Control of Coronary Blood Flow by an Autoregulatory Mechanism

Abstract

250heart. The present study examines mechanisms which are brought into play when, during a period of constant cardiac function, coronary flow rates are suddenly increased or decreased by the imposition of sudden changes in coronary perfusion pressure. A pressure-independent autoregulatory mechanism was observed. The transient characteristics of this mechanism, the pressure range over which it operates, the effects of alterations in cardiac function, and the instantaneous pressure-flow relationships at various levels of coronary vascular tone were examined and are the subject of the present report. These studies have been reported previously in preliminary form. 13 ' 14 MethodsStudies were conducted on 22 mongrel dogs weighing between 14 kg and 34 kg. After induction of anesthesia (see below), the animals were intubated and respired with intermittent positive pressure from a Harvard respiratory pump. A left thoracotomy was performed, the heart was suspended in a pericardial cradle, and the circumflex coronary artery was dissected free close to its origin. Heparin (10 mg/kg) was administered and the dose repeated every half hour during the experiment. The vessels were then cannulated and a complete exchange transfusion with mixed donor blood was performed.The extracorporeal circuit used to permit variation of coronary perfusion pressure independent of aortic pressure is shown in figure 1. The coronary artery was perfused either from the femoral artery or, by turning a stopcock, from a reservoir from which nonphasic perfusions were carried out for periods up to thirty minutes. No difference in the rate of coronary blood flow was noted when sequential perfusions from the femoral artery and from the bottle were performed at identical mean pressures. The reservoir was attached to a compressed air system; a 20-liter buffer bottle prevented decay of pressure during perfusion.The reservoir was filled between runs from one femoral artery while mixed donor venous blood was simultaneously transfused at a matched rate.

Clinical Quantification of Myocardial Blood Flow Using PET: Joint Position Paper of the SNMMI Cardiovascular Council and the ASNC

“…[76][77][78] Consequently, resting MBF is commonly higher in patients with higher arterial blood pressure or heart rate. 67,70,79,80 Age-related increases in resting MBF can be explained by rate-pressure product correction of increased systolic blood pressures. 67,81 Most of the reported PET-determined resting MBF values have been higher in women than in men.…”

Quantitative relationship between coronary vasodilator reserve assessed by 82Rb PET imaging and coronary artery stenosis severity

“…Multiple factors influence the shape and associated scatter of this relationship, including left ventricular haemodynamics, myocardial contractility, age-related changes in myocardial blood flow, collateral flow not visible on conventional angiography, and possibly others (20)(21)(22)(23)(24)(25). There are also inherent discrepancies between anatomical descriptors and functional behaviour of the human circulation.…”

Effects of perfusion pressure on energy and work of isolated rat hearts.

“…'-7 Vascular resistance depends on neurohormonal factors, myocardial contraction, myocardial metabolites, partial gas pressure, and alterations in the vascular endothelium. '- 10 Both in situ 7 and in the isolated perfused heart 8 there is a range of coronary perfusion pressures from about 100 to 180 cm H 2 O 7 -8 where coronary perfusion pressure does not influence coronary flow; however, with values lower than 100 cm H 2 O, alterations in perfusion pressure result in a direct correlation between coronary flow and coronary perfusion pressure. With coronary perfusion pressures below 100 cm H 2 O, coronary vessels become maximally dilated and flow becomes pressure dependent 7 ; that is, autoregulation of coronary blood flow is lost 7 and control resides mainly in the endothelium of the vascular bed.…”

“…'- 10 Both in situ 7 and in the isolated perfused heart 8 there is a range of coronary perfusion pressures from about 100 to 180 cm H 2 O 7 -8 where coronary perfusion pressure does not influence coronary flow; however, with values lower than 100 cm H 2 O, alterations in perfusion pressure result in a direct correlation between coronary flow and coronary perfusion pressure. With coronary perfusion pressures below 100 cm H 2 O, coronary vessels become maximally dilated and flow becomes pressure dependent 7 ; that is, autoregulation of coronary blood flow is lost 7 and control resides mainly in the endothelium of the vascular bed. An increase in coronary perfusion pressure results in an increase in water and cation content of endothelial cells, 2 which leads to stretch of endothelial cells and an elevation in coronary flow.…”