Effect of strophanthus on coronary blood flow and cardiac oxygen consumption of normal and failing human hearts

The rate of oxygen uptake of quiescent cardiac muscle

The rate of oxygen uptake of quiescent papillary muscle of the cat heart has been determined in a flow respirometer with the use of the oxygen electrode. The apparent rate of oxygen uptake as a function of the diameter of the muscle was also determined. It was found that papillary muscles from cat hearts use oxygen at a rate of 2.84 (microliters/mg. wet weight)/hour at a temperature of 35°C. Such muscles can be adequately supplied by diffusion when their surface is uniformly exposed to an atmosphere containing 95 per cent oxygen only if their diameter is 0.64 mm. or less. Papillary muscles from kitten hearts use oxygen at a rate of 4.05 (microliters/mg. wet weight)/hour at a temperature of 35°C. Such muscles can be adequately supplied by diffusion when their surface is uniformly exposed to an atmosphere containing 95 per cent oxygen only if their diameter is 0.53 mm. or less. If the muscles are small enough to be adequately supplied with oxygen by diffusion, the rate of oxygen uptake does not increase when the muscle is stretched.

Studies on digitalis. VI. Reduction of the oxygen debt after exercise with digoxin in cardiac patients without heart failure

Three patients with acquired valvular heart disease and cardiac enlargement who were able to perform normal everyday activity without difficulty in the absence of digitalis therapy were exercised while receiving a placebo and again while receiving digoxin. Digoxin administration did not produce a significant change in body weight or in the subjective condition of the individuals. Varying degrees of exercise were performed on a treadmill in a Metabolic Chamber and oxygen consumption was measured cotinuously before, during, and after the period of exercise, utilizing a continuous gas flow paramagnetic oxygen analyzer. The oxygen debt that developed during digoxin administration was compared to that observed during placebo administration.

In all patients the oxygen debt was smaller during the period of digoxin administration, although the external work performed was identical. In the first patient, following a 7-minute walk, the oxygen debt was 53 per cent more and following a 10-minute walk it averaged 40 per cent more while not receiving digoxin than when receiving this drug. In the second subject the oxygen debt following a 7-minute walk was 34 per cent more and following 10-minute walk it averaged 74 per cent more when he was not receiving digoxin than when receiving this drug. In the third subject the oxygen debts were 46 per cent and 41 per cent greater following 10- and 15- minute walks respectively, when she was not receiving digoxin.

The accumulation of a smaller oxygen debt following exercise while these subjects were receiving digoxin indicates that the functional status of their circulatory system was improved by the drug. It would appear that digitalis administration is beneficial to at least some patients who have cardiac disease and enlarged hearts and some decrease in cardiac reserve without signs or symptoms of heart failure.

Reduced left ventricular mechanical efficiency in elderly patients with coronary artery disease

We evaluated left ventricular (LV) mechanical efficiency in 23 elderly patients (mean age 67 +/- 2) with coronary artery disease (CAD) and in 22 patients younger than 65 years (mean age 49 +/- 8) with similar severity of CAD (2.4 +/- 0.8 and 2.2 +/- 0.8 vessels per patient, respectively) and history of myocardial infarction (34% and 41%, respectively). LV mechanical efficiency was calculated as the ratio of LV work per minute and myocardial O2 consumption. LV stroke volume was calculated from left ventriculography. Coronary blood flow was measured by thermodilution. Older patients had lower values of LV stroke volume (49 +/- 16 vs 73 +/- 16 mL, p < 0.005), ejection fraction (41 +/- 17 vs 58 +/- 17%, p < 0.05), LV stroke work (93 +/- 26 vs 131 +/- 41 g.m., p < 0.02) and LV work per minute (6.7 +/- 2.6 vs 9.3 +/- 2.7 kg.m./min, p < 0.05). Since myocardial O2 consumption was similar in the two groups, LV mechanical efficiency was lower in older CAD patients (16.2 +/- 15 vs 23.8 +/- 12%, p < 0.05). Thus, elderly patients with CAD show a reduced LV mechanical pump performance and efficiency, compared with younger patients with similar disease severity and history of myocardial infarction. These observations may contribute to understanding the higher frequency of congestive heart failure in elderly patients with CAD.

Reference values for resting blood flow to organs of man

The lack of a reliable quantitative description of blood flow in man has hampered the development of accurate biokinetic models of essential elements, drugs, imaging agents, and carcinogens. In this paper we review and analyse data on blood flow and identify representative percentages of cardiac output and absolute blood flow rates to organs and tissues of man for use as reference values for biokinetic models. To keep the review and analysis to a manageable size we have limited attention to the resting state and have suggested reference values for absolute and relative flow rates only for adult males and females.

Myocardial energetics in patients with dilated cardiomyopathy. Influence of nitroprusside and enoximone

Cardiotonic agents influence myocardial energy consumption by vasodilation, which may reduce energy demand, and by inotropism, which may increase it. To distinguish between the two effects, myocardial oxygen consumption must be analyzed in relation to its hemodynamic determinants. The coupling of myocardial oxygen consumption with its determinants was investigated in 22 patients with idiopathic dilated cardiomyopathy (NYHA Class II and III). Predicted myocardial oxygen consumption by the pressure-work index, the Bretschneider index, and the pressure-volume area correlated moderately with measured myocardial oxygen consumption (r = 0.57, p less than 0.001; r = 0.52, p less than 0.005; and r = 0.63, p less than 0.001). Multiple regression analysis, including left ventricular peak systolic wall stress, systolic stress-time integral, pressure-volume work, maximum rate of left ventricular pressure rise, and mean velocity of circumferential fiber shortening indicated that systolic stress-time integral is the major determinant of myocardial oxygen consumption (r = 0.75, p less than 0.001) in these patients. Enoximone, a phosphodiesterase inhibitor, has an inotropic and a vasodilating effect. To investigate the inotropic portion of the energy cost of this phosphodiesterase inhibitor, the influence of enoximone on myocardial oxygen consumption and systolic stress-time integral was compared with the effects of nitroprusside, which is a vasodilator only. Nitroprusside (10 patients) and enoximone (12 patients) reduced left ventricular systolic stress-time integral from 109 +/- 22 to 71 +/- 21 (p less than 0.005) and from 104 +/- 23 to 42 +/- 10 (p less than 0.001) 10(3) dynes.sec/cm2, respectively. Myocardial oxygen consumption decreased from 159 +/- 44 to 112 +/- 23 (p less than 0.005) and from 134 +/- 28 to 109 +/- 21 (p less than 0.001) microliters/beat/100 g, respectively. In both groups, there was a significant correlation between the decrease in myocardial oxygen consumption and the decrease in systolic stress-time integral. The slopes of the respective linear regression lines were significantly different (1.27 for nitroprusside and 0.51 nl.cm2/100 g.dynes.sec for enoximone, p less than 0.05), indicating a smaller decrease of myocardial oxygen consumption for a given decrease of stress-time integral with enoximone. Applying the pressure-work index or the pressure-volume area instead of systolic stress-time integral yielded comparable results. Thus, vasodilation reduces myocardial oxygen consumption in proportion to the reduction of stress-time integral. With enoximone, the energy-saving effect of vasodilation is counteracted in part by the increased energy d

Left ventricular mechanical efficiency in coronary artery disease

The effect of coronary artery disease and prior myocardial infarction on cardiac energetics was determined by measuring left ventricular myocardial blood flow, oxygen consumption (MVO2), efficiency and ejection phase indexes in 36 patients undergoing coronary arteriography. Eight control patients with normal coronary arteriograms and normal left ventricular function, 15 patients with coronary artery disease without prior myocardial infarction and 13 patients with coronary disease and prior myocardial infarction (greater than 6 months) were studied. Left ventricular efficiency was calculated from left ventricular work, myocardial blood flow (measured by clearance of intracoronary xenon-133), and aortic and coronary sinus oxygen content. Left ventricular volumes, mass and ejection phase indexes were measured by quantitative left ventriculography. Left ventricular myocardial blood flow per 100 g/min was reduced in patients with coronary artery disease (49.0 +/- 8; p less than 0.01) and in patients with myocardial infarction (51.6 +/- 10; p less than 0.05) compared with control subjects (62.4 +/- 16), but total left ventricular flow was not reduced because of increased left ventricular mass. As a result, MVO2 did not differ significantly for the three patient groups (control 13.3, coronary artery disease 14.0 and myocardial infarction 14.3 ml/min). In the patients with myocardial infarction, left ventricular work index was reduced (2.4 versus 4.0 kg X m/m2 per min in the control group; p less than 0.001), causing efficiency to be reduced (15.9 versus 28.8% in the control group; p less than 0.001). Decreased efficiency correlated with ejection fraction (r = 0.54), mean velocity of circumferential fiber shortening (MVcf) (r = 0.45) and mean percent chordal shortening (r = 0.43) (all p less than 0.01). These data indicate that in control patients with normal coronary arteriograms, left ventricular myocardial efficiency averages 29%; in patients with coronary disease without myocardial infarction, left ventricular MVO2 and efficiency are in the normal range; in patients with prior myocardial infarction, left ventricular efficiency is significantly reduced as a result of diminished left ventricular work and normal MVO2; and reduced efficiency after myocardial infarction correlates with reduced ejection phase indexes.

Methods for the assessment of the effects of drugs on coronary blood flow in man

The methods currently available for measurement of coronary blood flow in man are reviewed and their advantages and limitations discussed. Most of the techniques are invasive and involve cardiac catheterization. The least invasive isotope techniques are either not quantitative or involve expensive equipment not available in many centres. Two of the most suitable methods for assessing the effects of drugs on coronary flow are coronary sinus thermodilution and isotope washout curves using 133xenon or [125I]-iodo-antipyrine. The ideal technique for measuring coronary blood flow has yet to be developed.

Comparative influence of ouabain, norepinephrine and heart rate on myocardial oxygen consumption and inotropic state in dogs

The purpose of this study was to compare the myocardial oxygen cost of augmented inotropic state produced by ouabain, norepinephrine, or increased heart rate. This problem was examined in dogs using an isovolumically contracting left ventricular preparation. Inotropic state was measured as the maximum observed contractile element velocity at the lowest common level of wall stress (MAX V). Peak left ventricular wall stress was maintained constant in each dog so that it would not influence changes in myocardial oxygen consumption (MVO2). Ouabain (4 X 10(-2) mumoles/Kg.) and norepinephrine (2 X 10(-3) mumoles/Kg./minute) always augmented inotropic state (MAX V) and increased MVO2. The positive slopes of the regression of MVO2 on MAX V for ouabain (45.4 +/- 12.5 microliter/beat/100 Gm./muscle length/sec; mean +/- SEM) and norepinephrine (34.5 +/- 5.6 microliter/beat/100 Gm./muscle length/sec; mean +/- SEM) were not significantly different, indicating that for an equal augmentation of inotropic state, ouabain increases myocardial oxygen demands to the same extent as does norepinephrine. When the results with ouabain or norepinephrine were compared to results obtained by altering heart rate, it was found that increasing inotropic state by these pharmacologic agents is more costly in terms of myocardial energy demands than when inotropic state is enhanced by increasing heart rate.

Reduced myocardial blood flow in acute and chronic digitalization

The myocardial blood flow was measured by the 133Xenon disappearance curve from the left ventricular wall following an injection of 133Xenon in the left coronary artery in 8 dogs without digoxin pretreatment and in 8 chronically digitalized dogs. The myocardial blood flow was significantly less (30%) in the digitalized dogs than in the dogs without pretreatment. In the digitalized dogs as well as in those without pretreatment an intravenous injection of digoxin resulted in a further significant decrease of the myocardial blood flow of about 20% and a significant increase of the coronary vascular resistance. The reduced myocardial blood flow both during acute and chronic digitalization is beleived to be of clinical importance.

[Value and limitations of coronary blood flow measurement in man (author's transl)]

Attempts to measure coronary blood flow in man have made considerable progress during the last 25 years. The major techniques are based on the direct or indirect Fick principle; coronary flow is calculated from the arterio-coronary venous difference of inert gases or from the precordial recorded disappearance curve of radioactive gases or substances. The accuracy of the techniques depends upon the properties or the indicators used and the precision of their determination. All techniques applied hitherto are intricate and unsuitable for general use. -A lot of information is obtained about coronary circulation in health and disease by coronary flow measurements in man. Further studies in this field may influence pathophysiological and clinical concepts especially concerning coronary heart disease.

Effects of a digitalis glycoside on coronary and systemic dynamics in conscious dogs

The effects of ouabain (G-strophanthin), 20 µg/kg were compared in 12 conscious dogs with Doppler flow transducers on the ascending aorta and left circumflex coronary artery and pressure gauges in the aorta, and in 9 of these dogs after general anesthesia with Na pentobarbital. In conscious dogs ouabain caused an initial bradycardia, but heart rate returned almost to control at 15 to 30 minutes, while arterial pressure rose and remained elevated. Cardiac output and coronary blood flow decreased initially, returned to control by 5 minutes and then remained constant. Systemic, mean, and late diastolic coronary resistances were elevated within 1 minute and remained elevated for 30 minutes. After anesthesia, ouabain caused similar increases in arterial pressure and slightly greater increases in systemic resistance, but the bradycardia and reduction of cardiac output were more profound and sustained. In the anesthetized state, coronary resistance rose when heart rate was allowed to slow after ouabain but was not elevated when heart rate was returned to control. Thus, in the conscious state, ouabain caused a distinct elevation in coronary and systemic resistances with no change in cardiac output, while in the anesthetized state ouabain reduced cardiac output and when heart rate was controlled, did not alter coronary resistance.

he effect of acute digitalization on the hemodynamic response to exercise in coronary artery disease

Hemodynamic observations are made at rest and during exercise before and following the administration of 0.5 mg of ouabain in patients with coronary artery disease and in normal subjects. Patients with coronary artery disease and exertional angina showed evidence of reversible cardiac failure during exercise. The patients with coronary artery disease who did not have angina and the normal subjects had normal hemodynamic responses to exercise. Acute digitalization did not prevent angina in any of the symptomatic patients, although there was hemodynamic evidence of improved ventricular performance. In the patients with coronary disease without angina minor hemodynamic changes at rest and during exercise were suggestive of improved left ventricular function.

Effect of ouabain on the energy output of rabbit cardiac muscle

The effect of ouabain, 0.3 µg/ml, on the energy output of rabbit papillary muscles has been examined by a myothermic technique. The experiments were conducted at two temperature ranges, 19.2° to 22.8°C and 29.0° to 32.2°C, and both isometric and afterloaded isotonic contractions were studied. Temperature differences alone caused pronounced physiological changes, the higher temperature being associated with lower tension-independent heat and markedly higher active efficiency, external work /(external work + active heat production). The heat versus tension curve was rectilinear at higher temperatures but showed upward curvature at lower temperatures. At 19.2° to 22.8°C, ouabain increased the tension-independent heat by 23%, maximum tension development by 23%, and mean work output by 39%. Ouabain did not significantly alter the slope of the heat versus tension curve and increased mean efficiency only slightly. At 29° to 32.2°C, ouabain did not cause any significant change in the slope of the heat versus tension curve or in mean muscle efficiency. Ouabain produced significant increases in maximum tension development, mean work output, and the tension-independent heat. The effects of ouabain at the higher temperature were examined at two different calcium levels, 2.5 and 1.25 mM. In the isometric studies the effects of ouabain were independent of the calcium level, and the calcium level itself had no significant effect on the heat-tension relationship. In the isotonic studies, ouabain increased work output but more so at the 2.5 mM calcium level. Ouabain did not affect mechanical efficiency at either calcium level but muscle efficiency was higher at the 2.5 mM calcium level. It is concluded that any effects of the cardiac glycosides on energy expenditure are consequences of their inotropic actions and do not represent changes in the energy cost of contraction.

Role of acetylstrophanthidin in augmenting myocardial oxygen consumption. Relation of increased O-2 consumption to changes in velocity of contraction

A polarographic method was used to determine the effects of acetylstrophanthidin on myocardial oxygen consumption (MV · O 2 ) of 19 cat papillary muscles contracting under both afterloaded and isometric conditions. Under afterloaded conditions, acetylstrophanthidin shifted the force-velocity relation to the right and produced increments in both the extent and velocity of shortening at constant levels of developed force. These changes in myocardial mechanical behavior after strophanthidin were always associated with an increased MV · O 2 . Since both the extent and velocity of shortening increased following augmentation of the contractile state with glycoside, consideration of the individual effect of these variables in myocardial mechanical behavior on MV · O 2 was precluded. Therefore, experiments were performed on isometrically contracting muscle to evaluate the effect of changes in the velocity of contraction on MV · O 2 independent of changes in contractile element shortening. Comparison of the MV · O 2 of isometric contractions at equal levels of developed tension (and thus equivalent amounts of internal contractile element shortening) was accomplished by decreasing initial muscle length after augmentation of the contractile state by acetylstrophanthidin. Under these conditions, augmentation of the contractile state, characterized by an increase in the velocity of contraction, was associated with an increased MV · O 2 . Thus it is concluded that the effect of acetylstrophanthidin is to increase MV · O 2 at a constant load and that this augmentation of MV · O 2 can be related to the change in contractile state of the muscle.

Studies on digitalis. XVI. Effects on myocardial oxygen consumption

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Studies on digitalis. XV. Effects of cardiac glycosides on myocardial force-velocity relations in the nonfailing human heart

The effects of ouabain (0.01 mg/kg) on ventricular force-velocity relations were studied in six patients who had previously undergone corrective cardiac operations. The technique employed consisted of exposing cineradiograms at 30 frames per second and measuring the velocity of movement of roentgen-opaque markers that had been sutured to the external surfaces of the ventricles while simultaneously recording intraventricular pressures. A beat-to-beat analysis of the ventricular force-velocity relation was then accomplished by relating the velocity of marker movement and intraventricular pressure at constant ventricular dimensions. It was observed that ouabain always augmented myocardial contractility as reflected in the force-velocity relation. Velocity of shortening increased an average of 77±5 ( sem )% while intraventricular pressure rose by an average of 23±6%. Despite this improvement in contractility, no consistent changes in cardiac output were observed. Analogous changes in force-velocity curves were obtained when a cardiac glycoside was added to isolated papillary muscles removed from normal cats. It is concluded that the fundamental action of digitalis glycosides is to augment the contractile state of the heart, whether normal or failing, but that in the absence of heart failure this improvement is not translated into an increase in cardiac output.

Effects of Acetylstrophanthidin on Coronary Vascular Resistance and Myocardial Oxygen Consumption

The effects of acetylstrophanthidin on coronary circulation were studied in 31 dogs. Coronary blood flow was measured in empty beating hearts or in fibrillating hearts by collecting coronary venous return during perfusion of the systemic circulation (cardiopul-monary bypass). In 14 animals with ventricular fibrillation, acetylstrophanthidin caused an initial coronary constriction and fall in coronary blood flow. This was followed, after approximately 10 minutes, by a significant drop in resistance and a rise in coronary blood flow which persisted for the remainder of the experiment. Associated with the increase of blood flow was an increase of myocardial oxygen consumption. This effect was not abolished by ganglionic blockade, cardiac denervation or bilateral adrenalectomy.

In nine dogs with beating but empty hearts, after the initial constriction of the coronary vessels, there was only a small change in coronary blood flow and resistance, although myocardial oxygen consumption was increased. The lack of coronary vasodilatation was attributed to increased mechanical resistance due to the augmented force of contraction produced by the drug.

Left Ventricular Performance Following Digitalization in Patients with and without Heart Failure

Nine patients, three with left ventricular failure and six with compensated heart disease, were studied by means of right and transseptal left heart catheterization during acute digitalization with acetyl strophanthidin. One of the patients with heart failure and a compensated subject with the Wolff-Parkinson-White syndrome were also studied during supine left leg exercise.

In the decompensated group, digitalization produced a decrease in heart rate and increases in stroke index, stroke work, mean stroke power, mean systolic ejection rate, and the rate of pressure rise in the left ventricle. Left ventricular end-diastolic pressures were markedly lowered after digitalization.

In the compensated group, no significant changes in cardiac index, stroke index, or mean systolic ejection rate were observed. Although there were small increases in stroke work and power and moderate decreases in left ventricular diastolic pressures, the most striking finding was an increase in the rate of rise of left ventricular systolic pressure.

Digitalization produced considerable improvement in the circulatory response to light exercise in a patient with left ventricular failure. Less marked improvement in the exercise response was observed in a patient with normal hemodynamics. After digitalization, left ventricular function points plotted on the stroke work end-diastolic pressure diagram tended to shift upward and to the left in both decompensated and compensated patients. The shift of function points was most prominent in the decompensated group.

This study demonstrates that, in the presence of myocardial failure, acetyl strophanthidin markedly augments left ventricular performance. Furthermore, the data suggest that digitalization also improves left ventricular performance in patients with left ventricular enlargement but no clinical manifestations of heart failure.