Cardiovascular adjustments in breath-hold diving: comparison between divers and non-divers in simulated dynamic apnoea.

The diving response is the sequence of cardiovascular, respiratory and metabolic adjustments produced by apnoea and further strengthened by cooling of the facial area and/or hypoxia. This study aimed at comparing the cardiovascular response to diving of trained divers with that of a control group. In this order, 14 trained divers were compared with 14 non-divers. By means of impedance cardiography and continuous monitoring of arterial pressure, hemodynamic data were collected during three different experimental sessions. Each session included a cycle-ergometer exercise against a workload of 0.5 W kg(-1) of body mass, pedalling in a steady-state condition. During exercise, each subject randomly accomplished 40 s of breath-hold exercise with face immersion (test A) or in air (test B). A control exercise test with normal breathing (test C) was also performed. Divers showed a faster onset of bradycardic response (ANOVA, P < 0.01) and a faster adjustment in systemic vascular resistance (P < 0.001 for divers vs. controls) than did non-divers. Moreover, cardiac output decreased only in divers during the first phase of test A (P < 0.01 for divers vs. controls). The most striking findings were that divers showed a more rapid cardiovascular adjustment with respect to controls, in particular in heart rate and systemic vascular resistance; moreover, with continued apnoea, a delayed increase in myocardial performance and stroke volume occurred and obscured the cardiovascular effects of the diving response.