Sympathetic and parasympathetic activities evaluated by heart-rate variability in head injury of various severities

Objective To investigate the autonomic function in patients with brain damage of various extents. The purposes were to correlate the parameters derived from spectral analysis of the heart-rate variability (HRV) with the classic Glasgow coma scale (GCS), and to evaluate the possible clinical application of HRV in the autonomic functions in patients with various severities of brain-stem injury. Methods A total of 90 patients was divided into 5 groups based on the GCS: I: 15, II: 9–14, III: 4–8, no pupil dilatation, IV: 4–8, pupil dilatation, and V: 3, brain death. Electrocardiogram was recorded for frequency-domain analysis of RR intervals. HRV were categorized into the low-frequency (LF, 0.04–0.15 Hz) and high-frequency power (HF, 0.15–0.40 Hz), LF to HF power ratio (LF/HF), normalized powers (LF and HF%). These HRV parameters were correlated with the severity of brain damage. Results The LF, HF, LF%, and LF/HF in Group I were essentially similar to those in the normal subjects. LF and HF decreased from Group I to IV. All parameters were nearly absent in Group V. Conclusions The increases in LF% and LF/HF with the decrease in HF indicate augmented sympathetic and attenuated parasympathetic drive. These changes were related to the severity of brain-stem damage. Both LF and HF were nearly abolished in brain death. Significance Our analysis indicates that HRV may be an useful tool for evaluating the autonomic functions in patients with brain damage of various degrees.