Load-insensitive measurements from an isolated perfused biventricular working rat heart

To determine whether a rat heart model can provide load-insensitive measurements of cardiac function, a recently developed biventricular perfused preparation was tested. Using 29 Sprague-Dawley rat hearts perfused with modified Krebs-Henseleit buffer, ventricles functioned simultaneously with adjustable independent preload (venous reservoirs) and afterload (compliance chambers). Ultrasonic crystal pairs provided continuous left (LV) and right ventricular (RV) short-axis dimensions. LV and RV pressure-length loops (loop area = work) were generated from paired intraventricular pressure and short-axis dimensions. Load-insensitive measurements were obtained from the slopes (elastance) and x-intercepts (L₀) of regression lines generated from the end-systolic coordinates of these pressure-length loops over ranges of RV and LV preloads. Measurements were made after 15 min of stable function and after 20 min of warm (37°C) ischemia. During perturbations in LV afterload, there were linear changes in dP/dt, but loop work remained relatively unchanged. RV dP/dt and work varied little with physiologic ranges of afterload. Increased RV afterload had little effect on LV function. Ischemia affected LV function more than RV function using these measurements. Elastance, however, increased after ischemia with diastolic creep (increased L₀) for both ventricles. Load-insensitive and other sophisticated hemodynamic measurements are possible with this new preparation.