 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 tiltRiberholt et al 2016, Vistisen et al 2014. 