Face immersion increases vagal activity as assessed by heart rate variability

Abstract

We examined whether the diving reflex without breath-holding (face immersion alone) increases vagal activity, as determined by heart rate variability. A group of 15 men [mean age 20 (SD 3) years, height 172 (SD 5) cm, body mass 68 (SD 9) kg] performed 12 trials at various breathing frequencies (5, 10, 15, 20, 30 breaths · min⁻¹ and uncontrolled breath) 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. The subjects immersed their faces in 8–10°C water while breathing through a short snorkel. The subject sat in the same position either with or without face immersion. The mean R-R interval (RR_mean), standard deviations (SD_RR) and coefficient of variance (CV_RR) of the R-R interval were calculated from the R-R intervals during 30–120 s. The face immersion significantly increased SD_RR and CV_RR (P<0.05), and increased RR_mean (P<0.05) at 20 breaths · min⁻¹. Face immersion itself had no effect on oxygen uptake, tidal volume, end-tidal O₂ and CO₂ partial pressures. The diving reflex without breath-holding increased the heart rate variability, indicating that face immersion alone increases vagal activity.