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bioRxiv · 10.1101/2021.03.11.434655

Protocol-Dependence of Middle Cerebral Artery Dilation to Modest Hypercapnia

Al-Khazraji, B. K.·Buch, S.·Kadem, M.·Matushewski, B. J.·Norozi, K.·Menon, R. S.·Shoemaker, J. K.
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Abstract

There is a need for improved understanding of how different cerebrovascular reactivity (CVR) protocols affect vascular cross-sectional area (CSA) when measures of vascular CSA are not feasible. In human participants, we delivered ~{+/-}4mmHg end-tidal partial pressure of CO2 (PETCO2) relative to baseline through controlled delivery, and measured changes in middle cerebral artery (MCA) cross-sectional area (CSA; magnetic resonance imaging (7 Tesla MRI)), blood velocity (transcranial Doppler and Phase contrast MRI), and calculated CVR based on steady-state versus a ramp protocol during two protocols: a 3-minute steady-state (+4mmHg PETCO2) and a ramp (delta of -3 to +4mmHg of PETCO2). We observed that 1) the MCA did not dilate during the ramp protocol, but did dilate during steady-state hypercapnia, and 2) MCA blood velocity CVR was similar between ramp and steady-state hypercapnia protocols, although calculated MCA blood flow CVR was greater during steady-state hypercapnia than during ramp, the discrepancy due to MCA CSA changes during steady-state hypercapnia. Due to the ability to achieve similar levels of MCA blood velocity CVR as steady-state hypercapnia, the lack of change in MCA cross-sectional area, and the minimal expected change in blood pressure, we propose that a ramp model, across a delta of ~-3 to +4mmHg PETCO2, may provide one alternative approach to collecting CVR measures in young adults with TCD when CSA measures are not feasible.

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Al-Khazraji, B. K., Buch, S., Kadem, M., Matushewski, B. J., Norozi, K., Menon, R. S., Shoemaker, J. K.. 2021-03-12. Protocol-Dependence of Middle Cerebral Artery Dilation to Modest Hypercapnia. https://doi.org/10.1101/2021.03.11.434655

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