Measurement of the acoustic properties of a nerve-muscle preparation as a function of physiologic state.

Nerve-muscle preparations of Sprague Dawley rats were exposed to low dosage ultrasound. The objectives were to measure the velocity of propagation and attenuation of ultrasonic energy in both the relaxed and contracted states. A tension-measuring system and associated ultrasonic instrumentation were designed to measure the tension developed in stimulated muscle and its corresponding acoustic parameters, ie the attenuation coefficient, alpha (db cm-1) and the velocity of propagation, c (ms-1). Each test was performed at ultrasonic frequencies 3.1, 5.35, and 7.68 MHz and with the preparation maintained at 23 +/- 0.5 degrees C. Attenuation of ultrasonic energy was observed to increase by 10 +/- 0.5% in the active state from its value in the relaxed state. The relation between the attenuation and the acoustic frequency was found to be approximately linear over the frequency range tested. The velocity of propagation in the active state did not change appreciably from its value in the relaxed state and was observed to be independent of the acoustic frequency in the range used.