Local auxotonic systolic force and work in canine right ventricular free wall

Regional auxotonic force (F) and segment length (SL) were measured in the right ventricular (RV) free wall of 10 anesthetized dogs. F was obtained with a Feigl force gauge and SL with ultrasonic crystals positioned in the inflow or outflow region and in the longitudinal or transverse direction. Although the time courses of right ventricular pressure and force were almost identical, the timing of right ventricular ejection had little relationship to specific parts of the force-segment-length loop. Thus local F vs. SL loops were of irregular form signifying local lengthening or shortening in isovolumic periods. Local work, i.e., F vs. SL loop area, increased linearly with cardiac output (CO), which was varied by volume expansion or reduction. A predominant contribution to total RV work from any particular region and direction was not observed. A "local contribution factor" [eta, defined as (local work/local area)/(total RV work/free wall area)] fell with increased CO from 2.1 +/- 0.5 at 1.1 l/min to 0.7 +/- 0.2 at 4.8 l/min. This observation suggests that transformation of local into total work became more efficient at higher CO or that structures other than the free wall became increasingly important for RV pump function at higher output levels.