Small coronary vessel pressure and diameter in an intact beating rabbit heart using fixed-position and free-motion techniques.

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Abstract
A technique to measure small vessel pressures and diameters in the right ventricle of a beating rabbit heart was evaluated. The method allowed free motion of the heart while these measurements were performed. This was accomplished with a strobed light source synchronized with the heart. Thus the observer sees the vessels only at the same point in the cardiac cycle. By slowly advancing the strobe pulse, visualization of an entire cardiac cycle was possible. Pressure measurements with an electromechanical micromanipulator programmed to synchronize the motion of a micropipette to the motion of a small vessel were performed. For comparison, another technique was also used which fixed a portion of the right ventricle and allowed motion to be centered around this fixed point. Pressures in veins by the use of the free-motion and fixed techniques were compared and were statistically different (5.8 .+-. 0.7 compared to 13.5 .+-. 4.7 mm Hg, P < 0.01), with the free-motion technique recording the lower values. The phasic relationship between venous diameter variation and left ventricular pressure also was determined. This relationship was variable between venous networks but quite consistent within a network. The relationship between vessel pressure and vessel diameter revealed significant declines in pressure in relatively large vessels (< 140 .mu.m). This free-motion technique can be used to provide information concerning not only the normal physiology of the coronary circulation, in terms of pressure distributions and the effects of extravascular pressure, but also the changes in vascular pressure which occur in ischemic myocardium and other tissues with inherent motion.

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