RESUMO
BACKGROUND: It is well known that there is wide individual variation of responsiveness when parasympathetic nervous system is stimulated physiologically, pathologically, and therapeutically. But no appropriate explanation is present for that yet. So the purpose of this study is to verify individual diversity of vagal tone during resting state and after vagal stimulation and to find factor that may significantly contribute to it. METHOD: We serially measured variation of heart period(VHP : sec) which had been known to be an accurate index of cardiac parasympathetic tone during resting state(VHPb) and after vagal stimulation by ice water application to face(VHPv). And we analyzed correlation between VHPb, VHPv and ratio of VHPv to VHPb(ratio). RESULT: There was wide variation of vagal tone both in resting state (VHPb : 0.025-0.161) and after vagal stimulation (VHPv : 0.087-0.661). VHPb could be classified into 3 groups according to stem and leaf distribution(group A : VHPb could be classified into 3 groups according to stem and leaf distribution(group A : VHPb0.1). The low VHPb group A showed dramatic increase in vagal tone after vagal stimulation (ratio 2.21-20.24 mean 7.7), on the other hand high VHPb group C did not (ratio 0.80-2.55 mean 1.39). There ws also a significant negative correlation between VHPb and ratio (r=0.69, p<0.001). CONCLUSION: These results suggest that there is wide individual diversity of responsiveness to vagal stimulation and magnitude of vagal tone in resting state is an important factor to determine the responsiveness to vagal stimulation.