[Causes of excessive daytime sleepiness in hypercapnic and normocapnic obstructive sleep apnea patients].

UNLABELLED: Daytime sleepiness assessed using the Epworth sleepiness scale (ESS) and polysomnography results were compared in 43 patients with obstructive sleep apnea (OSA) with concomitant chronic hypercapnia (PaCO2 53 +/- 6 mmHg), and in 58 patients with the OSA syndrome accompanied by normocapnia (PaCO2 < or = 45 mmHg, mean 39 +/- 3 mmHg). The OSA patients with hypercapnia were more sleepy than those with normocapnia (ESS 18 +/- 7 vs 15 +/- 7, p < 0.05), but apnea index values were similar in both groups (54 +/- 20 and 49 +/- 17). The following parameters of electrophysiological sleep structure were obtained in the hypercapnic OSA patients: sleep stage 1: 66 +/- 28%, stage 2: 28 +/- 27%, stage 3 + 4: 1 +/- 1%, REM sleep 5 + 6% of the total sleep time, while in the OSA patients with normocapnia: stage 1: 39 +/- 19%, stage 2: 28 +/- 27%, stage 3 + 4: 2 +/- 2%, and REM sleep 6 +/- 7% of the total sleep time. Stage 1 NREM sleep was found to be longer, and stage 2 NREM--shorter in hypercapnic than in normocapnic OSA patients (p < 0.01).

CONCLUSION

Increased daytime sleepiness in both groups patients with the OSA syndrome is due to sleep fragmentation as well as to deficiency of deep and paradoxical sleep (almost absent deep sleep and extremely shortened REM sleep). Hypercapnic OSA patients' more marked sleepiness may result from a more pronounced disturbance of their sleep macrostructure, with a considerable predomination of stage I NREM sleep.