Interaction between systemic arterial reservoir behavior and cerebrovascular vasoreactivity during acute controlled hypocapnia

Abstract

Cerebral carbon dioxide (CO_2) vasoreactivity (CVR), defined as the dilatory capacity of cerebral vessels in response to CO_2, has pathophysiological importance and is clinically relevant. Reservoir–excess pressure analysis (REPA) of arterial blood pressure (ABP) waveforms, which estimates the pressure-buffering (reservoir) capacity of large arteries, provides contemporary insights beyond standard ABP measures by encompassing global arterial compliance and vascular tone. We examined the correlation between the systemic arterial reservoir behavior and CVR, as well as the coupling between peripheral and cerebrovascular hemodynamics. In 26 individuals, transcranial Doppler ultrasound (TCD) recordings of middle cerebral artery (MCA) flow velocity, simultaneous non-invasive ABP recordings and end-tidal CO_2 (etCO_2) were obtained at baseline and during intentional hyperventilation to lower CO_2. Reservoir–excess pressure parameters, including integral of reservoir pressure (IntPr) and diastolic rate constant (DRC) were extracted from ensemble-averaged ABP waveforms. CVR, defined as ΔMCA_V/ΔetCO2, and cerebrovascular resistance index (CVRi), defined as MAP/MCA_V, were calculated. Mean arterial pressure (MAP) was calculated as ABP averaged over the cardiac cycle. In participants in the below-mean CVR group, a lower DRC, reflecting slower diastolic decay, was associated with a higher CVRi ( r = -0.445; p = 0.029). By contrast, in the above-mean CVR group, a lower DRC correlated with a lower CVRi ( r = 0.807; p