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

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. 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. 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. 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. Rapid eye movement (REM) sleep is a distinct neurophysiological state associated with significant changes in breathing pattern and ventilatory control as compared with both wakefulness and non-rapid-eye movement (NREM) sleep (Douglas, 1994). In particular, changes in tidal volume, minute ventilation (Millman, Knight, Kline, Short, Chung & Pack, 1988) and the ventilatory responses to hypercapnia (Sullivan, Murphy, Kozar & Phillipson, 1979) have been shown to occur in association with the bursts of phasic eye movements that characterize REM sleep. Given the influence of REM sleep on respiration and ventilatory control, it can be hypothesized that upper airway physiology would also be influenced by REM sleep. This hypothesis is supported by clinical data that show that obstructive apnoeas are more frequent and longer during REM sleep (Findley, Wilhoit & Suratt, 1985; Series, Cormier & LeForge, 1990). However, there is a paucity of data on upper airway physiology during REM sleep. The most studied measure of upper airway patency, upper airway resistance, has been studied during REM sleep and has been found to be the same or decreased compared with NREM sleep (Hudgel, Martin, Johnson & Hill, 1984; Wiegand, Zwillich & White, 1989; Wiegand, Latz, Zwillich & Wiegand, 1990a). No previous work has investigated upper airway compliance during REM sleep. Thus, it is unclear if the upper airway behaves differently during REM and NREM sleep. Recently, it has been shown that fibre-optic imaging can be used to visualize the upper airway during sleep (Badr, Toiber, Skatrud & Dempsey, 1995; Morrell & Badr, 1998). Previous work from our laboratory showed that there are significant within-breath changes in the cross-sectional area of the retropalatal airway during sleep, particularly in those subjects with evidence of sleep-disordered breathing (Morrell & Badr, 1998). In this study, we have combined measures of cross-sectional area with measures of pharyngeal pressure in order to measure the compliance of the upper airway (Kuna, Bedi & Ryckman, 1988; Isono, Morrison, Launois, Feroah, Whitelaw & Remmers, 1993; Isono, Remmers, Tanaka, Sho, Sato & Nishino, 1997) and to study the hypothesis that the upper airway is more compliant during REM sleep than during NREM sleep. Thus, in this work we investigated the effect of REM sleep on retropalatal cross-sectional area (CSA), within-breath changes in CSA, upper airway compliance, and upper airway resistance in a group of subjects without significant sleep-disordered breathing.