Whether e-cigarettes are less harmful than traditional tobacco was investigated by examining heart rate variability in habitual users of e-cigarettes. A significant effect on cardiovascular function was observed through decreased vagal activity and increased oxidized LDL-cholesterol levels in e-cigarette users. Gone are the days when macho men of Hollywood, Clint Eastwood, James Dean and legendary beauty Audrey Hepburn appeared on screen with a cigarette in hand. With Johnny Depp puffing a new device called the electronic cigarettes or e-cigarette in the 2010 film, “The Tourist”, the audience was being shown an alternative and acceptable way to smoke.
E-cigarettes were introduced to the commercial market in 2004 as a technological surrogate of traditional tobacco-based cigarettes and as no combustion occurs, e-cigarettes are considered a less harmful alternative to tobacco cigarettes. The e-cigarette industry is now worth $3.7 billion US and continues to grow. The glamorization of e-cigarettes in Hollywood has penetrated youth who may consider that e-cigarettes are less harmful than traditional tobacco cigarettes.
Research has now shown that in smokers and non-smokers without cardiovascular disease, both tobacco and e-cigarettes are associated with an increase in oxidative stress and endothelial dysfunction with a reduction in vitamin E levels. However, the effect of traditional cigarettes on pathways associated with oxidative stress such as sNOX2-dp, 8-isoPGF2a, and NO bioavailability was more pronounced than e-cigarettes. Despite this, e-cigarettes that use heat to convert a nicotine solution into vapor has now shown to increase oxidative stress and shift cardiac autonomic balance towards sympathetic predominance, both of which increase cardiovascular risk.
The autonomic nervous system (ANS) is comprised of afferent nerve fibers located throughout the body, including the heart, lungs, and vasculature. These fibers are sensitive to metabolic and mechanical stimuli in order to maintain homeostasis. It is known that smoking alters the balance of the ANS with a predominance of sympathetic nerve activity, which contributes to risk for atrial and ventricular arrhythmias, sudden death and acute myocardial infarction, and hemodynamic changes that accelerate heart failure. It is not known whether e-cigarettes would do the same.
To investigate this, Royan Moheimani and colleagues at UC Los Angeles identified 42 habitual e-cigarette users between the ages of 21 and 45, who did not use tobacco cigarettes and examined heart rate variability (also known as R-R intervals) using electrocardiography, in order to identify beat-to-beat alterations in heart rate. Under resting conditions, healthy individuals show a periodic variation in R-R intervals in a rhythmic fashion that fluctuates with respiration. In this study, the main spectral components, high frequency (0.15-0.4 Hz), low frequency (0.04-0.15 Hz) and very low frequency (0.0003-0.04 Hz) were distinguished. The high-frequency component, an indicator of vagal activity (which regulates the resting state of major organs), was significantly decreased in e-cigarette users compared to control participants.
The high-frequency component was increased during controlled breathing compared with spontaneous breathing but was not different from the controls, suggesting a lower severity of abnormal autonomic function. The low-frequency component, a mixture of both vagal and sympathetic activity, was increased in the e-cigarette users and the ratio of low-frequency to high-frequency components, indicating the cardiac sympathovagal balance, was also increased in the e-cigarette users. The pattern of heart rate variability observed in e-cigarette users was similar to that of patients with increased cardiovascular risk. The levels of plasma cotinine, which reflect e-cigarette use, were significantly correlated with each of the components.
Compared to non-user control individuals, there was an increase in the levels of oxidized low-density lipoprotein and a decrease in paraoxanase-1 levels in the plasma of e-cigarette users, with no difference in the levels of the protective molecule high-density lipoprotein and the inflammatory marker C-reactive protein. These findings are a significant step towards identifying the harmful effects of aerosolized nicotine and its metabolites in habitual e-cigarette users and warrants further research into the cardiovascular effects of e-cigarettes.