Arterial stiffness increases during obstructive sleep apneas

STUDY OBJECTIVES: Obstructive sleep apnea (OSA) appears to be an independent risk factor for diurnal systemic hypertension, but the specific biologic markers for this association have not been well established. Increased arterial stiffness is an important measure of increased left ventricular load and a predictor of cardiovascular morbidity and may precede the onset of systemic hypertension in humans. However, arterial stiffness has not been measured in association with obstructive apneas in patients with OSA, nor related to systemic blood pressure (BP) activity in this setting. Our objective was to test the hypothesis that arterial stiffness may be utilized as a sensitive measure of arterial vasomotor perturbation during obstructive events in patients with OSA, by demonstrating that (1) arterial stiffness increases acutely in association with obstructive apnea and hypopnea, and that (2) such increased stiffness may occur in the absence of acute BP increase. DESIGN: Prospective, cross-sectional. SETTING: A tertiary-care university-based sleep and ventilatory disorders center. PATIENTS: Forty-four normo- and hypertensive adult patients (11 women, 33 men) with polysomnographically diagnosed moderate to severe OSA. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: Beat-to-beat BP was recorded from the radial artery by applanation tonometry during nocturnal polysomnography. Arterial augmentation index (AAI), a measure of arterial stiffness, was calculated as the ratio of augmented systolic BP (SBP) to pulse pressure and expressed as a percentage for the following conditions: awake, the first 10 ("early apnea") and last 10 ("late apnea") cardiac cycles of obstructive events, and the first 15 cardiac cycles following apnea termination ("post apnea"). Mean AAI (+/-SD) for the group was significantly increased during NREM sleep from early apnea to late apnea (12.02 +/- 2.70% vs 13.35 +/- 3.54%, p<0.05, ANOVA). During REM (analyzed in 20 patients), MI again significantly increased from early apnea to late apnea (11.75 +/- 2.81% vs 13.43 +/- 4.97%). Conversely, neither mean SBP nor mean arterial BP was significantly changed from early apnea to late apnea in NREM (SBP 130 +/- 14 mmHg vs 129 +/- 14 mmHg) or REM (SBP 128 +/- 22 mmHg vs 127 +/- 21 mmHg). CONCLUSIONS: Arterial stiffness increases acutely during obstructive apneas in both NREM and REM sleep, in the absence of measurable BP change. These data suggest that arterial stiffness may be a sensitive measure of acute arterial vasomotor perturbation in this setting and may have implications concerning cardiovascular sequelae in patients with OSA.     

Effect of sleep position and sleep stage on the collapsibility of the upper airways in patients with sleep apnea

Collapsibility of the upper airways has been identified as an important pathogenic factor in obstructive sleep apnea (OSA). Objective measures of collapsibility are pharyngeal critical pressure (Pcrit) and resistance of the upstream segment (Rus). To systematically determine the effects of sleep stage and body position we investigated 16 male subjects suffering from OSA. We compared the measures in light sleep, slow-wave sleep, REM sleep and supine vs. lateral positions. The pressure-flow relationship of the upper airways has been evaluated by simultaneous readings of maximal inspiratory airflow (Vimax) and nasal pressure (p-nCPAP). With two-factor repeated measures ANOVA on those 7 patients which had all 6 situations we found a significant influence of body position on Pcrit (p<0.05) whereas there was no significant influence of sleep stage and no significant interaction between body position and sleep stage. When comparing the body positions Pcrit was higher in the supine than in the lateral positions. During light sleep Pcrit decreased from 0.6 +/- 0.8 cm H2O (supine) to -2.2 +/- 3.6 cm H2O (lateral) (p<0.01), during slow-wave sleep Pcrit decreased from 0.3 +/- 1.4 cm H2O (supine) to -1.7 +/- 2.6 (lateral) (p<0.05) and during REM sleep it decreased from 1.2 +/- 1.5 cm H2O to -2.0 +/- 2.2 cm H2O (p<0.05). Changes in Rus revealed no body position nor sleep-stage dependence. Comparing the different body positions Rus was only significantly higher in the lateral position during REM sleep (p<0.05). The results indicate that collapsibility of the upper airways is not mediated by sleep stages but is strongly influenced by body position. As a consequence lower nCPAP pressure is needed during lateral positions compared to supine positions.     

Effect of expiratory positive airway pressure on sleep disordered breathing

STUDY OBJECTIVES: We sought to determine the effect of expiratory positive airway pressure on end expiratory lung volume (EELV) and sleep disordered breathing in obstructive sleep apnea patients. DESIGN: Observational physiology study PARTICIPANTS: We studied 10 OSA patients during sleep wearing a facial mask. We recorded 1 hour of NREM sleep without treatment (baseline) and 1 hour with 10 cm H2O EPAP in random order, while measuring EELV and breathing pattern. RESULTS: The mean EELV change between baseline and EPAP was only 13.3 mL (range 2-25 mL). Expiratory time was significantly increased with EPAP compared to baseline 2.64 +/- 0.54 vs 2.16 +/- 0.64 sec (P = 0.002). Total respiratory time was longer with EPAP than at baseline 4.44 +/- 1.47 sec vs 3.73 +/- 0.88 sec (P = 0.3), and minute ventilation was lower with EPAP vs baseline 7.9 +/- 4.17 L/min vs 9.05 +/- 2.85 L/min (P = 0.3). For baseline (no treatment) and EPAP respectively, the mean apnea+hypopnea index (AHI) was 62.6 +/- 28.7 and 56.8 +/- 30.3 events per hour (P = 0.4). CONCLUSION: In OSA patients during sleep, the application of 10 cm H2O EPAP led to prolongation of expiratory time with only marginal increases in FRC. These findings suggest important mechanisms exist to avoid hyperinflation during sleep.     

Pattern of snoring in obstructive sleep apnea patients and in heavy snorers.

We measured respiratory mechanical characteristics during sleep in five heavy, nonapneic snorers (HS) and in five obstructive sleep apnea (OSA) patients. In two HS and in two OSA patients we obtained lateral pharyngeal cineradiographic images during sleep while snoring. Flow limitation preceded all snores in both HS and OSA. Pattern of snoring, hysteresis and temporal relationship between supraglottic pressure (Psg) and flow rate were different in HS and OSA. Maximal flow during snoring was less (p less than 0.05) in OSA (0.18 +/- 0.07 liter/second) than in HS (0.36 +/- 0.06 liter/second). Linear supraglottic resistance during inspiratory snoring was higher, though not significantly, in OSA patients (7.11 +/- 3.01 cm H2O/liter/second) than in HS (4.80 +/- 2.83 cm H2O/liter/second). We conclude that: 1) Snoring is characterized by high frequency oscillations of the soft palate, pharyngeal walls, epiglottis and tongue. 2) Flow limitation appears to be a sine qua non for snoring during sleep. 3) The pattern of snoring is different in OSA and HS. 4) Pharyngeal size during snoring is probably larger in HS than in OSA patients.     

Airway Dilator Muscle Activity and Lung Volume During Stable Breathing in Obstructive Sleep Apnea

Study Objectives:

Many patients with obstructive sleep apnea (OSA) have spontaneous periods of stable flow limited breathing during sleep without respiratory events or arousals. In addition, OSA is often more severe during REM than NREM and more severe during stage 2 than slow wave sleep (SWS). The physiological mechanisms for these observations are unknown. Thus we aimed to determine whether the activity of two upper airway dilator muscles (genioglossus and tensor palatini) or end-expiratory lung volume (EELV) differ between (1) spontaneously occurring stable and cyclical breathing and (2) different sleep stages in OSA.

Design:

Physiologic observation.

Setting:

Sleep physiology laboratory.

Study Participants:

15 OSA patients with documented periods of spontaneous stable breathing.

Intervention:

Subjects were instrumented with intramuscular electrodes for genioglossus and tensor palatini electromyograms (EMG_GG and EMG_TP), chest and abdominal magnetometers (EELV measurement), an epiglottic pressure catheter (respiratory effort), and a mask and pneumotachograph (airflow/ventilation). Patients slept supine overnight without CPAP.

Measurements and Results:

Peak and Tonic EMG_GG were significantly lower during cyclical (85.4 ± 2.7 and 94.6 ± 4.7 % total activity) than stable breathing (109.4 ± 0.4 and 103 ± 0.8 % total activity, respectively). During respiratory events in REM, tonic EMG_GG activity was lower than during respiratory events in stage 2 (71.9 ± 5.1 and 119.6 ± 5.6 % total activity). EMG_GG did not differ between stable stage 2 and stable SWS (98.9 ± 3.2 versus 109.7 ± 4.4 % total activity), nor did EMG_TP or EELV differ in any breathing condition/sleep stage.

Conclusions:

Increased genioglossus muscle tone is associated with spontaneous periods of stable flow limited breathing in the OSA subjects studied. Reductions in genioglossus activity during REM may explain the higher severity of OSA in that stage. Increased lung volume and tensor palatini activity do not appear to be major mechanisms enabling spontaneous stable flow limited breathing periods.

Citation:

Jordan AS; White DP; Lo YL; Wellman A; Eckert DJ; Yim-Yeh S; Eikermann M; Smith SA; Stevenson KE; Malhotra A. Airway dilator muscle activity and lung volume during stable breathing in obstructive sleep apnea. SLEEP 2009;32(3):361–368.     

Sleep apnoea inducing hypoxemia is associated with early signs of carotid atherosclerosis in males

The intima-media thickness (IMT) of carotid arteries as a marker of preclinical atherosclerosis was measured by ultrasonography in 49 subjects to determine, how strongly the obstructive sleep apnoea (OSA) syndrome is associated with atherosclerosis. Maximal IMT was higher in patients with cardiovascular diseases and with or without risk factors of atherosclerosis, presenting also OSA (apnoea-hypopnoea index=26.1+/-15.6/h) compared to controls without OSA (0.91+/-0.21 mm versus 0.77+/-0.18 mm, p<0.05). The prevalence of IMT > or = 0.85 mm was also higher in patients with cardiovascular pathology presenting OSA than without it (p<0.05). IMT(max) was increased in subjects with mild to moderate OSA alone (AHI=20.4+/-8.7/h) versus healthy controls (0.83+/-0.14 mm versus 0.63+/-0.08 mm, p<0.01). Regression analysis revealed a correlation of IMT(max) with the frequency, intensity and duration of intermittent hypoxemia reflected by AHI (p<0.01), minimal oxygen saturation (p<0.01) and time spent with Sa(O2) < 90% (p<0.05) in patients presenting OSA. The results indicate clear association between early signs of carotid atherosclerosis and moderate OSA in males with and without concomitant cardiovascular pathology.     

Relations between sleep stage, posture and effective nasal CPAP levels in OSA.

A retrospective analysis of positional data from 100 male patients with obstructive sleep apnea (OSA) was conducted to determine whether or not 1) the degree of positional dependency was similar in rapid eye movement (REM) compared to non-REM (NREM) sleep, 2) positional dependency correlated with effective levels of nasal continuous positive airway pressure (CPAP) and 3) patients with positional OSA preferentially avoided sleeping in the supine position. The apnea-hypopnea index (AHI) was scored separately for sleep state (NREM and REM) and for posture [off back (AHI-O) and on back (AHI-B)]. The ratio of AHI-O/AHI-B was used to define positional OSA as AHI-O/AHI-B less than or equal to 0.50 (P group) and nonpositional OSA as 0.50 less than AHI-O/AHI-B (NP group). A group of 31 patients who had sufficient sleep time in NREM and REM sleep in both sleep postures was selected. In this group 9 out of 22 subjects who showed positional dependency during NREM sleep became nonpositional during REM sleep (0.05 less than p less than 0.10). The mean effective nasal CPAP level was slightly, but significantly, lower in the P group than in the NP group (8.0 versus 9.1 cm H2O; p less than 0.05). In addition, a correlation between AHI and effective nasal CPAP levels was found (r = 0.491; p = 0.0001). The P group had less supine sleep time (SST) than the NP group (32% versus 45% of total sleep; p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)     

Peri‐pharyngeal muscle response to inspiratory loading: comparison of patients with OSA and healthy subjects

Upper airway patency to airflow and the occurrence of obstructive sleep apnea involve a complex interplay between pharyngeal anatomy and synergic co‐activation of peri‐pharyngeal muscles. In previous studies we observed large differences in the response to sleep‐associated flow limitation between the genioglossus and other (non‐GG) peri‐pharyngeal muscles. We hypothesized that similar differences are present also during wakefulness. In the present study we compared the response to inspiratory loading of the genioglossus electromyogram and four other peri‐pharyngeal muscles. Studies were performed in eight obstructive sleep apnea patients, seven age‐matched healthy subjects and five additional younger subjects. Electromyogram activity was evaluated over a range of negative oesophageal pressures and expressed as % of maximal electromyograms. In healthy subjects, the slope response to inspiratory loading (electromyogram/pressures) was similar for the genioglossus and non‐GG muscles studied. However, the electromyogram responses were significantly higher in the young subjects compared with older subjects. In contrast, in the obstructive sleep apnea patients, the electromyogram/pressure response of the non‐GG muscles was similar to that of the age‐matched healthy subjects, whereas the slope response of the genioglossus electromyogram was significantly higher than non‐GG muscles. We conclude that both age and the presence of obstructive sleep apnea affect the response of peri‐pharyngeal muscles to inspiratory loading. In patients with obstructive sleep apnea the genioglossus seems to compensate for mechanical disadvantages, but non‐GG muscles apparently are not included in this neuromuscular compensatory mechanism. Our current and previous findings suggest that attempts to improve obstructive sleep apnea with myofunctional therapy should put added emphasis on the training of non‐GG muscles.     

Does nasal decongestion improve obstructive sleep apnea?

Whether nasal congestion promotes obstructive sleep apnea is controversial. Therefore, we performed a randomized placebo-controlled cross-over trial on the effects of topical nasal decongestion in patients with obstructive sleep apnea syndrome (OSA) and nasal congestion. Twelve OSA patients with chronic nasal congestion (mean +/- SD age 49.1 +/- 11.1 years, apnea/hypopnea index 32.6 +/- 24.5/h) were treated with nasal xylometazoline or placebo for 1 week each. At the end of treatment periods, polysomnography including monitoring of nasal conductance by an unobtrusive technique, vigilance by the OSLER test, and symptom scores were assessed. Data from xylometazoline and placebo treatments were compared. Mean nocturnal nasal conductance on xylometazoline was significantly higher than on placebo (8.6 +/- 5.3 versus 6.3 +/- 5.8 mL s(-1)Pa(-1), P < 0.05) but the apnea/hypopnea index was similar (29.3 +/- 32.5/h versus 33.2 +/- 32.8/h, P = NS). However, 30-210 min after application of xylometazoline, at the time of the maximal pharmacologic effect, the apnea/hypopnea index was slightly reduced (27.3 +/- 30.5/h versus 33.2 +/- 33.9/h, P < 0.05). Xylometazoline did not alter sleep quality, sleep resistance time (33.6 +/- 8.8 versus 33.4 +/- 10.1 min, P = NS) and subjective sleepiness (Epworth score 10.5 +/- 3.8 versus 11.8 +/- 4.4, P = NS). The reduced apnea/hypopnea index during maximal nasal decongestion by xylometazoline suggests a pathophysiologic link but the efficacy of nasal decongestion was not sufficient to provide a clinically substantial improvement of OSA.     

Night-to-night alterations in sleep apnea type in patients with heart failure

In patients with heart failure, apnea type can shift overnight from mainly obstructive to mainly central in association with reductions in PCO(2) and increases in periodic breathing cycle length, indicative of a fall in cardiac output. We hypothesized that the predominant apnea type could also vary from one night to another in association with alterations in PCO(2) and cycle length. We studied 12 men with heart failure in whom the predominant apnea type changed from one night to the next over periods of at least 1 month, and two groups with either predominantly obstructive or central sleep apnea (OSA or CSA) in whom apnea type remained stable over time. In patients with unstable apnea type (n = 12, duration between sleep studies 9.0 +/- 4.4 months), PCO(2) was significantly lower (37.6 +/- 1.6 mmHg versus 41.7 +/- 1.9 mmHg, P < 0.01), and cycle length significantly longer (61.9 +/- 3.4 s versus 51.0 +/- 1.9 s, P < 0.001) during nights with predominantly central than nights with predominantly obstructive apnea. In contrast, in both the stable central (n = 8, duration between sleep studies 11.9 +/- 5.3 months) and the stable obstructive (n = 8, duration between studies 6.9 +/- 5.2 months) sleep apnea groups, neither PCO(2) nor cycle length changed significantly between the baseline and follow-up sleep studies. We conclude that in some patients with heart failure, OSA and CSA are part of a spectrum of periodic breathing that can shift over time in association with alterations in PCO(2), cycle length and probably cardiac function.     

Brief airway occlusion produces prolonged reflex inhibition of inspiratory muscles in obstructive sleep apnea

STUDY OBJECTIVES: The human inspiratory muscles respond to a brief occlusion of the upper airway during inspiration with a profound short-latency reflex inhibition. This inhibition contrasts with the excitatory stretch reflex of limb muscles and may protect the airway from aspiration. It was postulated that this reflex would be altered in subjects with obstructive sleep apnea (OSA) who have repetitive upper airway occlusion. DESIGN: Subjects underwent overnight polysomnography, as well as muscle reflex studies. For the reflex studies (performed during wakefulness), occlusions lasting 250 milliseconds were delivered during inspiration. Surface electromyogram was recorded over the scalenes, parasternal intercostals, and chest wall (overlying diaphragm). SETTING: Research and sleep laboratories. PARTICIPANTS: Nineteen subjects with untreated OSA (9 moderate and 10 severe) and 9 healthy control subjects. MEASUREMENTS AND RESULTS: In the subjects with severe OSA, the duration of the inhibition was prolonged by at least 25% compared with control subjects. The peak of the inhibitory response for scalenes occurred significantly later for subjects with severe OSA than for control subjects (by 76 +/- 5 ms vs 60 +/- 3 ms [mean +/- SEM], respectively). Onset latencies of the later excitatory response were delayed for scalenes, parasternal intercostals, and chest wall recordings (eg, scalenes: 105 +/- 9 ms for subjects with severe OSA vs 83 +/- 5 ms for control subjects). CONCLUSIONS: The latency of peak inhibition and duration of inhibition were positively correlated with the respiratory disturbance index for all muscle groups. These changes may reflect adaptation in central respiratory paths due to repetitive loading during sleep.     

Sleep apnea and body position during sleep

In patients with obstructive sleep apnea, it is believed that body position influences apnea frequency. Sleeping in the lateral decubitus position often results in significantly fewer apneas, and some have recommended sleeping on the side as the major treatment intervention. Previous studies, although calculating apnea-hypopnea index (AHI) for supine and lateral decubitus positions, have not taken sleep stage into account. To examine the effect of both sleep stage and body position on apnea duration (AD) and frequency, we determined AHI and AD in all spontaneous body positions during rapid eye movement (REM) and non-REM (NREM) sleep by reviewing videotapes and polysomnograms from 11 overnight studies of 7 obese patients with severe sleep apnea. Consistent with previous work, AD was significantly longer in REM then in NREM (32.5 +/- 2.3 s versus 23.5 +/- 1.9 s; p less than 0.05). This difference persisted when adjusting for body position. AHI was greater on the back than on the sides (84.4 +/- 4.9/h versus 73.6 +/- 7.5/h, p less than 0.05), but after accounting for sleep stage, this difference remained only for NREM (103 +/- 4.8/h versus 80.3 +/- 9.2/h, p less than 0.05) and not for REM (83.6 +/- 5.3/h versus 71.1 +/- 4.2/h, p NS). Although reduced, AHI on the sides still remained clinically very high. Body position changed frequently throughout the night, but some patients spent little or no time on their back. We conclude that AD is longer in REM than NREM, regardless of position, and AHI is higher on the back only in NREM. As AHI remains very high on the sides, favoring the lateral decubitus position may not be as beneficial as previously thought in very obese patients. Less obese patients are more likely to benefit by position changes.     

The influence of lung volume on pharyngeal mechanics, collapsibility, and genioglossus muscle activation during sleep

STUDY OBJECTIVES: Previous studies in both awake and sleeping humans have demonstrated that lung-volume changes substantially affect upper-airway size and pharyngeal resistance and, thus, may influence pharyngeal patency. We sought to systematically investigate the isolated effects of lung-volume changes on pharyngeal collapsibility and mechanics and genioglossus muscle activation during stable non-rapid eye movement sleep. We hypothesized that lower lung volumes would lead to increased pharyngeal collapsibility, airflow resistance, and, in compensation, augmented genioglossus muscle activation. DESIGN: Nineteen normal individuals (age, 30.4 +/- 0.5 years; body mass index: 24.5 +/- 0.4 kg/m2) were studied during stable non-rapid eye movement sleep in a rigid head-out shell equipped with a variable positive/negative pressure attachment for manipulations of extrathoracic pressure and, thus, lung volume. SETTING: Sleep physiology laboratory. PARTICIPANTS: Normal healthy volunteers. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: We measured change in end-expiratory lung volume (EELV) (magnetometers), genioglossus electromyogram (GGEMG) (intramuscular electrodes), pharyngeal pressure, and collapsibility of the pharynx in response to a brief pulse of negative pressure (-8 to -15 cm H2O) under the following conditions: (1) baseline, (2) increased EELV (+1 liter), and (3) decreased EELV (-0.6 liter). Reduced lung volumes led to increased inspiratory airflow resistance (7.54 +/- 2.80 cm H2O x L(-1) x s(-1) vs 4.53 +/- 1.05 cm H2O x L(-1) x s(-1), mean +/- SEM, P = 0.02) and increased genioglossus muscle activation (GGEMG peak 14.6% +/- 1.5% of maximum vs 8.6% +/- 1.5% of maximum, maximum P = 0.001) compared to baseline. The pharynx was also more collapsible at low lung volumes (4.3 +/- 0.5 cm H2O vs 5.4 +/- 0.6 cm H2O, P = 0.04). CONCLUSIONS: We conclude that upper-airway muscles respond to changes in lung volumes but not adequately to prevent increased collapsibility. These results suggest that lung volume has an important influence on pharyngeal patency during non-rapid eye movement sleep in normal individuals.     

Influence of head extension, flexion, and rotation on collapsibility of the passive upper airway

STUDY OBJECTIVES: To determine the effect of head posture on upper airway collapsibility and site of collapse of the passive human upper airway. DESIGN: Pharyngeal critical closing pressure (Pcrit) and site of airway collapse were assessed during head flexion, extension and rotation in individuals undergoing propofol anesthesia. SETTING: Operating theatre of major teaching hospital. PARTICIPANTS: Fifteen healthy volunteers (8 male), including 7 who were undergoing surgery unrelated to the head or neck. MEASUREMENTS AND RESULTS: Applied upper airway pressure was progressively decreased to induce variable degrees of inspiratory flow limitation and to define Pcrit. Upper airway and oesophageal pressure transducers identified the site of collapse. Genioglossus muscle activity (EMGgg) was assessed using intramuscular fine wire electrodes inserted percutaneously. Data from 3 subjects were excluded from analysis due to persistent EMGgg. In the neutral posture Pcrit was -0.4 +/- 4.4 cm H2O and collapsed most frequently in the velopharyngeal region. Relative to neutral, Pcrit increased to 3.7 +/- 2.9 cm H2O (P < 0.01) and decreased to -9.4 +/- 3.8 cm H2O (P < 0.01) when the head was flexed and extended, respectively but was unchanged by rotation (-2.6 +/- 3.3 cm H2O; n = 10; P = 0.44). The site of collapse varied, in no consistent pattern, with change in head posture in 5 subjects. CONCLUSIONS: Head posture has a marked effect on the collapsibility and site of collapse of the passive upper airway (measured by EMGgg) indicating that controlling head posture during sleep or recovery from anesthesia may alter the propensity for airway obstruction. Further, manipulating head posture during propofol sedation may assist with identification of pharyngeal regions vulnerable to collapse during sleep and may be useful for guiding surgical intervention.     

Portable monitoring and autotitration versus polysomnography for the diagnosis and treatment of sleep apnea

STUDY OBJECTIVES: To compare a clinical pathway using portable monitoring (PM) for diagnosis and unattended autotitrating positive airway pressure (APAP) for selecting an effective continuous positive airway pressure (CPAP) with another pathway using polysomnography (PSG) for diagnosis and treatment of obstructive sleep apnea (OSA). DESIGN: Randomized parallel group SETTING: Veterans Administration Medical Center PATIENTS: 106 patients with daytime sleepiness and a high likelihood of having OSA MEASUREMENTS AND RESULTS: The AHI in the PM-APAP group was 29.2 +/- 2.3/h and in the PSG group was 36.8 +/- 4.8/h (P= NS). Patients with an AHI > or = 5 were offered CPAP treatment. Those accepting treatment (PM-APAP 45, PSG 43) were begun on CPAP using identical devices at similar mean pressures (11.2 +/- 0.4 versus 10.9 +/- 0.5 cm H2O). At a clinic visit 6 weeks after starting CPAP, 40 patients in the PM-APAP group (78.4% of those with OSA and 88.8% started on CPAP) and 39 in the PSG arm (81.2% of those with OSA and 90.6% of those started on CPAP) were using CPAP treatment (P = NS). The mean nightly adherence (PM-APAP: 5.20 +/- 0.28 versus PSG: 5.25 +/- 0.38 h/night), decrease in Epworth Sleepiness Scale score (-6.50 +/- 0.71 versus -6.97 +/- 0.73), improvement in the global Functional Outcome of Sleep Questionnaire score (3.10 +/- 0.05 versus 3.31 +/- 0.52), and CPAP satisfaction did not differ between the groups. CONCLUSIONS: A clinical pathway utilizing PM and APAP titration resulted in CPAP adherence and clinical outcomes similar to one using PSG.     

Neural drive to human genioglossus in obstructive sleep apnoea

One postulated mechanism for obstructive sleep apnoea (OSA) is insufficient drive to the upper-airway musculature during sleep, with increased (compensatory) drive during wakefulness. This generates more electromyographic activity in upper airway muscles including genioglossus. To understand drives to upper airway muscles, we recorded single motor unit activity from genioglossus in male groups of control ( n = 7, 7 ± 2 events h⁻¹) and severe OSA ( n = 9, 54 ± 4 events h⁻¹) subjects. One hundred and seventy-eight genioglossus units were recorded using monopolar electrodes. Subjects were awake, supine and breathing through a nasal mask. The distribution of the six types of motor unit activity in genioglossus (Inspiratory Phasic, Inspiratory Tonic, Expiratory Phasic, Expiratory Tonic, Tonic and Tonic Other) was identical in both groups. Single unit action potentials in OSA were larger in area (by 34%, P < 0.05) and longer in duration (by 23%, P < 0.05). Inspiratory units were recruited earlier in OSA than control subjects. In control subjects, Inspiratory Tonic units peaked earlier than Inspiratory Phasic units, while in OSA subjects, Inspiratory Tonic and Phasic units peaked simultaneously. Onset frequencies did not differ between groups, but the peak discharge frequency for Inspiratory Phasic units was higher in OSA (22 ± 1 Hz) than control subjects (19 ± 1 Hz, P = 0.003), but conversely, the peak discharge frequency of Inspiratory Tonic units was higher in control subjects (28 ± 1 Hz versus 25 ± 1 Hz, P < 0.05). Increased motor unit action potential area indicates that neurogenic changes have occurred in OSA. In addition, the differences in the timing and firing frequency of the inspiratory classes of genioglossus motor units indicate that the output of the hypoglossal nucleus may have changed.     

Prevalence of persistent sleep apnea in patients treated with continuous positive airway pressure

STUDY OBJECTIVE: There are limited data on the prevalence of persistent obstructive sleep apnea (OSA) in patients who are clinically asymptomatic with continuous positive airway pressure (CPAP). Our objectives were to estimate the prevalence of persistent OSA and to explore the parameters that may be capable of discriminating these patients. DESIGN: Prospective survey. SETTING: A tertiary-care sleep-disorders clinic. PARTICIPANTS: Consecutive patients treated with single-pressure CPAP for at least 3 months were studied. All had undergone CPAP titrations and were compliant with treatment. They denied snoring or persistent excessive daytime somnolence. Of 114 who qualified, 101 were studied. INTERVENTIONS: Subjects underwent 16-channel polysomnography with electroencephalogram and pneumotachometer while using their CPAP. MEASUREMENTS AND RESULTS: Seventeen of 101 subjects (17%) had an apnea-hypopnea index of over 10. Fifty-one had only split-night protocols for CPAP titration. There was no significant difference between participants with persistent OSA and those with an apnea-hypopnea index < 5 with regard to age, sex, time since diagnosis, reported snoring, change in weight, or quality of life (all p > .10). Mean current CPAP level was higher, with a mean +/- SD 10.6 +/- 2.8 versus 8.6 +/- 2.3 cm H2O (p = .002). Unresolved air leak related to CPAP was more frequent in the patients with persistent OSA. Morning headaches, nonrestorative sleep, and frequent central apneas on the CPAP titration were all associated with persistent OSA. CONCLUSIONS: Persistent OSA is frequent in patients treated with CPAP. This is more frequent in patients with high body mass index, higher prescribed pressures, and unresolved mask leak.     

Sleep apnea & automobile crashes.

BACKGROUND: As a group, patients with obstructive sleep apnea (OSA) are at increased risk of having automobile accidents. Previous studies using actual accident data have used only small numbers of subjects. OBJECTIVE: To determine the rate of automobile accidents in a large population of OSA patients using objective data from the Ministry of Transportation of Ontario (MTO). DESIGN: Retrospective study SETTING: Academic sleep disorders clinic and laboratory. PARTICIPANTS: All cases of OSA polygraphically confirmed between June 1990 and June 1994. INTERVENTIONS: Cases of OSA were a priori divided into groups based on apnea-hypopnea index (AHI): (OSA1 - AHI 10-25, OSA2 - AHI 26-40, OSA3 - AHI>40) and driving records were obtained from the MTO. Age and sex matched controls were selected at random from drivers in the MTO driver database who hold passenger vehicle licences. Analysis was restricted to drivers with the same licence class. MAIN OUTCOME MEASURES: Primary outcome measure was accidents in the five years preceding diagnosis. Secondary outcome was citations during the same period. RESULTS: There were 155 of 460 OSA patients with one or more accidents compared with 150 of 581 Controls for the same time period (x2=7.7,p<0.01).The rate of accidents/year, for the preceding five years, was 0.07+/-0.14 for Controls versus 0.09+/-0.14 for OSA (p <0.05). This difference could all be accounted for by increased accident rate in OSA patients with the highest AHI (OSA3) (MVA/yr: 0.11+/-0.15, 0.08+/-0.12, 0.06+/-0.14 for OSA groups 3,2,1 respectively) as there was no differences among Control, OSA1 and OSA2 accident rates. OSA patients had twice as many citations as Controls (1.74+/-2.13 vs 0.86+/-1.43 p<0.001) although the types of citation were the same. CONCLUSIONS: Increased automobile accidents in OSA may be restricted to cases with more severe apnea (AHI >40). Despite the large sample size (an order of magnitude greater than previous reports using accident data) further study is needed with even larger numbers, including more measures of disease severity and rigorously controlling for driving exposure.     

Discharge Patterns of Human Genioglossus Motor Units during Arousal from Sleep

Study Objectives:

Single motor unit recordings of the human genioglossus muscle reveal motor units with a variety of discharge patterns. Integrated multiunit electromyographic recordings of genioglossus have demonstrated an abrupt increase in the muscle''s activity at arousal from sleep. The aim of the present study was to determine the effect of arousal from sleep on the activity of individual motor units as a function of their particular discharge pattern.

Design:

Genioglossus activity was measured using intramuscular fine-wire electrodes inserted via a percutaneous approach. Arousals from sleep were identified using the ASDA criterion and the genioglossus electromyogram recordings analyzed for single motor unit activity.

Setting:

Sleep research laboratory.

Participants:

Sleep and respiratory data were collected in 8 healthy subjects (6 men).

Measurements and Results:

138 motor units were identified during prearousalarousal sleep: 25% inspiratory phasic, 33% inspiratory tonic, 4% expiratory phasic, 3% expiratory tonic, and 35% tonic. At arousal from sleep inspiratory phasic units significantly increased the proportion of a breath over which they were active, but did not appreciably increase their rate of firing. 80 new units were identified at arousals, 75% were inspiratory, many of which were active for only 1 or 2 breaths. 22% of units active before arousal, particularly expiratory and tonic units, stopped at the arousal.

Conclusions:

Increased genioglossus muscle activity at arousal from sleep is primarily due to recruitment of inspiratory phasic motor units. Further, activity within the genioglossus motoneuron pool is reorganized at arousal as, in addition to recruitment, ∼20% of units active before arousals stopped firing.

Citation:

Wilkinson V; Malhotra A; Nicholas CL; Worsnop C; Jordan AS; Butler JE; Saboisky JP; Gandevia SC; White DP; Trinder J. Discharge patterns of human genioglossus motor units during arousal from sleep. SLEEP 2010;33(3):379-387.     

Effects of a lifestyle intervention on REM sleep‐related OSA severity in obese individuals with type 2 diabetes

The aim of this study was to determine if an intensive lifestyle intervention (ILI) reduces the severity of obstructive sleep apnea (OSA) in rapid‐eye movement (REM) sleep, and to determine if longitudinal changes in glycaemic control are related to changes in OSA severity during REM sleep over a 4‐year follow‐up. This was a randomized controlled trial including 264 overweight/obese adults with type 2 diabetes (T2D) and OSA. Participants were randomized to an ILI targeted to weight loss or a diabetes support and education (DSE) control group. Measures included anthropometry, apnea–hypopnea index (AHI) during REM sleep (REM‐AHI) and non‐REM sleep (NREM‐AHI) and glycated haemoglobin (HbA1c) at baseline and year 1, year 2 and year 4 follow‐ups. Mean baseline values of REM‐AHI were significantly higher than NREM‐AHI in both groups. Both REM‐AHI and NREM‐AHI were reduced significantly more in ILI versus DSE, but these differences were attenuated slightly after adjustment for weight changes. Repeated‐measure mixed‐model analyses including data to year 4 demonstrated that changes in HbA1c were related significantly to changes in weight, but not to changes in REM‐AHI and NREM‐AHI. Compared to control, the ILI reduced REM‐AHI and NREM‐AHI during the 4‐year follow‐up. Weight, as opposed to REM‐AHI and NREM‐AHI, was related to changes in HbA1c. The findings imply that weight loss from a lifestyle intervention is more important than reductions in AHI for improving glycaemic control in T2D patients with OSA.