Patients with sleep-disordered breathing with recurrent apneas exhibit autonomic dysfunction including elevated sympathetic nerve activity (SNA) and hypertension.Studies on experimental animals show that chronic intermittent hypoxia (CIH) resulting from recurrent apneas is a major stimulus for evoking autonomic dysfunction.In rodent models,CIH enhances arterial chemoreflex function in part due to enhanced carotid body sensitivity to hypoxia.The enhanced chemo-reflex leads to elevated sympathetic nerve activity.Recent studies suggest that transcriptional changes involving hypoxiainducible factor-1 and 2 (HIF-1,HIF-2) and the resulting reactive oxygen species-mediated signaling are critical cellular mechanisms underlying the chemoreflex-mediated excitation of sympathetic nervous system by CIH.