NEURAL CIRCULATORY RESPONSES TO CARBON-MONOXIDE IN HEALTHY HUMANS

The contribution sf carbon monoxide (CO) to the acute cardiovascular e ffects of smoking is not clear, Using a double-blind, randomized, vehi cle-controlled study design, we examined the sympathetic and vascular responses to modest increases in carboxyhemoglobin in 10 healthy human s. We measured muscle sympathetic nerve activity (microneurography), f orearm blood flow (plethysmography): heart rate, blood pressure, and m inute ventilation at baseline and during 60 minutes of CO inhalation ( 1000 ppm during the first 30 minutes and 100 ppm during the last 30 mi nutes). The same measurements were made in a vehicle session (room air inhalation) on a separate clay. During the first 30 minutes: of CO in halation, carboxyhemoglobin levels increased progressively from 0.2+/- 0.1% ta 8.3+/-0.5% arid were maintained at about this level for a furt her 30 minutes. Forearm vascular resistance did not change with CO but increased slightly with vehicle; the effects of CO on muscle sympathe tic nerve activity, forearm blood flow, blood pressure, heart rate, an d minute ventilation were not significantly different from the effects of vehicle. Modest increases in carboxyhemoglobin levels equivalent t o those resulting from cigarette smoking are unlikely to contribute to the acute sympathetic and hemodynamic effects of smoking in healthy h umans.