[Hemorrhage exerts different effects on variabilities of heart rate and blood pressure in dogs]

The aim of the present study was to evaluate the effects of hemorrhage on heart rate variability (HRV) and blood pressure variability (BPV) as indicators of autonomic nervous system (ANS) and hypovolemia. We induced hemorrhagic hypovolemia in 7 dogs by removing blood in graded stages (0%, 10%, 20%, 30%, 40% of the estimated blood volume; EBV). HR was unchanged during hemorrhage, while mean BP decreased significantly after 30% EBV hemorrhage. Low frequency component (LF: 0.04-0.15 Hz) of HRV significantly increased after 20% EBV hemorrhage but high frequency component (HF: 0.15-0.4 Hz) of HRV was not altered. LF of BPV increased significantly stepwise after 20% EBV hemorrhage and HF of BPV increased significantly after 30% EBV hemorrhage, showing that both LF and HF of BPV might indicate the degree of hypovolemia. During hemorrhage LF of HRV and BPV increased and HF of HRV was unchanged, indicating the shift of the autonomic balance toward sympathetic dominance. An excellent quantitative correlation between LF of BPV and the degree of hypovolemia was demonstrated during graded hemorrhage, while LF of HRV plateaued at its maximum value at 20% EBV hemorrhage. In conclusion, our study suggests that the spectral analysis of HRV and BPV during graded hemorrhage shows different characteristics in the quantitative evaluation of ANS and hypovolemia.