MECHANICAL PROPERTIES OF HEART-MUSCLE IN PASSIVE STATE

The viscoelastic behavior of the heart muscle (papillary muscle) in the passive (unstimulated) state is studied by such methods as stress relaxation, creep, vibration and stress-strain testing. The tests are conducted on a newly developed electromechanical muscle testing device. The device consists of a linear vibrator whose spindle motion is controlled by a feedback servo controller. A linearly variable differential transformer is used to measure displacements. Force is measured by a modified pressure sensor. The displacement and force transducers are connected in series to the vibrator spindle. The displacement transducer is capable of 0. 002 mm resolution. A force of 50 mg can be resolved with the force transducer. In active contraction (stimulated muscle) experiments on papillary muscle, force resolution of about 10 mg can be achieved by recording repetitive signals on a tape recorder and then using a signal averaging device to obtain the average values from about 60 equivalent records.