Tobacco smoking: A stimulus for blood volume expansion

Tobacco smoking involves the inhalation of carbon monoxide (CO), a gas that binds to hemoglobin molecules to form carboxyhemoglobin (COHb), and thus acutely reduces arterial oxygen content. Whether regular tobacco smoking elicits a compensatory increase in hemoglobin mass (HbM) and concomitant gains in intravascular volumes of even relatively trained individuals was examined in the present study. Thirty young males were split in independent groups based on smoking status (CS; chronic smokers and NS; non-smokers) and aerobic fitness level (MF; more fit and LF; less fit) (CS-MF, CS-LF, NS-MF and NS-LF; n = 8 for all but the first group). CS had been smoking > 10 cigarettes·day^-1 at least for the last three years. Assessed using an incremental running exercise test to exhaustion, the age-adjusted VO_2peak was selected as the criterion for the inclusion in the MF and LF groups, respectively. The CO-rebreathing technique was applied to assess HbM and intravascular blood volumes. A two-way ANOVA was performed to detect differences in means of hematological and endurance performance parameters. VO_2peak was found higher in MF groups (p < 0.001) but was similar between groups of similar fitness level (p = 0.57). Accordingly, peak aerobic speed was lower in CS (p < 0.001) and LF groups (p = 0.004). HbM (p = 0.013), total blood (p = 0.001) and red cell (p < 0.001) volumes were higher in CS groups. Despite the underlying expansion in HbM and total blood volume in smokers of varying fitness levels, endurance performance seems to be impaired. Future research could develop insight into the regulation of hematocrit in smokers.