0685 Safety Evaluation Of An Algorithm Determining Needs For Treatment In Obese Sleep Apnea Patient Awaiting Bariatric Surgery: Results Of A Prospective 1103 Patients Cohort Study

Introduction

Screening for obstructive sleep apnea (OSA) is recommended before bariatric surgery. We developed an algorithm based on results of nocturnal oximetry and capillary gas. According to this algorithm, CPAP/BiPAP is prescribed only in severe OSA (ODI ≥ 25/h) and/or with features of hypoventilation. The objective of this prospective cohort study was to determine the safety of our algorithm comparing peri and post-operative outcomes in patients not receiving pre-operative treatment (without/mild OSA (ODI < 10 /h: controls or ODI 10-24 /h: OSA untreated) and in those receiving CPAP/BiPAP (severe OSA: OSA treated or hypoventilation).

Methods

We collected data from 1103 subjects undergoing bariatric surgery (447 controls; 358 OSA untreated, 289 OSA treated and 9 hypoventilation). For treated patients, a good CPAP/BiPAP compliance was mandatory for surgery with treatment installed immediately after extubation and continued after. Peri and post-operative outcomes were compared according to apnea status with adjustment for the type of surgery when applicable.

Results

Patients with severe OSA/hypoventilation were significantly older and heavier than other patients. Hypertension and diabetes were less prevalent in controls than in the other groups. No difference was found between the 3 groups regarding occurrence of 10 days reoperation and 30 days rehospitalisation. No difference was found regarding occurrence of cardiopulmonary complications except that admission to ICU was more frequent in patients with hypoventilation and occurrence of cardiac arrhythmia was higher in the OSA/hypoventilation treated patients than in the other groups (2.4%, 11.1 %, 0.4% and 0.6%, p = 0.01). OSA/hypoventilation patients had a longer length of stay in the recovery room (1.7 ± 0.5, 1.9 ± 0.6, 1.5 ± 0.5 and 1.5 ± 0.5 hours p<0.0001) and longer length of hospital stay (2.8 ± 1.8, 3.2 ± 1.1, 2.6 ±2.1 and 2.6 ±1.8 days, p<0.0001) than controls and OSA untreated patients.

Conclusion

Our algorithm safely selects patients who don’t need treatment before surgery, with no increase in risk of complications following bariatric surgery not treating OSA patients with mild/moderate sleep apnea without hypoventilation. Patients with severe OSA/hypoventilation, even when correctly treated remain at higher risk of complications.

Support

Fondation IUCPQ-UL

0564 Assessment of Tongue and Soft Palate Muscles Mechanical Properties in Patients with OSA

Introduction

Soft palate muscles are crucial in the maintenance of UA patency. Different contraction tasks have been used to investigate tongue mechanical properties, but not to soft palate muscles. This study aimed to investigate the mechanical consequences of tongue and soft palate muscles fatigue in moderate-severe OSA patients.

Methods

12 moderate and 8 severe patients with OSA were enrolled. Measurements include strength, endurance, and fatigue indices. During the soft palate fatiguing protocol, subjects were asked to develop repetitive intra-oral positive pressure during cheek-bulging maneuvers while wearing a mouth piece to keep the jaw opened. Tongue mechanical properties were also assessed using protrusion tasks with similar protocol. Subjects were encouraged to develop sustained maximal bulging pressure or tongue protrusion force for 5 sec every 10 sec until the peak pressure did not reach 85% of baseline maximal pressure for 2 consecutive times. The influence of age and BMI were also investigated.

Results

The sex, age were not significantly different between the 2 OSA groups. BMI was significantly higher in severe OSA patients (p<0.05). Overall, the tongue maximal voluntary contraction force (MVC), endurance time and total muscle work were respectively positively associated with the ones obtained from the soft palate fatiguing task (rs=0.51, 0.43, 0.66, respectively). The MVC of both tongue and soft palate muscles were positively correlated with BMI in all subjects (rs=0.43, 0.5 respectively). The recovery time from soft palate fatigue was significantly longer in moderate than severe OSA patients (270s ± 192.3s and 120s ± 0, p =0.02). Interestingly, the recovery time was positively correlated with AHI in tongue fatiguing task, while negatively correlated with supine AHI and age in soft palate fatiguing task (p<0.05). In both tasks, MVC was negatively correlated with the endurance time (p<0.05).

Conclusion

Moderate patients are less likely to recover from soft palate muscle fatigue. A more severe apneic disease is associated with longer recovery time from tongue fatigue, but with shorter recovery time from soft palate fatigue. Our results suggest that alteration in tongue and velopharyngeal muscles function may differ according to the severity of disease.

Support

SBD from IUCPQ Foundation.

Sibutramine versus continuous positive airway pressure in obese obstructive sleep apnoea patients

The aim of the present study was to compare the efficacy of 1 yr of sibutramine-induced weight loss versus continuous positive airway pressure (CPAP) treatment on sleep-disordered breathing, cardiac autonomic function and systemic blood pressure in obese patients with obstructive sleep apnoea. Subjects with a body mass index of > or =30 kg.m(-2) without previous treatment for obstructive sleep apnoea underwent either sibutramine (n = 22) or CPAP (n = 18) treatment for 1 yr. Sibutramine induced a 5.4+/-1.4 kg decrease in body weight compared to the CPAP group, in which no changes in anthropometric variables were observed. The CPAP treatment improved all sleep and respiratory variables, whereas sibutramine-induced weight loss improved only nocturnal arterial oxygen saturation profile. Only CPAP treatment improved night-time systolic and diastolic blood pressure and 24-h and daytime ambulatory diastolic blood pressure. Sibutramine-induced weight loss had no impact on indices of heart rate variability, whereas CPAP treatment increased daytime time domain indices. CPAP treatment for 1 yr had beneficial impacts on nocturnal breathing disturbances, and improved nocturnal oxygenation, night-time systolic and diastolic blood pressure, and daytime cardiac parasympathetic modulation. Sibutramine did not improve sleep-disordered breathing, systemic blood pressure or heart rate variability. There were no adverse effects, such as increment in blood pressure or arrhythmias, associated with this treatment regimen.

Impact of CPAP on asthmatic patients with obstructive sleep apnoea

The impact of continuous positive airway pressure (CPAP) treatment on the airway responsiveness of asthmatic subjects with obstructive sleep apnoea (OSA) has scarcely been studied. A prospective study was performed comparing the changes in airway responsiveness and quality of life in stable asthmatic OSA patients, before and 6 weeks after their nocturnal CPAP treatment. A total of 20 subjects (11 males and nine females) participated in the study. With the nocturnal CPAP treatment, the apnoea/hypopnoea index dropped from 48.1 +/- 23.6 x h(-1) to 2.6 +/- 2.5 x h(-1). There were no significant changes in airway responsiveness after CPAP treatment (provocative concentration causing a 20% fall in forced expiratory volume in one second (FEV(1); PC(20) 2.5 mg x mL(-1) (1.4-4.5)) compared with baseline (PC(20) 2.2 mg x mL(-1) (1.3-3.5)). There was no significant change in FEV(1) either. However, the asthma quality of life of the subjects improved from 5.0 +/- 1.2 at baseline to 5.8 +/- 0.9 at the end of the study. In conclusion, nocturnal continuous positive airway pressure treatment did not alter airway responsiveness or forced expiratory volume in one second in subjects with stable mild-to-moderate asthma and newly diagnosed obstructive sleep apnoea. However, nocturnal continuous positive airway pressure treatment did improve asthma quality of life.

Relationship between severity of nocturnal desaturation and adaptive thermogenesis: preliminary data of apneic patients tested in a whole-body indirect calorimetry chamber

The purpose of this study was to investigate the possibility of a relationship between the severity of obstructive sleep apnea syndrome (OSAS) and adaptive thermogenesis. Daily energy expenditure (DEE) and sleeping metabolic rate (SMR) were measured in apneic and a priori nonapneic subjects who were tested in a whole-body indirect calorimetry chamber for 24 h. The apneic patients were diagnosed by nocturnal home oximetry to determine the percentage of total recording time spent below 90% arterial oxygen saturation (% TRT <90% SaO(2)). Reference equations established from body weight and age in nonapneic subjects were used to predict DEE and SMR in apneic patients. The predicted values of the apneic patients were then compared to their measured values. No significant difference was found between predicted and measured values in SMR nor in DEE. We observed a significant relationship between the severity of nocturnal desaturation and the difference between predicted and measured DEE in apneic patients (r = -0.74, P < 0.05) and a similar negative trend with SMR (r = -0.65, P = 0.08). These preliminary data suggest that a nocturnal hypoxia may influence adaptive thermogenesis in apneic patients and complicate their body weight regulation.

Impediment in upper airway stabilizing forces assessed by phrenic nerve stimulation in sleep apnea patients

BACKGROUND

The forces developed during inspiration play a key role in determining upper airway stability and the occurrence of nocturnal breathing disorders. Phrenic nerve stimulation applied during wakefulness is a unique tool to assess Upper airway dynamic properties and to measure the overall mechanical effects of the inspiratory process on UA stability.

OBJECTIVES

To compare the flow/pressure responses to inspiratory and expiratory twitches between sleep apnea subjects and normal subjects.

METHODS

Inspiratory and expiratory twitches using magnetic nerve stimulation completed in eleven untreated sleep apnea subjects and ten normal subjects.

RESULTS

In both groups, higher flow and pressure were reached during inspiratory twitches. The two groups showed no differences in expiratory twitch parameters. During inspiration, the pressure at which flow-limitation occurred was more negative in normals than in apneic subjects, but not reaching significance (p = 0.07). The relationship between pharyngeal pressure and flow adequately fitted with a polynomial regression model providing a measurement of upper airway critical pressure during twitch. This pressure significantly decreased in normals from expiratory to inspiratory twitches (-11.1 +/- 1.6 and -15.7 +/- 1.0 cm H2O respectively, 95% CI 1.6-7.6, p < 0.01), with no significant difference between the two measurements in apneic subjects. The inspiratory/expiratory difference in critical pressure was significantly correlated with the frequency of nocturnal breathing disorders.

CONCLUSION

Inspiratory-related upper airway dilating forces are impeded in sleep apnea patients.

A new standardised and self-administered quality of life questionnaire specific to obstructive sleep apnoea

BACKGROUND

A short, standardised, self-administered quality of life questionnaire would be a useful addition to the outcome measures in obstructive sleep apnoea (OSA) research. A study was therefore undertaken to validate a new OSA specific self-administered questionnaire (the Quebec Sleep Questionnaire, QSQ) for use in clinical trials.

METHODS

This study followed a description of health related quality of life in patients with OSA. Construct validity and responsiveness were tested by comparing the baseline and changes in domain scores (daytime sleepiness, diurnal symptoms, nocturnal symptoms, emotions, social interactions) with those of questionnaires measuring related constructs (SF-36, Epworth Sleepiness Scale, Beck Depression Inventory, SCL-90, and Functional Outcomes in Sleep Questionnaire).

RESULTS

Sixty patients (48 men) of mean (SD) age 55 (10) years participated in the study. In the analysis of the discriminative function of the questionnaire, moderate to high correlations were found between the scores in each domain of the QSQ and the corresponding questionnaires. In the analysis of its evaluative function significant differences were found in score changes between patients who were treated and those who were not, and moderate to high correlations were seen between changes in scores in the QSQ and changes in the corresponding questionnaires. Most of these correlations met the a priori predictions made regarding their magnitude.

CONCLUSION

The QSQ is a valid measure of health related quality of life in patients with OSA and is sensitive to treatment induced changes.

[Health-related quality of life measurement: a critical reading guide]

INTRODUCTION

Quality of life is rarely assessed in the pulmonary function laboratory. Quality of life, or at least some of its domains, should be directly measured.

STATE OF ART

Quality-of-life questionnaires developed according to established protocols can be very useful in clinical practice. In clinical studies, the choice of a questionnaire depends on its function (evaluative or discriminative) which should be supported by its measurement properties (validity, reliability, responsiveness).

PERSPECTIVES AND CONCLUSIONS

The methodology of critical appraisal of an article about quality of life proposed in this reading guide are in keeping with the principles of evidence-based medicine.

Effects of continuous positive airway pressure on upper airway inspiratory dynamics in awake patients with sleep-disordered breathing

Continuous positive airway pressure (CPAP) is the main treatment of the obstructive sleep apnoea syndrome (OSAS). We assessed its effects on the upper airway (UA) dynamics in response to bilateral anterior magnetic phrenic nerve stimulation (BAMPS) in 17 awake untreated OSAS patients (15 males; 52 +/- 7 years) whose effective CPAP (P(eff)) had been determined beforehand by a conventional titration sleep study. All twitch-related inspirations were flow-limited, flow first rising to a maximum (V(Imax)), then decreasing to a minimum (V(Imin)), and then increasing again (M-shaped pattern). Up to V(Imin), the relationship between driving pressure (P(d)) and flow (V) could adequately be fitted to a polynomial regression model (V = k(1)P(d) + k(2)P(d)(2); r(2) = 0.71-0.98, P < 0.0001). At atmospheric pressure V(Imax) was 700 +/- 377 ml s(-1), V(Imin) was 458 +/- 306 ml s(-1), k(1) was 154.5 +/- 63.9 ml s(-1) (cmH(2)O)(-1), and k(2) was 10.7 +/- 7.3 ml s(-1) (cmH(2)O)(-1). CPAP significantly increased V(Imax) and V(Imin) (peak values 1007 +/- 332 ml and 837 +/- 264 ml s(-1), respectively) as well as k(1) and k(2) (peak values 300.9 +/- 178.2 ml s(-1) (cmH(2)O)(-1) and 55.2 +/- 65.3 ml s(-1) (cmH(2)O)(-1), respectively). With increasing CPAP, k(1)/k(2) increased up to a peak value before decreasing. We defined as P(eff,stim) the CPAP value corresponding to the highest k(1)/k(2) value. P(eff,stim) was correlated with P(eff) (P(eff) = 7.0 +/- 2.0; P(eff,stim) = 6.4 +/- 2.6 cmH(2)O; r = 0.886; 95 % CI 0.696-0.960, P < 0.001). We conclude that CPAP improves UA dynamics in OSAS and that the therapeutic CPAP to apply can be predicted during wakefulness using BAMPS.

Independent validation of the Sleep Apnoea Quality of Life Index

BACKGROUND

Obstructive sleep apnoea (OSA) affects important domains of quality of life which remain unexplored by conventional sleep recordings. The objective of this study was to examine the measurement properties (both discriminative and evaluative) of the Sleep Apnoea Quality of Life Index (SAQLI), a new OSA specific quality of life questionnaire.

METHODS

Consecutive patients recently diagnosed with OSA completed a French version of the SAQLI twice over a 3 month period. Its construct validity and responsiveness were tested by comparing baseline and change scores obtained in each domain (symptoms, activities, emotions, social interactions) with those of questionnaires measuring related constructs (SF-36, Epworth Scale, Beck Depression Inventory, and Symptom Checklist 90). The symptoms scores were also correlated with physiological measures obtained at baseline polysomnographic recording.

RESULTS

Forty seven patients (40 men) of mean (SD) age 53 (10) years and mean (SD) apnoea/hypopnoea index 38 (21) participated in the study. During the study period 33 of the 47 patients were treated for OSA (31 with nasal CPAP, one with uvulopalatopharyngoplasty, and one with an oral appliance). Moderate to high correlations were found between the scores in each domain of the SAQLI and the corresponding instruments. There were significant differences in change scores between patients who were treated and those who were not, moderate correlations between SAQLI change scores and changes in the corresponding instruments, and no correlation between the symptoms scores and the baseline nocturnal features. Most of these correlations met the a priori predictions made regarding their magnitude.

CONCLUSION

The SAQLI has strong construct validity and is responsive to change in quality of life but has the disadvantage of having to be administered by an interviewer.

Health-related quality of life in obstructive sleep apnoea

The identification of the areas of quality of life (QoL) most likely to be affected by obstructive sleep apnoea (OSA) would be an important step in the evaluation of the impact of the disease and its treatment modalities. The objective of this study was to describe the impact of OSA on patients' QoL. A list of 186 items potentially related to QoL of patients with OSA was constructed. From this list, consecutive patients were asked, at the time of the diagnosis, to identify the most significant items and to grade their importance on a 5-point scale. The item impact was determined from the proportion of patients who identified it as important, and the mean importance score attributed to this item (impact score=frequency x importance). One hundred patients (82 male; mean age: 51 yrs) were interviewed. The items having the most important impact on QoL clustered into five domains: 1) daytime symptoms; 2) nocturnal symptoms; 3) limitation of activities; 4) emotions; and 5) interpersonal relationships. The impact of obstructive sleep apnoea on quality of life is not limited to excessive daytime sleepiness. Obstructive sleep apnoea significantly contributes to the impairment of all domains of what is usually referred to as "health-related quality of life".

Usefulness of phrenic nerve stimulation to measure upper airway collapsibility in normal awake subjects

Upper airway (UA) collapsibility can be characterized during sleep by looking at the changes in inspiratory flow limitation (IFL) with changing nasal pressure. IFL can be induced during wakefulness using phrenic nerve stimulation (PNS) applied during exclusive nasal breathing. The aim of the study was to evaluate the possibility of measuring UA critical pressure (Pcrit) in normal awaked subjects using electrical PNS (EPNS) or bilateral anterior magnetic phrenic stimulation (BAMPS). Instantaneous flow, esophageal (Peso) and mask pressures (Pmask), and genioglossal (GG) end-expiratory EMG activity were recorded in 13 normal subjects (4F, 9M) with randomly changing Pmask (0 to -20 cmH2O). For each trial, we examined the relationship between maximal inspiratory flow (Vtmax) of IFL twitches and the corresponding Pmask. Pcrit could be determined in 12 subjects (mean -33.5 +/- 16.3 cmH2O). No difference in Pcrit values was found between the EPNS and BAMPS methods but the strength of the Vtmax/Pmask relationship was higher with BAMPS. GG end-expiratory EMG activity increased with decreasing Pmask but no significant relationship was found between the slope of the GG end-expiratory EMG activity/Pmask relationship and Pcrit. We conclude that: (1) Pcrit can be measured during wakefulness in normal using PNS: (2) Pcrit measurements may be easier and more reliable with BAMPS than EPNS: and (3) Pcrit does not seem to be influenced by the pressure-related changes in GG end-expiratory EMG.

Site of phrenic nerve stimulation-induced upper airway collapse: influence of expiratory time

Electrical phrenic nerve stimulation (EPNS) applied at end expiration during exclusive nasal breathing can be used to characterize upper airway (UA) dynamics during wakefulness by dissociating phasic activation of UA and respiratory muscles. The UA level responsible for the EPNS-induced increase in UA resistance is unknown. The influence of the twitch expiratory timing (200 ms and 2 s) on UA resistance was studied in nine normal awake subjects by looking at instantaneous flow, esophageal and pharyngeal pressures, and genioglossal electromyogram (EMG) activity during EPNS at baseline and at -10 cmH(2)O. The majority of twitches had a flow-limited pattern. Twitches realized at 200 ms and 2 s did not differ in their maximum inspiratory flows, but esophageal pressure measured at maximum inspiratory flow was significantly less negative with late twitches (-6.6 +/- 2.7 and -5.0 +/- 3.0 cmH(2)O respectively, P = 0.04). Pharyngeal resistance was higher when twitches were realized at 2 s than at 200 ms (6.4 +/- 2.4 and 2.7 +/- 1.1 cmH(2)O x l(-1). s, respectively). EMG activity significant rose at peak esophageal pressure with a greater increase for late twitches. We conclude that twitch-induced UA collapse predominantly occurs at the pharyngeal level and that UA stability assessed by EPNS depends on the expiratory time at which twitches are performed.

Influence of genioglossus tonic activity on upper airway dynamics assessed by phrenic nerve stimulation

Upper airway (UA) dynamics can be evaluated during wakefulness by using electrical phrenic nerve stimulation (EPNS) applied at end-expiration during exclusive nasal breathing by dissociating twitch flow and phasic activation of UA muscles. This technique can be used to quantify the influence of nonphasic electromyographic (EMG) activity on UA dynamics. UA dynamics was characterized by using EPNS when increasing tonic EMG activity with CO(2) stimulation in six normal awake subjects. Instantaneous flow, esophageal and nasopharyngeal pressures, and genioglossal EMG activity were recorded during EPNS at baseline and during CO(2) ventilatory stimulation. The proportion of twitches presenting an inspiratory-flow limitation pattern decreased from 100% at baseline to 78.7 +/- 21.4% (P = 10(-4)) during CO(2) rebreathing. During CO(2) stimuli, maximal inspiratory twitch flow (VI(max)) of flow-limited twitches significantly rose, with the driving pressure at which flow limitation occurred being more negative. For the group as a whole, the increase in VI(max) and the decrease in pressure were significantly correlated with the rise in end-expiratory EMG activity. UA stability assessed by EPNS is dramatically modified during CO(2) ventilatory stimulation. Changes in tonic genioglossus EMG activity significantly contribute to the improvement in UA stability.

Importance of sleep stage- and body position-dependence of sleep apnoea in determining benefits to auto-CPAP therapy

The influence of sleep stage- and body position-dependence of sleep apnoea on treatment efficacy and compliance between conventional continuous positive airway pressure (CPAP) and auto CPAP therapy was evaluated. Thirty-three newly treated sleep apnoea hypopnoea syndrome (SAHS) patients were randomly allocated to conventional or auto-CPAP therapy. Six patients of each treatment group were classified as having sleep stage- and body position-dependent obstructive breathing abnormalities according to the results of the baseline sleep study. After 3 weeks of treatment, the Epworth sleepiness score tended to be higher (p = 0.08) and the ability to stay awake lower (p = 0.02) in patients with dependent breathing abnormalities treated with fixed CPAP, than in the other patients. The effective pressure/time index was significantly lower in sleep stage- and body position-dependent patients treated with fixed CPAP, than in the other patients (p = 0.02). The number of hours the machine was turned on and a positive pressure applied, tended to be smaller in dependent patients treated with fixed CPAP than in independent patients of this treatment group and in patients treated with auto-CPAP. A night-to-night variability index (VI) of positive pressure changes was obtained in the auto-CPAP group. This index significantly decreased with time in the dependent patients while it remained unchanged in the independent group. It is concluded that auto-continuous positive airway pressure may have specific indications in a subset of obstructive sleep apnoea patients with sleep stage- and body position dependent nocturnal breathing abnormalities.

Comparison of two in-laboratory titration methods to determine effective pressure levels in patients with obstructive sleep apnoea

BACKGROUND

Treatment of the sleep apnoea/hypopnoea syndrome with nasal continuous positive airway pressure (CPAP) conventionally requires a titration procedure in a sleep laboratory. The upper airway has a hysteresis phenomenon which accounts for a decrease in the effective positive pressure level once an initial effective pressure setting has been reached. The aim of this study was to quantify the difference in the initial and final effective pressure settings when the titration sleep study takes into account these possible changes in the effective pressure level.

METHODS

Eighty five patients completed the study. During a titration sleep study the pressure was increased by 1 cm H2O in a stepwise fashion until obstructive respiratory events disappeared (effective pressure 1, Peff(1)). The pressure level was then decreased by increments of 1 cm H2O until breathing abnormalities reappeared. At this time pressure was re-increased by increments of 1 cm H(2)O to normalise breathing (Peff(2)).

RESULTS

The mean (SD) value of Peff(1) was 9.5 (2.6) cm H2O. The pressure was then reduced during 0.5 (0.6) hours to reach the minimal pressure (7.0 (2.0) cm H2O). The pressure obtained after a downward titration had to be re-increased in 79 patients, the Peff(2) level being significantly lower than Peff(1) (8.9 (2.8) cm H2O, p = 0.0002), mean difference 0.6 (1.5) cm H2O (95% confidence interval 0.29 to 0.93).

CONCLUSION

Attempts to decrease the positive pressure level during conventional determination of the effective pressure level allow a significant decrease in the pressure setting. This should be taken into account in each patient who requires an in-laboratory manual CPAP titration procedure.

Assessment of upper airway dynamics in awake patients with sleep apnea using phrenic nerve stimulation

Phrenic nerve stimulation can reproduce during wakefulness the dissociation between upper airway and inspiratory muscles that is associated with obstructive sleep-related breathing disorders. This could provide a useful management tool in the study of passive upper airway (UA) dynamics during wakefulness in patients with the obstructive sleep apnea-hypopnea syndrome (OSAHS). To assess the feasibility of the technique in this setting, we studied the dynamics of diaphragm twitch-associated inspiratory flow in eight patients with OSAHS. Cervical magnetic stimulation (CMS) and bilateral anterior magnetic phrenic stimulation (BAMPS) were applied at end-expiration during exclusive nasal breathing. Electrical phrenic nerve stimulation (ES) proved not feasible. The driving pressure and the respiratory resistance at peak twitch esophageal pressure obtained at maximal stimulation intensity were significantly higher with BAMPS than with CMS. A twitch-flow limitation pattern was observed in seven of eight subjects; VI(max) values of flow-limited twitches obtained at 100% stimulation intensity was 0.81 +/- 0.5 L/s with BAMPS and 0.87 +/- 0.5 L/s with CMS (p = 0.4). The number of flow-limited BAMPS twitches dropped from an average 77.5% to 18.4% with nasal continuous positive airway pressure (CPAP) levels corresponding to the patient's home treatment. We conclude that (1) BAMPS is potentially a useful tool to evaluate the dynamics of flow through the passive UA in awake OSAHS patients, (2) BAMPS may be superior to CMS in evaluating UA properties in OSAHS.

Accuracy of an unattended home CPAP titration in the treatment of obstructive sleep apnea

Treatment of sleep apnea-hypopnea syndrome (SAHS) by fixed continuous positive airway pressure (CPAP) requires an in-laboratory titration procedure to determine the effective pressure level (Peff ). We recently reported that one auto-CPAP machine can be used without titration study allowing Peff determination. The aim of this study was to evaluate the accuracy of an auto CPAP trial at home. A 1- or 2-wk automatic CPAP trial was done at home in 40 patients by estimating the reference pressure (Pref ) to be set and a Pref + 3 cm H(2)O/-4 cm H(2)O pressure interval. Peff was then determined according to the percentage of CPAP time that was spent </= Pref. This Peff value was set on a fixed CPAP machine for two additional weeks and a control sleep study was done. The pressure setting on fixed CPAP had to be increased by 1 +/- 1 cm H(2)O (mean +/- SD) above estimated Pref. Sleep improved with fixed CPAP, with a normalization of the apnea + hypopnea index (AHI) in 38 of 40 and resumption of diurnal hypersomnolence. CPAP compliance remained excellent (CPAP use: 6.1 +/- 1.7 h/ night) after 6.5 +/- 2.8 mo of CPAP treatment. These results indicate that auto-CPAP therapy represents a new useful and accurate way to identify conventional CPAP setting outside hospital and sleep laboratories.

Is treatment of obstructive sleep apnea syndrome with auto-CPAP useful?

Automatic CPAP therapy has been developed to constantly adapt the positive pressure level to the required needs. The automatic devices have been used in two different ways, one being to determine the pressure level to be prescribed at home for fixed CPAP therapy, and the other one to replace fixed CPAP as an home treatment. This last application should alleviate the need for a titration study. The benefits reported up to now in the literature vary from one machine to another, but usually these machine are effective in abolishing obstructive breathing disturbances and the consecutive sleep fragmentation. The mean positive pressure level applied during automatic CPAP treatment is usually less than the effective pressure level measured during a conventional titration sleep study. Some results suggest that automatic CPAP therapy may improve compliance to CPAP therapy. There is a need to better define if automatic CPAP therapy may benefit to specific groups of sleep apnea patients.

Muscle fiber area distribution of musculus uvulae in obstructive sleep apnea and non-apneic snorers

OBJECTIVE

To determine whether differences exist in the morphology of upper airway muscles between apneic and non-apneic snorers

DESIGN

Muscle characteristic analysis in patients undergoing upper airway surgery in a tertiary sleep center.

SUBJECTS

10 non-apneic snorers and 10 sleep apnea hypopnea syndrome (SAHS).

MEASUREMENTS

Frequency distribution of musculus uvulae (MU) muscle fiber area determined from 475+/-207 (mean s.d.) and 697 +/- 165 type IIA fibers and 92 +/- 32 and 68 45 type I fibers in snorers and SAHS, respectively.

RESULTS

Histochemical analyses of MU revealed as expected that type IIA fibers occupied a significantly larger area within that muscle in SAHS compared to Snorers (89.4 +/- 5.8% and 76.1 +/- 15.1% respectively, P= 0.01). No difference was found in the frequency distribution of type I and type IIA fiber areas between the two groups comparing the between-groups and within-group variance of individual area distributions found in snorers and SAHS.

CONCLUSION

There is no difference in muscle fiber area frequency distribution between non-apneic snorers and SAHS patients. This suggests that musculus uvulae of these groups of patients does not have a specific prevalence of atrophic or hypertrophic muscle fibers.

Transtracheal air in the treatment of obstructive sleep apnoea hypopnoea syndrome

A 49 year old woman with typical obstructive sleep apnoea hypopnoea syndrome underwent an unsuccessful trial with continuous positive airway pressure (CPAP) followed by uvulopalatopharyngoplasty with septorhinoplasty, treatment with protriptyline, and a second CPAP trial that was abandoned. Transtracheal air was then given and normalised sleep and breathing at a flow rate of 5 l/min. A sustained clinical improvement was observed at follow up visits. Transtracheal air could represent a simple and effective alternative to tracheotomy in patients with obstructive sleep apnoea hypopnoea syndrome in whom conventional treatments fail.

Inspiratory flow dynamics during phrenic nerve stimulation in awake normals during nasal breathing

The loss of upper airway (UA) dilators preactivation before inspiratory muscle contraction is an important determinant of the pathophysiology of obstructive sleep apnea. We hypothetized that phrenic nerve stimulation could provide a practical way to explore the effects of the dissociation between UA dilators and inspiratory muscles, and possibly to determine UA critical closing pressure during wakefulness. The pattern of inspiratory airflow was therefore studied in normal awake subjects during diaphragm twitches induced by either electrical phrenic stimulation (ES) or cervical magnetic stimulation (CMS) (n = 9) and with and without a nasal stent during ES (n = 7). End-expiratory stimulations applied during exclusive nasal breathing induced 200 to 300 ms twitch inspiratory flow. The average maximal twitch flow of flow-limited twitches was higher during CMS than ES (1.18 +/- 0.29 L.

Nasal pressure recording in the diagnosis of sleep apnoea hypopnoea syndrome

BACKGROUND

Nasal pressure tracing is now being used to measure breathing in ambulatory screening devices for sleep apnoea but it has not been compared with other methods of assessment.

METHODS

Sleep induced breathing disorders were scored by three different methods of analysis (thermistry, inductive plethysmography, and nasal pressure tracing) in 193 consecutive patients referred to our sleep laboratory. With the conventional thermistry method an apnoea was defined as the absence of oronasal flow on the thermistor signal for >/=10 s and a hypopnoea as a 50% decrease in the sum signal of inductive plethysmography tracing for >/=10 s associated with an arousal and/or a 2% decrease in SaO2. Nasal pressure was measured via nasal prongs connected to a pressure transducer. Using the thermistor signal alone, a hypopnoea was defined as a 50% decrease in the signal for >/=10 s associated with an arousal and/or a 2% decrease in SaO2. A similar definition of apnoea and hypopnoea was used for nasal pressure, the fall in pressure being substituted for the thermistor reading.

RESULTS

Impaired nasal ventilation prevented adequate measurements of nasal pressure in 9% of subjects. According to the conventional method of interpretation 107 subjects were identified as having the sleep apnoea hypopnoea syndrome (SAHS). The apnoea + hypopnoea index (AHI) was significantly lower using the thermistry method than with conventional analysis (mean difference -4.3/h, 95% CI -5.3 to -3.2, p<10(-4)); 39% of conventional hypopnoeic events were scored as apnoeas using nasal pressure scoring. Apnoeic and hypopnoeic events could also be observed without any change in thermistor and sum Respitrace signals that resumed with the occurrence of arousals or awakenings. The AHI was significantly higher with nasal pressure scoring than with the conventional method (mean difference 4.5, 95% CI 3.4 to 5.6, p<10(-4)). The mean difference in apnoea index between conventional and nasal pressure scoring was -7.5/h (95% CI -8.9 to -6.1). In the 78 patients who did not have SAHS according to the conventional method of analysis there was a significant positive relationship between the arousal index and AHI measured by nasal pressure tracing (R = 0.51, p<10(-4)). Seventeen of the 78 patients had an AHI of >15/h by the nasal pressure method of analysis.

CONCLUSIONS

Nasal pressure recording provides a simple and reliable measurement of nocturnal breathing abnormalities and may identify breathing abnormalities associated with arousals that are missed by other diagnostic methods.

Dysfunctional mechanical coupling of upper airway tissues in sleep apnea syndrome

The mechanical effect of musculus uvulae (MU) contraction on in vitro uvular shortening and/or displacement was measured in 15 patients with a sleep apnea hypopnea syndrome (SAHS) and in 8 snorers. Using freshly resected uvular tissues, passive and active uvular tissue-specific elastance and shortening were determined during stimulation of MU. No difference was found in maximum tetanic tension measured on uvular tissue between the two groups (47.2 +/- 14.8 g in SAHS and 39.1 +/- 16.5 g in snorers). Passive uvular-specific elastance was significantly less in snorers (0.36 +/- 0.27 g/% Lo) compared with patients with SAHS (0.84 +/- 0.39 g/% Lo) (p = 0.006). There was a negative correlation between uvular shortening and passive uvular specific elastance (r = 0.69, p = 0. 05). Maximal tetanic tension developed by isolated MU was higher in SAHS than in snorers (45.8 +/- 23.1 and 30.0 +/- 8.3 g, respectively, p = 0.04). A strong positive relationship was found between the apnea index and specific uvular elastance (r = 0.55, p = 0.007). We conclude that there is a significant difference between the uvular tissue elastance of SAHS and snorers, and that this difference influences the mechanical efficiency of MU contraction.

[Physiopathology of sleep obstructive respiratory disorders. Experimental methods and practical applications]

Recent progress in the physiology of the upper airways has led to significant advances in evaluating the dynamics of upper airway occlusion during sleep. Measuring the collapsibility of the upper airways and localizing the site of obstruction should theoretically lead to efficacious non-mechanical treatment and enable selection of patients susceptible of benefiting from surgical procedures. From a diagnostic point of view, fluctuations in the nasal pressure curve appear to give more precise information on ventilatory changes and their association with disrupted sleep pattern than conventional parameters such as thermistance signals or induction plethysmography. Again, from a pathophysiological point of view, little is known about the role or tissue inflammation and repeated upper airway trauma in the transition from simple snoring to sleep apnea syndrome. Current studies lead to the conclusion that the dilatroy muscles of the upper airways in the apneic subject are the target for adaptive trophic, immunohistochemical and metabolic phenomena in response to stimulation comparable to training against resistance. Although there is no evidence that sleep affects neuromuscular activity in apneic subjects, the disappearance of compensatory hyperactivity on awakening and the reduction of muscle contraction efficacy (transmission of the dilatory force to soft tissues) observed in patients may explain the greater instability of the upper airways characteristic of sleep apnea syndrome.

Effects of inspiratory and expiratory positive pressure difference on airflow dynamics during sleep

We measured the effects of dissociating inspiratory and expiratory positive pressure (PI and PE, respectively) on the inspiratory flow limitation pattern and on genioglossus (GG) activity in nine sleep apnea patients. Measurements were made at two different levels of PI with stepwise increases in PE. Flow-limited breaths were observed during each recording session. In six of nine subjects, maximal inspiratory flow (VImax) was correlated with the difference between PI and PE (correlations were negative in 5 subjects, positive in 1 subject). In three other patients, VImax was not influenced by the amount of pressure difference. A positive relationship between tonic and/or phasic GG electromyographic activities and PI-PE difference was observed at least at one PI level in all patients. This correlation was observed independently of the presence or absence of any relationship between VImax and the amount of pressure difference. Our results suggest that increasing the PI-PE difference (i.e., decreasing PE) may be associated with a significant worsening in inspiratory flow limitation and that the VImax-pressure difference behavior is not dependent on the GG electromyographic-pressure response.

Influence of nasal obstruction on auto-CPAP behaviour during sleep in sleep apnoea/hypopnoea syndrome

BACKGROUND

Auto-CPAP machines have been developed to adapt automatically the positive pressure level to the required needs. The auto-CPAP response to transient nasal obstruction was tested during sleep in patients with sleep apnoea/hypopnoea syndrome (SAHS).

METHODS

Nasal obstruction was induced by local instillation of histamine. Fourteen nasal challenges were performed on eight patients, seven while the patients were on the "Morphée plus" apparatus and the other seven with the patients on the "Horizon" machine.

RESULTS

Nasal resistance increased initially by a mean (SD) of 166 (66)% during the trials with the "Morphée plus" and by 118 (44)% with the "Horizon" machine. The increase in nasal resistance was always accompanied by flow limitation with one exception. Mask pressure initially decreased to the minimal permitted value as nasal resistance increased with the "Morphée plus" device. A late increase of the positive pressure level occurred sometimes. Mask pressure did not change with increasing nasal resistance when the "Horizon" device was used.

CONCLUSION

Neither the "Morphée plus" nor the "Horizon" device abolished flow limited breaths and resulting sleep fragmentation. We conclude that, despite the different algorithm of pressure changes, these auto-CPAP machines do not adequately respond to an acute increase in nasal resistance.

Upper airway mucosa temperature in obstructive sleep apnoea/hypopnoea syndrome, nonapnoeic snorers and nonsnorers

Upper airway (UA) inflammation (oedema and hyperaemia) is frequently observed in snorers and patients with sleep apnoea/hypopnoea patients. The temperature of different UA regions measured in 11 male nonsnorers, 13 nonapnoeic snorers and 10 untreated sleep apnoea/hypopnoea syndrome (SAHS) patients using infra-red video recording. Measurements were taken with the mouth open during tidal volume mouth breathing, and at the beginning and end of a 10 s end-inspiratory voluntary apnoea which followed either mouth or nasal breathing. Three measurements were obtained from the uvula and from each side of the posterior pharyngeal wall and two from each side of the soft palate. The different UA regions were characterized by their inspiratory temperature, the expiratory rewarming and the changes in UA temperature during apnoea. The temperature of the uvula was significantly lower than that of the other UA regions. For each anatomical region, there were no differences in inspiratory temperature between normals, snorers and SAHS. In normals, the expiratory rewarming was significantly higher in the uvula than in the velum and the posterior pharyngeal wall, whereas these regional differences were not observed in snorers and SAHS. The velum and posterior pharyngeal rewarming was significantly less in normals than in snorers and SAHS. During apnoea, the UA rewarming was similar to that observed during expiration. In conclusion, tissue temperature varies between the different upper airway regions and during tidal breathing and the intensity of the regional expiratory rewarming differs between normals, snorers and patients with sleep apnoea/hypopnoea syndrome.

Efficacy of automatic continuous positive airway pressure therapy that uses an estimated required pressure in the treatment of the obstructive sleep apnea syndrome

BACKGROUND

Continuous positive airway pressure (CPAP) is effective therapy for the obstructive sleep apnea syndrome (OSAS). Automatic CPAP devices continuously adjust the positive pressure to the required levels.

OBJECTIVE

To determine the efficacy of an automatic CPAP machine used with an estimated reference pressure value.

DESIGN

A before-and-after, single-blind trial in which patients were randomly allocated to one of three modes of CPAP administration.

SETTING

Referral-based sleep center in a public health care institution.

PATIENTS

36 outpatients with OSAS.

INTERVENTION

Continuous positive airway pressure was given at a conventional fixed pressure (group 1), automatic CPAP was given at a measured reference pressure (group 2), and automatic CPAP was given at an estimated reference pressure (group 3). In group 1, the effective pressure was determined during a titration sleep study. In groups 2 and 3, the pressure interval was allowed to vary from 4 cm H2O below reference pressure to 3 cm H2O above reference pressure. In group 3, the estimated value of the reference pressure was determined according to individual anthropometric characteristics.

MEASUREMENTS

Sleep studies were performed and measurements of diurnal sleepiness were obtained at each visit.

RESULTS

Sleep and breathing disorders and hypersomnolence were alleviated similarly in the three groups. The apnea + hypopnea index remained abnormal in one patient in group 3 for whom the reference pressure had been underestimated. A strong negative correlation was found between the percentage of time spent below reference pressure during CPAP and the difference between the effective and estimated pressures.

CONCLUSION

Automatic CPAP can be used with an estimated reference pressure without doing a titration sleep study. The positive pressure trend can be used to determine whether treatment failure is caused by an inadequate pressure setting and to determine the amount of pressure to apply.

Auto CPAP in the treatment of sleep apnea hypopnea syndrome

Auto CPAP machines represent the most recent development in the field of CPAP therapy. We compared the efficiency of one of these machines (Morphée Plus, Pierre Medical, France) to conventional CPAP treatment in untreated SAHS. With this apparatus, the positive pressure level automatically varies within pressure bounds on each side of a reference pressure, these pressure characteristics being defined by the user. Sleep architecture, fragmentation, and nocturnal breathing abnormalities improved similarly in the two treatment groups as well as subjective and objective diurnal sleepiness. The number of hours that an effective pressure was applied during the 3 weeks of treatment was significantly greater in the auto CPAP group than in the conventional CPAP group. In a second study we asked if the efficiency of this auto CPAP machine would be affected by using an estimated value of the reference pressure based on body mass index, neck circumference, and AHI. Preliminary results demonstrate that the underestimation of the effective pressure given by the formula is adequately compensated by the machine. Auto CPAP may be an effective alternative to conventional CPAP and preliminary results suggest that the Morphée Plus apparatus may be used accurately without titration sleep study by estimating the reference pressure.

Evaluation of treatment efficacy in sleep apnea hypopnea syndrome

The evaluation of treatment efficacy consists in evaluating their efficacy to normalize sleep-related breathing disorders and neuropsychological consequences and witness complaints, patients' compliance, and the risk or side effects to benefits ratio. Polysomnographic studies are the gold standard for assessing the effects of treatments on nocturnal breathing the sleep characteristics, but the timing of control sleep studies must take into account the possible changes in treatment efficacy with time. Determining the effective positive pressure level during split nights or with a multifactorial regression model may be helpful but can result in an underestimation of the pressure setting. The utility of unassisted home sleep recordings during CPAP therapy is limited by the number of signals recorded and the absence of sleep recording. The evaluation of neuropsychological improvements has to be multifactorial to evaluate the subjective and objective effects of SAHS treatments. The compliance to CPAP therapy must be evaluated by pressure counter or time counter measurements rather than on the reported use. CPAP observance can be reliably estimated after the first month of therapy is linked to improvement in diurnal symptoms. As for any disease, SAHS treatment must be adapted to the individual characteristics of the patient and of his or her disease. Therefore, the choice between weight loss, pharyngeal or maxillomandibular surgery, anterior mandibular positioners or tongue retaining devices, nasal CPAP, BiPAP, and tracheostomy depends on the patient's complaints and morbidity risk factors and on the respective side effects to benefits ratio of these therapeutic procedures.

Effects of naloxone on upper airway collapsibility in normal sleeping subjects

BACKGROUND

To evaluate the possible influence of endorphin release on upper airway collapsibility the effects of naloxone, an opiate receptor antagonist, were measured.

METHODS

The effects of naloxone on upper airway collapsibility were studied in five normal sleeping men in a pilot study. During a sleep fragmentation night the subjects received either naloxone or a volume matched saline placebo in a double blind crossover design. Critical pressure (Pcrit) was measured during a morning nap following sleep fragmentation.

RESULTS

The plasma levels of endorphins increased during sleep fragmentation nights. Pcrit was significantly greater after placebo than after naloxone infusion.

CONCLUSIONS

Naloxone may reduce upper airway collapsibility in normal sleeping subjects following sleep fragmentation.

Upper airway collapsibility, and contractile and metabolic characteristics of musculus uvulae

Physiologic, metabolic, and histochemical characteristics of one upper airway (UA) dilator muscle (musculus uvulae; MU) differ between sleep apnea hypopnea syndrome (SAHS) and nonapneic snorers. We hypothesized that these differences in MU characteristics could result from the cumulative effects of the diurnal and nocturnal intermittent contractions of UA muscles in order to compensate for a permanent increase in UA collapsibility. The aim of this study was to determine the influence of UA collapsibility on MU characteristics. Seventeen SAHS and three nonapneic snorers, who underwent an uvulo-palato-pharyngoplasty as a treatment for snoring or SAHS, participated in the study. Awake and sleeping UA critical pressure (Pcrit) was measured during continuous positive or negative airway pressure trials by analysis of the relationship between maximal inspiratory flow and the upstream pressure of flow-limited breathing cycles. Maximum isometric twitch (Pt) and tetanic tension (Po), fatigability measurements, activities of marker enzymes for anaerobic and aerobic-oxidative profile, and fiber type proportions and areas of MU were determined. There was a significant positive relationship between Pt, Po, and Pcrit measured during wakefulness and sleep. The fatigability index was negatively correlated with awake Pcrit values (r = -0.79). Activity level of the anaerobic enzymes as well as the percentage of surface occupied by type I and type IIA muscle fibers as correlated witb awake Pcrit. We conclude that the differences in awake UA collapsibility help to determine the contractile properties and metabolic and histochemical characteristics of MU.

Effects of genioglossal response to negative airway pressure on upper airway collapsibility during sleep

Continuous negative airway pressure (CNAP) trials can be used to measure upper airway (UA) collapsibility. This procedure can be accompanied by an increase in UA muscle activity. The purpose of this study was to evaluate the influence of CNAP-induced increase in genioglossal (GG) activity on UA collapsibility in 10 healthy sleeping men. UA collapsibility was measured on two occasions; each recording was preceded by the administration of a placebo or diazepam (0.15 mg/kg) in a randomized double-blind crossover design. In seven subjects, the decrease in mask pressure (Pmask) was associated with an increase in mean GG electromyographic (EMG) activity during the placebo trial, with a significant negative relationship between these two variables. This relationship was still observed with diazepam. In six subjects, the slope of the relationship between mean EMG and Pmask was less negative with diazepam. This was associated with an increase in critical pressure (Pcrit). With the placebo, a positive relationship was found between Pcrit and the slope of the mean EMG/Pmask relationship. We conclude that Pcrit is influenced by the GG response to the decrease in Pmask during CNAP.

Efficacy of auto-CPAP in the treatment of obstructive sleep apnea/hypopnea syndrome

The auto-CPAP (Morphée Plus) is characterized by its ability to modify the positive-pressure level applied during the night for the presence or absence of sleep-induced respiratory disorders. The aim of the study was to compare the efficacy of this new mode of CPAP therapy with that of conventional constant-CPAP in the treatment of sleep apnea/hypopnea syndrome (SAHS). Sixteen patients with SAHS were randomly allocated to two groups that were paired for age, apnea/hypopnea index, and mean sleep latency. In the auto-CPAP group, the pressure level could change within fixed limits in both directions (+2 to -4 cm H2O) of the previously determined effective pressure level (Peff). In the constant-CPAP group, patients used the same apparatus (Morphée Plus) in a constant mode at Peff level. At the beginning of the study, the Peff level was determined during a polysomnographic recording. Day-time vigilance was measured subjectively by a standardized questionnaire and objectively by the maintenance of wakefulness test (MWT); Trailmaking tests (TMT) were used to evaluate cognitive functions. After 3 wk of home CPAP therapy, a control sleep study was done with the CPAP machine used in the protocol, and daytime vigilance and cognitive function tests were obtained. Baseline sleep and nocturnal breathing disorders characteristics did not differ between the two groups, and daytime vigilance and cognitive function abnormalities were similarily altered. In both groups, the apnea/hypopnea index was within normal range at the final CPAP sleep study. In the auto-CPAP group, 49.3 +/- 14.9% (mean +/- SD) of home treatment time was spent at a pressure < or = Peff. Home amount of use estimated by the number of sleeping hours with a positive pressure applied was 6.5 +/- 1.0 h in the auto-CPAP group and 5.1 +/- 1.1 h in the constant-CPAP group (p = 0.02). During the control CPAP sleep study, the positive pressure level was significantly lower during Stage III-IV than during the other sleep stages (p = 0.004). The improvement in the MWT and the TMT observed with CPAP therapy was identical in both groups. We conclude that (1) the amount of use during CPAP treatment is higher with auto-CPAP than with constant-CPAP, and (2) Morphée+auto-CPAP is an efficient as conventional CPAP in correcting nocturnal breathing disorders, daytime sleepiness, and cognitive impairment in SAHS.

Effects of mouth opening on upper airway collapsibility in normal sleeping subjects

We investigated the influence of mouth opening on upper airway (UA) collapsibility in six healthy sleeping volunteers. UA collapsibility was measured during continuous negative airway pressure trials that consisted of the progressive decrease in pressure in a nasal mask, with simultaneous recording of esophageal pressure and instantaneous flow. Measurements were made under two experimental conditions: mouth closed (MC), and mouth open (MO). Cephalometric measurements were obtained with subjects awake in the same position for both experimental conditions. UA critical pressure (Pcrit) was derived from the relationship between the breath-by-breath values of the maximal inspiratory airflow and the corresponding mask pressure. Pcrit was significantly less negative during MO than during MC (MO, -12.7 +/- 4.8 cm H2O; MC, -16.4 +/- 6 cm H2O, mean +/- SD; p = 0.03). Mouth opening was associated with a significant increase in the total respiratory resistance (MO, 3.8 +/- 1.6 cm H2O/ml/s; MC, 3.0 +/- 1.6 cm H2O/ml/s-1, p = 0.03). Besides an increase in the distance between the teeth and a reduction in the distance between the hyoid bone and the mandible, no significant changes in cephalometric parameters were found between MO and MC. We conclude that mouth opening increases UA collapsibility during sleep and that mouth opening may contribute to the occurrence of sleep-related breathing abnormalities.