Abstract
This study investigated heating as the possible mechanism for the reduction in aortic pressure observed as a result of exposure of frog hearts in vivo to a single, high intensity pulse of ultrasound. The threshold for producing reduced aortic pressure with 5 ms pulses of ultrasound was found to be approximately 5–10 MPa peak positive pressure ( I SPPA ∼ 350–1000 W/cm 2) at both 1.2 MHz and 3.7 MHz. Theoretical estimates and experimental measurements of heating, though, indicate that heating rates at threshold exposures for these two frequencies differ by as much as a factor of 10. As a result, heat alone does not appear to be the primary mechanism responsible for the observed effects on the heart.
Published Version
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