Free-wall shortening and relaxation during ejection in the canine right ventricle

Relations between shortening, velocity of shortening, and relaxation of inflow and outflow segments of the right ventricular (RV) free wall (FW) were examined during ejection in 12 open-chest dogs after pharmacologic blockade by recording RV pressures, RVFW dimensions (piezoelectric crystals), and pulmonary blood flow. At heart rates of 113 +/0 8 (SD) beats/min, investigated segments remained isometric or even lengthened before the end of ejection. Tension-length data in the outflow tract converged at the time of peak systolic tension toward a common linear relation (average slope 65 +/- 10 cmH2O/mm, average intercept 5.9 +/- 0.9 mm), but markedly deviated from this line at the end of ejection. Consistent relations between peak tension and mean velocity of shortening were only observed during the first part of ejection. In addition the rate of segmental isometric relaxation, estimated from RV pressure fall was load dependent (e.g., +60% increase in relaxation rate when RVFW end-diastolic segment length increased from 12.9 +/- 0.8 to 13.5 +/- 0.8 mm). We conclude that under normal conditions, the tension-velocity-length relations of the RVFW are comparable to those of the left ventricle during the first part of ejection only. We also conclude that RV relaxation is load dependent and that a significant part of RV ejection occurs during RVFW relaxation.