Doppler echocardiographic assessment of changes in the central circulation of the fetal sheep induced by maternal oxygen administration

Eleven fetal sheep were studied to investigate if Doppler echocardiography could document redistribution of blood flow during maternal oxygen administration. Velocities through the pulmonary valve, aortic valve, common brachiocephalic trunk, aortic arch, descending aorta, umbilical and carotid artery were recorded before, during and after oxygen was delivered to the ewe by face mask. Indices of cardiac performance (shortening fraction, velocity of fiber shortening and systolic time intervals) were also obtained. The aortic arch was the only recording site where significant changes in mean velocity related to oxygen administration and withdrawal were demonstrated (p < 0.01). Changes in the velocity waveform suggesting an increase in cerebral vascular resistance during oxygen administration were found in the carotid artery. Thus, using Doppler velocimetry, the carotid artery and the aortic arch (equivalent to the human aortic isthmus) appear to be suitable sites to document changes induced by maternal oxygen administration.