Influence of continuous positive airway pressure on sleep apnea-related desaturation in sleep apnea patients.

To investigate the influence of nasal continuous positive airway pressure (CPAP) on apnea-related desaturation, we compared the sleep apnea-related desaturations obtained during a polysomnographic study before and during nasal CPAP in 15 sleep apnea patients. An individual desaturation curve was determined with a regression analysis by plotting the lowest SaO2 value reached during each apnea against its duration; these data were collected throughout the night. At baseline, we only considered the apneas with a preapneic SaO2 value greater than 90% and a minimal SaO2 value above or equal to 60%. For the CPAP study, the preapneic SaO2 value also had to be within 2% the baseline value for the apneas to be retained. Due to the restriction criteria imposed to characterize apnea-related SaO2 falls, residual apneas still had to be recorded with CPAP. These data were analyzed separately for obstructive apnea for non-rapid eye movement (REM) and REM sleep stages. A desaturation curve was obtained from 10 sec to a variable upper limit that corresponded to the longest apnea duration commonly reached during both baseline and CPAP for a given apnea-type and sleep stage. The individual apnea-related SaO2 fall was characterized by measuring a desaturation area corresponding to the area under the curve. It was expressed in % SaO2/sec of apnea. CPAP reduced the number of apneas per hour of sleep from 37.5 +/- 6.5 (mean +/- SEM) to 14.3 +/- 3.7 (p = 0.001), and improved the whole night SaO2 level as estimated by a cumulative SaO2 curve. The mean apnea duration was reduced from 22.9 +/- 1.5 sec at baseline to 16.8 +/- 0.5 sec during CPAP therapy (p = 0.005). The preapneic SaO2 value was 94.8 +/- 0.3% at baseline and 95.5 +/- 0.2% during CPAP (p = 0.5). The desaturation area decreased from 267 +/- 48% SaO2/sec at baseline to 152 +/- 41% SaO2/sec during CPAP (p less than 0.001). We conclude that CPAP improves the apnea-related desaturation independently of the shortening of apneas and of any difference in the preapneic SaO2 value.