PubMed Health⌕ Search

Biomedical subjects

M S Badr

Publications and source records attributed to M S Badr.

At least 19 recordsLinked to original sources
PubMed2002

Effect of testosterone on the apneic threshold in women during NREM sleep.

The hypocapnic apneic threshold (AT) is lower in women relative to men. To test the hypothesis that the gender difference in AT was due to testosterone, we determined the AT during non-rapid eye movement sleep in eight healthy, nonsnoring, premenopausal women before and after 10-12 days of transdermal testosterone. Hypocapnia was induced via nasal mechanical ventilation (MV) for 3 min with tidal volumes ranging from 175 to 215% above eupneic tidal volume and respiratory frequency matched to eupneic frequency. Cessation of MV resulted in hypocapnic central apnea or hypopnea depending on the magnitude of hypocapnia. Nadir minute ventilation as a percentage of control (%Ve) was plotted against the change in end-tidal CO(2) (Pet(CO(2))); %Ve was given a value of zero during central apnea. The AT was defined as the Pet(CO(2)) at which the apnea closest to the last hypopnea occurred; hypocapnic ventilatory response (HPVR) was defined as the slope of the linear regression Ve vs. Pet(CO(2)). Both the AT (39.5 +/- 2.9 vs. 42.1 +/- 3.0 Torr; P = 0.002) and HPVR (0.20 +/- 0.05 vs. 0.33 +/- 0.11%Ve/Torr; P = 0.016) increased with testosterone administration. We conclude that testosterone administration increases AT in premenopausal women, suggesting that the increased breathing instability during sleep in men is related to the presence of testosterone.

Administration, Cutaneous↗
PubMed2001

Effect of REM sleep on retroglossal cross-sectional area and compliance in normal subjects.

It has been proposed that the upper airway compliance should be highest during rapid eye movement (REM) sleep. Evidence suggests that the increased compliance is secondary to an increased retroglossal compliance. To test this hypothesis, we examined the effect of sleep stage on the relationship of retroglossal cross-sectional area (CSA; visualized with a fiber-optic scope) to pharyngeal pressure measured at the level of the oropharynx during eupneic breathing in subjects without significant sleep-disordered breathing. Breaths during REM sleep were divided into phasic (associated with eye movement, PREM) and tonic (not associated with eye movements, TREM). Retroglossal CSA decreased with non-REM (NREM) sleep and decreased further in PREM [wake 156.8 +/- 48.6 mm(2), NREM 104.6 +/- 65.0 mm(2) (P < 0.05 wake vs. NREM), TREM 83.1 +/- 46.4 mm(2) (P = not significant NREM vs. TREM), PREM 73.9 + 39.2 mm(2) (P < 0.05 TREM vs. PREM)]. Retroglossal compliance, defined as the slope of the regression CSA vs. pharyngeal pressure, was the same between all four conditions (wake -0.7 + 2.1 mm(2)/cmH(2)O, NREM 0.6 +/- 3.0 mm(2)/cmH(2)O, TREM -0.2 +/- 3.3 mm(2)/cmH(2)O, PREM -0.6 +/- 5.1 mm(2)/cmH(2)O, P = not significant). We conclude that the intrinsic properties of the airway wall determine retroglossal compliance independent of changes in the neuromuscular activity associated with changes in sleep state.

Adult↗
PubMed2001

Influence of gender on upper airway mechanics: upper airway resistance and Pcrit.

It has been proposed that the difference in sleep apnea prevalence is related to gender differences in upper airway anatomy and physiology. To explain the prevalence difference, we hypothesized that men would have an increased upper airway resistance and increased critical closing pressure (Pcrit) compared with women. In protocol 1, resistance at two points, fixed flow of 0.2 l/s (RL) and peak flow (Rpk), was measured in 33 men and 27 women without significant sleep-disordered breathing. We found no difference in either RL (-6.9 +/- 5.9 vs. -8.6 +/- 8.2 cmH2O) or Rpk (-9.3 +/- 6.8 vs. -10.0 +/- 11.9 cmH2O) between the men and women. A multiple linear regression to correct for the effects of age and body mass index confirmed that gender had no effect on resistance. In protocol 2, Pcrit was measured in eight men and eight women without sleep-disordered breathing. We found no difference in Pcrit (-10.4 +/- 3.1 vs. -8.8 +/- 2.7 cmH2O) between men and women. We conclude that there are no significant differences in collapsibility between men and women. We present an unifying hypothesis to explain the divergent findings of gender differences in upper airway physiology.

Adult↗
PubMed2001

Long-term facilitation in obstructive sleep apnea patients during NREM sleep.

Repetitive hypoxia followed by persistently increased ventilatory motor output is referred to as long-term facilitation (LTF). LTF is activated during sleep after repetitive hypoxia in snorers. We hypothesized that LTF is activated in obstructive sleep apnea (OSA) patients. Eleven subjects with OSA (apnea/hypopnea index = 43.6 +/- 18.7/h) were included. Every subject had a baseline polysomnographic study on the appropriate continuous positive airway pressure (CPAP). CPAP was retitrated to eliminate apnea/hypopnea but to maintain inspiratory flow limitation (sham night). Each subject was studied on 2 separate nights. These two studies are separated by 1 mo of optimal nasal CPAP treatment for a minimum of 4-6 h/night. The device was capable of covert pressure monitoring. During night 1 (N1), study subjects used nasal CPAP at suboptimal pressure to have significant air flow limitation (>60% breaths) without apneas/hypopneas. After stable sleep was reached, we induced brief isocapnic hypoxia [inspired O(2) fraction (FI(O(2))) = 8%] (3 min) followed by 5 min of room air. This sequence was repeated 10 times. Measurements were obtained during control, hypoxia, and at 5, 20, and 40 min of recovery for ventilation, timing (n = 11), and supraglottic pressure (n = 6). Upper airway resistance (Rua) was calculated at peak inspiratory flow. During the recovery period, there was no change in minute ventilation (99 +/- 8% of control), despite decreased Rua to 58 +/- 24% of control (P < 0.05). There was a reduction in the ratio of inspiratory time to total time for a breath (duty cycle) (0.5 to 0.45, P < 0.05) but no effect on inspiratory time. During night 2 (N2), the protocol of N1 was repeated. N2 revealed no changes compared with N1 during the recovery period. In conclusion, 1) reduced Rua in the recovery period indicates LTF of upper airway dilators; 2) lack of hyperpnea in the recovery period suggests that thoracic pump muscles do not demonstrate LTF; 3) we speculate that LTF may temporarily stabilize respiration in OSA patients after repeated apneas/hypopneas; and 4) nasal CPAP did not alter the ability of OSA patients to elicit LTF at the thoracic pump muscle.

Adult↗
PubMed2000

The use of clinical prediction formulas in the evaluation of obstructive sleep apnea.

STUDY OBJECTIVES: To prospectively study the utility of four clinical prediction models for either predicting the presence of obstructive sleep apnea (OSA, apnea-hypopnea index [AHI] > or = 10/hour), or prioritizing patients for a split-night protocol (AHI(3)20/hour). DESIGN: All patients presenting for OSA evaluation completed a research questionnaire that included questions from previously developed clinical prediction models. The probability of sleep apnea for each patient for each model was calculated based upon the equation used in the model. Based upon two cutoffs of apnea-hypopnea index, 10 and 20, the sensitivity, specificity, and positive predictive value were calculated. For the cutoffs AHI > or =10 and > or =20, receiver operating characteristic curves were generated and the areas under the curves calculated. Comparisons of demographic information and symptom response were compared between patients with and without OSA, and men vs. women. SETTING: Urban, accredited sleep disorders center. PATIENTS OR PARTICIPANTS: All patients referred for evaluation of OSA who underwent polysomnography. INTERVENTIONS: N/A. RESULTS: 370 patients (191 men, 179 women) completed the study. 248 of the 370 (67%) patients had an AHI(3)10; 180 of the 370 (49%) had an AHI> or =20. For AHI > or =10, the sensitivities ranged from 76 to 96%, specificities from 13%-54%, positive predictive values from 69%-77% using the probability cutoff of the original investigators; the areas under the curve from 0.669 to 0.736. For AHI(3)20, the areas under the ROC curves ranged from 0.700 to 0.757; using cutoffs to maximized specificity, the sensitivities ranged from 33%-39%, specificities from 87%-93%, and positive predictive values from 72%-85%. All the models performed better for men. CONCLUSIONS: The clinical prediction models tested are not be sufficiently accurate to discriminate between patients with or without OSA but could be useful in prioritizing patients for split-night polysomnography.

Adult↗
PubMed2000

Sleep apnea and quality of life.

OBJECTIVE: To investigate the effects of sleep apnea (SA) on the quality of life (QOL). DESIGN: A prospective study of QOL in patients with and without SA as defined by an apnea-hypopnea index (AHI) >5. SETTING: University-based outpatient clinics. PATIENTS: Primary care patients followed in a general internal medicine clinic as well as those referred to a sleep disorders clinic at the University of Wisconsin Hospital and Clinics were consecutively recruited and classified into 3 groups of subjects: (1) patients without SA (AHI<5) (n=46), (2) patients with mild SA (AHI 5-15) (n=16), and (3) patients with moderate to severe SA (AHI>15) (n=21). INTERVENTIONS: NA. MEASUREMENTS: QOL was assessed with the Medical Outcomes Study SF-36 Health Survey. Health history and demographic data were obtained via structured interview and medical record review. All subjects underwent overnight polysomnography for diagnosis of SA. RESULTS: After controlling for age, gender, body mass index, and number of comorbid conditions, the association between sleep apnea and QOL was significant in the domains of physical functioning and role limitation due to physical health problems (p<0.05) and was borderline in vitality (p<0.1). Patients with both mild and moderately severe SA scored significantly lower (worse) than did patients without SA in physical functioning and in role limitations due to physical-health (82 and 83 vs. 92, respectively). Moderate to severe SA subjects scored significantly lower in vitality than did subjects without SA (51 vs. 64, p<0.05). Subscales analysis revealed that subjects with moderate to severe SA had significantly lower scores that did those without SA in positive affect (69 vs. 79), current health perceptions (71 vs. 80) and vitality (50 vs. 70), p<0.05 for all comparisons. A large percentage of patients without SA had perfect scores of 100 (ceiling effect) on the physical, social, and role functioning scales. CONCLUSIONS: SA has an independent impact on several QOL domains after adjusting for differences in age, gender, body mass index, and comorbidity. QOL outcomes were likely attenuated by ceiling effects. Disentangling the scales that measure multidimensional QOL (positive and negative aspects) enhanced the ability of the SF-36 to detect important consequences of sleep apnea on QOL.

Depression↗
PubMed2000

Effect of gender on the development of hypocapnic apnea/hypopnea during NREM sleep.

We hypothesized that a decreased susceptibility to the development of hypocapnic central apnea during non-rapid eye movement (NREM) sleep in women compared with men could be an explanation for the gender difference in the sleep apnea/hypopnea syndrome. We studied eight men (age 25-35 yr) and eight women in the midluteal phase of the menstrual cycle (age 21-43 yr); we repeated studies in six women during the midfollicular phase. Hypocapnia was induced via nasal mechanical ventilation for 3 min, with respiratory frequency matched to eupneic frequency. Tidal volume (VT) was increased between 110 and 200% of eupneic control. Cessation of mechanical ventilation resulted in hypocapnic central apnea or hypopnea, depending on the magnitude of hypocapnia. Nadir minute ventilation in the recovery period was plotted against the change in end-tidal PCO(2) (PET(CO(2))) per trial; minute ventilation was given a value of 0 during central apnea. The apneic threshold was defined as the x-intercept of the linear regression line. In women, induction of a central apnea required an increase in VT to 155 +/- 29% (mean +/- SD) and a reduction of PET(CO(2)) by -4.72 +/- 0.57 Torr. In men, induction of a central apnea required an increase in VT to 142 +/- 13% and a reduction of PET(CO(2)) by -3.54 +/- 0.31 Torr (P = 0.002). There was no difference in the apneic threshold between the follicular and the luteal phase in women. Premenopausal women are less susceptible to hypocapnic disfacilitation during NREM sleep than men. This effect was not explained by progesterone. Preservation of ventilatory motor output during hypocapnia may explain the gender difference in sleep apnea.

Adult↗
PubMed2000

Sleep fragmentation, awake blood pressure, and sleep-disordered breathing in a population-based study.

Arousal from sleep produces transient increases in systemic blood pressure, leading to the suggestion that repeated arousals are associated with a sustained increase in daytime blood pressure. Using data from the Wisconsin Sleep Cohort Study, a population-based study, we tested the hypothesis that sleep fragmentation is associated with elevated awake blood pressure. Sleep, breathing, and seated blood pressure measurements from 1,021 participants (age 42 +/- 8 yr; 590 males) were analyzed. Sleep fragmentation was defined as the total number of awakenings and shifts to Stage 1 sleep divided by the total sleep time (sleep fragmentation index: SFI). To reduce the confounding influence of sleep-disordered breathing, which is related to both increased daytime blood pressure and sleep fragmentation, all participants with an apnea-hypopnea index (AHI) > or = 1 were analyzed separately. Accounting for the influences of sex, age, body mass index, and antihypertensive medication use, the SFI was significantly associated with higher levels of awake systolic blood pressure in people with an AHI < 1; a 2 standard deviation increase in the SFI was associated with a 3.1 mm Hg rise in awake systolic blood pressure. In participants with an AHI > or = 1, there was no independent association between the SFI and awake blood pressure after controlling for the influence of the AHI.

Adult↗
PubMed1998

Long-term facilitation of ventilation in humans during NREM sleep.

The purpose of this study was to determine whether episodic hypoxic exposure would elicit long term facilitation (LTF) of ventilation (V(I)) in sleeping humans. Twenty subjects gave written informed consent. Of these, six subjects were unable to maintain stable stage 2 sleep or deeper for a majority of the experiment and their data were excluded from the analysis. On night 1 after subjects had reached stable sleep (stage 2 or deeper), the subjects breathed room air for 5 minutes, followed by 3 minutes of hypoxia (F(I)O2 = 8%). This sequence was repeated 10 times, and the breathing pattern was observed for a further 60 minutes. Subjects returned to the laboratory for a second visit, which served as a sham night. Instrumentation and study time were the same as on night 1, but subjects breathed room air only. Airflow, tidal volume (V(T)), end tidal O2 and CO2, and estimation of arterial O2 saturation (%) were measured. Seven of the subjects had long-term facilitation (LTF), which was manifested as a significant increase in V(I) that persisted for up to 40 minutes following the last hypoxic exposure. In the other seven subjects, no substantial increase in V(I) was found. We could not explain this difference based on body size (BMI), gender, level of hypoxemia, or magnitude of the hyperpnea during hypoxia. The difference between the two groups was that the LTF group consisted of habitual snorers, and that the NLTF were not inspiratory-flow-limited during the experiment.

Adult↗
PubMed1998

The effect of rapid eye movement (REM) sleep on upper airway mechanics in normal human subjects.

1. It has been proposed that the upper airway is more compliant during rapid eye movement (REM) sleep than during non-rapid eye movement (NREM) sleep. The purpose of this study was to test this hypothesis in a group of subjects without sleep-disordered breathing. 2. On the first night, the effect of sleep stage on the relationship of retropalatal cross-sectional area (CSA; visualized with a fibre-optic scope) to pharyngeal pressure (PPH) measured at the soft palate during eupnoeic breathing was studied. Breaths during REM sleep were divided into phasic (associated with eye movements) and tonic (not associated with eye movements). There was a significant decrease in pharyngeal CSA during NREM sleep compared with wakefulness. There was no further decrease observed during either tonic or phasic REM sleep. Pharyngeal compliance, defined as the slope of the regression CSA versus PPH, was significantly increased during NREM sleep compared with wakefulness and REM sleep, with the compliance during both tonic and phasic REM sleep being similar to that observed in wakefulness. 3. On the second night, the effect of sleep stage on pressure-flow relationships of the upper airway was investigated. There was a trend towards the upper airway resistance being highest in NREM sleep compared with wakefulness and REM sleep. 4. We conclude that the upper airway is stiffer and less compliant during REM sleep than during NREM sleep. We postulate that this difference is secondary to differences in upper airway vascular perfusion between REM and NREM sleep.

Airway Resistance↗
PubMed1998

Pathophysiology of upper airway obstruction during sleep.

Obstructive sleep apnea is a common medical disorder with significant adverse health consequences. The pathogenesis of pharyngeal obstruction during sleep, however, remains elusive. This article addresses the key mechanisms of upper airway (UA) obstruction including the role of transmural pressure, pharyngeal compliance, pharyngeal dilating muscle activity and non-neuromuscular factors. A proposed scheme of the pathophysiology of UA obstruction is outlined.

Airway Obstruction↗
PubMed1998

Effects of NREM sleep on dynamic within-breath changes in upper airway patency in humans.

The purpose of our study was to compare inspiratory- and expiratory-related changes in retropalatal cross-sectional area (CSA) during wakefulness to those during non-rapid-eye-movement (NREM) sleep. We studied 18 subjects in whom the severity of sleep-disordered breathing varied. Relative changes in CSA were visualized by using fiber-optic endoscopy. For each breath analyzed (wakefulness n = 4-13; sleep n = 7-16), the CSA was measured at fixed points within inspiration and expiration (0, 25, 50, and 100% of the inspiratory and expiratory duration); these measurements were expressed as a percentage of the CSA that occurred at the start of inspiration. During wakefulness, there was a statistically significant increase in the retropalatal CSA (compared with the start of inspiration) only during early expiration (group mean: expiration, 0% = 112.6 +/- 3.2 (SE) %; 25% = 122.8 +/- 6.2%; 50% = 110.6 +/- 3.8%). In contrast, during sleep, significant changes in CSA occurred during both inspiration and expiration (group mean: inspiration, 25% = 75.3 +/- 6.0%; 50% = 66.7 +/- 7.7%; 75% = 64.6 +/- 8.1%; expiration, 0% = 126.8 +/- 11.8%; 25% = 125.3 +/- 6.9%). The expiratory-related increase in CSA was followed by narrowing such that at end expiration the caliber of the airway was returned to that occurring at the beginning of inspiration (group mean at end expiration = 98.6 +/- 3.1%). The largest changes in CSA occurred in the subjects with an increased body mass index (BMI). We conclude that, during NREM sleep, significant changes in CSA occur during both inspiration and expiration and that the magnitude of these changes is significantly influenced by BMI.

Adult↗
PubMed1998

Progressive retropalatal narrowing preceding obstructive apnea.

Pharyngeal occlusion during obstructive apnea is thought to be an inspiratory-related event; however, occlusion also occurs in the absence of negative intrathoracic pressure. We hypothesized that inspiratory-related pharyngeal occlusion would be preceded by significant expiratory narrowing. Eight sleeping patients with obstructive apnea were studied. Pharyngeal caliber, airflow, and esophageal pressure (Pes) were simultaneously monitored during three to four consecutive breaths preceding occlusion (between 3 and 22 events were studied per subject). Relative changes in retropalatal airway cross-sectional area (CSA) were determined from fiberoptic images (five frames per second) normalized to the maximum CSA. During inspiration, CSA was significantly reduced only during the breath immediately preceding the apnea (Group mean CSA +/- SEM: 51 +/- 8% at the start of inspiration compared with 37 +/- 8% at midinspiration). During expiration, for all breaths there was an initial significant increase in CSA compared with the nadir CSA during the preceding inspiration (CSA: breath-3, 57 +/- 10% to 79 +/- 3%; breath-2, 59 +/- 8% to 76 +/- 4%; breath-1, 37 +/- 8% to 64 +/- 8%), followed by a significant narrowing at end-expiration compared with the peak CSA during that expiration (CSA: breath-3, 79 +/- 3% to 62 +/- 6%; breath-2, 76 +/- 4% to 50 +/- 10%; breath-1, 64 +/- 8% to 36 +/- 10%). Occlusion occurred at a pressure significantly less than that generated during the previous unoccluded breath (Pes: breath-1, -10.8 +/- 2.9 cm H2O; occlusion, -8.2 +/- 1.9 cm H2O). These results show that expiratory narrowing produced a significant reduction of CSA at end-expiration prior to obstructive apnea.

Adult↗
PubMed1997

Effect of induced hypocapnic hypopnea on upper airway patency in humans during NREM sleep.

We wished to determine the effect of reduced ventilatory drive (hypopnea) on upper airway patency in humans during non-rapid-eye-movement (NREM) sleep. We studied nine subjects (58 trials) spanning the spectrum of susceptibility to upper airway collapse including normals, snorers and patients with mild sleep apnea. Hypocapnic hypopnea was induced by abrupt cessation of brief (1 min) nasal mechanical hyperventilation. Surface inspiratory EMG (EMGinsp) was used as an index of drive. Upper airway resistance and supraglottic pressure-flow plots were used as indexes of upper airway patency. Termination of nasal mechanical ventilation resulted in reduced VE to 4904 of pre-mechanical ventilation eupneic control. Upper airway resistance at a fixed flow did not change significantly in inspiration or expiration. Likewise, pressure-flow plots showed no increase in upper airway resistance except in one subject. However, maximum flow (Vmax) decreased during hypopnea in four subjects who demonstrated inspiratory flow-limitation (IFL) during eupneic control. In contrast, no IFL was noted in subjects who showed no evidence of IFL during eupnea. We concluded: (1) Reduced ventilatory drive does not compromise upper airway patency in normal subjects during NREM sleep; (2) the reduction in Vmax during hypopnea in subjects with IFL during eupneic control, suggests that reduced drive is associated with increased upper airway compliance in these subjects; and (3) upper airway susceptibility to narrowing/closure is an important determinant of the response to induced hypopnea during NREM sleep.

Adult↗
PubMed1997

Automated detection and classification of sleep-disordered breathing from conventional polysomnography data.

Efficient automated detection of sleep-disordered breathing (SDB) from routine polysomnography (PSG) data is made difficult by the availability of only indirect measurements of breathing. The approach we used to overcome this limitation was to incorporate pulse oximetry into the definitions of apnea and hypopnea. In our algorithm, 1) we begin with the detection of desaturation as a fall in oxyhemoglobin saturation level of 2% or greater once a rate of descent greater than 0.1% per second (but less than 4% per second) has been achieved and then ask if an apnea or hypopnea was responsible; 2) an apnea is detected if there is a period of no breathing, as indicated by sum respiratory inductive plethysmography (RIP), lasting at least 10 seconds and coincident with the desaturation event; and 3) if there is breathing, a hypopnea is defined as a minimum of three breaths showing at least 20% reduction in sum RIP magnitude from the immediately preceding breath followed by a return to at least 90% of that "baseline" breath. Our evaluation of this algorithm using 10 PSG records containing 1,938 SDB events showed strong event-by-event agreement with manual scoring by an experienced polysomnographer. On the basis of manually verified computer desaturations, detection sensitivity and specificity percentages were, respectively, 73.6 and 90.8% for apneas and 84.1 and 86.1% for hypopneas. Overall, 93.1% of the manually detected events were detected by the algorithm. We have designed an efficient algorithm for detecting and classifying SDB events that emulates manual scoring with high accuracy.

Adult↗
PubMed1997

Ventilatory response to induced auditory arousals during NREM sleep.

Sleep state instability is a potential mechanism of central apnea/hypopnea during non-rapid eye movement (NREM) sleep. To investigate this postulate, we induced brief arousals by delivering transient (0.5 second) auditory stimuli during stable NREM sleep in eight normal subjects. Arousal was determined according to American Sleep Disorders Association (ASDA) criteria. A total of 96 trials were conducted; 59 resulted in cortical arousal and 37 did not result in arousal. In trials associated with arousal, minute ventilation (VE) increased from 5.1 +/- 1.24 minutes to 7.5 +/- 2.24 minutes on the first posttone breath (p = 0.001). However, no subsequent hypopnea or apnea occurred as VE decreased gradually to 4.8 +/- 1.5 l/minute (p > 0.05) on the fifth posttone breath. Trials without arousal did not result in hyperpnea on the first breath nor subsequent hypopnea. We conclude that 1) auditory stimulation resulted in transient hyperpnea only if associated with cortical arousal; 2) hypopnea or apnea did not occur following arousal-induced hyperpnea in normal subjects; 3) interaction with fluctuating chemical stimuli or upper airway resistance may be required for arousals to cause sleep-disordered breathing.

Acoustic Stimulation↗
PubMed1997

Simultaneous digitization of upper airway fiber-optic images and respiratory signals.

We developed an inexpensive and efficient method for simultaneously digitizing respiratory signals and fiber-optic images of the upper airway. The main components of the system are a fiber-optic scope, a charge coupled device video camera, and a personal computer equipped with a frame grabber and an A/D board. The frame grabber digitizes images at five frames per second while the A/D board samples six respiratory signals at 25 samples per second. Digitized images are saved only in the event that the user instructs the computer to do so in order to limit disk space requirements. A circular buffering technique provides continuous storage of the most recent 50 frames in frame grabber memory. This feature gives the user up to 10 seconds, following the beginning of a respiratory event, to initiate the saving of images to computer hard disk. A postacquisition program displays the data acquired during the sleep study and allows the user to interactively select images for subsequent upper airway area measurement. This system enables us to observe and quantify the dynamics of the upper airway during different breathing conditions with minimal time and cost. It is also a potential clinical tool to use to determine the site of obstruction during sleep in patients with obstructive sleep apnea.

Computers↗