Joseph P. Archie

Experimental Subendocardial Ischemia in Dogs with Normal Coronary Arteries

Subendocardial ischemia without anatomic coronary artery obstruction may result from a discrepancy between metabolic needs and available blood supply. We studied this in open-chest anesthetized dogs and measured pressures in aorta and left ventricle (LV), phasic left coronary arterial blood flow (CBF) by electromagnetic flowmeter, total CBF and LV subendocardial (endo) and subepicardial (epi) flow with radioactive microspheres 8−10μ, in diameter. Since LV Subendocardial flow is mainly or entirely diastolic, it should depend on coronary driving pressure and duration of diastole (i.e., the area between aortic and left ventricular diastolic pressures). This diastolic pressure time index (DPTI) was varied by opening arteriovenous fistulas to lower aortic diastolic pressure, constricting the ascending aorta to raise LV diastolic pressure and pacing to shorten diastole. Myocardial oxygen needs were estimated from the tension time index (TTI). Normal endo-epi flow ratios per gram (1:1) fell to 0.1:1 with these procedures and paralleled a fall in diastolic flow fraction (often nearly zero) and postischemic coronary reactive hyperemic responses. These changes occurred despite normal or raised mean CBF and 300−500% increase in systolic CBF. The altered flow ratios were best predicted by relating them to the ratio of DPTI (supply) to TTI (demand).

Regional Myocardial Blood Flow in Lambs with Concentric Right Ventricular Hypertrophy

Chronically hypertrophied right ventricles function normally under high systolic pressures, whereas normal right ventricles fail when they are acutely subjected to similar pressures. This phenomenon may be partly due to adaptation of the coronary circulation as well as to hypertrophy. Knowledge of the magnitude and distribution of coronary blood flow and the degree of coronary vascular reserve are important in understanding the function of hypertrophied myocardium. We studied these variables in 16 awake, 5–12-week-old, tranquilized lambs; 9 of the lambs had had their main pulmonary artery banded at 2 days of age. Pressures, cardiac output, and coronary blood flow (radioactive microsphere method) were measured at rest and during two stress states—isoproterenol and dextran infusion. Ventricular function was similar in control and banded lambs. We found significant right ventricular hypertension and both right ventricular and septal hypertrophy in the banded lambs. Total coronary blood flow per gram was slightly higher in banded lambs in all states, and right ventricular flow per gram was significantly elevated at rest and during isoproterenol infusion. Right ventricular coronary resistance per gram was significantly lower in banded lambs in all states. These changes demonstrate that hypertrophied right ventricular tissue is not ischemic at rest, since there is vascular reserve. The changes also raise the question of increased vascularity in hypertrophied myocardium. Right ventricular oxygen supply per unit oxygen demand was increased in banded lambs at rest and during isoproterenol infusion. This finding suggests that hypertrophied myocardium has inefficient oxygen utilization, low oxygen extraction, or both.

Coronary Reserve and Right Ventricular Function in Awake Newborn Lambs with Persistent Right Ventricular Hypertension

Summary: Right ventricular function curves as measured by right ventricular stroke work were normal in all control lambs, whereas three of five lambs with banded pulmonary arteries had relatively flat curves. Left ventricular function was similarly normal in the control group as compared to a near zero slope function curve in the banded group. Regional myocardial blood flow to the septum and right and left ventricles was similar in control and banded lambs. At rest right ventricular coronary vascular resistance was lower in the handed than in the control group and decreased in both groups during both isoproterenol and dextran stress states. In general, both groups had a similar ratio of right to left ventricular oxygen supply to demand ratio. These results show first that there is minimal, if any, biventricular functional reserve in lambs with persistent right ventricular hypertension, and second, that there is substantial coronary vascular reserve in both normal and banded groups.Speculation: Although both right and left ventricular function are impaired in neonatal lambs with persistent right ventricular hypertension, the etiology is unclear. We have demonstrated right ventricular coronary vascular reserve in this group; however, we did not test for further reserve in the dextran stress state, and therefore cannot be certain that coronary blood flow was not maximal in the dextran state and hence ventricular function impaired by inadequate oxygen supply.

Regional coronary blood flow in awake resting and pharmacologically stressed dogs

Abstract To determine the transmural distribution of blood flow in the major regions of the heart we used the radioactive microsphere method to measure flow in multiple layers of the septum and right and left ventricle in four dogs. Studies were done in awake dogs in the resting, and isoproterenol infusion states, and in the sedated state during methoxamine- and propranolol-induced left ventricular failure. The transmural distribution of right ventricular flow was uniform at rest redistributed to higher midwall flow during isoproterenol infusion, and redistributed to a near linear decrease in flow from the endocardium to epicardium during ventricular failure. Left ventricular transmural flow decreased slightly from the endocardium to epicardium at rest, was near uniform during isoproterenol, but in failure there was a redistribution such that subendocardial flow was approximately twice subepicardial with a near linear decrease across the myocardium. Septal flow distribution tended to follow the absolute right and left ventricular flows. These results demonstrate that the transmural distribution of myocardial blood flow in septum right and left ventricles varies within and between hearts at rest and during isoproterenol and pharmacologically induced left ventricular failure.

Evaluation of a Doppler catheter probe to measure cardiac output

Abstract Although the present study demonstrated that a nondirectional Doppler catheter probe accurately measures unidirectional pulsatile flow velocity, the in vivo evaluation reveals several significant discrepancies. When positioned in the ascending aorta of dogs, the Doppler transducer underestimated changes in blood flow velocity and the degree of underestimation varied significantly between animals. Under these conditions the Doppler-recorded signal indicated nearly continuous aortic flow and a zero-flow reference level was not present in late diastole. The extent of apparent diastolic flow was greater at higher flow rates. These findings indicate that the nondirectional Doppler catheter tip velocity transducer in its present form is not suitable for accurately measuring changes in aortic blood flow velocity.