Influence of CO₂ on neurovascular coupling: interaction with dynamic cerebral autoregulation and cerebrovascular reactivity

Abstract

PaCO2 affects cerebral blood flow (CBF) and its regulatory mechanisms, but the interaction between neurovascular coupling (NVC), cerebral autoregulation (CA), and cerebrovascular reactivity to CO2 (CVR), in response to hypercapnia, is not known. Recordings of cerebral blood flow velocity (CBFv), blood pressure (BP), heart rate, and end‐tidal CO2 (EtCO2) were performed in 18 subjects during normocapnia and 5% CO2 inhalation while performing a passive motor paradigm. Together with BP and EtCO2, a gate signal to represent the effect of stimulation was used as input to a multivariate autoregressive‐moving average model to calculate their separate effects on CBFv. Hypercapnia led to a depression of dynamic CA at rest and during stimulation in both hemispheres (P <0.02) as well as impairment of the NVC response, particularly in the ipsilateral hemisphere (P <0.01). Neither hypercapnia nor the passive motor stimulation influenced CVR. Dynamic CA was not influenced by the motor paradigm during normocapnia. The CBFv step responses to each individual input (BP, EtCO2, stimulation) allowed identification of the influences of hypercapnia and neuromotor stimulation on CA, CVR, and NVC, which have not been previously described, and also confirmed the depressing effects of hypercapnia on CA and NVC. The stability of CVR during these maneuvers and the lack of influence of stimulation on dynamic CA are novel findings which deserve further investigation. Dynamic multivariate modeling can identify the complex interplay between different CBF regulatory mechanisms and should be recommended for studies involving similar interactions, such as the effects of exercise or posture on cerebral hemodynamics.

Neurovascular coupling in humans: Physiology, methodological advances and clinical implications

“…For example, many studies simply report the maximal change in CBF recorded during the ''activation'' period with 55,92,110 or without 111,112 addressing the temporal characteristics, while others attribute specific components and characteristics of the hyperemic contour to specific influences (i.e., perfusion pressure, neurogenic, autoregulation, blood gas concentration). 54,74 Our approach is to incorporate both amplitudinal and temporal characteristics by plotting the entire hyperemic contour, while extracting data from temporal subdivisions (i.e., early versus late/5 s duration bins, etc.) for further analysis.…”

The association between cerebrovascular reactivity and resting-state fMRI functional connectivity in healthy adults: The influence of basal carbon dioxide

“…In terms of Eq. (1), CVR is an important factor in determining the extent of CBF response to CMRO 2 changes (Maggio et al, 2014). One can also appreciate that CVR, which does not have direct neuronal effects, can substantially modulate the BOLD signal and thus introduce ambiguity into the measurement interpretations, particularly in the presence of vascular pathology.…”

Modelling of the Effect of End‐Tidal Carbon Dioxide on Cerebral Oxygen Saturation in Beach Chair Position under General Anaesthesia

“…Although increases in systemic arterial pressure may cause rapid increases in cerebral blood flow (CBF), CBF returns to its baseline value within a few seconds by the mechanism of cerebral autoregulation, which aims to maintain a stable CBF over a wide range of mean arterial pressures (MAP) of 70-150 mmHg [10][11][12]. Moreover, increases in arterial pressure may worsen visualization of the surgical field.…”