Aim: 

Bradycardia is the physiological autonomic response to apnea and immersion, aimed at improving survival in hypoxic conditions.The influence of cigarette smoking on autonomic function in humans is well known, but smoking effects on the diving bradycardia response have not yet been described in animals and humans.

Methods: 

Heart rate (HR) was recorded by performing electrocardiograms in a group of healthy habitual smokers (n = 10) and of healthy non-smokers (control group; n = 10) before and during simulated diving (facial immersion). In both conditions, subjects performed 30-s sessions of apnea and of breathing by means of snorkel, wearing or not wearing an underwater mask.

Results: 

Smoker HR before diving was not affected by apnea, nor by any breathing condition adopted. On the other hand, non-smokers showed a 15% decrease of basal HR seven seconds after the beginning of apnea in air. Bradycardia to apnea with face immersion in water was recorded in both subject groups. However, a delayed and lower amplitude response was recorded in smokers (a 15% decrease with respect to basal HR) compared to non smokers (a 31% decrease with respect to basal HR). HR was not influenced during diving in smokers breathing through snorkel and wearing underwater mask. On the other hand, bradycardia occurred in non smokers in same conditions of breathing and diving.

Conclusion: 

Results show that the autonomic response of bradycardia to apnea and to diving is impaired in habitual smokers. Besides causing a number of pathologies, cigarette smoking represents a high risk factor for the performing of such sport activities in habitual smokers.