An investigation into the cardiac implications of bradycardia in marine sports practitioners

Antony Cole


This study investigated the effect of the mammalian diving reflex (MDR) on the R-R intervals, mean heart rate (MHR) and mean arterial blood pressure (MABP) on 40 healthy subjects. Two groups were compared a group of SCUBA divers and a group of non SCUBA divers. Each group consisted of ten males and ten females. Subjects completed seven protocols: three in air; breathing (BA); apnea (AA); breathing through a snorkel (BSA) and three facially immersed; breathing through a snorkel (23±1°C) (BSI); apnea (35±1°C) (AWW); apnea (23±1°C) (AWR) apnea (10±1°C) (AWC). A negative correlation was observed between diving experience and bradycardia. A positive correlation was observed between MABP and R-R intervals with respect to diving experience. No relationship was observed between the MHR, MABP or the R-R intervals in either the male or female subject groups. However, there was significant variance between the MHR, MABP and R-R complex intervals of divers and non-divers (P ≤ 0.0085). Significant variance was observed between male scuba divers, female scuba divers, male non-scuba divers and female non-scuba divers in MHR, MABP and R-R interval (P ≤ 0.0085). The results of this study suggest that the mammalian diving reflex is exacerbated in humans by repeat exposure to apnea with immersion. It also suggests that males and females are physiologically similar when considering MDR.

Keywords: Apnea • Diving Reflex • Bradycardia • Cardiac Response

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