Increase in capillary perfusion following low-intensity ultrasound and microbubbles during postischemic reperfusion

Objectives. We postulated that the increase in shear stress caused by microbubbles in the presence of low-intensity ultrasound increases vasodilation in ischemia/reperfusion. Design: Prospective, randomized, and blinded experimental study. Setting. Research laboratory. Subjects: Forty hamsters were subjected to ischemia/reperfusion and observed by intravital microscopy. Interventions., Ultrasound (2.5MHz, 1.3 mechanical index, 2.0 peak pressure) was applied to the hamster cheek pouch in ischemia/reperfusion with and without microbubbles (Levovist or Sono Vue) at baseline (115 mins) and at the beginning (115 mins) of reperfusion after ischemia (30 mins). Measurements and Main Results., Arterial diameter (A2-A3, 38.5 +/- 5.3 mu m; A4,15.0 +/- 7.0 mu m), red blood cell velocity, wall shear stress, permeability, perfused capillary length, and adherent leukocytes in venules were evaluated. Lipid peroxides were also determined in the systemic blood. Ultrasound and microbubbles in reperfusion significantly increased the diameter (A2-A3 Sono Vue, 33%; Levovist, 53% vs. ischemia/reperfusion, p <.05; A4, Sono Vue, 93%; Levovist, 104% vs. ischemia/reperfuSion, p <.05), red blood cell velocity, flow, and shear stress in both A4 and A2-A3 arterioles. Shear stress was significantly higher with Levovist (A2-A3,105%; A4,185%) and Sono Vue (A2, 108%; A4, 140% vs. ischemia/reperfusion, p <.05) than ultrasound alone in arterioles. With ischemia/reperfusion, perfused capillary length was reduced significantly, whereas it increased with Levovist and Sono Vue (43%, 41% vs. ischemia/reperfusion p <.05). Lipid peroxides increased early during reperfusion and remained at increased levels throughout reperfusion. Lipid peroxides were unchanged after ultrasound alone or ultrasound with Sono Vue or Levovist during ischemia/reperfusion. With ultrasound there was a significant increase in vascular permeability vs. ischemia/reperfusion. Treatment with Sono Vue (-36%) and Levovist (-57%) decreased permeability vs. ischemia/reperfusion in reperfusion (p <.001). Ischernia/reperfusion had significantly increased leukocyte adhesion. Ultrasound alone (-39%) or with Sono Vue (-64%) and Levovist (-57%) caused smaller increases in leukocyte adhesion than ischemia/reperfusion (p <.05). Conclusions. Ultrasound and microbubbles equilibrate microvascular shear stress, thus avoiding the failure of capillary perfusion in postischemic reperfusion.