Frontal Cerebral Oxygenation in Humans at Rest: A Mirror Symmetry in the Correlation with Cardiorespiratory Activity.

Background: Although several studies published reference values for frontal cerebral tissue oxygen saturation (StO) measured with near-infrared spectroscopy (NIRS) based cerebral oximetry, a detailed investigation, whether and which factors from systemic physiology are related to the individual StO values, is missing.

Aim: We investigated how the state of the cardiorespiratory system is linked to StO values at rest.

Subjects And Methods: Absolute StO values (median over a 5 min resting-phase while sitting) were obtained from 126 healthy subjects (age: 24.0 ± 0.2 years, 45 males, 81 females) over the left and right prefrontal cortex (PFC) by employing frequency-domain NIRS as part of a systemic physiology augmented functional near-infrared spectroscopy (SPA-fNIRS) study. In addition, heart rate (HR) and respiration rate (RR) were measured, and the pulse respiration quotient (PRQ) was determined (PRQ = HR/RR). General additive models (GAM) were used to analyse the data.

Results: The GAM analysis revealed a specific relationship between the overall PFC StO values (mean over right and left PFC) and the variables HR and RR: HR was positively correlated with mean StO, while RR showed no correlation. In the mirror case, RR was negatively linearly correlated with the frontal cerebral oxygenation asymmetry (FCOA), which was not correlated with HR. The right PFC StO was not linked to the RR, whereas the left PFC StO was. Positive correlations of the PRQ with the mean PFC StO as well as the FCOA were also found. GAM modelling revealed that the individual FCOA values are explained to a large extent (deviance explained: 88.8%) by the individual mean PFC StO and PRQ. We conclude that (i) the state of the cardiorespiratory system is significantly correlated with StO values and (ii) there is a mirror symmetry with regard to the impact of cardiorespiratory parameters on the mean PFC StO and FCOA.