF] Proctor | Studies of respiratory air flow; significance of the normal pneumotachogram[END_REF],aratioT t /T I was measured in the range 1.57-2.9 during quiet breathing (including patients with pulmonary disease), versus 1.43-3.45 in our case (mean value 2.10 and 2.36, for male and female groups respectively).

Breathing amplitude

Values of the flow-rate maximal amplitudes Q max I are very different inter-tasks and inter-subjects, as detailed in Table 2.O v e rt h e whole database, the amplitudes are 30% higher for male than for female subjects. During spontaneous breathing, typical peak values ranged between 29 L.min -1 and 68 L.min -1 , with a mean value of 43 L.min -1 for males, and 32 L.min -1 for females. These results are in line with previous studies (see range of values from 13 L.min -1 to 78 L.min -1 in Proctor & Hardy [START_REF] Proctor | Studies of respiratory air flow; significance of the normal pneumotachogram[END_REF]).

Glottal motion

General features

Every mean breathing cycle of the database is characterized by a mean ratio A I g /A E g higher than 1. However, the time-variations of the detected glottal area demonstrate a substantial inter-subject variability. Within each gender and task category, the subjects were divided into two groups, represented in Table 3: • The 1st group (labeled as "static") gathers the subjects with a quasi-constant glottal area detected during the average breathing cycle. This group is characterized by a mean glottal area variation smaller than 10%. The limit was assessed as the accuracy of the detection procedure. This "static" glottal evolution during breathing has been reported in Hyatt et al. [START_REF] Hyatt | Extrathoracic airway resistance in man[END_REF] and in 1 subject out of 3 in Jackson et al. [START_REF] Jackson | Glottal aperture during panting with voluntary limitation of tidal volume[END_REF].

• The 2nd group (labeled as "dynamic") gathers the subjects with a time-varying glottal area during the average breathing cycle, so that the mean glottal area variation is higher than 10%. This group is characterized by a progressive glottal widening (resp. narrowing) during inspiration (resp. expiration), in agreement with previous reference studies [START_REF] Baier | Relationships among glottis opening, respiratory flow, and upper airway resistance in humans[END_REF][START_REF] Brancatisano | Respiratory movements of the vocal cords[END_REF][START_REF] England | Influence of human vocal cord movements on airflow and resistance during eupnea[END_REF]. In that case, the peak values reached during inspiration have been measured around 1.26 and 1.46 times higher than the minimum value achieved during expiration for males and females respectively. During slow breathing, the 2nd group is represented by 52.6% of subjects, against 44.4% during rapid breathing.

In the group as a whole, the average ratio A I g max /A E g min was ranging from 1.21 (subject F04) to 2.31 (subject M08). This ratio was evaluated at 1.8 in Brancatisano et al. [START_REF] Brancatisano | Respiratory movements of the vocal cords[END_REF] and between 1. [START_REF] Gemci | A CFD study of the throat during aerosol drug delivery using heliox and air[END_REF] 3.

Another important feature can be highlighted from the present work. In average on our database, the measured glottal areas are much higher than those measured with equivalent method in other works [START_REF] Baier | Relationships among glottis opening, respiratory flow, and upper airway resistance in humans[END_REF][START_REF] Brancatisano | Respiratory movements of the vocal cords[END_REF]. Indeed, Baier et al. [START_REF] Baier | Relationships among glottis opening, respiratory flow, and upper airway resistance in humans[END_REF] measured a mean area A g of 44 mm 2 and 48 mm 2 for 2 males. This area ranged from 43 mm 2 to 104 mm 2 for 4 females. Similarly, Brancatisano et al. [START_REF] Brancatisano | Respiratory movements of the vocal cords[END_REF] measured an area A g of 98 mm 2 (A I g max = 126 ± 8mm 2 , 12 subjects, 2 females). However, our results are in agreement with previous studies based on the acoustic reflection [START_REF] D'urzo | Comparison of glottic areas measured by acoustic reflections vs[END_REF][START_REF] Rubinstein | Glottic dimensions in healthy men and women[END_REF][START_REF] Martin | The effect of age, sex, obesity and posture on upper airway size[END_REF] or MRI technique [START_REF] Pritchard | Studies of the human oropharyngeal airspaces using magnetic resonance imaging. II. The use of three-dimensional gated MRI to determine the influence of mouthpiece diameter and resistance of inhalation devices on the oropharyngeal airspace geometry[END_REF].I n particular, D'Urzo et al. [START_REF] D'urzo | Comparison of glottic areas measured by acoustic reflections vs[END_REF] used both acoustic reflection and CT methods to measure glottal area of 11 subjects. The results der i v e df r o mb o t hm e t h o d sw e r es i m i l a r .T h ev a l u e so fA g were measured at functional residual capacity, and varied between 40 and 290 mm 2 (mean value of 180 ± 80 mm 2 ). Similarly, Martin et al. [START_REF] Martin | The effect of age, sex, obesity and posture on upper airway size[END_REF] measured an area of 170 mm 2 (114 subjects). Note that Rubinstein et al. [START_REF] Rubinstein | Glottic dimensions in healthy men and women[END_REF] found a range of values between 144 and 211 mm 2 on 25 males and between 137 and 207 mm 2 on 19 females during hyperpnea.

A glottal narrowing during expiration was observed in all studies. This is supported by the activity of the thyroarytenoid muscle during expiration [START_REF] Kuna | Arytenoideus muscle activity in normal adult humans during wakefulness and sleep[END_REF], which is an adductor muscle of the vocal folds.

Influence of subject gender

The influence of the subject gender on glottal variations during slow breathing is clearly highlighted in Fig. 4. In the upper panel (Fig. 4a andb), it is shown that 9 male subjects have much more representatives in the 2nd group "dynamic" (7/9) relative to the 1st group "static" (2/9). On the contrary, the lower panel (Fig. 4ca n dd ) shows that 10 female subjects are gathered together in the 1st group "static" (7/10), compared with the 2nd group "dynamic" (3/10). These

Slow Breathing trends are similar in rapid breathing, as displayed in Fig. 5 (6/9 males against 2/9 females only in 2nd group "dynamic"). Despite their minimal proportion within the 2nd group, females demonstrate glottal motion amplitudes larger than males. This result yields to higher ratios A I g /A E g and A I g max /A E g min for females, whatever the task (see Table 3, darkened rows). For both genders however, the mean loops A g (Q ) plotted in Fig. 4band4d do not exhibit ellipsoidal shapes, which would have been observed in case of sinusoidal dynamics. Instead, the shape-differences observed on the loops A g (Q ) of males and females mainly derive from the different time-variations of the glottal area recorded during inspiration for both genders: a A g plateau occurs during this phase for females, while a quasisinusoidal variation is measured for males (see Fig. 6). Note that during expiration, the glottal dynamics is similar for males and females: the glottis tends to stay opened in the narrowest posture (Fig. 6a andc).

F01 F02 F03 F04 F05 F06 F07 F08 F09 F10 Mean -50 0 50 Q [L/min] M01 M02 M03 M04 M05 M06 M08 M09

Influence of breathing task

The comparison of the loops A g (Q ) given in Figs. 4 and5 shows similar tendencies and orders of magnitude for eupnea and tachypnea. , and sinusoidal pattern for males (panels a and b, tasks Eup 15 and Tachyp 30 , respectively) and for females (panels c and d, tasks Eup 15 and Tachyp 30 , respectively). Results are given for the subjects with "dynamic" glottal variations (2nd group).

From our results, the influence of the breathing task on glottal motion is far less emphasized than the one of the subject gender.

The glottal aperture is larger during the whole cycle for tachypnea than for eupnea. This is confirmed in Baier et al. [START_REF] Baier | Relationships among glottis opening, respiratory flow, and upper airway resistance in humans[END_REF],w h om e a s u r e d larger glottal areas by both men and women during tachypnea than during quiet breathing.

Correlation between airflow-rate pattern and glottal motion

Fig. 6 shows the mean normalized glottal area dynamics (A g /A I g max )i nf u n c t i o no fn o r m a l i z e dt i m e( ωt) for subjects classified within the 2nd group only. The 1st group is not presented here as the glottal dynamics is steady and the resulting normalized pattern would be a straight line close to 1. Upper (resp. lower) panels correspond to male subjects (resp. female). The mean normalized airflow-rate pattern (Q/Q max I ) is also displayed, to analyze the correlation between airflow-rate and glottal area time-variations. For all 2nd group subjects and tasks, the glottal widening starts with the onset of inspiration, whereas the glottal narrowing precedes the expiration phase. For males, the peak glottal area A I g max is achieved after the peak inspiratory airflow Q max I , with a phase difference of 15.6°. For females, this delay is reduced and both peaks occur rather simultaneously. If the glottal motion seems related to the airflow dynamics during inspiratory phase, no correlation is brought out from the data registered during expiratory phase. Therefore, the same absolute airflow amplitude is associated with (at least) two different glottal openings.

Discussion

Toward the reasons for glottal motion and aerodynamics: an energy saving mechanism?

The respiratory-related glottal motion is generated by contractions of intralaryngeal muscles. The vocal-fold abductor (posterior cricoarytenoid muscle) dilates the glottis during inspiration by ab-duction rotation of the arytenoid cartilages. The adductor muscles narrow the glottis during expiration by adduction-rotation of the arytenoid cartilages. There is general agreement that this controlled motion is carried out in order to (i) help the air intake during inspiration by glottis widening, which lowers the UA resistance to flow, and (ii) to slow down the passive expiratory airflow by glottis narrowing, which enables a control of the end-expiratory lung volume and prevents alveoli to collapse [START_REF] Brancatisano | Respiratory movements of the vocal cords[END_REF][START_REF] Shiba | Chapter 9.1 -Functions of larynx in breathing, vocalization and airway protective reflexes[END_REF]. Note that several studies are dedicated to the restoration of an optimal laryngeal geometry after a surgical change of the vocal folds, which would minimize the airflow resistance in the UA [START_REF] Hundertmark-Zaušková | Numerical simulation of glottal flow[END_REF][START_REF] Templer | Laryngeal airway resistance: the relationships of airflow, pressure, and aperture[END_REF].

Thus, the results obtained in our study on glottal motion and aerodynamics during breathing were further analyzed to interpret the data in terms of energy efficiency. To this end, the power dissipated by an airflow (volume airflow rate Q 0 (t)) through a circular diaphragm ("glottis" of cross section area A 0 g ) across a cylindrical tube ("trachea" of cross section area A t = AP g ) was calculated in two comparative cases:

(i) a realistic case mimicking the measured unsteady flow and glottal conditions,whereQ 0 (t) = Q (t) and A 0 g (t) = A g (t).

(ii) an idealized case assuming unsteady sinusoidal flow conditions and steady glottis,w h e r eQ 0 (t

) = Q max I sin(ωt) with Q max I = π V I /T t ,andA 0 g = A g .
Considering the air as an incompressible Newtonian gas with typical flow Reynolds number Re < 10 5 ,t h ep o w e rP w [W] dissipated through a circular diaphragm is given by:

P w = p • Q 0 = 1 2 ρ U 2 λ Q 0 ,
where p [Pa] is the pressure drop through the singularity, ρ = 1.2

[kg.m -3 ] is the air density, U = 2V I /(T t A 0 g ) [m.s -1 ] is the mean flow velocity during inspiration phase and λ [-], the singular head loss coefficient [START_REF] Idel'cik | Mémento des pertes de charge coefficients de pertes de charge singulières et de pertes de charge par frottement[END_REF] shows a comparison of the power P w [mW] obtained from the data registered for female and male subjects, in the illustrative case of rapid breathing (Tachyp 30 ). Over the whole, it is interesting to note a substantial decrease of the power dissipated during the average breathing cycle in realistic case (i) as compared to idealized case (ii). The energy dissipated by head loss within the "glottal" diaphragm over a cycle, E [J], is defined as E = T t 0 P w dt. Average values are presented in Table 4 in function of gender and breathing task. During slow breathing (resp. rapid breathing), the relative decrease between idealized and realistic cases equals 4% (resp. 6%) and 12% (resp. 13%) for males and females group respectively. Therefore, it is shown that the realistic breathing mode (mobile glottis, non-sinusoidal airflow rate) is an energy saving maneuver in comparison with an idealized mode (steady glottis, sinusoidal airflow rate).

calculated by λ = (1 + 0.707 1 - A 0 g A t - A 0 g A t ) 2 .

Toward the aerodynamic impact of glottal motion

The database was also exploited to evaluate the impact of the measured glottal motion and airflow rates on characteristic flow parameters within the glottis, listed below:

• The maximum and mean flow velocity during inspiration, noted u max and u mean ;

• The local Reynolds numbers Re max and Re mean based on u max and u mean , respectively;

• The frequency parameter, given by α = R h √ ω/υ,w h e r eR h = D h /4, D h [m] being the hydraulic diameter and υ [m 2 .s -1 ]theair kinematic viscosity.

For each group, these parameters are function of the inspiratory volume V I , the breathing period T t and the glottal cross-section area A g (t). Table 5 presents the values obtained in conditions of slow and rapid breathing for males and females (based on data from Tables 2 and3). The mean Reynolds numbers range between 1900 and 3100 (peak values below 5000), corresponding to moderate mean velocity values expected within the glottis (peak values between 4 and 6m . s -1 ). Low values of the frequency parameter (in the range 1.8-2.7) are indicators of a flow comprising notable viscous effects, and whose time duration of the boundary layer development is comparable to the breathing cycle period. These parameters provide information, which could be used as input data to conduct further realistic numerical simulations of laryngeal airflow.

Finally, it is important to note, that the fraction of aerosols deposited on the laryngeal walls is highly dependent on the Stokes number, defined as: St=ρ p d p 2 u/(18μD h ),w h e r eρ p is the density of the particles, d p the particle diameter, μ the air viscosity, u the air inlet velocity and D h the glottal hydraulic diameter. Thus, the deposition dynamics in the larynx is likely to be altered (i) by unsteady flow velocity, as demonstrated in Jin et al. [START_REF] Jin | Large eddy simulation of inhaled particle deposition within the human upper respiratory tract[END_REF], in case of static wall conditions, but also (ii) by unsteady glottal dimensions during breathing. From this point of view, the clinical database reported in this study seems to us of primary interest to better evaluate the aerosol transport and deposition mechanisms in future work.

Conclusion

A clinical study was conducted to examine the glottal motion during eight breathing tasks by means of laryngofibroscopy and synchronized oral airflow measurements on 20 healthy non-smoking volunteers from 20 to 30 year-old. In total, 144 breathing sequences of 30s were recorded. Several results can be highlighted:

Two groups of subjects were identified: (i) a "static" group, gathering subjects with a constant glottal area detected during the average breathing cycle; (ii) a "dynamic" group, gathering subjects with a time-varying glottal area during the average breathing cycle. This latter group gathers 53% (respectively, 44%) of subjects during slow (respectively, rapid) breathing. During "slow" breathing tasks, for males, the peak value of glottal area narrowed from 217 ± 54 mm 2 during inspiration, to 178 ± 35 mm 2 during expiration. For females, the peak glottal area c h a n g e sf r o m1 8 9± 32 mm 2 during inspiration, to 168 ± 31 mm 2 during expiration. The mean value over the whole cycle was found at 196 ± 42 mm 2 for males, and 177 ± 27 mm 2 for females. These values are in agreement with previous studies based on acoustic reflection or MRI techniques. Yet, they are much higher than those previously determined by laryngofibroscopy, due to different spatial calibration.

A correlation motion related to the airflow dynamics was found during inspiratory phase, while no correlation was brought out from the data registered during expiratory phase.

Using a simple theoretical framework based on the power dissipated through a movable diaphragm, this study showed that the realistic breathing mode (mobile glottis, non-sinusoidal airflow rate) is an energy saving maneuver in comparison with an idealized mode (steady glottis, sinusoidal airflow rate).

Finally, this clinical database constitutes available input data which can be used to conduct further realistic numerical simulations of laryngeal airflow in realistic geometries of upper airways.

Fig. 1 .

 1 Fig. 1. (a) Superposed individual breathing cycles Q(t) (subject M01, task Eup 15 ) and resulting mean breathing cycle in function of time t [s]. (b) Example of laryngoscopic area. Corresponding contour of glottal area Ag, antero-posterior diameter APg and glottal width dg at the time of maximum opening t 1 (c) and at time of minimum opening t 2 (d).

Q

  z e r oa x i sw a su p d a t e ds ot h a tV E = C c V I ,w h e r eV E [L] is the average expiratory volume, V I [L] is the average inspiratory volume and C c [-] denotes for the BTPS conversion coefficient, C c = 310 Ta Pa-P WS Pa-6.26 . Pressure P WS [kPa] is the saturation pressure of water vapor at ambient temperature T a [K] and ambient pressure P a [kPa]. C c was quasiconstant over the whole database, equal to 1.07 (see Table

Fig. 2 .

 2 Fig. 2. Normalized mean flow rates Q/Q max I as function of ωt [rad] for slow breathing tasks (Eup f ,E u p 15 ,H y p e r f ) (Panels a and c for males and females, respectively) and rapid breathing tasks (Tachyp 30 ,T achyp 60 ,T achyp 90 ) (Panels b and d for males and females, respectively).

Fig. 3 .

 3 Fig. 3. Normalized mean flow rates Q/Q max I as function of ωt [rad] for the specific inhalation task Aerosol and males and females.

Fig. 4 .Fig. 5 .

 45 Fig.4. G l o t t a la r e av a r i a t i o n sd u r i n gslow breathing. Upper panels (a and b) are for male subjects, and lower panels (c and d) are for female subjects. Left panels (a and c) are dedicated to the 1st group (with "static" glottal movement) and right panels (b and d) are dedicated to the 2nd group (with "dynamic" glottal movement).

Fig. 6 .

 6 Fig. 6. Comparison of mean, normalized glottal area A g /A I g max , mean, normalized flow rate Q/Q max I

  Fig. 7

Fig. 7 .

 7 Fig. 7. Power Pw [mW] comparison of idealized and realistic case, obtained from the data registered for female and male subjects, in the illustrative case of rapid breathing (Tachyp 30 ).

Table 1

 1 Physical characteristics of the subjects. ( * subject finished only slow breathing tasks; † subject finished only Eup f task).

	Females			Males
	Subject	Age [year]	BMI [kg.m -2 ]	Subject	Age [year]	BMI [kg.m -2 ]
	F01	27	21.0	M01	25	21.2
	F02	24	20.0	M02	26	24.3
	F03	24	17.3	M03	24	22.5
	F04	22	21.1	M04	28	20.3
	F05	25	21.5	M05	25	23.1
	F06	23	22.5	M06	27	23.0
	F07	25	19.9	M07 †	26	20.5
	F08	23	23.4	M08	26	21.0
	F09 *	23	17.6	M09	26	20.1
	F10	26	21.3	M10	27	21.8
	Mean	24.2	20.6	Mean	26	21.8
	SD	1.5	1.9	SD	1.2	1.4

Table 2

 2 Measured airflow rate parameters in function of gender and breathing task (see chapter Airflow rate pattern in Results). Gray lines are the tasks further treated for the glottal motion analysis.

	Males
	Task	Tt [s]		Tt / TI [-]		Qmax I	[Lmin -1 ]		Qmax I	/ Qmax E	[-]	VI [L]	Cc [-]	N o
		mean	range	mean	range	mean	range		mean		mean	range	mean	sum
		SD		SD		SD				SD			SD	SD
	Eup f	2,96	1.5-5.8	2,10	1.43-3.45	42,7		11.5-84.8	0,88			0,66	0.12-1.42	1,08	256
		0,78		0,16		11,7				0,19			0,15	0,05
	Eup 15	3,99	3.7-4.5	2,26	1.82-3.04	49,3		30.8-86.6	1,11			0,98	0.52-2.11	1,07	68
		0,03		0,21		14,2				0,17			0,34	0,01
	Tachyp 30	2,00	1.8-2.4	2,13	1.69-2.55	72,4		37.6-167.6	0,98			0,81	0.42-1.99	1,07	145
		0,01		0,16		28,0				0,16			0.36	0,01
	Tachyp 60	1,02	0.8-1.3	2,10	1.72-2.99	93,2		49.3-271.5	1,02			0,55	0.20-1.66	1,07	327
		0,06		0,13		51,1				0,15			0,32	0,01
	Tachyp 90	0,75	0.6-0.9	2,11	1.70-3.02	102,6	45.9-343.8	1,02			0,45	0.18-1.47	1,07	393
		0,02		0,18		63,8				0,16			0,29	0,01
	Hyper f	7,39	3.5-12	2,20	1.73-2.67	125,7	56.1-329.4	1,11			3,82	2.38-8.90	1,07	38
		2,50		0,19		62,0				0,30			1.44	0,01
	Aerosol	3,29	1.4-5.8	3,55	2.09-6.82	263,1		118.5-586.7	3,58			1,83	1.19-3.96	1,07	38
		1,15		0,92		126,3				1,09			0,72	0,01
	Females
	Eup f	4,00	2.2-3.5	2,36	1.56-2.36	32,2		15.5-32.0	1,12			0,64	0.29-0.56	1,07	217
		1,04		0,22		7,2				0,17			0,18	0,02
	Eup 15	3,99	3.6-4.1	2,21	1.94-2.15	42,9		23.4-35.5	1,06			0,94	0.38-0.71	1,07	81
		0,03		0,10		8,4				0,09			0,23	0,02
	Tachyp 30	1,99	1.8-2.1	2,12	1.81-2.55	50,9		30.0-75.8	0,99			0,61	0.27-0.98	1,07	146
		0,00		0,12		9,1				0,11			0,13	0,02
	Tachyp 60	1,00	0.8-1.2	2,10	1.59-2.84	60,0		31.0-97.9		1,04			0,36	0.14-0.64	1,08	332
		0,00		0,11		13,2				0,12			0,08	0,02
	Tachyp 90	0,73	0.4-1.1	2,10	1.63-3.55	59,9		33.8-99.2	1,03			0,26	0.11-0.60	1,07	476
		0,04		0,15		15,4				0,16			0,08	0,01
	Hyper f	8,00	5.1-13.4	2,32	1.80-2.77	75,3		46.4-112.6	1,11			2,54	1.35-3.70	1,07	43
		2,53		0,19		22,2				0,09			0,57	0,01
	Aerosol	3,19	1.9-5.5	4,74	2.49-13.04	161,6		89.3-252.6	3,10			1,12	0.57-1.84	1,07	46
		1,05		1,92		35,9				0,92			0,24	0,01
				Slow Respiration					Rapid Respiration
		0.5 1				Eup f Eup 15 Hyper f Sinus					Ta chy p 30 Ta chy p 60 Ta chy p 90 Sinus
		0
		-0.5
		-1
		1
		0.5
		0
		-0.5
		-1
		0	π/2	π	3/2π		2π	0	π/2		π	3/2π	2π

  Hyper f , and around 39.3°for Eup 15 task. At last, for both genders, the phase difference for Aerosol task reached the highest values (up to 79°

	27.1°i
	n comparison with 36.0°), and smaller for inspiration than for ex-
	piration (26.8°in comparison with 36.3°). Over the whole database,
	the smallest phase difference was found for task Eup f (8.0°for males, inspiration). Considering males and females together, over the whole
	cycle a phase difference around 21.1°was measured for tasks Eup f , Tachyp 30 ,T a c h y p 60 ,T a c h y p 90 and

Table 3

 3

	summarizes the primary glottal dimensional parameters
	(A g , A I g and A I g	max ) measured during slow breathing (Eup 15 )andrapid
	breathing (Tachyp 30 ). Area A g is the mean glottal area obtained over
	the average cycle Q; A I g is the mean glottal area obtained during in-
	spiration (resp. A E g during expiration), and A I g	max is the peak value of
	A I g area (resp. A E g	min is the minimum value of A E g ). The derived ratios
	A I g /A E

g (resp. A I g max /A E g min ), representing the ratio of the mean (resp. peak) A g amplitude during inspiratory and expiratory phases, are also reported. The variations of A g in function of Q for all subjects are shown in Figs.

4 and 5

,forslow and rapid breathing respectively.

Table 3

 3 Measured glottal dimensions parameters in function of gender, group of subjects and breathing rate. Gray lines are the groups for which a time-varying glottal area was detected during the average breathing cycle.

Table 4

 4 Energy loss E [mJ] within a circular diaphragm in two breathing modes: (i) mobile glottis, non-sinusoidal airflow and (ii) steady glottis, sinusoidal airflow.

	Slow breathing-Eup 15
	Group	Realistic case (i)	Idealized case (ii)
	Males	2.73	2.84
	Females	2.73	3.10
	Rapid breathing-Tachyp 30
	Males	5.28	5.62
	Females	2.86	3.28

Table 5

 5 Glottal airflow parameters derived from the present clinical database in function of gender and breathing rate.

		Females		Males
	Flow parameter	Slow breathing	Rapid breathing	Slow breathing	Rapid breathing
	umax [m.s -1 ]	4.17	5.41	3.93	5.99
	umean [m.s -1 ]	2.66	3.45	2.50	3.81
	Remax [-]	3069.2	4001.1	3087.9	4852.2
	Remean [-]	1953.9	2547.2	1965.8	3089.0
	α [-]	1.76	2.51	1.88	2.74
	D h [mm]	10.7	10.8	11.44	11.8

Acknowledgement

We thank Dr. M. Penicaud, Dr. C. Zielinski and also all the subjects for their participation in the clinical study. Further we would like to acknowledge P. Sudour for his valuable administrative support and statistician B. Piednoir for his helpful suggestions.

Funding

The research was supported by a grant from CNRS PEPS INSIS AéroVAS 2011-2012. The laboratory 3SR is part of the LabEx Tec21 (Investissements d'Avenir-grant agreement n°ANR-11-LABX-0030). IRPHE institute is part of the LabEx MEC.

Conflicts of interest

None declared.

Ethical approval

Ethical approval was given by the Committee on the Protection of People (CPP) in Biomedical Research (CPP Sud Méditerranée I, n°2012-A01390-13).


Daphne Guenoun
email: daphne.guenoun@ap-hm.fr

Julien Vaccaro
email: julien.vaccaro@yahoo.fr

Thomas Le Corroller
email: thomas.lecorroller@ap-hm.fr

Pierre-Antoine Barral
email: pierre-antoine.barral@ap-hm.fr

Aude Lagier
email: aude.lagier@laposte.net

Vanessa Pauly
email: vanessa.pauly@ap-hm.fr

Benjamin Coquart
email: benjamin.coquart@ap-hm.fr

Joel Coste
email: joel-alain.coste@ap-hm.fr

Pierre Champsaur
email: pierre.champsaur@ap-hm.fr

Keywords: Dynamic MRI, Anterior cruciate ligament, Knee, Open field, Anatomy

A dynamic study of the anterior cruciate ligament of the knee using an open MRI Daphne Guenoun 1

• Julien Vaccaro 1

• Thomas Le Corroller Abstract Recent anatomical and radiological studies of the anterior cruciate ligament (ACL) suggest the ACL length and orientation change during knee flexion, and an open MRI sequencing during knee flexion enables a dynamic ACL analysis. This study's goal is to describe a normal ACL using a 1T open MRI and, in particular, variations in length and insertion angles at different degrees of flexion. Twenty-one volunteers with clinically healthy knees received a dynamic MRI with their knees in hyperextension, neutral position, and flexed at 45°and 90°angles. For each position, two radiologists measured the ACL lengths and angles of the proximal insertion between the ACL's anterior edge and the roof of the inter-condylar notch. Additionally, we measured the ACL's and the tibial plateau's distal angle insertion between their anterior edges and then compared these with the nonparametric Wilcoxon test. The ACL had a significant extension between the 90°flexion and all other positions (hyperextension: 31.75 ± 2.5 mm, neutral position: 32.5 ± 2.6 mm, 45°:35.6 ± 1.6 mm, 90°:35.6 ± 1.6 mm).

There was also a significant increase of the angle insertion between the proximal 90°flexion and all other positions, as well as between hyperextension and bending to 45°(hyperextension: 2.45°± 3.7°,n e u t r a l :1 3 . 4 °± 9.7°,4 5 °:3 3 25 ± 9.3, 90: 51.85°± 9.3°). Additionally, there is a significant increase in the distal angle insertion for all positions (hyperextension: 133.2°± 5.4°, neutral position: 134.95°± 4.4°,45 °:13 8. 35 °± 5.9°,90 °:14 9. 15 °± 8.6°). Our study is the first to exhibit that a dynamic MRI has a significant ACL extension in vivo during bending. This concept opens the way for further studies to improve the diagnosis of traumatic ACL injuries using a dynamic MRI.

Introduction

The anterior cruciate ligament (ACL) is one of the key knee stabilizers, and the most frequently injured ligament structure in knee trauma. In France, there are nearly 15,000 ACL tears per year from skiing as compared to 175,000 ligamentoplasty surgeries performed in the United States [START_REF] Guenoun | Apport de l'IRM dans le diagnostic des ruptures traumatiques du ligament croise ´ante ´rieur[END_REF]. The biomechanical changes, loss of function and premature degenerative changes which can result from an ACL tear mandate an early diagnosis of a partial or complete ACL rupture.

While diagnosing an ACL tear is clinical, an MRI has long been the complementary examination of reference for confirmation. Because of its 92-97 % sensitivity and 92-99 % specificity [START_REF] Cotten | MR imaging of the knee at 0.2 and 1.5 T: correlation with surgery[END_REF][START_REF] Klass | MR imaging of acute anterior cruciate ligament injuries[END_REF][START_REF] Tsai | Magnetic resonance imaging of anterior cruciate ligament rupture[END_REF], it is particularly informative for the impossible or doubtful clinical examinations as well as for related injury research. Therefore, the ACL has long been a preferred topic of study.

The evolution of medicine's knowledge of anatomy and biomechanics along with imaging's evolving, descriptive precision has improved patient care and functional prognosis.

Long considered isometric, new studies have recently demonstrated ACL's extension during flexion [START_REF] Muhle | Diagnosis of ACL and meniscal injuries: MR imaging of knee flexion versus extension compared to arthroscopy[END_REF][START_REF] Pereira | Evaluation of the Anterior cruciate ligament of the knee: comparison between partial flexion true sagittal and extension sagittal oblique positions during MR imaging[END_REF][START_REF] Zaffagini | Computer investigation of ACL orientation during passive range of motion[END_REF]. Additionally, some pre-existing dynamic knee studies better visualize the ACL during flexion despite using a closed rigid antenna which technically limits range of motion [START_REF] Niitsu | Knee extension and flexion: MR delineation of normal and torn anterior cruciate ligaments[END_REF][START_REF] Pereira | Evaluation of the Anterior cruciate ligament of the knee: comparison between partial flexion true sagittal and extension sagittal oblique positions during MR imaging[END_REF]. The development of open MRIs and mobile surface antennas allow the realization of a dynamic MRI without any movement restrictions. This study's goal is to describe a normal ACL using a 1T open MRI, and particularly variations in length and insertion angles at different degrees of flexion.

Materials and methods

In compliance with institutional ethics regulations and after obtaining an informed consent, we performed MRI knee examinations on 21 volunteers between January and March 2016. None had any history of knee trauma or surgery and all were asymptomatic. One patient was excluded from the study upon discovering an old ACL injury. The examinations were performed with a 1T open MRI (Panorama HFO 1 Tesla, Philips).

Each patient was placed in a lateral position and the knee was fixed using a graduated wedge angle system (graduated dynamic kit) to achieve different standardized and reproducible degrees of flexion (Fig. 1). Images were obtained using a standard, flexible knee surface antenna centered on the tip of the patella.

The protocol included coronal STIR sequences (TR = 2530 ms; TE = 20 ms; FOV = 160 9 148 mm 2 ; Gap = 0) with a 3.5 mm slice thickness to identify ACL femoral insertions and achieve the sagittal sequences. This was followed by dynamic T2 fat sat (TR = 1812 ms; TE = 20 ms; FOV = 250 9 250 mm 2 ; Gap = 0) sagittal obliques sequences, with a 3 mm slice thickness, ACL centered and successively realized while hyperextended, in a neutral position, and with 45°and 90°flexion positions.

For each knee, we measured:

• ACL at its greatest length in the sagittal plane between its intercondylar notch proximal insertion and its distal insertion on the tibial spines. • The angle of proximal insertion, formed between the anterior ACL edge and the roof of the intercondylar notch (Blumensaat's line). • The angle of distal insertion formed between the ACL and the anterior edge of the tibial plateau.

The morphological analysis and different measurements were successfully and independently achieved by both a senior and junior physician. When there was a disparity in their independent results, they jointly chose the measurements.

The data's statistical analysis was performed with the SAS Ò V9.4. A comparison of different measurements of the four positions (hyperextension, neutral position, and 45°,9 0 °angles) was performed using the nonparametric Wilcoxon test for paired data. In cases of globally significant statistical differences in the Wilcoxon test alpha level

Results

We studied MRIs of 20 healthy knees in positions of hyperextension, neutral, 45°and 90°flexion.

Volunteers included 9 men and 11 women, from 24 to 47 years old (mean age = 32 years old).

Lengthening of ACL

In our group, the average ACL lengths were 31.75 ± 2.5 mm hyperextended, 32.5 ± 2.6 mm in a neutral position, and 33.5 ± 1.8 mm at 45°flexion and 35.6 ± 1.6 mm 90°flexion (Table 1;F i g .2) with an average elongation of 3.85 mm between the hyperextension and the 90°flexion.

The statistical analysis shows there is a significant difference in elongation between the different positions (p \ 0.0001; global Wilcoxon test). The side by side post hoc test comparisons show these differences are between the 90°flexion and all other positions [hyperextension vs. 90°flexion (p \ 0.0001)]; neutral position vs 90°flexion (p = 0.0016); 45°flexion vs 90°flexion (p = 0.0052) (Fig. 3). There was, however, no significant difference observed between hyperextension and the 45°angle.

Insertion angles

Proximal angle

Mean values were calculated at 2.45°± 3.7°for hyperextension; 13.4°± 9.7°in the neutral position; 33.25 ± 9.3 with 45°of flexion; and 51 85°± 9.3°with 90°flexion (Table 2; Fig. 4).

The statistical analysis showed a significant difference in the increase between the different positions (p \ 0.0001; global Wilcoxon test). Side by side post hoc test comparisons show that these differences are between 90°flexion and all other positions [hyperextension vs 90°flexion (p \ 0.0001); the neutral position vs a 90°flexion (p \ 0.001); 45°flexion vs 90°flexion (p = 0.0008); and between the 45°flexion and hyperextension (p = 0.04)]. 3; Fig. 5).

The statistical analysis showed a significant difference in the increase between the various positions (p \ 0.0001; global Wilcoxon test). Side by side post hoc test comparisons showed that these differences exist with all compared positions (with p values all \0.0001).

In general, the 90°flexion is the only position where a significant difference is demonstrated both for ACL elongation, the increased angle between the ACL and the anterior tibial plateau; as well as an increase between the antrum angle and Blumensaat's line.

Discussion

The ACL, a key stabilizing element of the knee, prevents anterior tibial translation and medial rotation. This is a ligamentous structure, formed of dense connective intraarticular tissue, with an oblique, forward extra synovial downward trajectory. Its distal fibers fan out in the tibial spines and are easily visible with conventional MRI sequencing. Its proximal fibers are, however, less distinct and more difficult to isolate with an MRI due to an insertion on the medial surface of the lateral femoral condyle [START_REF] Girgis | The cruciate ligaments of the knee joint. Anatomical, functional and experimental analysis[END_REF], which can be responsible for partial volume artifacts [START_REF] Guenoun | Apport de l'IRM dans le diagnostic des ruptures traumatiques du ligament croise ´ante ´rieur[END_REF][START_REF] Mink | MRI of the knee[END_REF].

Its average measurement is 38 mm long and 11 mm wide [START_REF] Cohen | MRI measurement of the two bundles of the normal anterior cruciate ligament[END_REF][START_REF] Girgis | The cruciate ligaments of the knee joint. Anatomical, functional and experimental analysis[END_REF] from one knee to the other for the same patient [START_REF] Cle ´ment | Statistical analysis of the knee ligaments lengths[END_REF]. It consists of two distinct bundles: an anteromedial (AM) and posterolateral (PL), which are named in function of their tibial inserts. The AM is longer (36.9 ± 2.6 mm) and wider than the PL (20.5 ± 2.6 mm). It is situated higher and behind the femur, and in front of the tibial spines. Because of this length difference and study design, the ACL's greatest length actually corresponds to the AM measurement. We were able to substantiate that our various benchmarks actually corresponded to the AM insertion points and that the structure visualized and measured was in fact the AM.

Digitally measuring, the ACL is one of the strengths of our study. Considering the ACL's short length, this type of measure is more accurate and less prone to error than the biomechanical techniques previously used on cadavers. In addition, an open MRI allows imagery without any amplitude limits.

Our study is limited by the small number of patients examined. Similarly the choice of imagery protocol in the oblique sagittal plane is debatable because it does not allow a distinction between AM and PL, but it is the only one to allow visualization and an accurate measurement of the ligament in its entirety on a single cut. The ACL is the most commonly injured structure during knee trauma. Its rupture most often follows a lateral rotating mechanism, flexion and a forced valgus. The rupture diagnosis is essentially clinical, substantiated with a positive anterior drawer, Lachman test, and joint effusion.

In clinically doubtful cases, an MRI can assist with a diagnosis, especially when pre-operatively detecting any associated injuries. The MRI is the examination of reference for diagnosing ACL injuries because of its sensitivity (92-97 %) and specificity (92-99 %) [START_REF] Cotten | MR imaging of the knee at 0.2 and 1.5 T: correlation with surgery[END_REF][START_REF] Klass | MR imaging of acute anterior cruciate ligament injuries[END_REF][START_REF] Tsai | Magnetic resonance imaging of anterior cruciate ligament rupture[END_REF]. Good visualization and knowledge of the ACL's normal appearance are essential for an accurate diagnosis [START_REF] Lee | Anterior cruciate ligament tears: MR imaging compared with arthroscopy and clinical tests[END_REF]. In cases of a rupture, an early diagnosis is crucial because of the instability and stress related changes, which in turn, are responsible for early meniscal and cartilage degenerative lesions [START_REF] Arnoldi | MRI based volumetric assessment of knee cartilage after ACL-reconstruction, correlated with qualitative morphologic changes in the joint and with clinical outcome. Is there evidence for early posttraumatic degeneration?[END_REF][START_REF] Logan | Tibiofemoral kinematics following successful anterior cruciate ligament reconstruction using dynamic multiple resonance imaging[END_REF].

The ACL normality criteria are well defined. The ligament presents as a T1-and T2-hypointense, continuous, sharply contoured and stretched with a parallel orientation to the roof notch (Blumensaat's line). However, due to its orientation and partial volume artifacts, the ACL is not completely viewed in 5-10 % of the cases [START_REF] Mink | MRI of the knee[END_REF], particularly to its proximal insertion where lesions are the most frequent [START_REF] Guenoun | Apport de l'IRM dans le diagnostic des ruptures traumatiques du ligament croise ´ante ´rieur[END_REF][START_REF] Mink | MRI of the knee[END_REF]. An MRI ACL tear diagnosis remains difficult and subjective with a 20 % false negative depending on the experience of the observer. This is most notable with partial lesions which represent between 10 and 48 % of ACL injuries (Se 40-75 %, Sp 51-89 %) [START_REF] Umans | Diagnosis of partial tears of the anterior cruciate ligament of the knee: value of MR imaging[END_REF][START_REF] Yao | Partiel ACL rupture: an MR diagnosis?[END_REF].

To improve the exam's sensitivity in doubtful cases, many indirect signs have been described to confirm an ACL rupture. These include a loss of parallelism relative to the Blumensaat's line; presence of bone bruises; a Segond fracture; a tibial plateau anterior subluxation [5m m between the lateral femoral condyle and lateral tibial plateau; ACL verticality or the distension of the patellar tendon [START_REF] Guenoun | Apport de l'IRM dans le diagnostic des ruptures traumatiques du ligament croise ´ante ´rieur[END_REF], with sensitivity and specificity varying greatly between studies.

Our study, the first to investigate the normal radioanatomy of the ACL in vivo during dynamic maneuvers, demonstrates the significant ACL lengthening during flexion. The average ACL length measured was 31.75 ± 2.5 mm hyperextended and 35.6 ± 1.6 mm in 90°flexion (Table 1; Fig. 2), i.e. an average elongation of 3.85 mm between extension and a 90°flexion. This is in accord with recent literature which highlights an elongation observed during biomechanical cadaver studies [START_REF] Hoseini | In vivo anterior cruciate ligament elongation in response to axial tibial loads[END_REF][START_REF] Zaffagini | Computer investigation of ACL orientation during passive range of motion[END_REF], despite limited and imprecise measurement techniques.

Indeed biomechanical measurements based on skin markings have an error risk due to the likelihood of mobilizing these markings. Measures taken on cadavers are error-prone because of manual measures and conservation conditions of the knee which may modify the physiological tissue elasticity and suppress the muscular strength.

During flexing, the size of the two bundles varies nonuniformly since the AM extends (from 3 to 3.6 mm) while the PL shortens (-1t o-7.1 mm) [START_REF] Hollis | The effects of knee motion and external loading on the length of the anterior cruciate ligament (ACL): a kinematic study[END_REF][START_REF] Takai | Determination of the in situ loads on the human anterior cruciate ligament[END_REF]. The ACL ''global'' lengthening highlighted during bending is mainly due to the AM lengthening and confirms its principal role in knee stability in this position [START_REF] Amis | Anterior cruciate ligament: functional anatomy f its bundles actions related to ligaments replacement and injuries[END_REF][START_REF] Hirokawa | Hyper-elastic model of anterior cruciate ligament[END_REF][START_REF] Hollis | The effects of knee motion and external loading on the length of the anterior cruciate ligament (ACL): a kinematic study[END_REF][START_REF] Takai | Determination of the in situ loads on the human anterior cruciate ligament[END_REF].

Because of tube size technical constraints and movement restrictions with rigid surface antennas, the vast majority of pre-existing ACL MRI studies was carried out on extended knees. A few dynamic studies that was done and showed the value of this technique by demonstrating better ligament visualization and flexion anomalies. This allowed a better distinction between simple deformation, irregularity and actual damage, most notably through an expansion of the space between the intertubercular groove and the tibial spines [START_REF] Niitsu | Slightly flexed knee position within a standard knee coil: MR delineation of the anterior cruciate ligament[END_REF].

Niitsu, Muhle and Pereira all demonstrated better visualization of ACL damage when flexing. They were able to detect significant rupture increases of the ligament, by enhanced visualization of the femoral and tibial ligament insertions [START_REF] Muhle | Diagnosis of ACL and meniscal injuries: MR imaging of knee flexion versus extension compared to arthroscopy[END_REF][START_REF] Niitsu | Slightly flexed knee position within a standard knee coil: MR delineation of the anterior cruciate ligament[END_REF][START_REF] Pereira | Evaluation of the Anterior cruciate ligament of the knee: comparison between partial flexion true sagittal and extension sagittal oblique positions during MR imaging[END_REF]. Despite the small number of patients (5), Pereira noted improved detection of ruptures (60 %) with a sensitivity of 96 % on flexion [START_REF] Pereira | Evaluation of the Anterior cruciate ligament of the knee: comparison between partial flexion true sagittal and extension sagittal oblique positions during MR imaging[END_REF]. Comparing the results with arthroscopy, Muhle notes an improved overall sensitivity in detecting ruptures, particularly of partial lesions (50 vs 63 % in extension flexion to 55°) [START_REF] Muhle | Diagnosis of ACL and meniscal injuries: MR imaging of knee flexion versus extension compared to arthroscopy[END_REF]. Since this mainly affects the AM [START_REF] Sbihi | Arthroscopie:genou, cheville, hanche, e ´paule, coude, poignet, extra-articulaire[END_REF], the ligament elongation caused by bending helps unmask those lesions as a result of the bundle's primary role in this position.

Nenezic, when comparing classical and flexion sequences of ACL centered oblique sagittal sections, showed a better visualization of partial ruptures on the flexion sequences relative to extension (78 vs. 48 %) without any significant differences between the flexion and oblique sagittal sequences [START_REF] Nenezic | The value of the sagital-oblique MRI technique for injuries of the anterior cruciate ligament in the knee[END_REF]. However, the absence of an arthroscopic correlation limits his study.

There were no significant differences demonstrated in the meniscus or other associated injuries [START_REF] Muhle | Diagnosis of ACL and meniscal injuries: MR imaging of knee flexion versus extension compared to arthroscopy[END_REF]. Other meniscal ligamentous structures are comparable in extension and flexion, with a sensitivity of 82 % for the lateral meniscus and between 81.5 and 96 % for the medial meniscus [START_REF] Niitsu | Slightly flexed knee position within a standard knee coil: MR delineation of the anterior cruciate ligament[END_REF].

Additionally, we noted a significant increase in the proximal insertion angle with average values of 133.2°± 5.4°during hyperextension and 149.15°± 8.6°t o 90°with flexion (Table 2; Fig. 3). There was also a closed distal angle with mean values of 2.45°± 3.7°during hyperextension and 51.85 ± 9.3 at 90°with flexion (Table 3; Fig. 4).

Only one study reviewed ACL angle insertion variations based on the degree of knee flexion. Zaffagnini demonstrated, as did we, a reduction of the angle insertion (56.5°± 11.8°vs 33.5°± 6.8°), and an increase of the proximal angle insertion (4.6°± 11.4°vs 58.4°± 7.3°) during flexion, first at the expense of the PL between 0°a nd 80°then the AM, confirming the latter's major role in the ligament tension during flexion [START_REF] Zaffagini | Computer investigation of ACL orientation during passive range of motion[END_REF]. Our distal angle measurements vary inversely due to using the tibial plateau anterior edge as our reference, while Zaffagnini used the posterior edge.

A dynamic MRI of a knee flexion could be significant in diagnosing traumatic ACL injuries by enhancing a full or partial ACL rupture, particularly regarding the AM. Furthermore, understanding both normal and pathological anatomy in different positions can provide additional semiotic analysis in any doubtful cases. Understanding ACL's normal lengthening may also be useful during a remote-site postoperative follow-up if there are persistent abnormal symptoms. The dynamic MRI could thus seek and detect defects or excessive elongations which signify kinetic disturbances in the operated knee. Moreover, an ''anatomical'' or a ''non-anatomical'' surgical techniques remain controversial, and the comparative study of postoperative ligament elongation versus either of the two techniques could help bring arguments in favor of the one that best restores knee kinetics.

Our study complements existing data by examining the ACL's morphology and biomechanics during full flexion with an open MRI and flexible antenna so as to circumvent the previous studies' technical limitations. Our results are consistent with the recent literature which confirm an ACL extension during flexion and the AM's central role.

Conclusions

To the best of our knowledge, this study is the first descriptive radio-anatomical study to analyze a normal ACL in vivo in different positions, confirming it is significantly longer when flexed to 90°as a result of the AM's elongation. Understanding both the normal and abnormal ACL length in its different positions could allow us to improve diagnosing partial or complete ACL tears.

A study of traumatic ACL injuries using a dynamic MRI is imminent. Furthermore, the possibility of a dynamic knee joint examination with an open MRI may even extend to studying all articulations.

Compliance with ethical standards

Conflict of interest The authors declare that they have no conflict of interest.

Fig. 1 a

 1 Fig. 1 a Patient position in the open-field MRI; b graduated dynamic kit

Fig. 3

 3 Fig. 3 Distribution of ACL length in various positions (p \ 0.001)

Fig. 4 Fig. 5

 45 Fig. 4 Angle increase of proximal insertion during bending: a hyperextension: 135°; b neutral position: 139°; c 45°flexion: 143°; d 90°flexion: 159°T

Table 1

 1 Summary of ACL measurements in different positions

		Hyperextension	Neutral position	45°Flexion	90°Flexion
	Average	31.75	32.5	33.55	35.6
	Standard deviation	2.5	2.6	1.8	1.6
	Minimum	28	28	28	33
	Maximum	35	36	36	39
	Median	32	32.5	34	35

Fig. 2 Oblique sagittal cuts showing ACL's elongation during flexion. a Hyperextension; b neutral position; c 45°flexion; d 90°flexion

Table 2

 2 Summary of angle measurements in various positions between the ACL and the anterior tibial tray

		Hyperextension	Neutral position	45°Flexion	90°Flexion
	Average	133.2	134.95	138.35	149.15
	Standard deviation	5.4	4.3	5.9	8.6
	Minimum	119	125	126	135
	Maximum	145	145	52	163
	Median	134.5	135.5	139	149


Chantal Enguehard¹
email: chantal.enguehard@univ-nantes.fr

Harouna Naroua²
email: ²hnaroua@yahoo.com

Evaluation of Virtual Keyboards for West-African Languages

West African languages are written with alphabets that comprize non classical Latin characters. It is possible to design virtual keyboards which allow the writing of such special characters with a combination of keys. During the last decade, many different virtual keyboards had been created, without any standardization to fix the correspondence between each character and the keys to press to obtain it. We define a grid to evaluate such keyboards and apply it to five virtual keyboards in relation with the five main languages of Niger (Fulfulde, Hausa, Kanuri, Songhai-Zarma, Tamashek), Bambara and Soninke from Mali and Dyoula from Burkina Faso. We conclude that the African LLACAN keyboard should be recommended in Niger because it covers all the characters used in the alphabets of the main languages of this country, it produces valid Unicode codes and it minimizes the number of keys to be pressed.

Context

Localization of software has become an important activity since the Unicode standard appeared in 1992 which gives a unique code to each character [START_REF] Andries | Introduction à Unicode et à l'ISO 10646[END_REF].

Fifty years after the Bamako conference which started work on the definition of the official alphabets of many African languages, these alphabets appear now to be stable. Official decrees which fix these alphabets have been published for the last ten years in Niger and Mali. These alphabets are Latin based but also include several characters which cannot be found amongst the 26 alphabetical letters required to write in English [START_REF] Chanard | Encodage informatique multilingue : application au contexte du Niger[END_REF], [START_REF] Mbodj | Orthographe commune et législations nationales. Writing African -The Harmonisation of Orthographic Conventions in African Languages[END_REF]. This situation is not unusual. Several European languages, such as French, Spanish and Czech make use of additional characters or characters with diacritics.

Keyboards are the main devices used to enter text into computers. Different types of keyboards have been designed, initially for typewriters, and now for computers. Keyboards may differ according to which language will be used [START_REF] David | Comprendre les aspects économiques de qwerty la contrainte de l'histoire. Réseaux[END_REF]. This paper will deal with the historical development of keyboards [START_REF] Lilen | La saga du micro-ordinateur[END_REF]. Producing a material keyboard should be a profitable business but this may not be possible in the case of many of the less widely spoken languages where the market is too small. In such cases it is possible to design virtual keyboards: the Unicode code which is mapped to each key or combination of keys can be easily modified. This approach allows the addition or the substitution of signs to standard keyboards.

Because there was a strong need for such localized keyboards, the past decade has seen the definition of many keyboards for West African languages, without any standardization. This situation is quite confusing because the users of these keyboards are faced with different keyboards, and many of them may find the situation very uncomfortable.

Goal

The story of the Qwerty or Azerty keyboards (used to write in English and French, respectively) shows that the design quality of a keyboard (the way the keys are situated on the keyboard) is not the most important feature. These two keyboards, even if they are not properly designed, became de-facto standards because they are widespread and because it is extremely difficult for a user who has learned to type on one keyboard, to become accustomed to another. This research does not intend to design keyboards but rather to evaluate different virtual keyboards by defining an evaluation grid and applying its criteria to the different virtual keyboards which we have decided to compare.

Evaluation grid

We defined several criteria to evaluate keyboards.

Firstly, it is important to determine whether the keyboard has the capacity to associate Unicode codes for each key or combination of keys which corresponds to a character, and not ASCII codes.

Secondly, Western African countries generally have several national languages and one official language. Several of these countries, like Mali or Niger, started to include their national languages in education programmes and these languages are widely used by Non Governmental Organisations. These activities produce written documents which are produced in coordination with linguists and typed by the secretaries of these organisations. A secretary may frequently be required to type texts in different languages. It is then important to have a single keyboard which may be used to produce texts in as many languages of a country as possible, including the official language.

Thirdly, it is important that all the characters on the original keyboard continue to be accessible on the virtual one.

Fourthly, the number of keys that have to be pressed to produce a text must be kept as low as possible.

Fifthly, a user-friendly documentation must accompany the keyboard.

The three first criteria we chose are mandatory. The two last criterion can be used to decide between keyboards that fill the three mandatory criteria.

Even if these criteria are quantitative, the final evaluation should be qualitative, based on the five previously established measures.

We did not consider as a criterion the ergonomic key placement on the keyboard because history taught us that this feature is not crucial for the massive use of a specific keyboard, as we saw with the cases of the Qwerty and Azerty keyboards. For instance, the Dvorak Simplified Keyboard (DSK) that were developed by August Dvorak to be ergonomically adapted to English, never succeed to dethrone the Qwerty keyboard. The French version of this keyboard, ergonomically adapted to French failed also to become essential [START_REF] Liebowilz | La fable des touches. Réseaux[END_REF].

Experiments

We have evaluated five virtual keyboards for the five main national languages of Niger which are used in educational programmes. In addition, we examined two languages of Mali and one of Burkina Faso.

The five virtual keyboards are: AfricainLLACAN, AfricaKeyboardDead, AfricaKeyboardUS, Pan-Sahelien, SIL_IPA_Unicode.

The five languages of Niger are: Fulfulde (ful), Hausa (hau), Kanuri (kau), Songhai-Zarma (son), Tamashek (tmh). We also added Bambara (bam) and Soninke (snk) from Mali and Dyoula (dyu) from Burkina Faso.

The transcription of these languages encounters several signs which are not accessible on usual keyboards as shown in Table 1.

Name Sign Languages Unicode

Latin

Results

The evaluation of the number of keys that have to be pressed to produce a text has been determined using corpora of the different languages.

Virtual keyboard

Analysis

The Pan-Sahelien keyboard must be disqualified because it does not produce Unicode codage. The AfricaKeyboardDead, AfricaKeyboardUS and SIL_IPA_Unicode keyboards must be also disqualified because they don't cover all the characters that are used in the five languages we consider.

Thus, The African LLACAN keyboard is the only one to meet the three mandatory criteria we defined. In addition, it is provided with a documentation. written in French. This documentation should be translated in other languages (of course in English, but also in the West-African languages that can be easily written with this keyboard).

The African LLACAN keyboard can be downloaded on the Tavulsoft website 1 : choose Niger, then any of the languages that has been studied in this paper

Conclusion

The African LLACAN keyboard should be recommended in Niger because it covers all the characters used in the alphabets of the different languages of this country and produces valid Unicode codes. In addition, this keyboard minimizes the number of keys to be pressed and covers also all the alphabetic characters of Bambara, Soninke and Dyoula. It will soon be fully evaluated for the main languages of Mali.

Table 1 :

 1 special characters used in the alphabets of the studied languages

	letter e with tilde	e	son	U+0065 U+0303
	Latin letter i with tilde	i	son	U+0069 U+0303
	Latin letter o with tilde	o	son	U+006F U+0303
	Latin letter r short stroke overlay	r ̵	kau	U+0072 U+0335
	Latin letter u with tilde	u	son	U+0075 U+0303
	Latin letter a with tilde	ã	son	U+00E3 or U+61 U+303
	Latin letter a with breve	ă	tmh	U+0103 or U+61 U+306
	Latin letter ENG	ŋ	bam, ful, son U+014B
	Latin letter s with caron	š	tmh	U+0161 or U+73 U+30C
	Latin letter k with hook	ƙ	hau	U+0199
	Latin letter y with hook	ƴ	ful, hau	U+01B4
	Latin letter turned e	ǝ	kau, tmh	U+01DD or U+259

Table 2 :

 2 number of keys that have to be pressed for languages from Niger

		Fulfulde	Hausa	Kanuri	Songhai-	Tamashek	Total
					Zarma
	AfricainLLACAN	87,066	163,225	109,542	82,234		213,230	655,297
	AfricaKeyboardDead	87,871	165,551	109,593	85,606		217,512	666,133
	AfricaKeyboardUS	87,871	165,551	109,593	85,606		217,512	666,133
	Pan-Sahelien	91,329	168,623	109,703	87,989		221,903	679,547
	SIL_IPA_Unicode	89,048	165,001	108,175	82,866		213,850	658,940
	Virtual keyboard	Unicode	Fulfulde Hausa	Kanuri	Songhai-	Tamashek
						Zarma
	African LLACAN	Yes	Total	Total	Total		Total	Total
	AfricaKeyboardDead	Yes	Total	Total	Total		Partial no Ɲ (13/14)	Partial (14 / 24)
	AfricaKeyboardUS	Yes	Total	Total	Total		Partial no Ɲ (13/14)	Partial (14 / 24)
	Pan-Sahelien	No	None	None	Partial		None	Partial
					(1 / 4)			(16 / 24)
					(ə only)
	SIL_IPA_Unicode	Yes	Partial	Partial	Partial		Partial	Partial
			(4 / 8)	(3 / 8)	(1 / 4)		(4 / 14)	(6 / 24)
					(ə only)

Table 3 :

 3 code types and coverage of special characters of languages from Niger