The Effect of Ultrasound on Microvascular Hemodynamics in Skeletal Muscle" Effect on Arterioles

-A skeletal muscle model (rat cremaster muscle) has been described for the evaluation of ultrasonic bioeffects on the microscopic vasculature. One MHz pulsed ultrasound (mark-space 100tzsec:100/~sec) was administered to the tissue at 1.25, 2.5, 5.0 and 10.0Wcm -2 (temporal average) while continuously measuring lumen diameter, volume flow, and rate of vasomotion (intrinsic cyclic constriction and relaxation) in three different sizes of arterioles (100, 50, 30 #m inner diameter). No change in these parameters was noted at intensities below 5 Wcm -2. Above 5 Wcm -2 there was a 25% decrease in diameter and a 44% decrease in volume flow in the smallest arterioles observed, as well as a 29% decrease in flow in the largest arteriole feeding the tissue. The rate of vasomotion in the smallest arterioles increased 20x in the same intensity range. None of these effects or their magnitude could be attributed to simple tissue heating in the same temperature range t34-36.5°C) as obtained with ultrasound exposures.