EFFECTS OF ALCOHOL ON SYMPATHETIC ACTIVITY, HEMODYNAMICS, AND CHEMOREFLEX SENSITIVITY

Alcohol intake has been shown to worsen obstructive sleep apnea and in crease nocturnal hypoxemia. The mechanisms of this action are unclear. Animal studies suggest that a reduction in chemoreflex sensitivity ma y be implicated. Using a double-blind, randomized, vehicle-controlled design, we tested the hypothesis that oral alcohol intake depresses ch emoreflex sensitivity in humans. We examined the effects of oral alcoh ol intake (1.0 g/kg body wt) on blood pressure, heart rate, heart rate variability, muscle sympathetic nerve activity, forearm vascular resi stance, and minute ventilation in 16 normal male subjects. Peripheral and central chemoreflex sensitivity were measured in response to hypox ia (n=10) and hypercapnia (n=6), respectively. Plasma alcohol increase d from 0 to 23.2 +/- 1.5 mmol/L (107 +/- 7 mg/dL) at 60 minutes and 20 .2 +/- 1 mmol/L (93 +/- 4 mg/dL) at 85 minutes after alcohol intake (P <.0001). Alcohol induced an increase in heart rate from 59 +/- 2 to 66 +/- 2 beats per minute (P<.01) and increased the ratio of low- to hig h-frequency variability of heart rate (P<.05). Although alcohol increa sed sympathetic nerve activity by up to 239 +/- 22% of baseline values (P<.01), forearm vascular resistance after alcohol was lower than tha t after vehicle (P<.05). Blood pressure did not increase compared with the vehicle session. Oxygen saturation during hypoxia after alcohol w as 4 +/- 1% lower than it was during hypoxia after vehicle (P<.05) alt hough arterial blood P-O2 was unchanged. Alcohol did not affect the ca rdiovascular, sympathetic, or ventilatory responses to either hypoxia or hypercapnia. Acute increases in plasma alcohol increase heart rate and sympathetic nerve activity; blood pressure is not increased, proba bly because of vasodilator effects of alcohol. Alcohol does not alter chemoreflex responses to hypoxia or hypercapnia; thus, alterations in chemoreflex sensitivity are unlikely to explain the effects of alcohol on sleep apnea. Alcohol may reduce the affinity of hemoglobin for oxy gen.