Smoking effects on diurnal variations of cardiovascular parameters

Previous studies have reported that nicotine increases heart rate and blood pressure, showing a peak 10 min after intake. But most of the work has focused on the period of maximum effect on cardiovascular parameters and has been limited to morning measurements. The aim of this study is to evaluate the effects of smoking in diurnal variations of heart rate and blood pressure, when no restrictions are placed on the pattern of consumption and activity is controlled. The sample consisted of healthy subjects, 21 smokers and 21 non-smokers, from 18 to 26 years. The recordings were carried out hourly from 8:00 to 21:00 h in resting conditions. Heart rate was measured beat-to-beat for 2 min, and blood pressure was assessed by conventional electronic monitor. Smokers and non-smokers did not differ in diurnal levels of heart rate nor blood pressure when time of day was not considered. However, when time of day was taken into account, the groups differed significantly for heart rate and systolic blood pressure, while diastolic blood pressure only showed differences for post-lunch period. The influence of nicotine on the cardiovascular system of young and healthy smokers is more apparent in the diurnal variations than in the mean level of heart rate and blood pressure. The results emphasize the importance of a chronobiological approach in the study of the early stages of smoking on cardiovascular parameters.