Biomedical subjects

H Asanoi

Publications and source records attributed to H Asanoi.

At least 55 records · Page 3Linked to original sources

PubMed1992

Continuous measurement of the pressure-volume relationship in experimental heart failure produced by rapid ventricular pacing in conscious dogs.

The contractile function of the left ventricle has been defined within the framework of the pressure-volume relationship. We employed a conductance catheter, together with a high-fidelity micromanometer, to obtain accurate pressure and volume data continuously on a beat-to-beat basis in conscious dogs. Reproducibility of conductance volumetry was proven by repeated in situ measurements of left ventricular volume on separate days in the same dog. Heart failure, produced by rapid ventricular pacing, was characterized by impaired systolic shortening, depressed contractility indices and incomplete left ventricular relaxation. The magnitude of the cardiotonic effects of dobutamine was significantly attenuated after development of heart failure. Dobutamine improved left ventricular early relaxation but did not affect chamber distensibility. In heart failure, the load sensitivity of relaxation was enhanced and the force-frequency response attenuated. This may elucidate the mechanisms of early diastolic dysfunction and the deleterious effect of an increase in heart rate in the failing heart. Thus, the conductance catheter provided a reliable and simple method of obtaining left ventricular volume continuously in conscious dogs.

Animals↗

PubMed1992

Effects of chronotropic responsive cardiac pacing on ventilatory response to exercise in patients with complete AV block.

To identify the effect of chronotropic responsive cardiac pacing on the ventilatory response to exercise, ten selected patients with complete atrioventricular block underwent paired cardiopulmonary exercise tests in fixed rate ventricular (VVI) and dual chamber (DDD) or rate responsive ventricular (VVIR) pacing modes. Compared to VVI pacing, DDD or VVIR pacing increased peak oxygen uptake (P < 0.005) and augmented anaerobic threshold (P < 0.001). In eight patients, dyspnea was the major symptom limiting exercise with VVI pacing and this was markedly attenuated with DDD or VVIR pacing. In all patients, ventilation (VE) and the ratio of ventilation to CO2 production (VE/VCO2) were consistently higher with VVI pacing during exercise. To compare the response of the two pacing modes at the same workloads in an aerobic condition, we measured ventilatory variables 1 minute prior to the anaerobic threshold obtained with VVI pacing. When DDD or VVIR pacing was compared with VVI pacing, VE and VE/VCO2 significantly decreased from 20.5 +/- 5.3 L/min to 18.3 +/- 5.0 L/min (P < 0.005) and from 35.9 +/- 5.8 to 31.9 +/- 5.0 (P < 0.001), respectively. Respiratory frequency rose significantly more with VVI pacing (P < 0.001) despite an unchanged tidal volume. Although peak VE did not differ between the two pacing modes, VE/VCO2 at the peak exercise increased significantly more with VVI pacing (P < 0.005). Respiratory frequency also rose more with VVI pacing (P < 0.005) and tidal volume did not change. This study suggests that chronotropic responsive cardiac pacing attenuates the exertional dyspnea by improving the ventilatory response to exercise as well as increasing the cardiac output in patients with complete atrioventricular block.

Anaerobic Threshold↗

PubMed1992

Serial reproducibility of conductance catheter volumetry of left ventricle in conscious dogs.

Although the conductance catheter technique has been currently applied to in situ measurement of left ventricular volume, reproducibility of this method has not been examined within the same subject on separate days. Accordingly, serial catheter volumetries (mean 5 days apart) were performed in 10 normal conscious dogs, which were chronically instrumented with the conductance catheter, a micromanometer, and caval cuff occluders. Left ventricular end-systolic pressure-volume relationship was also determined during transient caval occlusion. All hemodynamic variables were compared at the same heart rate. There were no significant changes in blood resistivity (10 +/- 7 omega cm, 8%) and the parallel conductance of the surrounding tissues (7 +/- 6 ml, 10%). The mean difference was 3 +/- 2 ml (7%) for end-diastolic volume and 3 +/- 2 ml (11%) for end-systolic volume. Stroke volume and ejection fraction were also reproducible with mean difference of 2 +/- 1 ml (9%) and 3 +/- 2% (8%) respectively. The end-systolic pressure-volume relationships were nearly superimposable with the slope being 6.05 +/- 1.82 mmHg/ml on day 1 and 6.13 +/- 2.22 mmHg/ml on day 2. The difference averaged 0.63 +/- 0.42 mmHg/ml (11%). These results suggest that highly reproducible volume estimates by conductance catheter offer its feasibility of serial assessment of ventricular performance in vivo.

Analysis of Variance↗

PubMed1992

Dobutamine improves afterload-induced deterioration of mechanical efficiency toward maximal.

We studied the effect of increased afterload on the ratios of O2 consumption (VO2) to external work (EW), VO2 to the systolic pressure-volume area (PVA), and PVA to EW at control state and with dobutamine in the left ventricles of open-chest dogs. Left ventricular volume was measured with a volumetric conductance catheter and coronary flow with an electromagnetic flowmeter. Hexamethonium bromide and atropine sulfate were administered before changes in end-systolic pressure (Pes) with an infusion of nitroprusside or angiotensin II. Dobutamine enhanced ventricular end-systolic elastance by 100%. In the control, with increases in Pes, EW/VO2 remained unchanged, PVA/VO2 increased by 48%, and EW/PVA decreased by 26%. Dobutamine increased both EW/VO2 and EW/PVA at any given Pes but decreased PVA/VO2. During dobutamine, EW/VO2 increased significantly with increases in Pes. The ratio of measured EW/VO2 to the theoretically predicted maximal EW/VO2 value for a given end-diastolic volume and contractility was 0.83 at a Pes of 70 mmHg, and this ratio decreased by 33% with increases in Pes in the control. During dobutamine, measured EW/VO2 values were almost equal to each corresponding theoretical maximal value, and the average decrease in the ratio with increases in Pes was 7%. Thus the enhanced inotropic state by dobutamine can restore the afterload-induced deterioration of EW/VO2 toward the normal maximal level.

Animals↗

PubMed1992

Energy conversion efficiency in human left ventricle.

BACKGROUND: Left ventricular mechanical efficiency is one of the most important measures of left ventricular pump performance. Several clinical studies, however, have shown that mechanical efficiency does not fall substantially as the heart fails. To clarify the insensitivity of mechanical efficiency to the change in pump performance, we analyzed human left ventricular mechanical efficiency, applying the concept of left ventricular systolic pressure-volume area (PVA). METHODS AND RESULTS: PVA correlates linearly with myocardial oxygen consumption per beat (MVO2): MVO2 = a.PVA+b, and represents the total mechanical energy of contraction. We determined MVO2-PVA relation and external work in 11 patients with different contractile states. We also calculated the energy transfer from MVO2 to PVA (PVA/MVO2 efficiency), that from PVA to external work (work efficiency), and mechanical efficiency (external work/MVO2). Left ventricular pressure-volume loops were constructed by plotting the instantaneous left ventricular pressure against the left ventricular volume at baseline and during pressure loading. The contractile properties of the ventricle were defined by the slope of the end-systolic pressure-volume relation (Ees). Pressure elevation raised external work by 41.4%, PVA by 71.2%, and MVO2 by 54.5%. These changes were associated with a decrease in work efficiency and an increase in PVA/MVO2 efficiency. The opposite directional changes in these two efficiencies rendered the mechanical efficiency constant. The slope, a, of the relation between MVO2 and PVA was relatively constant (2.46 +/- 0.33) over the range of 0.8-8.8 mm Hg/ml of Ees, but the oxygen axis intercept, b, tended to decrease with the reduction in Ees. PVA/MVO2 efficiency correlated inversely (r = -0.66, p less than 0.05) with Ees, whereas work efficiency correlated linearly with Ees (r = 0.91, p less than 0.01). CONCLUSIONS: Mechanical efficiency is not appreciably affected by changes in loading and inotropic conditions as long as the left ventricular contractility is not severely depressed.

Cardiac Catheterization↗

PubMed1992

New redistribution index of nutritive blood flow to skeletal muscle during dynamic exercise.

BACKGROUND: Cardiac output is effectively redistributed to working muscle by regional changes in vascular resistance. However, there has been no suitable method to quantify blood flow distribution to large working and nonworking muscles involved in ergometer or treadmill exercise. METHODS AND RESULTS: To quantify the redistribution of blood flow, we compared thallium activity in a bicycle pedaling leg with that in the contralateral resting leg in 10 normal subjects. The regional thallium activity was expressed as a percentage of the whole-body radioisotope activity. Comparison of thallium activity between legs was performed at rest and at the work rates of anaerobic threshold and peak exercise during one-leg exercise. Thallium distribution of both legs was essentially the same at rest. At the anaerobic threshold, thallium activity increased about threefold to fourfold in the exercising thigh and about twofold in the exercising calf. The thallium distribution in these muscles at peak exercise was the same as at the anaerobic threshold. In the nonexercising calf, thallium distribution during exercise decreased significantly, and it was unchanged in the nonexercising thigh. Consequently, the ratio of thallium activity between the exercising and nonexercising thighs increased from 1.1 +/- 0.1 to 4.0 +/- 0.9 at the anaerobic threshold and to 3.3 +/- 0.6 at peak exercise. Similarly, the ratio between the exercising and nonexercising calves increased from 1.0 +/- 0.0 to 3.8 +/- 1.3 at the anaerobic threshold and to 3.5 +/- 1.0 at peak exercise. The ratios at peak exercise, however, did not differ significantly from those at the anaerobic threshold. CONCLUSIONS: These findings suggest that the redistribution of blood flow occurs predominantly during mild to moderate exercise; therefore, blood flow in the leg during strenuous exercise would depend primarily upon an increased cardiac output. Thus, the thallium activity ratio of exercising and nonexercising legs reflects the difference in vascular tone of each leg and could provide a noninvasive and quantitative index of blood flow redistribution.

Adult↗

PubMed1992

Ventricular-load optimization in patients with heart failure.

The effects of unloading or inotropic agent in 22 patients with dilated cardiomyopathy were assessed in terms of optimal coupling between the ventricle and arterial system. In 13 patients (group A), lower body negative pressure (LBNP) was applied to reduce preload and nitroprusside was used to decrease afterload. In 9 patients (group B), dobutamine was used to enhance inotropic state. In all patients, the direct arterial pressure was simultaneously recorded with left ventricular echocardiogram as the pressure was elevated by phenylephrine. The left ventricular contractile properties were defined by the slope (Ees) of the end-systolic pressure-volume relation. The arterial system properties were expressed by the slope (Ea) of the end-systolic pressure-stroke volume relation. When the Ea/Ees ratio ranged from 0.5 to 1.0, both external work and mechanical efficiency are nearly maximized. In group A, baseline ventricular-load coupling was characterized by an increase in the Ea/Ees ratio (1.96 +/- 1.08) where the heart could maximize neither external work nor mechanical efficiency. Ea/Ees significantly fell to 1.45 +/- 0.77 with nitroprusside, while increasing to 2.37 +/- 1.17 during LBNP. In group B, Ea/Ees was decreased from 1.43 +/- to 0.82 +/- 0.47 with dobutamine. It is concluded that reduction in afterload rather than preload, or augmentation of contractility could restore optimal ventricular-load coupling in patients with severe cardiac dysfunction.

Cardiomyopathy, Dilated↗

PubMed1992

Pathogenesis of unstable angina with 0- or 1-vessel disease. Important role of coronary artery spasm.

In order to examine the possible role of coronary artery spasm in the pathogenesis of unstable angina, provocative testing for coronary spasm was performed in 43 patients with unstable angina who had 0- or 1-vessel disease. Coronary spasm was induced in 20 (65%) of 31 patients by hyperventilation testing (ST increases in 18, ST decreases in 2). Anginal attacks with either ST-segment elevation or ST-segment depression in patients without a significant organic stenosis were induced in 23 (55%) of 42 patients during treadmill exercise testing. Coronary artery spasm, showing severe (> or = 90%) vasoconstriction with angina and/or ischemic electrocardiographic ST-segment deviation, was also documented angiographically in 42 (98%) of 43 patients following intracoronary injection of acetylcholine. We conclude that dynamic coronary obstruction plays an important role in the genesis of attacks in patients with unstable angina who had 0- or 1-vessel organic coronary artery disease.

Acetylcholine↗

PubMed1992

[Effects of chronotropic responsive cardiac pacing on ventilatory response to exercise in patients with bradycardia].

To identify the effect of chronotropic responsive cardiac pacing on ventilatory responses to exercise, 9 patients with chronotropic incompetence underwent paired cardiopulmonary exercise tests with fixed demand rates (AAI, VVI) and chronotropic responsive (AAIR, VVIR, DDD) pacing modes. Compared with fixed rate pacing, chronotropic responsive pacing increased peak oxygen uptake and delayed the attainment of the anaerobic threshold (AT) with a higher level of oxygen consumption (p < 0.01). Dyspnea was a major symptom that limited exercise time in 7 patients with fixed rate pacing, which was prominent with chronotropic responsive pacing. Ventilation (VE) and the ratio of ventilation to CO2 production (VE/VCO2) were consistently higher with fixed rate pacing during exercise. To compare the responses between the 2 pacing modes with the same work loads under aerobic conditions, we measured ventilatory variables one min prior to the AT as obtained with fixed rate pacing. When switching the pacing mode from fixed rate pacing to chronotropic responsive pacing, VE and VE/VCO2 decreased significantly from 22.0 +/- 7.8 to 19.8 +/- 6.8 l/min, and from 37.4 +/- 5.4 to 33.6 +/- 5.2, respectively. Tidal volume did not change, but respiratory frequency decreased more with chronotropic responsive pacing (p < 0.05). Although peak VE did not differ between the 2 pacing modes, VE/VCO2 decreased more with chronotropic responsive pacing (p < 0.01). Respiratory frequency decreased and tidal volume increased more with chronotropic responsive pacing (p < 0.05). This study suggests that chronotropic responsive cardiac pacing attenuates exertional dyspnea by improving ventilatory responses to exercise as well as increasing the cardiac output in patients with chronotropic incompetence.

Adult↗

PubMed1991

Coupling between the heart and arterial system in heart failure.

A number of experimental studies have demonstrated the optimal coupling between the ventricle and arterial load, under physiologic and pathologic circumstances, directed to produce maximal stroke work. We investigated matching of the ventricular properties, quantified by the slope of end-systolic pressure-volume relationship, with arterial load properties, expressed by the slope of end-systolic pressure-stroke volume relationship. In normal subjects, with ejection fraction of greater than or equal to 60%, ventricular elastance was nearly twice as large as arterial elastance. This condition affords maximal mechanical efficiency. In patients with moderate heart failure, with ejection fraction of 40-59%, ventricular elastance was almost equal to arterial elastance. This condition affords maximal stroke work from a given end-diastolic volume. In patients with severe heart failure, with ejection fraction of less than 40%, ventricular elastance was less than half of arterial elastance, which resulted in increased potential energy and decreased work efficiency. Ventriculoarterial coupling is normally set toward higher left ventricular work efficiency, whereas in patients with moderate cardiac dysfunction, ventricular and arterial properties are matched, in order to maximize stroke work at the expense of work efficiency. Neither the stroke work nor work efficiency is near maximum for patients with severe cardiac dysfunction.

Arteries↗

PubMed1991

Ventricular-load optimization by inotropic stimulation in patients with heart failure.

To evaluate the effects of inotropic stimulation on ventriculo-arterial coupling, we determined both the slope of the end-systolic pressure-volume relationship (ventricular elastance) and the slope of end-systolic pressure-stroke volume relationship (arterial elastance) at rest and during dobutamine infusion (5 micrograms/kg/min). We also determined stroke work, end-systolic potential energy and the ventricular work efficiency defined as stroke work per pressure volume area (stroke work + potential energy). In the resting state, ventricular elastance was lower than arterial elastance and work efficiency was about 59.7 +/- 9.3% (mean +/- SD). This condition is remote from the point where stroke work or mechanical efficiency is optimal. Enhanced ventricular elastance by 41% with dobutamine resulted in a significant reduction in both left ventricular end-diastolic and end-systolic volumes and was accompanied by the reduction in arterial elastance by 23%. Consequently, the ratio of arterial elastance to ventricular elastance decreased from 1.43 +/- 0.57 to 0.82 +/- 0.47, which resulted in an increase in stroke work, a decrease in potential energy and hence a marked increase in work efficiency. Thus, inotropic stimulation of depressed hearts could modulate ventriculo-arterial coupling towards optimization of either stroke work or mechanical efficiency.

Adult↗

PubMed1991

Ventricular load optimization by unloading therapy in patients with heart failure.

The effects of unloading a depressed heart were assessed in terms of optimal coupling between the ventricle and arterial system. To assess the effects of preload on ventricular load coupling, preload was reduced with a lower body negative pressure of -20 mm Hg. Nitroprusside was used to evaluate the effects of afterload on the coupling under the condition that preload reduction was comparable to that with lower body negative pressure. In 13 patients with heart failure (ejection fraction 32 +/- 3%, mean +/- SE), direct arterial pressure was simultaneously recorded with the left ventricular echocardiogram as the pressure was elevated by phenylephrine. Left ventricular contractile properties were defined by the slope (Ees) of the end-systolic pressure-volume relation. The effective arterial elastance (Ea) was expressed by the slope of the end-systolic pressure-stroke volume relation. Left ventricular external work, end-systolic potential energy and work efficiency, defined as external work per pressure volume area (external work + potential energy), were determined. Baseline ventricular load coupling in these patients was characterized by an increase in the ratio of arterial elastance to ventricular elastance (Ea/Ees) (1.96 +/- 0.31). This ratio decreased significantly, to 1.45 +/- 0.22, with nitroprusside, and increased to 2.37 +/- 0.34 with lower body negative pressure. Therefore, end-systolic potential energy was decreased by nitroprusside but was unaltered by lower body negative pressure while external work was comparably decreased by both manipulations, indicating that work efficiency was significantly augmented with nitroprusside but declined with lower body negative pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Echocardiography↗

PubMed1991

Mechanics of contraction and relaxation of the ventricle in experimental heart failure produced by rapid ventricular pacing in the conscious dog.

A model of heart failure produced by rapid ventricular pacing in the conscious dog instrumented with a conductance catheter to monitor instantaneous left ventricular volume has been developed. This experimental model is capable of analysis of the left ventricular pressure-volume relationship on a beat-to-beat basis, and has been used to assess ventricular function serially in the progress of heart failure and effects of pharmacological intervention. In seven dogs the magnitude of cardiotonic effects were significantly attenuated after development of heart failure. These findings support the concept that in the failing heart there is subsensitivity to beta-adrenergic stimulation in proportion to the severity. The failing heart was characterized by incomplete left ventricular relaxation. Dobutamine improved left ventricular early relaxation but did not affect chamber distensibility. In contrast new phosphodiesterase inhibitor, E-1020, improved ventricular distensibility with less marked changes in active relaxation; improved left ventricular relaxation appeared to be mediated by increased systolic shortening with enhancement of internal restoring forces, and improved distensibility by accelerated function of sarcoplasmic reticulum through increased intracellular cyclic AMP.

Animals↗

PubMed1991

Importance of coronary collateral circulation for increased treadmill exercise capacity by nitrates in patients with stable effort angina pectoris.

The purpose of this study was to elucidate the mechanism that induces an improvement in exercise capacity by nitrates in patients with stable effort angina pectoris. The study population was composed of 19 patients: group A, 10 patients with chronic stable effort angina who had a well-developed coronary collateral circulation to the potentially ischemic region; group B, 9 patients with chronic stable effort angina who had no collateral circulation to the jeopardized myocardium. Treadmill exercise was performed according to the standard Bruce protocol with and without pretreatment with orally administered 10 mg isosorbide dinitrate. Percent increases (mean +/- SE) in exercise duration were not significantly different between groups A and B (25 +/- 6 vs. 14 +/- 6%). Percent increases in the maximal rate-pressure product tended to be greater in group A than in group B (27 +/- 6 vs. 10 +/- 6%). Percent increases in the rate-pressure product at the onset of angina pectoris were significantly greater in group A than in group B (37 +/- 7 vs. 7 +/- 6%; p less than 0.01). Percent increases in the rate-pressure product at 0.1 mV S-T segment depression were also significantly greater in group A than in group B (26 +/- 6 vs. 1 +/- 5%; p less than 0.01). These results suggest that isosorbide dinitrate dilates epicardial collateral vessels with smooth muscle layers, but fails to dilate the coronary arteries with significant organic stenoses.

Angina Pectoris↗

PubMed1991

[End-systolic pressure-volume relationships obtained by conductance catheter and transient inferior vena caval occlusion: their clinical usefulness].

Whether beneficial hemodynamic effects of cardiovascular drugs are due to changes in the inotropic or loading conditions has been difficult to determine in clinical settings. In this study, the end-systolic pressure-volume relationship, known as a load-independent measurement of cardiac contractility, was obtained by a volumetric conductance catheter and transient inferior vena caval occlusion. We applied this technique to determine the major mode of hemodynamic action of a new inotropic vasodilator, OPC-8490, in comparison to that of dobutamine. In 7 patients with anterior myocardial infarction, an 8F conductance catheter with pressure micromanometer was inserted into the left ventricle. Absolute volume calibration was accomplished by injection of hypertonic saline into the pulmonary artery. Left ventricular pressures and volumes were simultaneously and continuously measured during transient inferior vena caval occlusion using a balloon catheter. Left ventricular end-systolic pressure-volume relationships were determined during the initial 8-sec of balloon occlusion, before baroreceptor-mediated cardiac stimulation was initiated. OPC-8490 decreased both the left ventricular systolic pressure and end-systolic volume without changing the heart rate. Dobutamine increased the systolic pressure and heart rate but decreased the end-systolic volume. The reduction in the end-systolic volume with dobutamine, was caused by an increase in the slope of the end-systolic pressure-volume relationship, while with OPC-8490, it resulted from a decrease in the end-systolic pressure without an appreciable change in the slope of the end-systolic pressure-volume relationship.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

[Primary cardiac malignant mesenchymal tumor containing chondrosarcomatous component--a case report].

A case of 70 years old female bearing a primary cardiac tumor was presented. Mitral valve replacement and reconstruction of the interatrial septum were necessary because the tumor originated from the left atrial side of the interatrial septum and invaded the anterior mitral valve leaflet and around the annular area. Pathological examination of the resected specimens revealed mesenchymal tumor containing chondrosarcomatous component. The patient received radiation therapy (50 Gy) postoperatively and she resumed normal daily activity. Preoperative echocardiographic manifestations were of proved benefit in the diagnosis of malignant cardiac tumor and a proper therapeutic strategy could be chosen.

Aged↗

PubMed1990

Significance of collateral circulation in reversible left ventricular asynergy by nitroglycerin in patients with relatively recent myocardial infarction.

To evaluate the functional role of coronary collateral circulation in reversible asynergy of the left ventricle, cineventriculography was performed before and after the administration of sublingual nitroglycerin in 19 patients with complete occlusion of the proximal part of the left anterior descending coronary artery. In nine patients who had significant collateral circulation to the infarct-related coronary artery (group A), there was significant improvement in both the left ventricular ejection fraction (53% to 60%, p less than 0.05) and regional wall motion in the infarct zone (8% to 18%, p less than 0.01 in the anterolateral area) with administration of nitroglycerin. In contrast, in the remaining 10 patients without significant collateral perfusion (group B), there were no detectable changes in either global function (49% versus 50%) or regional wall motion (6% versus 8% in the anterolateral area) before and after nitroglycerin. Changes in heart rate and left ventricular peak systolic and end-diastolic pressures with nitroglycerin were comparable in both groups. These results suggest that angiographically demonstrable collaterals preserve viable myocardium, which can improve its contraction when the supply-demand relationship is favorably affected because of increased collateral flow and/or more favorable loading conditions produced by nitroglycerin.

Cineradiography↗

PubMed1990

Comparative hemodynamic effects of intravenous dobutamine and dibutyryl cyclic AMP, a new inotropic agent, in severe congestive heart failure.

In nine patients with chronic congestive heart failure, the acute hemodynamic response to intravenous (i.v.) dibutyryl cyclic AMP (DBcyclicAMP) administration was compared with i.v. dobutamine administration. Both agents led to a significant and similar increase in cardiac index. Dobutamine caused a significant increase in mean arterial pressure but did not produce a significant change in pulmonary capillary wedge, mean pulmonary artery, or mean right atrial pressures. In contrast, DBcyclicAMP caused a significant decrease in mean arterial, mean pulmonary capillary wedge, mean pulmonary artery, and mean right atrial pressures, reflecting vasodilator activity. The fall in systemic vascular resistance was larger after DBcyclicAMP than after dobutamine. DBcyclicAMP achieves an optimal improvement in cardiovascular hemodynamics in concert with substantial vasodilating effect. This pharmacologic action constitutes the mainstay of i.v. therapy for severe congestive heart failure (CHF).

Adult↗