Demonstration of subclinical autonomic dysfunction following severe traumatic brain injury using serial heart rate variability monitoring

Objectives: To explore the subclinical autonomic dysfunction following severe TBI by serially monitoring the Heart rate Variability (HRV) parameters. Methods: Thirty subjects with severe TBI were recruited from the emergency services of our institute. BioHarness™ (Zephyr technologies) a non-invasive telemetric device was used to procure the Lead II ECG. The recordings were done on day 1, day 3 and day 10 after trauma. A 5 minute artifact free segment from the recording was analysed with the LabChart© software. The HRV parameters were compared between patients based on their outcome. Results: The mean age of the patients was 32.44 ± 9.26 years. In patients, all the mean values of both time domain and frequency domain parameters were less than the normal values. There was significant reduction in the Standard Deviation of NN intervals (SDNN) (p = 0.03), Low Frequency (LF) (p = 0.03) and High Frequency power (HF) (p = 0.04) on day 1 recording, in patients who died when compared with the patients who survived. Similarly the LF and HF power on day 10 were also significantly reduced in patients with unfavourable outcome. Conclusion: This pilot study reveals the definitive autonomic dysfunction following severe TBI. It also shows that there is significant autonomic dysfunction in subjects with unfavourable outcome. Autonomic dysfunction occurs invariably in these patients due to the damage to the central autonomic network, but the degree of dysfunction varies between subjects with favourable and unfavourable outcome. HRV parameters can be considered as adjunct predictors of mortality in severe TBI.