SYMPATHETIC NEURAL MECHANISMS IN OBSTRUCTIVE SLEEP-APNEA

Blood pressure, heart rate, sympathetic nerve activity, and polysomnog raphy were recorded during wakefulness and sleep in 10 patients with o bstructive sleep apnea. Measurements were also obtained after treatmen t with continuous positive airway pressure (CPAP) in four patients, Aw ake sympathetic activity was also measured in 10 age- and sex-matched control subjects and in 5 obese subjects without a history of sleep ap nea. Patients with sleep apnea had high levels of nerve activity even when awake (P < 0.001), Blood pressure and sympathetic nerve activity did not fall during any stage of sleep, Mean blood pressure was 92+/-4 .5 mmHg when awake and reached peak levels of 116+/-5 and 127+/-7 mmHg during stage II sleep (n = 10) and rapid eye movement (REM) sleep (n = 5), respectively (P < 0.001). Sympathetic activity increased during sleep (P = 0.01) especially during stage II (133+/-9% above wakefulnes s; P = 0.006) and REM (141+/-13%; P = 0.007), Peak sympathetic activit y (measured over the last 10 s of each apneic event) increased to 299/-96% during stage II sleep and to 246+/-36% during REM sleep (both P < 0.001), CPAP decreased sympathetic activity and blood pressure durin g sleep (P < 0.03). We conclude that patients with obstructive sleep a pnea have high sympathetic activity when awake, with further increases in blood pressure and sympathetic activity during sleep, These increa ses are attenuated by treatment with CPAP.