The stress-strain relationship of the diastolic cardiac muscle and left ventricular compliance in the pressure-overload canine heart.

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Abstract
The relation between left ventricular (LV) compliance, chamber geometry and LV muscle compliance in pressure-overload hearts was studied. The diastolic pressure (P)-volume (V) relationship was evaluated at different ventricular volumes of isovolumic beat in 4 pressure-overload hypertrophied (H) and 5 normal (N) hearts. In H, the ratio of the LV volume at the EDP of 15 mmHg to LV weight (LVW) was 0.34 +/- 0.08 (SD) ml/g (N: 0.63 +/- 0.07, p less than 0.01). Thus the occurrence of concentric hypertrophy due to pressure-over-load was confirmed. The P-V relation was expressed as, delta V = a - b.exp (-cP), where a, b and c were constants, delta V = V - V0, and V0 was the initial volume at EDP = 0 cmH2O. Since this equation leads to the relation: d delta V/dP = c (a - delta V), c may be regarded as a parameter which represents the LV chamber compliance. In H, c was 0.074 +/- 0.024 (SD) mmHg-1 (N: 0.109 +/- 0.008 mmHg-1, p less than 0.01). Therefore, H was found to show decrease of LV compliance. The biaxial stress (sigma)-strain (epsilon) relation was derived from the P-V relation based on large deformation theory. The sigma-epsilon relationships of myocardium in H were not apparently different from that in N. However, there was a close correlation between c and LV volume (at EDP = 15 mmHg)/LVW (r = 0.83). Thus it was found that the change in LV compliance in H resulted from the change in LV chamber geometry.

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