Evaluation of cardiac autonomic responses to painful stimulus in patients with disorders of consciousness

Abstract

Background: Disorders of consciousness (DOC) are characterized by a disrupted relationship between the two consciousness’ components: arousal and awareness. In particular main consciousness disorders are coma, vegetative state and minimally conscious state. Spectral analysis of cardiovascular signal variability is a widely used procedure to investigate autonomic cardiovascular control and/or target function impairment. Nevertheless, in literature there are few studies about autonomic nervous system in patients with disorders of consciousness. Aim: The aim of the study is to evaluate the autonomic nervous system responses to a standardized pain stimulus in patients with DOC. Methods: We selected 13 clinically stable patients from Vegetative State Unit at Don Gnocchi Foundation, with minimally conscious state and vegetative state diagnosed with Giacino et. al. (2002) criteria. We recorded the cardiorespiratory activity for about half an hour with BT16Plus System (Marazza Spa, Monza), meanwhile we subjected all patients to a standardized painful stimulus applied on the nail of the third finger with an algometer (power setting: 10 kg for 5 seconds). Autonomic cardiac control was evaluated using spectral analyses of HRV, which identifies two oscillatory components, LF, marker of sympathetic, and HF, marker of vagal modulation. Results: Results showed an increased heart rate and sympathetic activity (LF/HF and LFnu) in 2 patients, due to the painful stimulus. All the other subjects had no evident cardiac autonomic changes to pain stimulus. Conclusions: Further investigations are needed to understand whether these differences are related to illness progression or to the primary CNS damage.