Cerebral microvascular responses to air embolism-reperfusion in the cat using fluorescence videomicroscopy.

Cerebral microvascular changes due to air embolism-reperfusion in the cat were investigated. Air embolism-reperfusion was produced in the cerebral microvessels by an intra-carotid injection of air (0.2-0.3 ml). Air emboli in the cerebral arterioles were observed continuously from the air injection to reperfusion using fluorescence videomicroscopy. Arteriolar diameter was measured based on video images of arterioles filled with rhodamine-B isothiocyanate dextran, and red cell velocity was measured using a dual window technique with FITC-labeled red cells. Air bubbles ceased to move in the arterioles of 20-70 microm diameter and blood flow was almost stopped in distal arterioles. The air emboli were of cylindrical shape in the arterioles, with hemispherical end caps. The emboli progressed slowly at rates of 7-73 microm/sec and then flowed away. The air emboli induced ischemia-reperfusion with the ischemic duration of approximately 1 minute (10 sec-3 min) at the arteriolar level. Cerebral arterioles began to dilate after the formation of the air emboli and significantly dilated by approximately 50% after reperfusion. A transient increase in red cell velocity was observed after reperfusion. Arteriolar dilation and the increase in velocity led to a hyperemic response in arteriolar flow to ischemia-reperfusion.