A Pilot Observational Study of the Effects of Physical Activity on Heart Rate Variability in Patients With Severe Acquired Brain Injury

Background Severe acquired brain injury is usually associated with permanent disabilities in motor skills and cognitive functions that inhibit patients level of functioning, communication, participation in social activities and ability to work [Faul et al 2015, McLafferty et al 2016]. Patients with severe brain injury often have reduced level of consciousness in the early stages after the incident. Studies have shown that the autonomic nervous system can be affected in these patients, shown by analysis of the heart rate variability in the low frequency domain [Riberholt et al 2016, Vistisen et al 2014]. Signals from motor- and sensory cortex can influence sympathetic and parasympathetic activity and thus be a part of the cardiovascular adaptation during function [Sequeira et al 2000]. Aerobic exercise has been demonstrated to be effective regarding to autonomic cardiovascular regulation among healthy workers [Hallman et al 2017].

One method to assess sympathetic- and parasympathetic activity of the autonomous nervous system, as well as baroreflex sensitivity, is through the analysis of heart rate variability (HRV) [van de Vooren et al 2007]. A study of traumatic brain injured patients admitted to a neurocritical intensive care unit reveals that reduced HRV and baroreflex sensitivity within the first week of admission is associated with a poor neurological outcome at 1 year post-injury [Henden et al 2014]. Patients with severe acquired brain injury and low state of consciousness has demonstrated vastly reduced HRV and baroreflex sensitivity 40 days post injury during rest and head-up tilt[Riberholt et al 2016, Vistisen et al 2014].

Rehabilitation of patients with severe acquired brain injury and low state of consciousness is multimodal. Physical stimulation of the cardiovascular system can be exercised through an array of interventions such as mobilization, standing using a tilt-table, bed-biking, robot-assisted walking or other methods. To the authors' knowledge, no studies have been published researching the association between physical stimulation and HRV in patients with severe acquired brain injury in the subacute phase.

Hypotheses

• Patients with low state of consciousness have reduced HRV during rest.
• HRV is affected by physical activity such as, tilt-table mobilization, bed-biking or robot assisted walking.
• HRV is altered over time if patients are subjected to multiple bouts of physical exercise such as tilt-table mobilization, bed-biking or robot assisted walking.