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#90

Association of Body Position With Severity of Apneic Events in Patients with Severe Nonpositional Obstructrive Sleep Apnea

SUMMARY The authors undertook to compare the severity (as distinct from the frequency) of apneic events in two sleeping positions: supine (on the back) and lateral (on the side). They examined the results of sleep polysomnography in 30 patients with Obstructive Sleep Apnea (OSA) of severe degree, with an average Respiratory Distress Index (RDI= number of apneas per hour of sleep) equal to 70. Their OSA was Nonpositional, that is to say, the RDI in the supine position was less than twice the RDI in the lateral position. Each subject had to have at least 30 apneas in the supine position and 30 in the lateral position during stage 2 (light) sleep. The 30 patients found to meet these criteria came from examination of sleep study results of 92 consecutive patients with Nonpositional OSA. These 30 subjects were predominantly male (26 or 87%), middle-aged (average=58 years), and overweight (average Body Mass Index=32). In the supine position, their average RDI was 86; in the lateral position, it was 65. Apneic events occurring in the supine position proved to be more severe by all measures than apneic events in the lateral position. The measures of severity included: apnea duration, blood oxygen desaturation, duration of consequent arousal, loudness of snoring, and extent of change in heart rate. Moreover, apneas in the supine position were more likely to cause arousals (lightening of sleep, short of awakening) and outright awakenings, than apneas in the lateral position. The authors noted that, in their clinic, patients with Positional OSA, representing 56% of all OSA patients, had less severe apnea, better nighttime sleep, and less daytime drowsiness, than patients with Nonpositional apnea. These patients with Positional OSA are susceptible to treatment with positional techniques designed to keep them off their backs while sleeping. Nonpositional OSA patients, in contrast, have more severe OSA as measured by the frequency of apneic events (the RDI or Apnea Hypopnea Index, AHI). This has been demonstrated repeatedly. However, as the authors point out, their study looks at other measures of apnea severity besides frequency. They attributed their findings to the effects of gravity on the tongue and soft palate. In the supine position, gravity would pull both back into the throat, reducing the size of the airway. It would also make the airway more difficult to open after an obstructive event, resulting in a longer arousal and a greater cardiorespiratory response. As apneas increased in length, so did the resulting arousals. The authors noted another study that disagreed with their results, and offered some possible explanations in different techniques and numbers of subjects (this study had about twice as many as the other). They also noted some limitations to their study, such as the exclusion of hypopneas, and the restriction to stage 2 sleep (which typically occupies the largest proportion of sleep). They also acknowledged that even their Nonpositional patients had significantly higher frequencies of apneas in the supine than in the lateral position. They drew from their results the clinical implication that the supine position should be avoided in Nonpositional as well as in Positional OSA, though this represents less of a solution for the Nonpositional patients. They suggested that this measure might prove especially important for Nonpositional patients attempting to deal with their OSA by weight loss, which has been observed to convert Nonpositional OSA to Positional OSA in the course of lessening the severity of the disorder. They referred to the results of other researchers which suggest that supine apneic events may contribute more to daytime sleepiness than events in other positions. They hypothesized this might also prove true of hypertension as a consequence of OSA--having previously shown that avoidance of the supine position reduces blood pressure in OSA patients whether or not they have high blood pressure. The supine position also appears to increase the minimum necessary CPAP pressure by 2.0 cm H2O.

This is another good example of a study which is, essentially quite simple, but becomes difficult to read for a lay person mostly because of the erudite structure of its report and the frequent use of abbreviations and acronyms easy to lose track of. Although I have encountered OSA worse in the supine than the lateral position, the reverse seems far more frequent. The authors' explanation seems plausible enough, but the adverse effects of the supine position may depend in part on the axis of closure of the upper airway, which may differ from person to person. Nevertheless, it strikes me as new to suggest that, even with CPAP, a person should avoid sleeping on the back. This is especially striking since some people complain that the CPAP mask and hose force them to sleep in this unfamiliar and uncomfortable position! In fact, it does not seem difficult to sleep on one's side without displacing the mask. Their findings on CPAP pressure and sleeping position raise the question in my mind as to which position should best be used to set the CPAP pressure. The pressure needed to suppress apneas and hypopneas in both positions may be higher than necessary for people who sleep mainly on their sides. I disagree with the authors acceptance of weight loss, so rarely accomplished and maintained for substantial lengths of time, as a real alternative to CPAP, and correspondingly I disagree with presenting positional change to patients as a plausible alternative, whether or not combined with weight loss. All these measures may help, but to allow for a true comparison of their effect with the "gold standard" of CPAP, it seems to me that all patients should first undergo a full, fair trial of CPAP, with close follow-up to help them overcome the many soluble problems that often lead to OSA patients giving up on CPAP without even knowing that its difficulties can often be dealt with by a variety of measures. It is the idea--really, the prejudice on the part of people who haven't given a fair try to CPAP--that it represents an odious form treatment, which must be combatted, not supported by clinicians willing to acknowledge alternatives that have no comparable consistency or magnitude of therapeutic effect on OSA.

"Life is something that happens when you can't get to sleep." Fran Lebowitz

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