ROLE OF HYPOXEMIA IN SLEEP APNEA-INDUCED SYMPATHOEXCITATION

The importance of hypoxemia in determining sympathoexcitation during o bstructive sleep apnea was examined by comparing changes in efferent s ympathetic nerve activity (SNA) during spontaneous obstructive apneas with hypoxemia alone of similar magnitude and duration induced by 1-4 breaths of 100% nitrogen in six patients with obstructive sleep apnea and with spontaneous apneas while breathing 100% oxygen (apnea without hypoxemia) in three patients, In addition, eight control subjects wer e studied during induced hypoxemia, The magnitude of sympathoexcitatio n during spontaneous apneas (103 +/- 15%) was more than twice that obs erved during induced hypoxemia (47 +/- 14%) during episodes in which t he nadir of oxygen desaturation (78 +/- 2 and 75 +/- 2%, respectively) and duration of hypoxemia (27 +/- 3 and 33 +/- 3 s, respectively) wer e the same (P > 0.20). Similarly, in three patients SNA increased 115% during normoxic spontaneous obstructive apneas, but increased only 43 % during hyperoxic spontaneous obstructive apneas in which oyxgen satu ration did not decrease significantly, Sympathetic neural responses to induced hypoxemia in control subjects (17 +/- 7%) were significantly less than that of the sleep apnea patients. We conclude that hypoxemia contributes importantly, but is not the sole determinant of the sympa thoexcitation provoked during episodes of obstructive sleep apnea.