Detection of Blood CO2 Influences on Cerebral Hemodynamics Using Transfer Entropy

TL;DR

This study uses transfer entropy to detect how blood CO2 levels affect brain blood flow during hyperventilation in healthy individuals.

Contribution

The study introduces conditional transfer entropy as a method to quantify CO2's causal influence on cerebral hemodynamics.

Findings

CO2 levels showed increased influence on cerebral blood velocity during hyperventilation.

The influence remained elevated during the recovery phase compared to normal breathing.

Left and right hemispheres showed distinct but similar patterns of CO2 influence.

Abstract

Cerebral hemodynamics describes an important physiological system affected by components such as blood pressure, CO2 levels, and endothelial factors. Recently, novel techniques have emerged to analyse cerebral hemodynamics based on the calculation of entropies, which quantifies or describes changes in the complexity of this system when it is affected by a pathological or physiological influence. One recently described measure is transfer entropy, which allows for the determination of causality between the various components of a system in terms of their flow of information, and has shown positive results in the multivariate analysis of physiological signals. This study aims to determine whether conditional transfer entropy reflects the causality in terms of entropy generated by hypocapnia on cerebral hemodynamics. To achieve this, non-invasive signals from 28 healthy individuals who undertook a hyperventilation maneuver were analyzed using conditional transfer entropy to assess the variation in the relevance of CO2 levels on cerebral blood velocity. By employing a specific method to discretize the signals, it was possible to differentiate the influence of CO2 levels during the hyperventilation phase (22.0% and 20.3% increase for the left and right hemispheres, respectively) compared to normal breathing, which remained higher during the recovery phase (15.3% and 15.2% increase, respectively).

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