heart rate variability in Disorders of Consciousness

Functional neuroimaging has provided indications of direct/indirect functional links between the autonomic control and higher brain activities. An integrated model (the central autonomic network) has been contrived to describe the interaction among neuronal structures involved in cognitive, sensory, or affective processes and autonomic regulation. The measures of heart rate variability (HRV) are thought to indirectly reflect these activities and interaction; integrative models equate HRV to autonomic nervous system outputs, with HRV reflecting affective, physiological, “cognitive,” and behavioural elements and homeostatic responses.
HRV provides tools for the evaluation of responsiveness in Disorders od Consciousness (DoC) and it has proved reliable in physiological research in the absence of conscious behaviour.
Previous studies have evidenced a correlation between autonomic activity and emotion evoked, for example by music listening, in healthy subjects as well as in patients with Disorders of Consciousness, finding a correlation between HRV parameters (in particular with the entropy) and complexity of the musical stimuli.
Again, the incidence of established clinical indicators of responsiveness (e.g. visual pursuit) in patients with DoC has been proven variable at the single subject, and a correlation with HRV measures has been observed describing a correlation between sympathetic/parasympathetic balance and responsiveness.
However, most of the studies were realized in a clinical setting with controlled ambient parameters, and the models developed loss of reliability in a natural ambient. A correct interpretation of data would require also a recording of biometric parameters in the patient's room, and possibly with a recording of 24h, correlating the biometric data with the ambient parameters.
Disrupted sleep, in the critically ill patients, is associated with increased morbidity and mortality, and there is sufficient scientific evidence that noise exposure can induce hearing impairment, hypertension and ischemic heart disease, annoyance, sleep disturbance. Similarly, temperature and humidity also play a role for the patient’s conditions.
The extensive monitoring of all aspects of the subject’s functional condition and reactivity in his/her daily activity is a prerequisite to understanding the real efficacy of ambient conditions/changes potentially contributing to the recovery of the consciousness in the rehabilitative milieu.