Assessment of Passive Elastic Stiffness for Isolated Heart Muscle and the Intact Heart

A sensitive method was developed for detecting stiffness changes in the left ventricle. Stress-strain relationships (σ--ε) were obtained in the form dσ/dε = kσ + c from published studies on eight normal canine hearts, five infarcted canine hearts, and seven isolated cat papillary muscles. Utilizing pressure-volume relationships, the elastic stiffness (dσ/dε) and the stiffness constant ( k ) were also evaluated in patients with normal ventricles, inappropriate hypertrophy, and congestive cardiomyopathy. The k values were 35.0 ± 1.7 (isolated muscle, 30°C), 37.3 ± 1.9 (normal canine, 23°C), and 23.9 (infarcted). For the patient groups, k and the passive elastic stiffness were 15.8 ± 0.3 and 249 ± 22.4 g/cm 2 for 13 normal patients, 26.4 ± 1.7 and 286 ± 32.0 g/cm 2 for 7 patients with inappropriate hypertrophy, and 20.1 ± 1.2 and 1360 ± 209 g/cm 2 for 6 patients with congestive cardiomyopathy. The results indicate that (1) k is sensitive to stiffness changes due to infarction, (2) hypertrophy causes an increase in the value of k although elastic stiffness remains within normal limits, and (3) k for the intact human heart is lower than it is for isolated muscle.