Towards quantitative assessment of cerebrovascular autoregulation in human neonates using ultrafast ultrasound imaging.

Newborns with congenital heart diseases requiring cardiopulmonary bypass (CPB) are at risk of neurodevelopmental impairment. The impact of deep hypothermia cardiopulmonary bypass (DH-CPB) on cerebrovascular autoregulation (CAR) that controls brain perfusion in the presence of blood pressure variation is not well understood. Recently, ultrafast power Doppler (UPD) showed potential to study CAR in neonates based on cerebral blood volume (CBV). However, since CAR relies mainly on arterial vasoconstriction/vasodilation, monitoring of brain perfusion variation based on CBV requires the discrimination of arterial from venous CBV. This study aims to use UPD combined with an algorithm for the discrimination of arteries and veins to monitor CAR during DH-CPB in neonates. Transfontanellar ultrafast power Doppler was performed in two groups of newborns: those undergoing deep hypothermic cardiopulmonary bypass with circulatory arrest (18-20 °C, n = 6, "DH group") and those undergoing full-flow CPB at mild hypothermia (32-34 °C, n = 6, "non-DH group"). Blood flow directionality was used to differentiate arterial compartments of CBV from venous CBV in specific brain regions where arterial and venous flows exhibit opposite directions. To study CAR, a linear mixed effect model was used to find the association between arterial CBV and mean arterial blood pressure (MAP). In the "non-DH group", we found a negative association between arterial CBV and MAP, indicating that an increase in MAP is associated with a decrease in arterial CBV (slope = -0.020 [Formula: see text], p = 0.047). Conversely, in the "DH group" no significant association was found such that arterial CBV remained stable as MAP increased (p = 0.314). We interpret the reduction in arterial CBV with increasing MAP in the "non-DH group" as an active arterial vasoconstriction triggered by CAR, whereas the lack of variation of arterial CBV in the DH group suggests impaired CAR response. Our findings highlight the potential of ultrafast ultrasound imaging for intra-operative CAR monitoring, paving the way for a better understanding of the impact of different types of CPB on cerebral perfusion.