Heart Rate Variability and Arterial Blood Pressure Variability Show Different Characteristic Changes During Hemorrhage in Isoflurane-Anesthetized, Mechanically Ventilated Dogs

We assessed the changes in heart rate variability (HRV) and blood pressure variability (BPV) as indices of autonomic nervous system and volume status during hemorrhage in isoflurane-anesthetized, mechanically ventilated dogs. Nine dogs were used. They were sequentially subjected to withdrawal of 30% estimated blood volume and graded isoflurane inhalation of 1% and 2% followed by discontinuation of isoflurane and retransfusion. The power spectra of HRV and BPV were computed using the fast Fourier transformation, and were quantified by determining the areas of the spectrum in two component widths: low-frequency component (LF) (0.04–0.15 Hz) and high-frequency component (HF) (0.15–0.4 Hz). During hemorrhage and isoflurane anesthesia, both HRV-LF and HRV-HF were decreased and plateaued at the smaller concentration of isoflurane, whereas BPV-LF decreased concentration-dependently. BPV-HF showed a completely different response and increased significantly during 2% isoflurane. We speculate that HRV and BPV-LF would be affected by the autonomic nervous activity, whereas BPV-HF would depend on relative/absolute change in circulating blood volume.