Interactions between the right ventricle and pulmonary vasculature in the fetus

A midsystolic plateau differentiates the pattern of fetal pulmonary trunk b lood flow from aortic flow. To determine whether this plateau arises from i nteractions between the left (LV) and right ventricle (RV) via the ductus a rteriosus or from interactions between the RV and the lung vasculature, we measured blood flows and pressures in the pulmonary trunk and aorta of eigh t anesthetized (ketamine and alpha-chloralose) fetal lambs. Wave-intensity analysis revealed waves of energy traveling forward, away from the LV and t he RV early in systole. During midsystole, a wave of energy traveling back toward the RV decreased blood flow velocity from the RV and produced the pl ateau in blood flow. Calculations revealed that this backward-traveling wav e originated as a forward-traveling wave generated by the RV that was refle cted from the lung vasculature back toward the heart and not as a forward-t raveling wave generated by the LV that crossed the ductus arteriosus. Elimi nation of this backward-traveling wave and its associated effect on RV flow may be an important component of the increase in RV output that accompanie s birth.