Factors affecting the end-systolic pressure-volume relationship.

The end-systolic pressure-volume relationship (ESPVR) defines the systolic limits of cardiac performance. Using an isolated cross-circulated canine heart preparation, we examined the influence of afterload impedance changes, changes in coronary artery pressure (CAP), and regional ischemia on the ESPVR. We found that afterload impedance did not change the slope of the ESPVR but that increases in resistance and characteristic impedance did shift the relation slightly to the left. There was no change in the ESPVR with changes in CAP above a certain critical value. A decrease in CAP below this value caused a progressive decline in the slope of the ESPVR. With regional ischemia the ESPVR became nonlinear, and there was a near parallel downward shift of the ESPVR in the high-volume range. This shift was directly proportional to the extent of ischemic area. We conclude that an adequate measurement of the ESPVR demands at least three pressure-volume points to check for linearity and characterization of both the slope and volume intercept.