摘要:

Pericardial pressure was studied in chronic experiments on dogs with relation to intrathoracic pressure in the normal state and in cardiac tamponade. In the normal resting animal, the two pressures were in good agreement throughout the respiratory cycle. The cardiac cycle produced superimposed pressure fluctuations amounting to 30% of the respiratory swings.Adding saline to the pericardial sac produced sigmoid pressure-volume curves; tamponade required 100 to 330 ml of fluid. Although during tamponade the pericardial pressure greatly exceeded the intrathoracic pressure, the pericardial pressure invariably fell with inspiration, generally by the same amount as the intrathoracic pressure. The cardiac cycle produced greater pressure fluctuations (50% of the respiratory pressure fluctuations). The superior vena caval pressure always fell with inspiration in the normal state and during tamponade.Hypovolemia did not change the resting pericardial pressure, but decreased the slope of the pressure-volume curve measured during cardiac tamponade. Hypervolemia increased the resting pericardial pressure considerably, and increased the slope of the pericardial pressure-volume curve.The results suggest that pleural pressure is a reasonable approximation of the pericardial pressure in normal dogs. There appears to be no substantial evidence that pulsus paradoxus is due to failure of the pericardial sac to transmit inspiratory reductions of pleural pressure.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

The hemodynamic effects of hyperbaric oxygenation were investigated in anesthetized dogs with acute myocardial embolism and infarction produced by injecting plastic spheres 325 micra in diameter. In 50 “control” animals with acute myocardial infarction induced while breathing either air at one atmosphere, 100% oxygen at one atmosphere or 7% oxygen at three atmospheres, 24-hour mortality was 85 to 90%. In 23 animals that received the same dose of microspheres and breathed 95 to 100% oxygen at three atmospheres for two hours following embolization, there was significantly less 24-hour mortality (30%), less ventricular fibrillation, and less advanced atrioventricular block. Hyperbaric oxygenation afforded protection against immediate mortality from ventricular fibrillation and also against later death, in shock, occurring within 24 hours of coronary embolization but after the immediate postembolization period had passed. In the animals exposed to hyperbaric oxygenation, declines of cardiac output and of central aortic pressure occurring 60 and 90 minutes after coronary embolization were significantly less than in the other animals.In normal animals, hyperbaric oxygenation reduced cardiac output moderately, increased systemic vascular resistance, and elevated aortic pressure slightly.The anatomic extent of the infarction did not differ detectably between the “control” animals and those treated with hyperbaric oxygenation.It is concluded that hyperbaric oxygenation provides protection against mortality in the early period after coronary embolization by preventing ventricular fibrillation. In addition, prevention of major declines in aortic pressure and cardiac output during the later postembolization period in the group with hyperbaric oxygenation was associated with diminished rates of late mortality.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

The effects on directly measured renal blood flow, mean blood pressure, and calculated renal vascular resistance of intravenous infusions of dopamine, isoproterenol, and norepinephrine were compared. Dopamine, at doses not affecting mean blood pressure, decreased renal vascular resistance and increased renal blood flow. In contrast, isoproterenol decreased both blood pressure and renal vascular resistance but did not consistently increase renal blood flow. Renal artery injection of dopamine produced vasodilatation at doses ranging from 0.75 to 12 μg and biphasic flow responses including transient vasoconstriction at higher doses. It is concluded that the probable basis for the effect of intravenous dopamine infusion on renal blood flow is its direct renal vasodilating action.The direct effect of dopamine on the femoral vascular bed is vasoconstriction. The combination of renal vasodilating, and femoral vasoconstricting, effects is unique and is interpreted as evidence for a renal vasodilating effect of dopamine distinct from the conventional beta-adrenergic mechanism. A possible physiological role for dopamine other than as a precursor to norepinephrine may be related to this property. It is also suggested that the ability of dopamine to alter the distribution of cardiac output in favor of visceral organs may find useful clinical applications.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

The progressive changes in ventricular volumes and pressures created by repeated coronary artery embolizations with lycopodium spores were studied in fifteen intact dogs. In eight of the animals SV increased over control values following the initial embolization. Subsequent embolizations produced a pronounced decrease in SV and SW, an enlarged EDV, and a high ESV/EDV ratio. Left ventricular systolic pressure fell as EDP rose. The progressive increase observed in the ESV/EDV ratio between successive embolizations was the most sensitive functional expression of the deteriorating myocardial performance.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

Intracoronary infusions of acetylcholine have demonstrated two actions of this neurohumoral agent on ventricular myocardium: 1) an antagonism to the more forceful contractions evoked by adrenergic stimuli (sympathomimetic drugs or stellate stimulation), and 2) a sympathomimetic or positive inotropic effect (? release of a positive inotropic substance from the myocardium). The increased contractility (“rebound”) was observed only after the infusion of acetylcholine was stopped; in the presence of physostigmine the “rebound” was absent. Atropine blocked both the cardio-inhibitory and cardio-excitatory actions of acetylcholine. Failure of hexamethonium and bretylium to block the “rebound” suggests that acetylcholine acts at a peripheral site. The possible catecholamine nature of the agent could not be established by direct analysis of coronary venous blood, by the use of an adrenergic beta receptor blocking agent or by pretreatment of the animals with reserpine; neither drug blocked the “rebound.”

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

Simultaneous determinations of myocardial blood volume (using I131-PVP), myocardial blood flow (using H32O), and coronary collateral myocardial blood flow (using retrograde flow) were made in dogs after left circumflex artery ligation. Intravascular H32O content at the end of the H32O infusion was calculated as the product of myocardial blood volume and the final arterial H32O concentration.When correction is made for intravascular H32O content the resulting flow measured by H32O is nearly identical to the retrograde flow. These results indicate that radioactive isotopes can be used to measure blood flow if correction is made for the intravascular isotope content. The identity of corrected H32O flows with retrograde flows also indicates the applicability of isotopic methods for the measurement of coronary collateral blood flow.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

1) Changes of oxygen uptake and energy output by the left ventricle were investigated during increased peripheral resistance (aortic occlusion) and increased cardiac output (induced muscular activity) in open-chest dogs under pentobarbital anaesthesia.2) Evidence has been provided to show that energy expenditure during the isovolumic period (E1) participates significantly in the total oxygen consumption of the left ventricle (QO2). The correlation ofE1+E2(compound energy expenditure during the whole cardiac cycle) to QO2was closer than the correlation of the stroke work (E2) to QO2under the experimental conditions studied. The increase of QO2during increased peripheral resistance is due to a proportional increase ofE1.3) The determination of the total amount of compound energy released by the left ventricle, makes the estimation of the performance of the heart possible in a more specific way. Besides the classical mechanical efficiency, ηm=E2/QO2, an index of the chemomechanical turnover (compound index), ic= (E1+E2)/QO2), and the so-called pumping index of the left ventricle, ip=E2/(E1+E2), have been calculated. During increased peripheral resistanceicdid not change whileipdecreased, indicating that it is not the index of the chemomechanical turnover but the matching between the heart and the periphery which is impaired. On the other hand, during induced muscular activity, onlyipincreased, thus indicating an improvement of this matching.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

Some effects of a relatively low molecular weight substance, isolated from human plasma, on isolated amphibian and mammalian cardiac muscle and on intact rabbits have been studied. This cardioactive plasma substance elicited a positive inotropic response from isolated isometrically contracting papillary muscle of rabbits, dogs, and monkeys, from trabeculae carneae of rats, and from ventricular muscle of toads. Its positive inotropic activity was associated with a shortened duration of action potentials. Studies on intact animals showed that the intravenous injection of this substance raised systemic pressures, raised right and left ventricular systolic pressures, and increased cardiac output. Adrenergic blocking drugs failed to block the inotropic and pressor effects of freshly isolated cardioactive plasma substance.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

摘要:

Reciprocal responses (ventricular “echoes”) were initiated by premature stimuli applied directly to the bundle of His in dog hearts perfused from donor animals. The time relations of the responses in the His bundle and at the atrial margin of the exposed A-V node were studied under a number of conditions. It was found that:1. The earliest premature response that can be induced in the His bundle is not propagated back to the atrium and does not lead to an echo.2. There is, in most hearts, a continuous range of H1H2intervals (the echo “zone”) within which reciprocal responses of the His bundle occur.3. The earliest effective H2propagates slowly to the atrium, and the echo returns quickly.4. The latest effective H2responses propagate more quickly to the atria, but return more slowly.5. The atrium is an essential link in the echo pathway; i.e., the H2response must reach and activate the atrium before a return is possible.6. Direct stimulation of the atrium in advance of the expected arrival of the A2response propagated from the His bundle can initiate a response which propagatestothe bundle; i.e., two responses can travel in opposite directions on a collision course, yet one of them can complete its journey.7. The limiting parameter of the return pathway is the refractory period of that portion of the lower node which must fire twice in the echo circuit.8. The limiting element is not the bundle of His.9. The limiting element can be discharged by early H2responses which fail to reach the atrium.10. The refractory period of the limiting element is a function of the preceding cycle length.It was also demonstrated that the echo “zone” is shifted to a range of longer H1H2intervals when the basic driving frequency is increased, or when the vagi are stimulated. Epinephrine shifts the echo zone to a range of briefer H1H2intervals.It is suggested that echo responses occur when a retrograde impulse is arrested at one site within the node and continues to propagate to the atrium through collateral pathways. If the retrograde propagation time is long enough to permit the recovery of the lower elements of the node, an echo response reaches the His bundle. It was concluded that a self-sustained repetitive circuit may be possible when the round-trip conduction time exceeds the refractory period of the limiting tissue in the node.

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1965

数据来源: OVID