Analyzing the Loss and the Recovery of Consciousness: Functional Connectivity Patterns and Changes in Heart Rate Variability During Propofol-Induced Anesthesia

Abstract

The analysis of the central and the autonomic nervous systems (CNS, ANS) activities during general anesthesia (GA) provides fundamental information for the study of neural processes that support alterations of the consciousness level. In the present pilot study, we analyzed EEG signals and the heart rate (HR) variability (HRV) in a sample of 11 patients undergoing spinal surgery to investigate their CNS and ANS activities during GA obtained with propofol administration. Data were analyzed during different stages of GA: baseline, the first period of anesthetic induction, the period before the loss of consciousness, the first period after propofol discontinuation, and the period before the recovery of consciousness (ROC). In EEG spectral analysis, we found a decrease in posterior alpha and beta power in all cortical areas observed, except the occipital ones, and an increase in delta power, mainly during the induction phase. In EEG connectivity analysis, we found a significant increase of local efficiency index in alpha and delta bands between baseline and loss of consciousness as well as between baseline and ROC in delta band only and a significant reduction of the characteristic path length in alpha band between the baseline and ROC. Moreover, connectivity results showed that in the alpha band there was mainly a progressive increase in the number and in the strength of incoming connections in the frontal region, while in the beta band the parietal region showed mainly a significant increase in the number and in the strength of outcoming connections values. The HRV analysis showed that the induction of anesthesia with propofol was associated with a progressive decrease in complexity and a consequent increase in the regularity indexes and that the anesthetic procedure determined bradycardia which was accompanied by an increase in cardiac sympathetic modulation and a decrease in cardiac parasympathetic modulation during the induction. Overall, the results of this pilot study showed as propofol-induced anesthesia caused modifications on EEG signal, leading to a “rebalance” between long and short-range cortical connections, and had a direct effect on the cardiac system. Our data suggest interesting perspectives for the interactions between the central and autonomic nervous systems for the modulation of the consciousness level.

Brain-heart interactions in the neurobiology of consciousness

“…On the heart side, the existence of complex patterns on heart-rate variability (HRV) has been reported at different contexts ( Sassi et al, 2015 ). Experimental evidence has shown HRV complexity as a potential marker of states-of-consciousness ( Riganello et al, 2018a , 2018b ; Sattin et al, 2021 ). The brain structures associated with autonomic activity, and part of the central autonomic network, span from high-order regions (e.g., medial prefrontal cortex and insula), the forebrain (e.g., hypothalamus and amygdala), and several nuclei in the medulla (e.g., nucleus of tractus solitarius, nucleus ambiguous, parabrachial Kolliker fuse nucleus) ( Beissner et al, 2013 ; Silvani et al, 2016 ; Valenza et al, 2019 ).…”

Brain-heart interactions in the neurobiology of consciousness

“…On the heart side, the existence of complex patterns on HRV has been reported at different contexts [130]. Experimental evidence has shown HRV complexity as a potential marker of states-of-consciousness [131][132][133]. The brain structures associated with autonomic activity, and part of the central autonomic network, span from high-order regions (e.g., medial prefrontal cortex and insula), the forebrain (e.g., hypothalamus and amygdala), and several nuclei in the medulla (e.g., nucleus of tractus solitarius, nucleus ambiguous, parabrachial Kolliker fuse nucleus) [134][135][136].…”

Propofol-induced Unresponsiveness Is Associated with a Brain Network Phase Transition

“…These observations are not new but have been reported in several previous papers. 6,34 The mechanisms by which propofol causes these effects are less clear. We would propose that these are the manifestations of generic network-level phenomena that are well established in other fields of network science and percolation theory, and can be described using the conventional existing nomenclature and methods of random network dynamics.…”