Characteristics of coronary blood flow and transmural distribution in miniature pigs

Abstract

The relationship between phasic systolic and diastolic coronary blood flow and its transmural distribution has been studied in 29 Yucatan miniature pigs at rest and during heavy exercise, with and without adenosine infusion (1.5 mg . kg-1 . min-1) and with and without a subtotal coronary artery occlusion. Altered factors that affected coronary flow included vascular resistance, perfusion pressure, myocardial oxygen demand, and extra-vascular pressure. The data indicate that, at rest, endomural perfusion is significantly dependent on diastolic blood flow. However, the ability of the myocardial vessels to autoregulate during systole as well as during diastole was clearly shown with the use of adenosine infusion. This ability to regulate flow intrinsically appeared to transcend the endocardial dependency on diastolic perfusion under certain stressful conditions, e.g., during heavy exercise, when the diastolic duration was significantly reduced. Systolic transmural perfusion may then become a significant factor in meeting the blood flow demands of the myocardium. However, due to gradients in vascular resistance, perfusion pressure, and oxygen demand, the coronary reserve of the epicardium appears to be greater than that of the endocardium under any condition.

Autonomic Control of Vasomotion in the Porcine Coronary Circulation During Treadmill Exercise

“…39 In addition, nearly identical treadmill exercise-induced increases in blood flow have been observed with simultaneous flow probe (to 321% of resting values) and microsphere (to 315% of resting values) measurements in swine. 40 In our laboratory, we previously observed that the vascular resistance responses to dopamine receptor stimulation were similar when measured with a Doppler coronary flow probe or radioactive microspheres. 33 Finally, we observed in 5 swine that coronary artery blood flow increased from 40Ϯ3 mL/min at rest to 71Ϯ6 mL/min (176Ϯ8% of resting values) during exercise at 3 to 4 km/h, while simultaneous microsphere measurements demonstrated an increase in myocardial blood flow from 1.52Ϯ0.07 mL ⅐ min Ϫ1 ⅐ g Ϫ1 at rest to 2.82Ϯ0.32 mL ⅐ min Ϫ1 ⅐ g Ϫ1 (184Ϯ18% of resting values) (authors' unpublished data, 1998).…”

Regulation of Coronary Blood Flow

“…The pressure at which endocardial flow begins to decrease is even higher during exercise, which augments MVO 2 , heart rate, and myocardial tissue pressure (47). Despite this recognition, limitations in endocardial flow (i.e., low ENDO/EPI ratios) are not evident in normal hearts under physiologic conditions across a wide range of heart rates and MVO 2 in either the left (53, 122, 606, 642, 752, 825) or right ventricle (39, 48, 606, 739, 1024). Therefore, under normal physiologic conditions the coronary circulation is able to integrate compressive forces and microvascular resistances in a manner that allows for adequate delivery of substrates to all myocardial layers.…”

Mental stress-induced myocardial ischaemia

“…However, transmural microvascular resistance is heterogeneous, with higher minimum resistance (less relaxation) in the subendocardium than the subepicardium. The subendocardium is further disadvantaged by the direction of blood flow, which is from the epicardium to endocardium 50. Furthermore, during exercise the contractile forces within the heart exert pressure on the microvasculature.…”