Enhanced ventricular pump function and decreased reservoir backflow sustain rise in pulmonary blood flow after reduction of lung liquid volume in fetal lambs

摘要

Little is known, however, about changes in central flow patterns that sustain increased pulmonary perfusion after a decrease in lung liquid volume. This is especially pertinent as recent findings from wave intensity (WI) and phasic blood flow profile analyses indicate that the fetal PT, DA and pulmonary artery (PA) region exhibits prominent phasic interactions in systole and diastole (36, 39). Thus, unlike the distribution of mean PT blood flow, the initial systolic right ventricular (RV) flow impulse transmitted into the PT as a forward-running compression wave (FCW_(is)) mainly passes into major branch PAs rather than the DA, as PA characteristic impedance is lower (36). However, PA flow then falls abruptly in midsystole because of an extremely large PA flow-reducing, backward-running compression wave (BCW_(ms)), which arises from the pulmonary microvasculature in response to the PA FCW_(is) (35, 37). Furthermore, this BCW_(ms) undergoes retrograde transmission into the PT as a BCW_(ms) that produces a midsystolic fall in PT flow (35, 37), but antegrade transmission into the DA as a forward-running compression wave (FCW_(ms)) that augments DA flow (36). Finally, a portion of RV output is transiently stored in a central PT and main PA reservoir which, together with backflow from a conduit PA reservoir, discharges across the DA in diastole (36, 39).