Intermittent hypoxemia and sleep fragmentation: associations with daytime alertness in obese sleep apnea patients living at moderate altitude.

Although obstructive sleep apnea (OSA) has long been associated with daytime sleepiness, far less is known about its association with the ability to remain awake. The aim of this study was to examine the relative importance of inter-correlated measures of OSA severity (eg, various indices of oxygen saturation and sleep fragmentation) in the ability to stay alert as measured objectively by the Maintenance of Wakefulness Test (MWT), defined by a mean sleep latency of ≥12 min.

Seventy-eight obese women and men of similar age and body mass index living at altitude (Mexico City) underwent standard polysomnography, MWT, and completed validated sleep-related questionnaires.

Men had more severe sleep apnea than women (p = 0.002) and were also less alert on MWT (p = 0.022). Logistic regression models indicated that measures of desaturation consistently predicted MWT-defined alertness, whereas varied measures of sleep fragmentation did not. Nearly a third of the variance (r(2) = 0.304) in MWT-defined alertness was accounted for by the number of desaturations per hour of sleep (p = 0.003), which is considerably higher than other studies have reported in different populations.

The ability to remain awake in obese patients is best accounted for by hypoxemia rather than sleep fragmentation. Whether the size of this effect reflects differences in the population under study (eg, extent of obesity, racial background, residence at moderate altitude) and/or is a function of the measurement of alertness with the MWT remains uncertain.