CIGARETTE-SMOKING INCREASES SYMPATHETIC OUTFLOW IN HUMANS

Background-It is generally accepted that smoking increases blood press ure and inhibits muscle sympathetic nerve activity (SNA). The decrease in muscle SNA with cigarette smoking might be secondary to baroreflex responses to the pressor effect of smoking, thus obscuring a sympathe tic excitatory effect of smoking. We tested the hypothesis that smokin g increases sympathetic outflow. Methods and Results-We examined the e ffects of sham smoking, cigarette smoking, and cigarette smoking in co mbination with nitroprusside on muscle (baroreflex-dependent) SNA in 1 0 healthy habitual smokers. The 3 sessions were performed in random or der, each study on a separate day. In an additional study, we also inv estigated the effects of sham smoking and cigarette smoking on skin (b aroreflex-independent) SNA in 9 subjects. Compared with sham smoking, cigarette smoking alone increased blood pressure and decreased muscle SNA. When the blood pressure increase in response to smoking was blunt ed by nitroprusside infusion, there was a striking increase in muscle SNA. Muscle SNA increased up to 3-fold the levels seen before smoking (P < 0.001), accompanied by an increase in heart rate of up to 37 +/- 4 bpm. Cigarette smoking also induced a 102 +/- 22% increase in skin S NA (P = 0.03). Conclusions-These data provide the first direct evidenc e that cigarette smoking increases sympathetic outflow.