FACE IMMERSION INCREASES VAGAL ACTIVITY AS ASSESSED BY HEART-RATE-VARIABILITY

We examined whether the diving reflex without breath-holding (face imm ersion alone) increases vagal activity, as determined by heart rate va riability. A group of 15 men [mean age 20 (SD 3) stars, height 172 (SD 5) cm, body mass 68 (SD 9) kg] performed 12 trials tit various breath ing frequencies (5 10, 15, 20, 30 breaths.min(-1) and uncontrolled bre ath) with or without face immersion. The R-R intervals of the ECG and gas exchange variables were recorded during the 2 min of each trial. T he subjects immersed their faces in 8-10 degrees C water while breathi ng through a, short snorkel. The subject sat in the same position eith er with or without face immersion, The mean R-R interval (RRmean), sta ndard deviations (SDRR) and coefficient of variance (CVRR) Of the R-R interval were calculated from the R-R intervals during 30-120 s. The f ace immersion significantly increased SDRR and CVRR (P <0.05), and inc reased RRmean (P < 0.05) at 20 breaths min Face immersion itself had n o effect on oxygen uptake, tidal volume, end-tidal O-2 and CO2 partial pressures. The diving reflex without breath-holding increased the hea rt rate variability, indicating that face Immersion alone increases va gal activity.