Exploring 5-minute heart rate variability in spinal cord injury during acute inpatient rehabilitation

Objective To explore the use of 5-minute heart rate variability (HRV) during inpatient rehabilitation in the acute phase of traumatic spinal cord injury (SCI).Design Longitudinal observational study.Setting Acute inpatient rehabilitation (AIR).Participants 10 patients with acute traumatic SCI.Interventions 5-minute HRV supine recordings twice daily on three different days per patient.Outcomes Measures HRV values were evaluated (1) within a single day (Early versus Late); (2) across the inpatient admission (initial, mid, and discharge); (3) by SCI phenotypes and by clinical outcomes (ex. pressure injuries (PI)).Results Patients had an average age of 38 years, 80% male, and 40% with tetraplegia. There were no HRV differences between Early and Late recordings, across the inpatient admission, demographics, or SCI phenotype. However, improvement in neurologic exam was accompanied by increased parasympathetic tone (mean RR increased by 172 ms SD 61, P = .005). Patients with PI demonstrated lower sympathetic (SNS) activity (decreased LF by 472 ms2 SD 240, P = .049) and lower PNS activity (decreased RMSSD by 1.2 ms SD 0.5, P = .02), compared to no PI. Comparisons to uninjured reference values and chronic SCI suggest a changing autonomic nervous system (ANS) from uninjured to acute to chronic as measured by HRV.Conclusions This preliminary evidence suggests HRV in acute SCI is stable across time and day during inpatient rehabilitation and may be correlated to clinical sequalae of ANS dysfunction and neurologic recovery. Comparisons to published work suggest that HRV may measure the progression in the ANS from acute to chronic phase after SCI.