Influence of the rate of coronary plasma flow on the extraction of Rb86 from coronary blood.

To determine whether myoeardial uptake of Rb 80 can be used as a useful index of coronary plasma flow, the extraction of Rb S(i from arterial plasma during one passage through the myocardium of dogs was measured at varying rates of flow. At rates of flow which are encountered in man, changes in the rates of flow and uptake of isotope by the myocardium paralleled each other closely. Rb 86 uptake is a useful index of coronary blood flow in dogs. P REVIOUS studies have suggested that the rate of coronary blood flow can be estimated in man without cardiac eatheteriza-tion by the use of a precordial monitor to measure the rate at which the myocardium takes up Rb 80 from the blood during an infusion of this isotope. The rate of uptake of Rb 86 by the heart was found to be decreased by intravenous administration of pitressin in dogs and increased by levarterenol (1-norepi-nephrine). 1 These changes are in the same direction as those which these drugs produce on coronary blood flow. Differences in the rate of myoeardial Rb 8(i uptake in dogs were measured within 20 per cent by placing a scintillation counter over the precordium of the intact animal j reasonable values for coronary blood flow in man have been obtained with similar methods. Since this previous evidence is indirect, the present study was undertaken to determine directly the relationship of coronary blood flow and myoear-dial uptake of Rb. METHODS Dogs weighing 8.3 to 16.7 Kg1, were anesthetized with 30 mg./Kg. sodium pentobarbital intravenously , and a right thoraeotomy incision was performed , with artificial respiration. After adrnin-istration of 100 mg. heparin* a flexible cannula of 6.5 mm. outside diameter and 3 mm. inside diameter was passed through the right jugular vein and its tip guided approximately 2 cm. into the coronary sinus. Coronary venous blood flowed through the cannula into the left jugular vein, except when the rate of outflow was measured by timed collection of 10 to 50 ml. in a graduated cylinder. To provide a stable concentration of Rb 86 in arterial plasma, a standard intravenous infusion of Rb 86 in 0.15 M sodium chloride solution was administered at a decreasing rate for 15 to 73 min. 1 At intervals the rate of outflow of blood from the coronary sinus was measured, and specimens of arterial and coronary sinus blood were collected. The …