LOAD-INSENSITIVE MEASUREMENTS FROM AN ISOLATED-PERFUSED BIVENTRICULARWORKING RAT-HEART

To determine whether a rat heart model can provide load-insensitive me asurements of cardiac function, a recently developed biventricular per fused preparation was tested. Using 29 Sprague-Dawley rat hearts perfu sed with modified Krebs-Henseleit buffer, ventricles functioned simult aneously with adjustable independent preload (venous reservoirs) and a fterload (compliance chambers). Ultrasonic crystal pairs provided cont inuous left (LV) and right ventricular (RV) short-axis dimensions. LV and RV pressure-length loops (loop area = work) were generated from pa ired intraventricular pressure and short-axis dimensions. Load-insensi tive measurements were obtained from the slopes (elastance) and x-inte rcepts (L-0) of regression lines generated from the end-systolic coord inates of these pressure-length loops over ranges of RV and LV preload s. Measurements were made after 15 min of stable function and after 20 min of warm (37 degrees C) ischemia. During perturbations in LV after load, there were linear changes in dP/dt, but loop work remained relat ively unchanged. RV dP/dt and work varied little with physiologic rang es of afterload. Increased RV afterload had little effect on LV functi on. Ischemia affected LV function more than RV function using these me asurements. Elastance, however, increased after ischemia with diastoli c 'creep' (increased L-0) for both ventricles. Load-insensitive and ot her sophisticated hemodynamic measurements are possible with this new preparation.