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At least 1,513 records · Page 84Linked to original sources
PubMed1981

Left ventricular hypertrophy improves cardiac function in spontaneously hypertensive rats.

1. The influence of different arterial pressures on the relationship between diastolic filling pressure and stroke volume was studied during pharmacological cardiac nerve blockade in adult, anaesthetized spontaneously hypertensive rats in comparison with matched normotensive Wistar--Kyoto rats. 2. Peak stroke volumes, obtained by rapid blood volume expansion were similar in both types of rat, despite a more than 40% higher mean arterial pressure in the spontaneously hypertensive rats. 3. When peak stroke volumes were compared in the two groups at equal 'normotensive' or 'hypertensive' arterial pressures, they were always greater in the spontaneously hypertensive rats. 4. Calculation of diastolic wall/lumen ratios indicated that the increase of maximal stroke work in the spontaneously hypertensive rats closely matched the hypertrophic increase in wall/lumen ratio of the left ventricle. 5. These results indicate that left ventricular hypertrophy in established primary hypertension is a physiological adaptation to match left ventricular performance to the raised afterload.

Animals↗
PubMed2002

Cardiac function and electrical remodeling of the calcineurin-overexpressed transgenic mouse.

OBJECTIVE: To study the specificity of contractile phenotype and electrophysiological remodeling in transgenic (Tg) mice with cardiac directed calcineurin (phosphatase 2B) overexpression and evaluate a possible negative role of chronically activated calcineurin in beta-adrenergic mediated contractile response. METHODS: The patch-clamp technique was used to characterize electrophysiological properties of action potentials and inward rectifier (I(K1)), and transient outward potassium currents (I(to)). The analysis of the contractile performance was carried out on isolated retrograde perfused hearts at constant aortic pressure. RESULTS: Tg mice demonstrated a hypercontractile phenotype characterized by a profound beta-adrenergic hypo-responsiveness at 2.0 mM [Ca2+](o). Transgenic cardiomyocytes showed marked action potential prolongation (209% in APD(90)) with increased I(to,peak) and I(sus) and decreased protein expression level of Kv1.5 and Kv2.1. Lowering [Ca2+](o) to 0.75 mM restored the beta-adrenergic response, indicating that the calcineurin/calmodulin/adenylyl cyclase (AC) pathway may not be directly responsible for the blunted beta-adrenoreceptor mediated inotropism. CONCLUSIONS: Calcineurin overexpression leads to development of a hyperdynamic phenotype with a cellular profile of increased calcium influx. This type of functional hypertrophic remodeling is accompanied by a negative feedback regulation between increased calcium handling and beta-adrenergic contractile activation.

Action Potentials↗
PubMed1976

Effects of angiotensin, vasopressin, and methoxamine on cardiac function and blood flow distribution in conscious dogs.

A comparison was made of the effects of vasopressin (ADH), methoxamine (MX), and angiotensin II (AN) on coronary and left ventricular dynamics, cardiac output, and regional blood flow distribution in intact, consci9us dogs. At an equal percent pressure elevation, ADH reduced cardiac output and cardiac rate the most, while AN had the least effect. After denervation of arterial baroreceptors, ADH still reduced heart rate, while AN increased it, suggesting nonbaroreceptor negative and positive chronotropic effects, respectively. A differential pattern on peak dP/dt was also observed, with ACH causing a greater reduction than MX while AN did not decrease dP/dt. With heart rate held constant, AN did not reduce dP/dt, suggesting a direct positive inotropic effect since dP/dt should have fallen slightly due to reflex mechanisms, as was observed with MX and ADH. ADH induced the greatest increase in coronary resistance (140%), while the least (46%) was observed with AN, which could be explained, in part, by the differential effects observed on cardiac rate and contractility. The greatest increase in resistance in the iliac bed occurred with ADH (30%), and the least with AN (34%). Conversely, the greatest constriction in the renal bed occurred with AN (95%), and lesser amounts were observed with ADH (36%) and MX (35%). Thus ADH, MX, and AN exert potent yet differential vasoconstricting actions on peripheral beds. In addition, while all three agents elicited coronary vasoconstriction, the differential effects on coronary vascular resistance appeared to be due predominantly to a difference in chronotropic and inotropic actions.

Angiotensin II↗
PubMed1994

The effect of peep-ventilation on cardiac function in closed chest pigs.

OBJECTIVE: Does ventilation with positive end-expiratory pressure (PEEP) depress myocardial contractility? DESIGN: Ten piglets were anaesthetized and prepared for the measurement of cardiac output (SV) and right (MRAPtm) and left (MLAPtm) mean transmural atrial pressure, the latter serving as indices of preload. 500 ml of autologous blood was re-transfused during intermittent positive pressure ventilation without PEEP (IPPV) and continuous positive pressure ventilation with 15 cm H2O PEEP (CPPV). MEASUREMENTS AND RESULTS: Right and left ventricular function curves were drawn by plotting MRAPtm and MLAPtm respectively versus the corresponding strokevolumes before and after re-transfusion. Similar inclinations were obtained during IPPV and CPPV on either side of the heart. CONCLUSIONS: Although the ventricular function curves during IPPV and CPPV covered partially different preload levels, the results suggest that CPPV i.e. PEEP does not affect myocardial contractility.

Animals↗
PubMed1992

The use of dopexamine after cardiac surgery: acute and long-term effects in patients with impaired cardiac function.

The haemodynamic efficacy of dopexamine, a beta 2-adrenergic agonist with dopaminergic activity, was evaluated during dosetitration and longterm infusion in 20 cardiosurgical patients with low cardiac output following coronary artery bypass grafting and/or valve replacement or repair. After infusion of four doses (1, 2, 4, and 6 micrograms/kg/min), the dose producing the optimal response was administered for up to 36 h. Dopexamine infusion resulted in a dose-dependent significant increase in cardiac index (CI: 2.2-->3.3 L/min/m2) associated with a marked reduction of systemic vascular resistance (SVR: 1820-->1144 dyn.sec.cm-5). Heart rate increased significantly (HR: 89-->117 beats/min), while mean arterial blood pressure remained unchanged (MAP: 94-->89 mmHg). Unwanted effects (tachycardia and hypotension) were chiefly seen at higher doses (-->4 micrograms/kg/min). The beneficial haemodynamic effects were well maintained during the extended infusion period up to 36 hours at a mean dopexamine dose of 2.8 micrograms/kg/min. At these low doses, the positive chronotropic response to the drug remained within the limits of clinical acceptability. During long-term infusion up to 36 hours there was no indication of tolerance or an effect attenuation. It can be concluded that dopexamine acting as "inodilator" with dopaminergic properties is an useful adjunct to the pharmacological spectrum in the management of low-output states following cardiac surgery.

Adrenergic Agonists↗
PubMed2006

Fetal aortic distension waveforms for evaluating cardiac function and changes in blood pressure: fetal lamb validation.

AIM: To investigate which part of the fetal aortic distension waveform is mainly influenced by changes in fetal cardiac contractility and aortic blood pressure. METHODS: In acute preparation, aortic distension waveforms were recorded using an echo-tracking system, and aortic and left ventricular pressure waveforms were obtained from six late-gestation catheterized fetal lambs. Dobutamine and angiotensin II were separately infused and the correlations between the maximum value in the first derivative of left ventricle pressure waveforms (Max dP/dt) and fetal blood pressure, and the parameters obtained from aortic distension waveforms were analyzed using linear regression analysis. RESULTS: With a change in cardiac contractility, the maximum value of first derivative of the systolic rising slope in the aortic distension waveform had a positive correlation with Max dP/dt (r = 0.93, P < 0.0001). With changes in fetal blood pressure, both the amplitude and the ratio of increase from the end diastolic diameter obtained from the aortic distension waveform had a significant positive correlation with aortic blood pressure amplitude (r = 0.60, P < 0.01; r = 0.61, P < 0.01, respectively). CONCLUSION: The maximum first derivative of the systolic rising slope in the aortic distension waveform and the amplitude in the aortic distension waveform enable us to non-invasively substitute for fetal cardiac contractility and aortic blood pressure amplitude, respectively.

Animals↗
PubMed1977

Effect of acute stress and ouabain administration on adrenal catecholamine content and cardiac function of rats pretreated with diazepam.

The experiments described were carried out in an attempt to determine the participation of adrenal catecholamines in the higher incidence of cardiac arrhythmias produced by acute stress or ouabain injections in diazepam-treated animals. The pretreatments of rats with diazepam (150 mg kg-1 d-1) increase significantly the adrenal catecholamine content. Consequently, the application of electrical and immobilization stress releases more catecholamines from the adrenal glands of the diazepam-treated rats and also produces higher incidence of ventricular extrasystoles. Furthermore, various pretreatments of rats with diazepam (5-150 mg kg-1 d-1) also lead to an increase in the catecholamine content of the adrenal gland. In diazepam-treated rats, the intravenous administration of ouabain produces a greater release of adrenal catecholamines as well as a greater incidence of cardiac arrhythmias. Several hypotheses are proposed to explain the elevation of adrenal catecholamines and also the higher incidence of ventricular arrhythmias.

Adrenal Glands↗
PubMed1989

Effects of PAF and BN 52021 on cardiac function and regional blood flow in conscious rats.

The effect of intravenous injections (0.1-3 nmol/kg) of platelet-activating factor (PAF) on blood pressure, heart rate, cardiac output, and blood flow (hindquarter, renal, mesenteric) were studied in conscious rats. PAF decreased blood pressure and total peripheral resistance (TPR) but increased heart rate; cardiac output was reduced by the highest dose. Low doses of PAF increased blood flow and decreased vascular resistance in all vascular beds, whereas high doses reduced mesenteric blood flow in part by increasing mesenteric vascular resistance. The hypotensive and cardiac effects of PAF were blocked by intravenous infusions of the selective PAF-receptor antagonists, 15 mg/kg BN 52021 and 1 mg/kg SDZ 63-441. BN 52021 also attenuated the hindquarter and renal responses to PAF, but the mesenteric responses remained relatively unchanged. The results indicate that PAF is a potent vasodilator of mesenteric greater than hindquarter = renal vessels at low doses and a cardiac depressant at high doses. A therapeutic role for the PAF antagonists BN 52021 and SDZ 63-441 is suggested in endotoxemia, anaphylaxis, and other disease states in which increased release of PAF contributes to key hemodynamic derangements.

Animals↗
PubMed1986

Hyperbaric exposure to a 5 ATA He-N2-O2 atmosphere affects the cardiac function and organ blood flow distribution in awake trained rats.

Previous studies on rats have demonstrated an increased myocardial blood flow (MBF) in spite of an unchanged cardiac output (CO), mean arterial pressure (MAP), and heart rate (HR) when rats were exposed to a 5 ATA ambient pressure (PN2 = 4.8 ATA, PO2 = 0.2 ATA). We have investigated the changes in CO and organ blood flow by the microsphere method on 9 awake, trained rats exposed to a 5 ATA ambient pressure with surface pressure of N2 (= 0.8 ATA) and O2 (= 0.2 ATA), increasing the ambient pressure with He. The chamber temperature was 30-31 degrees C. CO and organ blood flow were measured in control and after 15 min under pressure. No changes were observed in CO, HR, or MAP during the hyperbaric exposure, indicating unchanged external work of the heart when calculated as MAP X HR. The pulse pressure however increased significantly (P less than 0.05). MBF increased at the same time by 36% (P less than 0.01), equally distributed in the right and left ventricles (P less than 0.01). The fact that myocardial perfusion increases when ambient pressure is elevated, independent of atmospheric inert gas composition, invites the conclusion that this change is due to the ambient pressure itself and not to a specific effect of N2 or He as inert gas at 5 ATA. The blood flow to the adrenals increased by 77% (P less than 0.01), the liver by 105% (P less than 0.05), while the blood flow to the skeletal muscles decreased by 30% (P less than 0.05). The blood flow to the lungs, the paws, and the outer ear increased, most likely due to the high ambient temperature in the chamber. We may conclude that HR does not change in a normoxic hyperbaric atmosphere. High ambient pressure increases the pulse pressure, but the MAP and CO remain unchanged. These changes and the changes in organ blood flow need well-balanced neuronal or hormonal reflexes to distribute an unchanged CO under pressure. The exact explanation is not known.

Animals↗
PubMed2000

Studies of cardiac function and myocardial tissue characterization.

The heart can be studied using ultrasound techniques. The shape of the heart, its chambers, wall thicknesses, wall tissue characteristics as well as motion of walls and valve leaflets are all diagnostic information. In addition, the blood velocity and its timing within the cardiac cycle is an important diagnostic tool. In the present paper focus will be limited to the analysis of the left ventricular function as observed with two-dimensional and three-dimensional echocardiography and the characteristics of backscattered ultrasound information from the left ventricular chamber wall. Function of the heart is often studied by observation of local wall motion or comparison of chamber volume in maximum and minimum shapes during the cardiac cycle (ejection fraction). Integrated backscatter from the wall is described in examples of cardiac transplantation and hypertrophy. Study of cyclic variation of frequency-dependent attenuation and integrated backscatter indicates that these are independent parameters.

Animals↗