Selective potentiation of peripheral chemoreflex sensitivity in obstructive sleep apnea

Background-The chemoreflexes are an important mechanism for regulation of b oth breathing and autonomic cardiovascular function. Abnormalities in chemo reflex mechanisms may be implicated in increased cardiovascular stress in p atients with obstructive sleep apnea (OSA), We tested the hypothesis that c hemoreflex function is altered in patients with QSA. Methods and Results-We compared ventilatory, sympathetic, heart rate, and b lood pressure responses to hypoxia, hypercapnia, and the cold presser test in 16 untreated normotensive patients with OSA and 12 normal control subjec ts matched for age and body mass index. Baseline muscle sympathetic nerve a ctivity (MSNA) was higher in the patients with OSA than in the control subj ects (43+/-4 versus 21+/-3 bursts;:per minute; P<0.001). During hypoxia, pa tients with OSA had greater increases in minute ventilation (5.8+/-0.8 vers us 3.2+/-0.7 L/min; P=0.02), heart rate (10+/-1 versus 7+/-1 bpm; P=0.03), and mean arterial pressure (7+/-2 versus 0+/-2 mm Hg; P=0.001) than control subjects. Despite higher ventilation and blood pressure (both of which inh ibit sympathetic activity) in OSA patients, the MSNA increase during hypoxi a was similar in OSA patients and control subjects. When the sympathetic-in hibitory influence of breathing was eliminated by apnea during hypoxia, the increase in MSNA in OSA patients (106+/-20%) was greater than in control s ubjects (52+/-23%; P=0.04). Prolongation of R-R interval with apnea during hypoxia was also greater in OSA patients (24+/-6%) than in control subjects (7+/-5%) (P=0.04). Autonomic, ventilatory, and blood pressure responses to hypercapnia and the cold presser test in OSA patients were not different f rom those observed in control subjects. Conclusions-OSA is associated with a selective potentiation of autonomic, h emodynamic, and ventilatory responses to peripheral chemoreceptor activatio n by hypoxia.