Application of ice water to the face during controlled respiration—a measure of basal vagal tone

We examined the effectiveness of the application of ice water to the face during metronome-controlled respiration (15 breaths per minute) for vagalstimulation. We also examined the importance of basal vagal tone and sympathovagal interaction in determining the individual response to the stimulation. Fifty-three boys, aged 12 and 13, were included in this study. Vagal tone and sympathovagal interaction were assessed by power spectral analysis of the variability of the RR interval (heart rate). Basal heart rate, high frequency power, and low-to-high frequency power ratios were 81 ± 13(58–110 beats/min), 791 ± 1061(56–4161 m.sec2) and 1.08±1.22 (0.04–4.85) during controlled respiration. After application of ice water, 23 children developed frequent nodal escape beats due to severe sinus bradycardia. Minimum heart rate, high frequency power, and low to high power ratios changed to 42± 12 (19–72 beats/min), 1890±1882 (211–7258 m.sec2) and 0.64±0.43 (0.12–1.46). The increased ratio of high frequency power, maximum decrement in heart rate, and its percent after stimulation were 5.44±5.62 (0.63–24.26), 39±14 (10–81 beats/mm) and 47±15 (16–81%), respectively. The increased ratio of high frequency power was correlated with basal logarithmic high frequency power (r=−0.60, p=O.0004). Maximum heart rate decrement was correlated with basal logarithmic high frequency power (r=−0.60, p=O.OO18) and low-to-high frequency power ratio (r=0.27, p=O.O4). We conclude that application of ice water to the faceduring controlled respiration induces powerful vagal stimulation and bradycardia similar to, or even greater than, facial immersion in cold water. There is wide variability of individual response which can be explained by the magnitude of absolute basal vagal tone.