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

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 < 0.001), suggesting effective flow redistribution to support the brain when vasoreactivity is intact. REPA revealed subtle differences between the below- and above-mean CVR subgroups, despite comparable mean arterial, systolic, and diastolic blood pressures. The interplay between systemic arterial reservoir function and cerebral perfusion is modulated by the extent of CVR. When CVR is higher, increased peripheral vascular tone (reflected by a lower DRC) coincides with lower cerebrovascular resistance, which may contribute to effective redistribution of blood flow to preserve brain perfusion. In contrast, when vasoreactivity is lower, peripheral and cerebral vascular tone tend to rise in tandem, which may lead to reduced cerebral flow velocity and potentially compromised perfusion.