Smoking two cigarettes acutely reduced baseline vagal-cardiac and muscle sympathetic nerve activity, but augmented sympathetic activity increases triggered by brief arterial pressure reductions.
Does smoking acutely alter muscle sympathetic nerve activity and autonomic reflex control in healthy habitual smokers?
Acute cigarette smoking in habitual smokers alters autonomic function by reducing baseline vagal-cardiac and muscle sympathetic nerve activity while augmenting sympathetic responses to hypotensive stimuli.
BACKGROUND: Although cigarette smoking is known to lead to widespread augmentation of sympathetic nervous system activity, little is known about the effects of smoking on directly measured human sympathetic activity and its reflex control. METHODS AND RESULTS: We studied the acute effects of smoking two research-grade cigarettes on muscle sympathetic nerve activity and on arterial baroreflex-mediated changes of sympathetic and vagal neural cardiovascular outflows in eight healthy habitual smokers. Measurements were made during frequency-controlled breathing, graded Valsalva maneuvers, and carotid baroreceptor stimulation with ramped sequences of neck pressure and suction. Smoking provoked the following changes: Arterial pressure increased significantly, and RR intervals, RR interval spectral power at the respiratory frequency, and muscle sympathetic nerve activity decreased. Plasma nicotine levels increased significantly, but plasma epinephrine, norepinephrine, and neuropeptide Y levels did not change. Peak sympathetic nerve activity during and systolic pressure overshoots after Valsalva straining increased significantly in proportion to increases of plasma nicotine levels. The average carotid baroreceptor-cardiac reflex relation shifted rightward and downward on arterial pressure and RR interval axes; average gain, operational point, and response range did not change. CONCLUSIONS: In habitual smokers, smoking acutely reduces baseline levels of vagal-cardiac nerve activity and completely resets vagally mediated arterial baroreceptor-cardiac reflex responses. Smoking also reduces muscle sympathetic nerve activity but augments increases of sympathetic activity triggered by brief arterial pressure reductions. This pattern of autonomic changes is likely to influence smokers' responses to acute arterial pressure reductions importantly.
Niedermaier et al. (Sun,) conducted a other in Healthy habitual smokers (n=8). Cigarette smoking was evaluated on Muscle sympathetic nerve activity and arterial baroreflex-mediated changes of sympathetic and vagal neural cardiovascular outflows. Smoking two cigarettes acutely reduced baseline vagal-cardiac and muscle sympathetic nerve activity, but augmented sympathetic activity increases triggered by brief arterial pressure reductions.