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

Abstract

To explore the use of 5-minute heart rate variability (HRV) during inpatient rehabilitation in the acute phase of traumatic spinal cord injury (SCI).

Longitudinal observational study.

Acute inpatient rehabilitation (AIR).

10 patients with acute traumatic SCI.

5-minute HRV supine recordings twice daily on three different days per patient.

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)).

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.

Keywords: Autonomic nervous system; Electrocardiography; Heart rate variability; Spinal cord injuries.

Figure 1

Uninjured references, acute spinal cord injury (SCI) and chronic SCI arranged by HRV measures. (A) SDNN (standard deviation of normal sinus heart beats) and RMSSD (root mean square of successive differences) follow similar pattern of decreased values in acute SCI and increasing towards uninjured reference values in chronic SCI. (B) Mean RR (interval of time between two consecutive R waves of the QRS complex) follows the pattern of an acute decrease after SCI and increase towards uninjured reference values. LF (low frequency) and HF (high frequency) decrease after SCI and further decrease in chronic SCI. Grey arrows highlight the trends in HRV values from uninjured to acute SCI to chronic SCI. Data outliers, defined as a number which is greater than the third quartile by more than 1.5 times the interquartile range, are shown as separately plotted points (circle, diamond, square) above the box plot.