Development and use of a new high-frequency, low mechanical impedance strain gauge

Abstract

A low mechanical impedance strain gauge that imposed insignificant preload to the myocardial fibers was tested in vitro and in vivo. The dynamic response of the gauge to an abrupt change in length (step response) and to sinusoidal perturbation was determined. The electrical output reached 95% of maximum steady-state response within 3-5 ms after a step displacement. Frequency analysis indicated a flat response up to 80 oscillations/s. In vivo testing of the gauges was performed on intact, working swine hearts during control and ischemic flow in a regionally perfused preparation. During control perfusion, the gauges demonstrated epicardial shortening in systole and early-to-mid diastole. Relaxation was confined to late diastole. With ischemic perfusion there was a progressive loss of systolic shortening, but minimal disruption in global hemodynamics. Correlative measurements were made with sonomicrometer positioned in subepicardial myocardium. Patterns of motion shortening and changes in strain were similar between the 2 types of gauges.