Patterns of Human Myocardial Oxygen Extraction During Rest and Exercise*

Abstract

Myocardial oxygen requirements are met by coronary blood flow and oxygen extraction from the arterial blood. The myocardial oxygen extraction coefficient (1) expresses the fraction of available oxygen in arterial blood removed by the myocardium: coronary A-Vo2/Ao2 X 100 = myocardial extraction percentage. Myocardial oxygen extraction during rest is approximately 70 to 75 per cent, exceeding that of all other organs (1, 2). This degree of extraction is equalled only by exercising skeletal muscle, in which increased oxygen requirements are met both by additional blood flow and by increased oxygen extraction. Earlier workers have noted a relative constancy of myocardial oxygen extraction under the widely varying conditions of rest, anemia, hypoxia, and increased left ventricular work, suggesting that coronary blood flow is altered commensurate with myocardial oxygen requirements (1, 3, 4). Case, Berglund and Sarnoff demonstrated that when coronary blood flow reserve was limited by experimental coronary constriction, myocardial extraction increased due to the combined stress of anemia and increased left ventricular work (3).The effect of exercise on coronary hemodynamics has received little attention. Lombardo and co-workers reported observations in 13 human subjects with various forms of heart disease (5). As part of another study, Regan and associates reported on the effects of exercise on the coronary circulation in nine normal subjects (6). This report will present myocardial oxygen extraction data from 108 patients at rest, and from 79 subjects during mild exercise. The physiological significance of myocardial oxygen extrac-* This work was supported by grants from the U. S. (7), and routine cardiac catheterization findings. The exercise electrocardiograms were interpreted according to the criteria of Mattingly, Fancher, Bauer and Robb (8).Four clinical states were selected for correlation with myocardial oxygen extraction patterns. The patients were grouped clinically according to the following criteria.Control. Patients having no symptoms or electrocardiographic, radiologic or physical findings suggesting coronary artery disease or congestive heart failure served as controls. Pulmonary capillary pressures were normal in all subjects except those with mild mitral stenosis. The range of diagnoses included functional systolic murmurs, patent ductus arteriosus, ventricular and atrial septal defects, mild aortic insufficiency, noncritical mitral stenosis (valve area greater than 1.5 cm'), tetralogy of Fallot, and mild coarctation of the aorta. Two had atypical chest pain without evidence to suggest coronary insufficiency.Coronary insufficiency. Patients judged to have coronary insufficiency on the basis of classical angina pectoris, documented myocardial infarction, and positive Master's test were placed in this group. In several cases the coronary vessels were assessed at operation, by coronary arteriography (9), or at necropsy. Several patients had coexisting congestive heart failure.Congestive heart failure. Th...

Hemodynamics, coronary blood flow, and myocardial metabolism in coronary shock; response to l-norepinephrine and isoproterenol

“…Previous studies have shown that oxygen extraction ratios vary widely even in severe coronary artery disease (64,65) and appear to be a poor indicator of myocardial hypoxia (65). Presumably the scattered distribution of myocardial lesions, normal areas masking diseased areas, accounts for this insensitivity.…”

Hemoglobin Affinity for Oxygen in the Anginal Syndrome with Normal Coronary Arteriograms

“…This would, at least in theory, be manifested by appropriate changes in coronary venous oxygen content, the fraction of oxygen extracted and resting coronary blood flow (since arterial saturation tends to remain constant at normal levels of Po2). Such findings have not been described in either patients with the anginal syndrome and normal coronary arteriograms, nor in those with documented coronary artey disease (4,8,9,31).…”

Myocardial Lactate and Pyruvate Metabolism*

“…Left ventricular failure was defined as an end-diastolic pressure greater than 10 mm Hg at rest, or a pulmonary wedge pressure greater than 12 mm Hg at rest or 17 on exercise. Coronary insufficiency (including angina pectoris alone) was defined as described elsewhere (17). No patients had diabetes mellitus, elevated fasting blood sugar,' or severe nutritional deprivation.…”

“…In most cases no premedication was necessary; in a few, 1 ml of a mixture of meperidine (25 mg per ml), Phenergan (6.25 mg per ml), and chlorpromazine (6.25 mg per ml) was given intramuscularly. Special care was taken to place the catheter deep in the proximal coronary sinus where homogeneity of sampling has been observed (17), and maximal representation of left ventricular events may be expected (20). Measurements of blood oxygen content were made immediately prior to and at least 3 minutes after onset of supine leg-raising; exercise was sufficient to raise mean myocardial oxygen consumption by 42 per cent (11.2 to 15.9 ml per 100 g per minute) and total body oxygen consumption by 112 per cent (145 to 307 ml per minute per m2).…”