Static Apnea Effect on Heart Rate and Its Variability in Elite Breath-Hold Divers

Description

Background: The diving response includes cardiovascular adjustments known to decrease oxygen uptake and thus prolong apnea duration. As this diving response is in part characterized by a pronounced decrease in heart rate (HR), it is thought to be vagally mediated.Methods: In five professional breath-hold divers (BHDs) and fi ve less-trained controls (CTL), we investigated whether the diving response is in fact associated with an increase in the root mean square successive difference of the R-R intervals (RMSSD), a time-domain heart rate variability (HRV) index. HR behavior and arterial oxygen saturation (S a O 2) were continuously recorded during one maximal apnea. Short-term changes in S a O 2 , HR, and RMSSD were calculated over the complete apnea duration.Results: BHDs presented bi-phasic HR kinetics, with two HR decreases (32 6 17% and 20 6 10% of initial HR). The second HR decrease, which was concomitant to the pronounced S a O 2 decrease, was also simultaneous to a marked increase in RMSSD. CTL showed only one HR decrease (50 6 10% of initial HR), which appeared before the concomitant S a O 2 and RMSSD changes. When all subject data were combined, arterial desaturation was positively correlated with total apnea time (r 5 0.87, P , 0.01).Conclusion: This study indicates that barorefl ex stimulation and hypoxia may be involved in the bi-phasic HR response of BHDs and thus in their longer apnea duration.

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