End-systolic pressure-volume relations of isolated ejecting rabbit left ventricles after quick diastolic volume changes.

The aim of the study was to investigate the influence of quick diastolic volume changes on systolic performance of ejecting left ventricles. To measure left ventricular systolic performance the maximum ratio of ventricular pressure (P) and volume (V) was calculated on beat-to-beat basis when the diastolic loading conditions were varied in different ways. These end-systolic P-V (P-VES) points were obtained from both isovolumic and ejecting contractions. A deviation from the P-VES relation is thought to result from factors changing the inotropic condition of the heart. When steady state isovolumic and ejecting P-VES data were collected linear P-VES relations were found. The relations coincided when stroke volumes were not too large. When the diastolic volume was quickly changed (ie 10 to 20 ms) late in diastole, the P-VES points of the resulting contractions showed a significant deviation from the steady state relation (p less than 0.001). This deviation was dependent on the magnitude of the volume step. After quick volume infusions the heart ejected to end-systolic volume (ESV) values that were smaller than expected from the steady state P-VES relation and the end-systolic pressure (ESP) was larger. After quick volume withdrawals ESV values were larger and ESP was smaller than expected. The magnitude of the effect was not dependent on the preset basic diastolic volume if the volume changes were considered as fractions end-diastolic volumes (EDV). It is concluded that when diastolic volumes are varied just before stimulation, a significant deviation of the P-VES point from the steady state P-VES relation is found in the following contraction. This phenomenon suggests an alteration in the inotropic state of the heart.