Optimal and actual end systolic pressure-volume relations in dogs and rabbits. Including new method of Emax determination.

Under the assumption that a ventricle and its arterial load are normally matched according to work optimization, a relation between left ventricular (LV) mechanical performance as described by the slope (Emax) of the end systolic pressure-volume relationship (ESPVR), mean systolic pressure during ejection (mSLVP), and stroke volume (SV), is proposed: optimum Emax = E' = mSLVP/SV. Slope (Emax) was obtained, in 6 dogs and 9 rabbits, by establishing relations among ejected volume and LV diameter squared (D2) in control beats, and among pressure and D2 at end systole (ES) in series of beats of varying load, accomplished either by acute aortic constriction (AOC) or inferior caval occlusion (IVCO). Slope in dogs was also obtained by direct measurements of ventricular volume by a conductance catheter and the results were compared with the above method. A dimensionless index, alpha = Emax/E', (optimal value = 1.0) was calculated to indicate how well the ventricle and arterial system were matched. In dogs, E' = 10.9 +/- 2.1 mmHg ml-1, Emax = 8.1 +/- 2.6 (AOC) and 7.1 +/- 2.5 (IVCO), hence alpha = 0.79 +/- 0.23 (AOC) and 0.68 +/- 0.15 (IVCO). In rabbits, E' = 54.1 +/- 20.0 mmHg ml-1, Emax = 64.8 +/- 15.9 (mmHg ml-1), hence alpha = 1.23 +/- 0.33. Alpha = 1.0 fell outside the 95% confidence interval only in experiments of dogs subjected to IVCO.