Correlation between fetal carotid artery Doppler velocimetry and physiological variables affecting cerebral resistance during experimental increase of resistance to umbilical blood flow

Objective: The objective of this study was to investigate if Doppler velocimetric indices of the carotid artery could be correlated to physiological variables known to affect cerebral vascular resistance methods. Seven fetal sheep were studied in acute experiments. Carotid artery blood gases and Doppler recordings from the ascending aorta, aortic isthmus, umbilical artery, and carotid artery were obtained at basal state and after three levels of increase in resistance to umbilical blood flow. Results: Due to a decrease in left ventricular output, the left ventricular oxygen delivery started to decrease at the first level of increase in resistance. pCO(2) increased significantly at the second step, Using multiple linear regression it could be demonstrated that the best prediction of carotid artery pulsatility index (r = 0.77, P < 0.0001) was obtained with pCO(2) (P < 0.005) and left ventricular oxygen delivery (P < 0.005) as independent variables. Good correlations between carotid artery pulsatility index and other Doppler variables of the fetoplacental circulation, i.e., the temporal mean velocities of the umbilical artery (r = 0.76, P < 0.0001) and of the aortic isthmus (r = 0.72, P < 0.001), in turn related to left ventricular oxygen delivery and brood flow redistribution could also be demonstrated. Conclusion: These findings provide indirect evidence that Doppler velocimetric indices from arteries supplying the brain can be used as estimates of cerebral vascular resistance.