INFLUENCE OF TREATMENT ON MUSCLE SYMPATHETIC-NERVE ACTIVITY IN SLEEP-APNEA

Obstructive sleep apnea (OSA) is a common disorder associated with sys temic hypertension, myocardial infarction, stroke, and premature death . Elevated sympathetic tone has been documented previously in OSA and may contribute to the cardiovascular risk. As OSA therapy appears to r educe mortality, we wondered if decreased apnea activity would attenua te the sympathetic hyperactivity of untreated patients. Muscle sympath etic nerve activity (MSNA) was measured during wakefulness via peronea l microneurography in seven patients with documented OSA before and at least 1 mo after compliance monitored nasal continuous positive airwa y pressure (CPAP) therapy. Before institution of CPAP therapy, MSNA wa s high in all patients and decreased after CPAP therapy (baseline vers us CPAP: 69.4 +/- 15.3 versus 53.9 +/- 10.5 bursts/min, mean +/- SD; p < 0.01). However, the decrease in MSNA was limited to the four patien ts with the greatest nightly use of CPAP (greater than or equal to 4.5 h/night), whereas it remained unchanged in the three patients who wer e less compliant. There was a direct linear correlation between the de crease in MSNA (bursts/min) and the average hours of CPAP use per nigh t (r = 0.87, p = 0.01). We conclude that in patients with OSA effectiv e reduction in apnea activity with CPAP therapy diminishes the high sy mpathetic tone present during resting wakefulness.