Abstract: Objective To investigate the effect of therapeutic ultrasound-induced microbubble destruction on the microcirculation of rat skeletal muscle.Methods Thirty SD rats were randomized into 5 groups(n=6),namely normal saline,microbubble,ultrasound,high-energy ultrasound microbubble and low-energy ultrasound microbubble groups.Before and after the treatments,the diameter and blood flow velocity in the microvessels in the skeletal muscle were measured,and the structural changes of the injured microvessels observed by electron microscopy.Results Microbubble cavitation did not produce significant effect on the mean arterial pressure and diameter of microvessels in rat skeletal muscle(P>0.05),but the blood flow velocity was obviously lowered and blood flow volume reduced in the microvessels.The reduction of the flow velocity and blood flow volume and their subsequent recovery were associated with ultrasound energy,and in the low ultrasound energy group,the flow velocity and blood flow volume in the of venules recovered obviously after about 15 min,which,however,took approximately 1 h for the arterioles.In contrast,recovery of the flow velocity and blood flow volume in the microvessels took more than 2 h in the high ultrasound energy group.Cavitation resulted in endothelium cell rupture,widening of the endothelial interspace and entry of the red blood cells into the extravascular tissues as revealed by electron microscopy,but no rupture of the lining endothelium was observed 2 h after the treatment.Conclusions Endothelium cell rupture induced by microbubble cavitation may affect the local microcirculation,and lower ultrasound energy exposure is associated with milder endothelial injury and more rapid recovery.