752-1 Microcirculatory Flow Dynamics During Peripheral Intravenous Injection of EchogenTM: Microscopic Visualization of Mesenteric Microcirculatory Flow with Simultaneous Transthoracic Echo Imaging in Cats

Abstract

Echogen TM , a phase shift, fluorocarbon gas echo contrast agent, has been shown capable of producing left ventricular and robust myocardial opacification, persisting up to 35 to 40 mm after peripheral venous injection. We investigated the microcirculatory flow dynamics of this agent in the cat mesenteric vascular bed using microscopic visualization of capillary flows. Four cats (weight 2 to 5.2 kg, mean = 3.2 kg) were anesthetized and ventilated. Systemic arterial blood pressure was monitored by cannulation of the carotid artery. Microscopic examination (x 400) with an instrument calibrated for scale was performed by placing a loop of small intestine on awarm water bath stage and transilluminating the mesentery with a xenon light source while videotape recording the images for off-line analysis. Transthoracic echocardiography was performed simultaneously using a TOSHIBA 140A system with a 7 MHz transducer. Doses of 0.4, 06, 0.8 ml/kg (a total of 15 injections) of Echogen were administered intravenously. For all the injections, Visually apparent left ventricular and intense myocardial opacification was achieved lasting up to 20 minutes. A transient drop in arterial blood pressure (25 ± 13.2 mmHg) was observed with the high dose 10.8 ml/kg). which returned to baseline within 5 mins. Capillary flow velocities of the red blood cells before and after Echogen injection were 4.3 ± 1.7 mm/sec dropping to 2.3 ± 0.9 mm/sec, the drop occurred 5 to 20 seconds following injections and recovery was within 40–70 seconds. Transient slowing and periodicity of flow was noted in the venule side of the capillaries. but arteriolar capillary flow changed little during brisk transit of the observed bubbles. There was no significant difference in flow velocity changes associated with different doses (p > 0.05). Also, margination and endothelial adhesion of bubbles observed in larger arteriolar feeding vessels without slowing of central RBC flow suggests a mechanism for the long persistence of echo contrast bubbles in the tissue without vascular blockage or evidence of myocardial tissue damage.