Richard W. Eckstein

Effect of Exercise and Coronary Artery Narrowing on Coronary Collateral Circulation

The effect of chronic coronary arterial narrowing on the coronary collateral circulation has been studied in rested and exercised dogs. The data indicate that moderate and severe arterial narrowing results in extensive collateral development proportional to the degree of narrowing, further that exercise leads to even greater anastomoses. The results also show that while mild arterial narlowing fails to initiate collateral growth by itself, the addition of exercise promotes an effective collateral circulation. An attempt is made to define the gross factors in the development of collateral vessels and to correlate them with the concept that exercise may play a beneficial role in building collateral vessels in patients with coronary disease.

Coronary Interarterial Anastomoses in Young Pigs and Mongrel Dogs

Interarterial anastomoses in young pigs have been compared with those in mongrel dogs by direct flow measurements during life and by injections after death. Results indicate that pigs have minimal functional collaterals in comparison with dogs and that injection studies roughly predict the Degrees of collateral function. The data indicate that the extent of collateral development in dogs is independent of dog or heart weight and hence offers more protection against the effects of coronary occlusion in small hearts than in large hearts. Other studies indicate that coronary flow, myocardial oxygen consumption and coronary vasomotor responses in pigs are similar to those in dogs.

Acute Effects of Elevation of Coronary Sinus Pressure

The acute physiologic effects of the aorta to coronary sinus anastomosis of Beck have been studied. The evidence presented shows that arterialization of the coronary sinus results in a small retrograde flow from the sinus through capillaries into the occluded artery and that such retrograde flow supplies from 14 to 25 per cent of the normal myocardial oxygen requirement. It is suggested that this is insufficient to maintain normal myocardial contraction, but probably prevents ventricular fibrillation. However, when the sinus is arterialized in the presence of normal or reduced coronary flow electrocardiographic and coronary inflow data show that there is myocardial anoxia. This is probably due to the restriction in capillary outflow and results in an expansion of the coronary vascular bed.

Development of Interarterial Coronary Anastomoses by Chronic Anemia. Disappearance Following Correction of Anemia

The effect of chronic severe anemia upon functional interarterial coronary anastomoses has been studied in dogs. Retrograde flow measurements at controlled aortic pressures and under conditions of normal viscosity and hemoglobin concentration indicate that severe chronic anemia stimulates growth of collaterals to a significant degree. On the other hand, removal of this stimulus by spontaneous recovery from anemia induces regression of collateral function to control levels.

Chronic effects of aorta-coronary sinus anastomosis of Beck in dogs.

Studies were made on dogs at various times up to one year following the coronary sinus anastomosis of Beck to determine the chronic effects of the operation. The results indicate that the graft perfuses the capillary bed of the occluded circumflex artery for about five weeks after the operation and then loses its functional contact with the capillary bed probably because of obliterative venous changes. However, as a result of an anoxia, there is definite development of intercoronary collateral vessels during the first few weeks, which persist throughout the year even though there is no arterial occlusion. It is concluded that in dogs the Beck operation is protective against the major effects of coronary ligation because of retrograde capillary flow early and intercoronary anastomoses later.

Coronary Inflow and Outflow Responses to Coronary Artery Occlusion

Sudden complete occlusion of a major coronary artery (left circumflex or right coronary artery) was produced in anesthetized dogs. The effect on arterial inflow, venous outflow and O2 saturation of coronary venous blood from the nonischemic left ventricle was studied. The usual response to occlusion of the left circumflex artery was an increase in flow in the left anterior descending artery and in outflow from the great cardiac vein. The O2 saturation of venous blood from the nonischemic muscle decreased. These changes did not occur following occlusion of the right coronary artery. It was not possible to measure tissue pressure accurately to relate this measurement to flow changes. Observations on coronary sinus flow and O2 saturation were also made following occlusion of the left circumflex artery and retrograde flow collection from it. These observations plus the changes in anterior descending inflow and great cardiac vein outflow with coronary occlusion suggest that these changes are more likely due to alterations in O2 consumption of the nonischemic muscle rather than to changes in flow through interarterial or non-interarterial collateral vessels.

Correlation of renal blood flow determined by the single injection of Hippuran-I131 with direct measurements of flow☆

Abstract 1. 1. In 21 determinations in 11 dogs, the clearance values of I131-labeled Hippuran calculated from the time-concentration curve of arterial blood after a single injection were compared with flows measured simultaneously by collecting the total renal venous drainage from one kidney. 2. 2. The average agreement was 7.6 per cent in a range of flows from 94 to 340 ml. per minute and under conditions of altered blood and urine flow rates. 3. 3. The accuracy and simplicity of the method indicates its clinical usefulness in the area of renal blood flow studies. 4. 4. Classic clearance techniques utilizing Hippuran-I131 also gave excellent agreement with simultaneously measured flow, although renal A-V differences were large.

Autoregulation of Coronary Blood Flow: Effect of Interarterial Pressure Gradients

In the normal heart, transient and adjusted steady state coronary flow rates in response to changes in perfusion pressure are not significantly affected by collateral flow into and from heart muscle surrounding the area perfused by a test artery. An active autoregulatory adjustment tends to counteract flow changes after perfusion pressure is changed. This adjustment is sometimes sufficient to increase vascular resistance above control values. Usually, however, coronary resistance decreases at higher perfusion pressures even though autoregulation is present. The experiments provide no evidence for reflex control of coronary resistance in response to increases in aortic pressure; the initial flow changes can be accounted for by the corresponding increase in perfusion pressure. It is necessary to examine the entire coronary flow pattern after a sudden change in perfusion pressure in order to formulate concepts which include all the important determinants of coronary blood flow.

Thebesian Drainage in the Left Heart of the Dog

Direct left heart drainage from the common left coronary artery has been demonstrated in the normally beating dog heart by an isotope dilution technique. The major portion of this drainage has been shown to be through the left circumflex branch of the common left coronary artery. The left anterior atrial artery, a branch of the left circumflex, has in turn been shown to be the major pathway of drainage from the latter. Left heart drainage could not be demonstrated from isotope injections into the left anterior descendens artery, and in only one preparation could such drainage be documented from the septal branch of the common left artery. The magnitude of left heart Thebesian drainage has been estimated by analysis of time-concentration curves recorded from the aorta. An average of 2% of total common left coronary artery inflow drains directly into the left heart. Although the major drainage is probably into the left atrium, left ventricular drainage has not been excluded.

Thebesian Drainage of the Septal Artery

Direct right ventricular drainage of I131 serum albumin injected into the septal artery of the normally beating dog heart has been demonstrated. By the application of standard dilution equations to the time-concentration curves recorded in the pulmonary artery, estimates of the magnitude of this Thebesian drainage have been made. Approximately 80% of septal artery outflow has been estimated to drain directly into the right ventricle; this amount comprises about 12.8% of total common left coronary flow and, in part, explains the discrepancy found between common left coronary inflow and coronary sinus outflow. The implications of Thebesian drainage of a branch of the common left coronary artery relative to the use of coronary sinus sampling for left ventricular metabolic studies have been discussed.