Figure 4.
Relationship between the change in nicotine and heart rate and between the change in each ECG index of ventricular repolarization to change in nicotine and heart rate. A: overall moderate, positive correlation between change in nicotine and change in heart rate (Spearman, rs, 0.682, P = 0.001), consistent with the notion that nicotine drives the increase in heart rate observed during acute tobacco cigarette and electronic cigarette use. This correlation was also present in males (blue squares; rs, 0.628, P < 0.001) and females (red circles; rs, 0.756, P < 0.001). B: correlation between the change in nicotine and change in heart rate is weak but still detectable following standing (Spearman, rs, 0.298, P < 0.001), consistent with the notion that standing additionally increases cardiac sympathetic nerve activity and heart rate beyond the acute nicotine effect. This correlation was present in males (rs, 0.260, P = 0.03) and females (rs, 0.378, P = 0.007) when separately analyzed. C: change in Tpeak-Tend (Tp-e) adjusted for heart rate was not correlated with the change in nicotine. This was true when the whole group was analyzed (rs, 0.11, P = 0.24) or separately analyzed by sex, (male: rs, 0.117, P = 0.31; female: rs, 0.058, P = 0.69). D: change in Tp-e/QT adjusted for heart rate was not correlated with the change in nicotine. This was true when the whole group was analyzed (rs, 0.130, P = 0.14) or separately analyzed by sex, (male: rs, 0.159, P = 0.17; female: rs, 0.044, P = 0.76). E: change in Tp-e/QTc adjusted for heart rate was not correlated with the change in nicotine. This was true when the whole group was analyzed (rs, 0.058, P = 0.52) or separately analyzed by sex, (male: rs, 0.0.085, P = 0.46; female: rs, 0.025, P = 0.856). F: mean Tp-e change adjusted for change in heart rate and nicotine. After the adjustment for nicotine and heart rate, Tp-e interval remained persistently prolonged in males (ANOVA, P < 0.0001) but not in females (P = 0.41), after using the electronic cigarette with nicotine. Change in Tp-e was significantly longer after using the electronic cigarette with nicotine compared with each of the other three exposures. Male, blue squares; female, red circles (t test, *P < 0.0001). EC5%, electronic cigarette with 5% nicotine; TC0%, tobacco cigarette (research) with minimal nicotine; TCN, commercial tobacco cigarette with nicotine.