Cardio-respiratory autonomic responses to nociceptive stimuli in patients with disorders of consciousness

The autonomic response to pain might discriminate among consciousness disorders. Therefore, aim of this study was to describe differences between minimally conscious state (MCS) and unresponsive wakefulness syndrome (UWS) patients in their autonomic response to a nociceptive stimulus. ECG, respiration, finger blood pressure (BP) and total peripheral resistances (TPR) were continuously recorded before, during and after a standardized noxious stimulus in 20 adult brain-injured patients, 14 in UWS and 6 in MCS. Occurrence of fast autonomic responses synchronous with the stimulus was detected by visual inspection of the tracings; short-term (<20 s) and long-term (between 20s and 50 s from the stimulus) responses were evaluated by beat-by-beat quantitative analysis. The noxious stimulus elicited fast responses in both groups, but only MCS patients showed a significant short-term response in TPR and long-term response in HR. Thus, short- and long-term cardiovascular responses to pain might integrate neuro-behavioural assessments to discriminate between MCS and UWS.