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 pa tients with obstructive sleep apnea (OSA), We tested the hypothesis th at 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 th e effects of chemoreflex deactivation (by comparing effects of breathi ng 100% oxygen for 15 minutes with effects of breathing room air for 1 5 minutes) on MSNA, heart rate, blood pressure, and minute ventilation in 14 untreated patients with OSA and in 12 normal subjects matched f or age and body mass index. AU control subjects underwent overnight po lysomnography to exclude the existence of occult OSA. Baseline MSNA wa s markedly elevated in the patients with OSA compared with the control subjects (44+/-4 versus 30+/-3 bursts per minute; P=.01). In both con trol subjects and patients with OSA, heart rate decreased during admin istration of 100% oxygen but did not change during administration of r oom air. By contrast, both MSNA (P=.008) and mean arterial pressure (P =.02) were significantly reduced during chemoreflex deactivation by 10 0% oxygen only in patients with OSA but not in control subjects. Concl usions-Tonic activation of excitatory chemoreflex afferents may contri bute eo increased efferent; sympathetic activity to muscle circulation in patients with OSA.