EARLY EFFECTS OF DIGITALIS ON CENTRAL HEMODYNAMICS IN NORMAL SUBJECTS

Clinical implications of differences in pharmacodynamic action of polar and nonpolar cardiac glycosides

The principal effects of cardiac glycosides probably can be classified as parasympathomimetic or sympathomimetic. Data from animals and from man suggest that polar cardiac glycosides, such as ouabain and digoxin, possess greater parasympathomimetic (vagal) cardiac effect for a given amount of sympathomimetic (positive inotropic) cardiac effect than do less polar cardiac glycosides, such as digitoxin. Polar glycosides therefore offer some advantage in uncomplicated paroxysmal atrial tachycardia and in uncomplicated atrial flutter and atrial fibrillation when the principal desired effect is reduction in the number of atrial impulses reaching the ventricles or conversion to normal sinus rhythm. Non-polar glycosides offer an advantage when positive inotropicity is desired but when there is some degree of atrioventricular block or when inappropriate sinus bradycardia or anorexia, nausea, or vomiting are present. Ecotopic impulse formation when due to cardiac glycosides is a toxic manifestation of excessive sympathomimetic effect, but is aggravated by vagal-induced sinus bradycardia, so that both parasympathomimetic and sympathomimetic capability of cardiac glycosides must be considered when dealing with myocardial electrical instability.

Pathophysiologic studies of the pulmonary and coronary circulations in man

Studies of the pulmonary circulation in normal man, performed with external radiation detectors, have shown that pulmonary blood volume is about 10% of total blood volume. Pulmonary blood volume was unchanged in patients with acute or chronic left atrial hypertension and in normal persons during expansion of total blood volume in spite of marked increases in pulmonary vascular pressures. However, pulmonary blood volume was greatly increased in patients with polycythemia rubra vera and a large total blood volume and in patients with a left to right shunt but normal pulmonary intravascular pressure. Studies of regional myocardial perfusion with injection of xenon-133 solution into the left coronary artery revealed localized areas of ischemia distal to stenotic lesions even when the patient was at rest. During angina produced by pacing, more severe ischemia occurred, thus suggesting that functional factors reduce local perfusion below resting levels. In patients with "variant" angina, intravenous injection of thallium-201 chloride during spontaneous attacks has revealed large cold areas in myocardial scintigrams not present under control conditions, thus suggesting severe transmural reduction of perfusion in heart muscle corresponding to S-T segment elevation in the electrocardiogram.

Mixing in the right ventricle and pulmonary artery in man: evaluation of ventricular volume measurements from indicator washout curves

To assess the mixing characteristics of the right ventricle and pulmonary artery, radioiodinated (131)I serum albumin and indocyanine green dye were injected simultaneously in 16 subjects. One indicator was injected into the atrium and the other into the ventricle, or both were injected at different sites in the ventricle. Washout curves were obtained by rapid catheter sampling alternately just above or just below the pulmonic valve. The washout of radioisotope was also recorded with a precordial scintillation detection probe. Indicator washout from the ventricular inflow tract was rapid, while washout from the region of the ventricular apex was quite slow. Protosystolic dips in indicator concentration, noted in curves drawn below the pulmonic valve, suggest that the ventricle emptied sequentially. Flow values computed from curves sampled below the valve, when compared with reference values, suggest that a significant volume of atrial blood passed through the ventricle without mixing, or mixing to only a small extent, with the residual volume of the chamber. Peak concentration of indicator was higher below the pulmonic valve than above. This finding, plus the close agreement between flow values computed from curves sampled above the valve and the reference values, indicates that further mixing occurred above the valve. Ventricular volumes computed from washout downslopes are systematically falsely high. This overestimate appeared to be larger in normal subjects than in patients with low stroke volumes. Progressive mixing of blood leaving the atrium occurs during its passage through the ventricle, pulmonic valve, and pulmonary artery and permits accurate estimation of flow.