Coronary and transmural myocardial blood flow responses in awake domestic pigs

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Abstract
The coronary vascular and regional myocardial blood flow responses to transient ischemia were characterized in awake, chronically instrumented domestic pigs. Resting data were: heart rate 108 .+-. 4 beats/min; mean left anterior coronary flow, 43.6 .+-. 3.5 ml/min; and mean transmural blood flow, 1.28 .+-. 0.12 ml/min .cntdot. g. Subendocardial (endo) flow exceeded subepicardial (epi) flow; endo/epi = 1.38 .+-. 0.07. During brief complete coronary occlusion, mean transmural flow was 0.01 .+-. 0.01 ml/min .cntdot. g in the most ischemic region. In all ischemic regions, a uniform reduction in transmural flow occurred; endo/epi .apprxeq. 1.0. During partial coronary occlusion, transmural maldistribution of flow occurred; endo/epi = 0.38 .+-. 0.10. During reactive hyperemia following a 45-s occlusion, mean transmural flow = 4.06 .+-. 0.24 ml/min .cntdot. g; endo/epi = 1.07 .+-. 0.09. The percentage flow debt repayment after 5-45 s transient coronary occlusions ranged from 610 .+-. 182% to 282 .+-. 46%. The minimal flow debt repayment necessary to restore coronary vascular tone ranged from 120-200%. Canine and porcine coronary circulations have marked similarities in the following respects: flow/g of myocardium and transmural distribution of flow during rest; the reactive hyperemic response to transient ischemia and transmural distribution of blood flow during partial coronary occlusion. In contrast to canine circulation, the innate porcine coronary collateral circulation functions minimally and shows no preferential perfusion of the subepicardial layers.