Contribution of tonic chemoreflex activation to sympathetic activity and blood pressure in patients with obstructive sleep apnea

Background - Muscle sympathetic nerve activity (MSNA) is increased in patients with obstructive sleep apnea (OSA). We tested the hypothesis that tonic activation of excitatory chemoreceptor afferents contributes to the elevated sympathetic activity in OSA. Methods and Results - Using a double- blind, randomized, vehicle-controlled design, we examined the effects of chemoreflex deactivation (by comparing effects of breathing 100% oxygen for 15 minutes with effects of breathing room air for 15 minutes) on MSNA, heart rate, blood pressure, and minute ventilation in 14 untreated patients with OSA and in 12 normal subjects matched for age and body mass index. All control subjects underwent overnight polysomnography to exclude the existence of occult OSA. Baseline MSNA was markedly elevated in the patients with OSA compared with the control subjects (44±4 versus 30±3 bursts per minute; P=.01). In both control subjects and patients with OSA, heart rate decreased during administration of 100% oxygen but did not change during administration of room air. By contrast, both MSNA (P= .008) and mean arterial pressure (P=.02) were significantly reduced during chemoreflex deactivation by 100% oxygen only in patients with OSA but not in control subjects. Conclusions - Tonic activation of excitatory chemoreflex afferents may contribute to increased efferent sympathetic activity to muscle circulation in patients with OSA.