Reducing lung liquid volume increases biventricular outputs and systemic arterial blood flows despite decreased cardiac filling pressures in fetal lambs.

As prior work has shown that reducing lung liquid volume 1) increases pulmonary arterial (PA) blood flow, 2) augments right ventricular (RV) output/power, and 3) decreases left atrial (LA) pressure, we tested the hypothesis that this perturbation has global cardiovascular effects. Ten anesthetized, open-chest fetal lambs (gestation 128±2d, term=147d) were acutely instrumented with 1) LA and right atrial (RA) catheters, 2) aortic and pulmonary trunk catheters, 3) brachiocephalic trunk (BCT), aortic isthmus (AI), ductal and left PA flow probes to obtain left ventricular (LV) and RV outputs and hydraulic power, and flow in the descending thoracic aorta (DTA), and 4) an endotracheal tube to remove lung liquid. Reducing lung liquid volume by 17±7 ml/kg 1) decreased LA and RA pressures similarly (1.5-1.6 mmHg, P<0.001), 2) augmented LV and RV outputs (21-24%, P<0.001) and total power (27-28%, P<0.005), 3) increased systolic flows in the BCT (18%, P<0.001), AI (29%, P<0.005), ductus (12%, P<0.005) and DTA (16%, P<0.001), 4) increased mean PA flow via a higher systolic inflow (37%, P<0.001) and lower diastolic backflow (-16%, P<0.05), and 5) did not change systemic vascular conductance or arterial compliance but increased both pulmonary vascular conductance and arterial compliance (1.8-fold, P<0.001). These data suggest that hemodynamic effects of reducing lung liquid volume are not confined to the lungs but extend to all cardiac chambers via rises in LV and RV outputs and power despite falls in cardiac filling pressures, as well as the systemic circulation via downstream increases in systolic flows of major central arteries.