Effect of brief ultrasound exposure on post-tetanic potentiation in cardiac muscle

The effect of a short 4 second ultrasound application (1.0 W/cm2 sATA at 963 KHz) on the post-tetanic-potentiation of isolated isometrically contracting rat papillary muscle has been evaluated. Post tetanic-potentiation was produced in hypoxic isolated papillary muscle by interrupting the control stimulation rate of 6/minute with 10 stimulating pulses at 0.2 sec intervals for one cycle. Ultrasound application varied from one second prior to the stimulating train to a period covering the entire train. Ultrasound application just preceding and impinging upon the pulse train, enhanced post-tetanic-potentiation contractions. However, delay in ultrasound application and covering the stimulating pulse train, reduced post-tetanic-potentiation contractions. These data suggest that a window exists for the effects of ultrasound on contracting myocardium which may be used to probe critical events in the cardiac cycle.