Patients with obstructive sleep apnea experience repetitive apneic events during sleep, with consequent hypoxia and hypercapnia. Hypoxia and hypercapnia, acting via the chemoreflexes, elicit increases in sympathetic nerve activity. The sympathetic responses to hypoxia and hypercapnia are potentiated during apnea, when the sympathetic inhibitory influence of the thoracic afferent nerves is eliminated. As a consequence of the sympathetic vasoconstrictor response to apneic events, patients with obstructive sleep apnea manifest marked increases in blood pressure during sleep, especially evident at the end of the apnea.