The effectiveness for vagal stimulation by ice water aplication to face during metronome-controlled respiration of 15 breaths/minute was examed. The importance of basal vagal tone and sympathovagal interaction in the individual variability of responsiveness to the vagal stimulation was investigated.

Fifty three 12~13 year old healthy volunteers were included. Vagal tone and sympathovagal interaction before and after application of ice water to the face were assessed by power spectral analysis of RR interval(heart rate) variability.

Basal heart rate, high frequency power, and low to high frequency power ratio were 81±13(58~110 beats/min), 791±1061(56~4161 msec²) and 1.08±1.22(0.04~4.85) during controlled respiration. After ice water application twenty three children developed 5 more nodal escape beats due to severe bradycardia. Minimum heart rate, high frequency power and low to high power ratio changed to 42±12(19~72/min), 1890±1882(221~7258msec²) and 0.64±0.43(0.12~1.46). The increased ratio of high frequency power, maximum heart rate decrement and its percent after stimulation were 5.44±5.62(0.63~24.26), 39±14(10~81/min) 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=0.0004). Maximum heart rate decrement was correlated with basal logarithmic high frequency power(r=-0.41, p=0.0018) and low to high frequency power ratio(r=0.27, p=0.04).

Application of ice water to the face during controlled respiration produces powerful vagal stimulation and bradycardia, however, there is a wide individual variability of responsiveness to it. The absolute basal vagal tone contribute to this individual variability.