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Passive Stiffness of Pressure‐Induced Hypertrophied Cat Myocardium

The effect of myocardial hypertrophy on passive stiffness waa determined from the stress (σr)-strain relationship of right ventricular papillary muscles from 18 pulmonary artery-banded and 21 non-banded cats. By use of Lagrangian strain, (1–10)Io where U is initial muscle length, and instantaneous stress elastic constants β and α were calculated from the equation σ - α(eβe − 1). Elastic stiffness (dσ/d&epsis;) was determined from the formula dσ/d&epsis; - βσ + σβ. Banding produced an average increase in RV mass of 70%. β averaged 14.2 ± 0.9 (SEM) and 16.0 ± 0.8 in the non-hypertrophied and hypertrophied muscles, respectively (0.10 > P > 0.05), whereas a averaged 0.17 ± 0.01 and 0.19 ± 0.01 g/mm1, respectively (NS). However, elastic stiffness was significantly greater in hypertrophied muscles over the entire stress range. Contractile function varied widely among hypertrophied muscles but was not related to changes in stiffness. Thus, moderate degrees of pressure-induced hypertrophy are associated with a modest increase in the passive stiffness properties of the muscle, independent of changes in contractile function.