Significant Increase In Cardiac Output Research Articles

Cardiovascular Responses to Changes in Carotid Sinus Transmural Pressure in Man

To study the relative importance of cardiac and peripheral effector mechanisms in the carotid sinus baro-reflex in man cardiovascular responses to equal changes of the carotid sinus transmural pressure (Ptm) in either direction of the normal were recorded and compared in eight physically well-trained young male volunteers. In both the supine and the 70 degrees head-up position, a decrease in Ptm produced a more potent reflex response of the systemic arterial pressure than did a similar increase in Ptm. Whereas the arterial pressure response to increased Ptm was due solely to a reduction in vascular resistance, a significant increase in cardiac output contributed to the more potent pressor response to a decrease in Ptm and thus to the predominantly antihypotensive properties that characterize the carotid sinus baroreceptor control system in man. However, since combined beta-adrenergic and parasympathetic blockade abolished the effect of reduced Ptm on cardiac output without greatly impairing the blood pressure response, it is concluded that adjustments in cardiac output are not of critical importance in the buffering function of the carotid sinus baroreceptors. Autonomic cardiac blockade exaggerated the fall in cardiac output on head-up tilt, the arterial pressure remaining unaffected due to a compensatory increase in systemic vascular resistance.

Negative influences of ascites on the cardiac function of cirrhotic patients

Right and left ventricular function was evaluated in 21 men with cirrhosis and tense ascites during staged removal of ascitic fluid. During paracentesis it was observed (1) that there was a significant increase in cardiac output, stroke volume, right and left ventricular stroke work and mean rate of systolic ejection; (2) that up to a certain stage of drainage (about 5,000 ml), there was a relationship between the amount of fluid removed and the intraabdominal and right atrial pressures and (3) that there was a direct relationship between improvement of cardiac function and normalization of right atrial pressure. It is believed that the increased intra-abdominal hydrostatic pressure acting upon the diaphragm affects the intrathoracic pressure to such an extent that the transmural filling pressure of the heart is reduced, and the mean pressure and respiratory pulsations of the right atrium increased, all of which impede venous return. Improved cardiac function during paracentesis appears to be due to an augmented filling of the heart and to a larger venous return.

Hemodynamic effect of dobutamine in patients with severe heart failure

Dobutamine, a derivative of dopamine, was infused at a rate of 10 μg/kg per min in 15 patients with severe congestive heart failure. Cardiac output increased from an average of 3.1 to 5.6 liters/min ( P < 0.001) with no change in mean arterial pressure (93.3 to 98.2 mm Hg) and only a slight increase in heart rate (98.5 to 105.2 beats/min) ( P < 0.02). Pulmonary wedge pressure was decreased from an average of 27.4 to 21.1 mm Hg ( P < 0.001). In seven patients a dose of 5 μg/kg per min also produced a significant increase in cardiac output but the effect was less than with the 10 μg/kg per min dose. No side effects were observed during the infusion. Dobutamine therefore is a potent inotropic drug with limited chronotropic and peripheral vascular effects and deserves therapeutic trial in the short-term management of low output heart failure.

THE EFFECT OF ADRENAL DENERVATION ON ACTH-INDUCED HYPERTENSION IN SHEEP

SUMMARY 1. The effect of surgical denervation of the adrenal gland on ACTH-induced hypertension in the sheep has been examined. ACTH (80 iu/day) was administered for 5 days to eight sheep before and after bilateral surgical denervation of the adrenal. 2. In intact sheep, ACTH-induced hypertension is associated with a significant increase in cardiac output and heart rate. Adrenal denervation obtained by sectioning of the lumbar sympathetic and splanchnic nerves supplying the adrenal gland did not alter the magnitude or time course of the hypertension, or the increase in heart rate. 3. Adrenal denervation did not affect the increase in plasma sodium, the fall in plasma potassium, the initial urinary sodium retention, the increase in water turnover or the changes in blood corticosteroids which are seen during ACTH administration to intact sheep. However, in these adrenally denervated sheep ACTH treatment did not significantly change cardiac output. 4. This study suggests an important role for a factor or factors from the adrenal cortex in causing ACTH-induced hypertension.

HAEMODYNAMIC EFFECTS OF COMBINED OESTROGEN/PROGESTOGEN ORAL CONTRACEPTIVES

SummaryThe effects of a combined contraceptive pill, and of its oestrogen and progestogen components, on the haemodynamics in the recumbent and upright positions were studied in 49 healthy young women. Twenty‐nine women were given a contraceptive pill containing 2.5 mg. of lynestrenol and 0.075 mg. of mestranol (Lyndiol 2.5) for two months, while 10 women received mestranol only and 10 women lynestrenol only for 10 to 13 days. A significant increase in cardiac output, blood volume and stroke volume was observed after combined oral contraceptive therapy. Similar changes were recorded in the women given mestranol, but not in those given lynestrenol. The tilt response was not influenced by any treatment. The present results indicate that the haemodynamic changes observed during combined (oestrogen/progestogen) oral contraceptive treatment are caused by oestrogens.

Cardiovascular and respiratory responses to severe hypoxaemia under anaesthesia. II. Spontaneous and controlled ventilation during methoxyflurane anaesthesia.

Beagle dogs were anaesthetised with halothane, trichlorethylene or methoxyflurane, at various end-tidal concentrations and were ventilated to maintain arterial carbon dioxide tension constant. Under light anaesthesia, severe arterial hypoxaemia caused significant increases in cardiac output, stroke volume and heart rate and a decrease in total systemic vascular resistance. Oxygen transport values during hypoxaemia remained close to control levels measured when the dogs were breathing air, unless the arterial oxygen tension fell below 25 mm Hg. Then the oxygen transport values fell despite significant increases in cardiac output. The clinical signs of hypoxaemia were clear in the lightly anaesthetised dogs. Under deep anaesthesia, the rise in cardiac output during hypoxaemia was not significant and the total systemic vascular resistance did not fall. Oxygen transport values decreased from the control levels. Some clinical signs of hypoxaemia were less striking than in the lightly anaesthetised hypoxaemic dogs. Morbidity and mortality rates were high in this group. We conclude that the cardiovascular response to hypoxaemia was well maintained only in those dogs under light anaesthesia with the agents studied.

Effect of physical training on anatomical R-L shunt at rest and pulmonary diffusing capacity during near-maximal exercise in boys 11-13 years old.

Anatomical R-L shunt at rest and the pulmonary diffusing capacity during near-maximal exercise were studied in 9 boys aged 11 to 13 years before and after a 16-week period of systematic physical training. Physical training resulted in a significant decrease of resting anatomical R–L shunt from 4.6 to 2.9 per cent of cardiac output, corresponding to a Pao2 of 607 and 635 mm Hg during oxygen breathing respectively. Physical training failed to induce any change in exercise DLCO despite a significant increase of cardiac output and ventilation.

Exercise-induced hemodynamic effects of arteriovenous fistulas used for hemodialysis

Exercise-induced hemodynamic effects of arteriovenous fistulas used for hemodialysis. The hemodynamic burden of arteriovenous fistulas or shunts used for chronic hemodialysis in patients with renal failure was investigated in eight patients. Occlusion of the A-V fistula produced no significant difference in resting measurements of cardiac output, heart rate, brachial artery pressure, mean right atrial pressure, systemic vascular resistance, or estimated myocardial oxygen demand. During graded recumbent bicycle exercise the patients demonstrated a small but significant increase in cardiac output when the A-V shunt was open. At the peak level of exercise for each patient there was no significant difference in heart rate, stroke volume, arterial pressure and right atrial pressure. It is concluded from this study that an A-V fistula created for hemodialysis produces little hemodynamic deterioration. Patients who appear to develop congestive heart failure while on dialysis are most likely underdialyzed or volume overloaded and therapy should be directed toward alleviating these problems.

Significance of chronic sinus bradycardia in elderly people.

It may be difficult to evaluate sinus bradycardia in the elderly since sinus rates below 50 beats/min may occur normally with aging. Seven asymptomatic bradycardic subjects (heart rates 41-51 beats/min), ages 67-79 years, with no evidence of impaired cardiac performance and taking no drugs, were compared with four age-matched controls (heart rates 60-84 beats/min). Autonomic function was tested with the Valsalva maneuver, amyl nitrite inhalation, methoxamine infusion, head-up tilt, and atropine intravenously (2 mg). Cardiac index at rest was normal in bradycardic subjects (2.4 ± 0.1 sem ); increased cardiac stroke volume (SV) compensated for the slow heart rate. With supine bicycle exercise, increase in cardiac output per 100 ml increase in oxygen consumption was normal in bradycardics (885 ± 60 ml compared to 907 ± 171 ml in controls). This exercise response was achieved mainly by increased SV in bradycardics and by increased heart rate in controls. Significant increases in cardiac output occurred with both atropine and atrial pacing in bradycardics, but not in controls. Autonomic impairment was not found. Increased vagal tone in bradycardics was suggested by a lesser heart rate response to exercise and passive tilting. Hence, a heart rate below 50 beats/min in elderly people does not necessarily indicate depressed cardiac performance. Further evaluation of the significance of bradycardia in these subjects requires long-term observation.

Haemodynamic effects of glucagon after mitral valve replacement.

We have studied six patients who had undergone mitral valve replacement. Estimations of cardiac output and of pulmonary vascular resistance were made, beginning two hours after the finish of the operation. Glucagon, 10 mg, was given intravenously, and cardiac output and pulmonary vascular resistance were measured 5 minutes and 30 minutes later. In all six cases there was a significant decrease in pulmonary vascular resistance and this occurred whether the resistance was slightly, moderately or greatly elevated. There was a highly significant increase in cardiac output in all cases.

Cardiovascular and respiratory responses to severe hypoxaemia during anaesthesia. 1. The effect of various concentrations of three anaesthetic agents upon the cardiovascular response and oxygen transport.

Beagle dogs were anaesthetised with halothane, trichlorethylene or methoxyflurane, at various end-tidal concentrations and were ventilated to maintain arterial carbon dioxide tension constant. Under light anaesthesia, severe arterial hypoxaemia caused significant increases in cardiac output, stroke volume and heart rate and a decrease in total systemic vascular resistance. Oxygen transport values during hypoxaemia remained close to control levels measured when the dogs were breathing air, unless the arterial oxygen tension fell below 25 mm Hg. Then the oxygen transport values fell despite significant increases in cardiac output. The clinical signs of hypoxaemia were clear in the lightly anaesthetised dogs. Under deep anaesthesia, the rise in cardiac output during hypoxaemia was not significant and the total systemic vascular resistance did not fall. Oxygen transport values decreased from the control levels. Some clinical signs of hypoxaemia were less striking than in the lightly anaesthetised hypoxaemic dogs. Morbidity and mortality rates were high in this group. We conclude that the cardiovascular response to hypoxaemia was well maintained only in those dogs under light anaesthesia with the agents studied.

CENTRAL HAEMODYNAMIC EFFECTS OF DIHYDROERGOTAMINE IN PATIENTS WITH ORTHOSTATIC HYPOTENSION

AbstractThe effects of dihydroergotamine (DHE) on heart rate, cardiac output, stroke volume, arterial and central venous pressures, systemic resistance, and central blood volume have been analysed in ten patients suffering from orthostatic hypotension. The patients were placed on a tilt‐table and studied in the supine as well as in the erect body position. In the supine position DHE caused a significant increase of cardiac output, stroke volume, arterial systolic and mean pressures, and central venous pressure. In the erect position DHE raised cardiac output, stroke volume, and central blood volume, and lowered heart rate. Systemic resistance was unaltered by the drug. The effects of DHE on the central circulation can largely be explained by its powerful and relatively selective constrictor action on the capacitance vessels in the peripheral circulation. The results indicate that DHE can have beneficial effects in patients with orthostatic hypotension.

HAEMODYNAMIC CHANGES IN WOMEN TAKING ORAL CONTRACEPTIVES

SummaryHaemodynamic changes were monitored serially in a group of 30 healthy young women receiving combined oestrogen‐progestogen oral contraceptive therapy. Significant increases in cardiac output (expressed as cardiac index), systolic and mean blood pressures and plasma volume occurred during therapy. Changes in heart rate and diastolic blood pressure were not significant. An increase in stroke volume was mainly responsible for the increase in cardiac output.Plasma renin substrate and renin activity increased, renin concentration decreased, while blood angiotensin levels increased markedly during oral contraceptive administration in all 13 of the 30 subjects in whom these investigations were carried out.A significant increase in body weight occurred in most subjects while receiving oral contraceptive therapy.

THE EFFECT OF CARDIAC SYMPATHETIC BLOCKADE ON THE RELATIONSHIP BETWEEN CARDIAC OUTPUT AND CARBON DIOXIDE TENSION IN THE ANAESTHETIZED DOG

SUMMARY In dogs anaesthetized with either halothane or chloralose cardiac output was measured at three levels of arterial carbon dioxide tension. As the carbon dioxide tension was raised there were significant increases in cardiac output. After the administration of a selective cardiac beta-receptor blocking agent (practolol) there were no significant changes in cardiac output as the carbon dioxide tension was increased. It was concluded that the increased cardiac output seen with a raised arterial carbon dioxide tension was brought about by an increased activity in the sympathetic nervous system.

Haemodynamic effects of glucagon

The central and peripheral vascular haemodynamic effects of glucagon were studied in 29 patients. With a single dose method of 2 or 5 mg. glucagon intravenously the inotropic action of the drug produced immediate increased myocardial contractility with significant increase in cardiac output and enhanced cardiac performance, and lowering of pulmonary arterial pressure and pulmonary vascular resistance. No primary peripheral vascular effect was evident, and the increased systemic pressure and lowered systemic resistance appear to be secondary to the central action of the drug. With the dosage used there were no undesirable side-effects apart from a feeling of slight nausea. Though the haemodynamic effects are abrupt, reaching their maximum values in the first 10 minutes after injection, they tend to be dissipated within half an hour, presumably due to the very rapid destruction of the drug. Repeated booster doses rather than continuous infusion may be the method of choice to maintain an increased cardiac output. The positive chronotropic action of the drug may cause transient palpitations. Glucagon increased the cardiac output in the acute phase of myocardial infarction by 42 per cent. The haemodynamic effects in chronic rheumatic heart disease are more varied, and it may increase left atrial pressure in mitral stenosis, which is undesirable. Hyperglycaemia results from liver glycogenolysis but blood sugar levels rarely exceeded 200 mg./100 ml. These results warrant further study of the value of glucagon as a positive inotropic agent in low output heart failure, especially in acute myocardial infarction with cardiogenic shock, or after cardiac surgery, or in unrelieved chronic congestive heart failure.

Effects of bradykinin on the pulmonary vascular bed of the intact dog

Intravenous infusion of bradykinin in intact dogs resulted in a significant increase in cardiac output, pulmonary blood volume, pulmonary artery pressure and pulmonary vein pressure and a significant decrease in systemic and total pulmonary vascular resistances. The decrease in total pulmonary vascular resistance was due to dilatation of the pulmonary arterioles, whereas the increase in pulmonary vein pressure was considered to be due to a shift of blood into the pulmonary venous system. The increase in pulmonary vein pressure with no change in left atrial pressure suggested a throttle valve action of the pulmonary veins, probably at the veno-left atrial junction. No evidence was obtained during these experiments to indicate that bradykinin actively dilates the pulmonary veins.

CARDIOVASCULAR DYNAMICS IN WOMEN RECEIVING ORAL CONTRACEPTIVE THERAPY

The results of a serial study of hæmodynamic changes in the first 6 of 30 healthy young women being investigated while receiving combined œstrogen-progestogen oral contraceptive therapy are presented. Significant increases in cardiac output (expressed as cardiac index), systolic and mean blood-pressures, and plasma-volume occurred during the 2-3 months of therapy. Heart-rate and diastolic-blood-pressure changes were not significant. The increase in cardiac output was due mainly to a concomitant signifiant increase in stroke-volume. Body-weight also increased significantly in all subjects while receiving oral contraceptive therapy, probably largely as a result of fluid retention.

Left heart hemodynamics during angina pectoris induced by atrial pacing.

In order to determine the associated hemodynamic events, angina pectoris was induced by an atrial pacing technic. In all patients developing angina pectoris, ischemic changes were noted electrocardiographically. The hemodynamic findings were variable: in some patients no changes were noted; in others, significant increases in cardiac output, left ventricular end-diastolic pressures (LVEDP), and femoral arterial and pulmonary arterial pressures occurred. These changes suggest that, initially, ischemia produces a decrease in myocardial compliance and this may also be associated with enhanced sympathetic nervous system activity. Myocardial failure may subsequently ensue, however. The administration of nitroglycerin, during angina at a fixed rapid heart rate, resulted in a reduction in LVEDP and cardiac work. Chest pain was always relieved following these hemodynamic changes, indicating a dependence upon these changes for the effectiveness of nitroglycerin.

Cardiovascular effects of infusion of lidocaine on patients with heart disease

The cardiovascular effects of constant infusion of lidocaine were determined during right heart catheterization in 10 unanesthetized patients with significant myocardial disease. Three patients were receiving digitalis. A 1.5 mg./kg. bolus or a brief infusion of 300 μg./kg. per min., followed in each instance by a 50 μg./kg. per min. (3 to 3.5 mg./min.) infusion, was used. Atrial or ventricular pacing, or both, was utilized in 5 patients to obviate cardiovascular changes resulting from varying rates or rhythms. Atrioventricular conduction time measured in 4 instances did not change. Radioactive lidocaine plasma levels, determined in 4 patients, were in a therapeutic range of 1.5 to 5.5 μg./ml. Little change in heart rate, intracardiac or systemic arterial pressures, or myocardial contractility occurred. No significant decrease in cardiac output was noted. Significant increases in cardiac output occurred in 3 of the 4 studies in which lidocaine terminated frequent ventricular extrasystoles. No adverse hemodynamic effects of continuous infusion of lidocaine were observed.

Left heart hemodynamics during angina pectoris induced by atrial pacing

In order to determine the associated hemodynamic events, angina pectoris was induced by an atrial pacing technic. In all patients developing angina pectoris, ischemic changes were noted electrocardiographically. The hemodynamic findings were variable: in some patients no changes were noted; in others, significant increases in cardiac output, left ventricular end-diastolic pressures (LVEDP), and femoral arterial and pulmonary arterial pressures occurred. These changes suggest that, initially, ischemia produces a decrease in myocardial compliance and this may also be associated with enhanced sympathetic nervous system activity. Myocardial failure may subsequently ensue, however. The administration of nitroglycerin, during angina at a fixed rapid heart rate, resulted in a reduction in LVEDP and cardiac work. Chest pain was always relieved following these hemodynamic changes, indicating a dependence upon these changes for the effectiveness of nitroglycerin.