Analysis of diastolic pressure-volume relation of the canine left ventricle: half-inflation pressure as an index of left ventricular compliance.

A sensitive index was proposed for the determination of left ventricular compliance. In the isolated potassium-arrested canine left ventricle, the pressure-volume (P-V) relationship was expressed as deltaV=a-be-cP throughout the range of filling pressure from 0 to 40 cmH2O, where deltaV and P were the actual volume change and intraventricular pressure, and a, b and c were constants. Then, half-inflation pressure (h) was calculated from h=[ln(2b/a)]/c. Left ventricular weight (LVW), intraventricular volume (LVV), ventricular external radius (ro) and internal radius (ri) were obtained from the measurements on the left ventricle, fixed at a filling pressure of 10 cmH2O. Then, LVVp=h, ro and ri at h were calculated. In the normal canine hearts, h was well correlated to LVW/LVVp=h and [(ro-ri)/ri]p=h. On the other hand, h/LVW/LVVp=h and h/[(ro-ri)/ri]p=h were constant and independent of LVW within a range of 40 to 150 g. These ratios rose markedly in the state of rigor mortis. From these results, it was concluded that h/LVW/LVVp=h and h/[(ro-ri)/ri]p=h depended on the left ventricular wall stiffness. And h was influenced by changes in LVW/LVVp=h and [(ro-ri)/ri]p=h in the absence of changes in intrinsic muscle stiffness.