Effect of increased pulmonary vascular resistance on right ventricular systolic performance in dogs

We tested the possibility that for a given contractile state and right ventricular systolic pressure (RVSP), rate and extent of ventricular shortening would be reduced as resistance to ejection increased. In eight anesthetized, ventilated dogs, we measured RV and pulmonary artery pressure (Ppa), blood pressure, heart rate, cardiac output (CO), and RV dP/dt before (condition 1) and after (condition 2) pulmonary vascular resistance (PVR) was increased by injection of small (80 micron) glass beads. Glass beads caused a large increase (P less than 0.001) in Ppa and in RVSP and, despite increased RV end-diastolic pressure (EDP), CO and stroke volume (SV) were reduced. A third set of measurements was obtained following a further increase in resistance (condition 3). A comparison of condition 2 with condition 3, despite constant RVSP, constant mean Ppa, and increased EDP, showed a marked fall in CO and SV (P less than 0.001) when glass bead injection increased calculated resistance from 21 (condition 2) to 34 (condition 3) mmHg X 1(-1) X min. RV contractility, as assessed by Vmax and peak dP/dt was similar in both conditions. In five additional dogs, we measured the same parameters as before plus instantaneous pulmonary artery flow in all conditions. In a comparison of conditions 2 and 3, despite constant RVSP and increased EDP, peak and total flow (P less than 0.05) were reduced as resistance to RV ejection increased. We conclude that the right ventricle shortens more slowly and to a smaller extent against the same systolic pressure when its resistive afterload increases.