A controlled study of the autonomic changes produced by habitual cigarette smoking in healthy subjects

Abstract

Objectives: An increased sympathetic drive, in view of its proarrhythmic, proatherosclerotic, and prothrombotic actions, could contribute to the elevated cardiovascular risk of habitual smokers. However, the underlying mechanisms are still debated. In this study we address the hypothesis that spectral analysis of RR interval and systolic arterial pressure short-term variabilities may be used to assess the complex autonomic changes produced by habitual cigarette smoking. Methods: A cross-sectional design compared heavy (> 20 cigarettes/day) habitual smokers (n = 20; 40 + 3 years), with similar age controls. Spectral analysis of RR interval variability provided markers of the sympatho-vagal balance modulating the SA node, by way of the normalised low frequency (LF ≃ 0.10 Hz) and high frequency (HF ≃ 0.25 Hz) components. The LF component of systolic arterial pressure (SAP) variability assessed the sympathetic vasomotor modulation. The frequency domain index (α) measured the baroreflex gain of the SA node. Subjects were studied at rest, and during the sympathetic excitation produced by active standing. Results: In smokers LF(RR) was, at rest, greater than in controls (70.6 + 3.8 vs 46.0 ± 2.5 normalised units, nu); concurrently HF(RR) was reduced (22.1 ± 3.2 vs 42.0 ± 2.8 nu). Baroreflex gain and RR variance were also smaller in smokers. LF(SAP) was, instead, similar in the smokers and control groups. The standing induced increase in LF(RR) was blunted (P < 0.001) in smokers. Conclusions: Spectral analysis of RR interval and systolic arterial pressure variability indicates that habitual cigarette smoking induces selective alterations in neural control of the SA node. An increase at rest in markers of sympathetic modulation is accompanied by signs of reduced vagal drive and depressed baroreflex gain; while sympathetic vasomotor modulation appears similar in controls and smokers. Data are consistent with the hypothesis that autonomic alterations may contribute to the increased cardiovascular risk present in smokers.