The dive response is highly prevalent in aquatic mammals and has been observed to a lesser degree in humans. Stimulated by cold-water facial submersion, this response involves a series of reflexes characterized by a decrease in heart rate (HR), constriction of peripheral blood vessels, and an increase in mean arterial pressure (MAP). Involving the co-activation of both the parasympathetic (PNS) and sympathetic nervous systems (SNS), this response is hypothesized to help conserve oxygen by shunting blood to vital organs. PURPOSE: To observe if the SNS activation associated with high intensity exercise could attenuate the decrease in HR associated with the diving response. METHODS: Eight female and six male subjects (21±2 years) participated in this study and visited the lab on three occasions. The order of visits was counterbalanced. For one visit, subjects rested for 10 minutes prior to submerging their face up to the temples in 5ºC water for 20 seconds while breathing through a snorkel (RS). The other visits involved high intensity intermittent sprinting cycle ergometer exercise, consisting of ten maximal effort 6 second sprints against a resistance of 7.5% of their body weight, followed by 30 seconds of light cycling without resistance. The exercise test was followed immediately by either seated recovery for 3 minutes (EXNS) or facial submersion (EXS) as described above. HR and BP were monitored throughout the experiment. The control for this experiment was resting without facial submersion, which was assumed to have no effect on HR or MAP. A repeated measures ANOVA was used to compare the magnitude of the change in HR and MAP (expressed as the percent change). RESULTS: Compared to control, there was a 17.2 % decrease in HR the RS condition (97.7 ± 13.0 vs. 81.1 ± 19.0 min-1, ppppp=0.150), nor MAP (p=0.198) deviated from the control during the EXSN trial. CONCLUSION: A near-maximal cycling sprinting exercise does not diminish the effects of the diving response with respect to HR or MAP. Since the bradycardia response remained intact, it appears that the PNS response associated with dive response is powerful enough to overcome the high catecholamine response associated with this type of exercise.

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