The upper airway is influenced by body position due to the effects of gravity on pharyngeal structures and lung volumes (44). In particular, the pharyngeal airway is less collapsible in the lateral position than in the supine position (45), and consequently, AHI is often less in the lateral position (46). Positional sleep apnea is defined as: a total AHI > 5 events/hour, a 50% reduction in the AHI between the supine and nonsupine postures, and an AHI that normalizes in the nonsupine posture. In a large series of patients referred for overnight polysomnography (PSG) to rule out OSA, Mador et al. (47) found a high prevalence (49.5%) of positional sleep apnea in patients with mild disease (AHI 5-15), which decreased to 19.4% in patients with moderate disease (AHI, 15-30) and only 6.5% in severe patients (AHI > 30).
Positional therapy could be considered, if positional sleep apnea can be documented by PSG [including a period of rapid eye movement (REM) sleep in the lateral position]. This consists of using methods to prevent individuals from sleeping in the supine posture; selected patients may have an efficacy similar to CPAP (48).
Techniques used include sewing a tennis ball onto the back of the pajama top, attaching a pillow to the sleeper's back with a belt, or wearing a knapsack to bed. Gravity-activated alarms may also be useful in keeping subjects in the lateral position during sleep (49). Simple elevation of the upper body does not reduce sleep apnea indices but does stabilize the airway and may allow therapeutic levels of CPAP to be substantially reduced (45). Once positional therapy is prescribed, careful follow-up of symptoms is necessary to ensure adequate therapy.
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