Dominance in cardiac parasympathetic activity during real recreational SCUBA diving.

It was already established that exposure to hyperbaric conditions induces vagal-depended bradycardia but field study on autonomic nervous system (ANS) activity during self-contained underwater breathing apparatus (SCUBA) diving is lacking. The aim of the present study was to evaluate ANS modifications during real recreational SCUBA diving using heart rate variability analysis (timedomain, frequency-domain and Poincaré plot) in 10 experienced and volunteers recreational divers. Mean RR, root mean square of successive differences of interval (rMSSD), high frequency of spectral analysis and standard deviation 1 of Poincaré Plot increased (P < 0.05) during dive. Low frequency/high frequency ratio decreased during dive (P < 0.05) but increased after (P < 0.05). Recreational SCUBA diving induced a rise in vagal activity and a decrease in cardiac sympathetic activity. Conversely, sympathetic activity increases (P < 0.05) during the recovery.