Atrium Of Dogs Research Articles

Concentration of Myocardial Cyclic AMP and Ventricular Fibrillation Induced by Aminophylline

The concentration of myocardial cyclic AMP was measured in 9 dogs by radioimmunoassay after the administration of aminophylline. Fourteen dogs served as control. The concentration of cyclic AMP in the left ventricle was the highest and the lowest value was obtained in the right atrium in the control dogs. Ventricular fibrillations were induced immediately after the injection of 30 mg/Kg aminophylline in 3 dogs out of 9. The concentration of the left ventricular cyclic AMP in 6 dogs which tolerated aminophylline was significantly elevated compared with that of the control dogs (p less than 0.05). The left ventricular cyclic AMP in 3 dogs with ventricular fibrillation was significantly higher compared with that in the aminophylline tolerated dogs with non-fibrillating hearts (p less than 0.01). These results showed that the concentration of cyclic AMP was elevated in the fibrillating heart.

Effects of pulmonary congestion and of left atrial distention on breathing in dogs.

Prior experiments showed that pulmonary congestion may initiate tachypnea from lung receptors and that left atrial distention has no significant effect on breathing, but in those experiments secondary reflexes could have determined the results. In this study we separately distended the entire pulmonary vascular bed, the arterial compartment, and the left atrium in dogs perfused and oxygenated by an external system while ventilating and while not ventilating the lungs. Distending pressures ranged from 20 to 70 Torr, and as output variables we measured the initial rate of inspiration, peak inspiratory magnitude, inspiratory duration, expiratory duration, and breathing frequency from the diaphragmatic electromyogram. Total vascular congestion caused prolongation of expiration and lowering of frequency without effect on inspiratory duration, its rate or magnitude. A smaller depression was induced from the arterial compartment. Left atrial distention, which failed to occur sufficiently often to be attributable to dogs in general, had much less effect. However, when a related change in breathing did occur, it was limited to a shortening of inspiratory duration.

The effect of Swan-Ganz catheter height on the wedge pressure-left atrial pressure relationships in edema during positive-pressure ventilation.

We have studied the effect of the ventrical height of the pulmonary wedge catheter in the lung on the pulmonary wedge pressure-left atrial relationship during positive end-expiratory pressure ventilation in oleic acid-induced pulmonary edema. Pulmonary wedge catheters were placed above and below the left atrium in normal dogs and in dogs with oleic acid-induced edema. Wedge pressure and left atrial pressure were measured simultaneously during positive end-expiratory pressure ventilation (range, 0 to 30 cm H2O positive end-expiratory pressure). Pulmonary wedge catheters below the left atrium correctly recorded left atrial pressure and change in left atrial pressure at all positive end-expiratory pressures studied. Pulmonary wedge catheters above the atrium consistently recorded pressures higher than the normal left atrial pressure. They did not correctly respond to increases in left atrial pressure until it was increased to a value higher than the initial upper pulmonary wedge pressure. Pulmonary arterial catheters, when properly placed, should be reliable indicators of left atrial pressure during positive-pressure ventilation in normal and edematous lungs.

The effects of changes in inspired oxygen concentration on the experimental production of pulmonary edema in the dog with chronic left ventricular overload.

A twofold increase in left ventricular output was achieved by suturing a Telfon graft between the aorta and left atrium in dogs. Three weeks after surgery the animals were anesthetized and found to have left ventricular end-diastolic pressures averaging 36 mmHg with markedly elevated right ventricular systolic pressures (RVSP). Oxygen breathing resulted in a decrease in left ventricular pressures, RVSP, and arterial pressure in those animals which survived hypoxia. Fifty percent of the shunted dogs subsequently developed fatal pulmonary edema when allowed to breathe 10% oxygen in nitrogen. These animals showed no change in left ventricular function or pulmonary artery pressure (RVSP) in response to pure oxygen administration. It is suggested that there is a gradation of hemodynamic response to pure oxygen depending on the severity of left ventricular overload. In the severest case the 'fixing' of pulmonary hypertension may be due to neurohumoral mechanisms. The subsequent development of pulmonary edema in these animals with hypoxia either involves a change in permeability or a redistribution of hydrostatic pressure within the pulmonary vasculature.

Chronotropic effects of ouabain and heart rate on canine atrium in vivo.

Positive chronotropic effects from the combination of ouabain administration and rapid stimulation were sought in the atrium and ventricle of ten anesthetized vagotomized dogs with intact atrioventricular conduction during the infusion of ouabain (1 µg/kg min -1 ) until the onset of ventricular tachycardia. Sinus rhythm was interrupted every minute by 15 seconds of atrial pacing at either 150 or 200 beats/min. Positive chronotropic effects were recognized immediately after pacing as (1) early ventricular escape beats during vagal stimulation, (2) early atrial escape beats during vagal stimulation, or (3) blunting of the normal postpacing atrial depression. Positive chronotropic effects were rate dependent in both chambers, but they were seen less often in the atrium than in the ventricle. Early ventricular escape beats occurred in all ten dogs at a pacing rate of 200 beats/min when 69 ± 12% of the dose of ouabain required to induce ventricular tachycardia had been administered. They occurred in six of ten dogs at 150 beats/min after infusion of 81 ± 6% of the dose of ouabain which induces tachycardia. Early atrial escape beats did not occur when the hearts were paced at 150 beats/min. However, they appeared in three of ten dogs paced at 200 beats/min after infusion of 93 ± 5% of the dose of ouabain which induces tachycardia. Blunting of the normal postpacing atrial depression occurred in six of ten dogs at both 150 and 200 beats/ min at 100 ± 4% and 89 ± 5%, respectively, of the dose of ouabain required to induce ventricular tachycardia. Six additional dogs with heart block were paced at an atrial rate of 250 beats/min to facilitate positive chronotropic effects in the atrium with simultaneous ventricular pacing at 60 beats/min to delay the onset of positive chronotropic effects in the ventricle. This procedure allowed more consistent and relatively earlier detection of atrial positive chronotropic effects. In these experiments, early atrial escape beats occurred in five dogs after infusion of 80 ± 3% of the dose of ouabain required to induce ventricular tachycardia, and blunting of the normal postpacing atrial depression occurred in all six dogs after 78 ± 3% of the tachycardia-inducing dose of ouabain had been infused. It was concluded that toxic doses of ouabain induce positive chronotropic effects in the atrium of intact dogs. The effects occur later than do similar effects in the ventricle. Moreover, the positive chronotropic effects are heart rate dependent in both chambers and can be studied by atrial-ventricular; differential rate experiments.

Block allotransplantation of both lungs with pulmonary trunk and left atrium in dogs.

Eleven dogs received a double-lung-block allotransplantation under cardiopulmonary bypass. Six dogs survived over one hour with spontaneous breathing and normal right ventricular pressures. Postoperative blood gases and pressures are given for six animals. These data show a fall in systemic blood pressure and arterial oxygen partial pressure, a rise in PCO₂, and no change in pH after completion of transplantation. Causes of death were haemorrhage (7), inadequate cardiopulmonary bypass (2), early anoxic heart lesion (1), and post-perfusion low output syndrome (1).

Retrograde catheterization of the left atrium in intact conscious dogs.

ARTICLESRetrograde catheterization of the left atrium in intact conscious dogsR. Kumar, M. Collins, and W. B. Hood JrR. Kumar, M. Collins, and W. B. Hood JrPublished Online:01 Feb 1971https://doi.org/10.1152/jappl.1971.30.2.287MoreSectionsPDF (460 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat "Retrograde catheterization of the left atrium in intact conscious dogs." Journal of Applied Physiology, 30(2), pp. 287–288 Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation More from this issue > Volume 30Issue 2February 1971Pages 287-288 Copyright & PermissionsCopyright © 1971 the American Physiological Societyhttps://doi.org/10.1152/jappl.1971.30.2.287PubMed5543872History Published online 1 February 1971 Published in print 1 February 1971 Metrics

The efficacy of antiarrhythmic drugs in the prevention of recurrence of aconitine-induced atrial fibrillation after electrical conversion

We have developed an experimental model to assess the ability of drugs to maintain slow supraventricular rhythm after electrical conversion of atrial fibrillation. Fibrillation was produced by application of a saturated solution of aconitine to the surface of the right atrium of open-chest dogs. Right and left atrial electrograms, the lead II electrocardiogram, and blood pressure were recorded. A capacitor discharge (30 watt-seconds) was applied through electrodes placed on the right atrium and the left ventricle. Atrial rhythm was improved for 1 to 20 s following defibrillation; then atrial fibrillation returned owing to the continued presence of aconitine. Quinidine in doses up to 4 mg/kg did not convert the arrhythmia but increased the duration of recovery after defibrillation up to 49 s. Pronethalol in doses up to 8 mg/kg and propranolol in doses up to 0.8 mg/kg occasionally converted atrial fibrillation to normal rhythm, but had no effect upon the duration of recovery after defibrillation. Diphenylhydantoin was tested in doses up to 20 mg/kg. Rapid injection of doses above 10 mg/kg slowed or converted the arrhythmia. Slow injections of diphenylhydantoin had no direct effect on the atrial fibrillation, but the period of recovery after defibrillation was prolonged up to 700 s. These experiments show that drugs can enhance the ability of the heart to maintain a slow rhythm following electrical conversion of atrial fibrillation. Those agents which most effectively convert atrial fibrillation are not the most effective agents for preventing the return of fibrillation after conversion.

Phasic Color Changes in the Right Atrium of Dogs

SummaryHigh speed color motion pictures of the heart in 10 dogs have shown rapid phasic color changes in the right atrium which alternate between red and cyan with each cardiac cycle. Frame by frame measurement of color at 10 msec intervals throughout one cardiac cycle in one dog has shown a major red peak beginning approximately 195 msec after the onset of the P wave. Although the cause of these color changes is not yet known, they may result from phasic changes in coronary arterial flow through the atrial wall.

Particulare radiographic contrast material in quantitative evaluation of experimental mitral insufficiency.

An experimental macroparticulate contrast material (contrast-impregnated gelatin spherules) proved to be a sensitive indicator of patterns of intracardiac blood flow. To evaluate its use in the quantitative assessment of mitral regurgitation, the following technique was developed: Transseptal catheterization of the left atrium of dogs with experimentally induced mitral insufficiency was followed by high-speed cinefluorography of the left heart during intra-atrial injection of the radiopaque particles. Slow projection of completed films allowed the enumeration of particles expelled from the left ventricle into the aorta and of particles regurgitating into the left atrium. If one assumes proportionality between the flux of counted particles and the corresponding blood flows, the determined degree of mitral regurgitation ranged from 35 to 73% of the total left ventricular output (with standard deviations of 3.3 to 12.2 for consecutive groups of 100 particles employed). Good correlation was obtained with the results of indicator-dilution studies, using double sampling and continuous infusion techniques.

Relationship of myocardial blood flow and 86Rb clearance in left atrium of dogs

ARTICLESRelationship of myocardial blood flow and 86Rb clearance in left atrium of dogsLD Lyon, MC Craig, JL Davis, DC McDaniel, and WD LoveLD Lyon, MC Craig, JL Davis, DC McDaniel, and WD LovePublished Online:01 Jun 1967https://doi.org/10.1152/ajplegacy.1967.212.6.1512MoreSectionsPDF (665 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation More from this issue > Volume 212Issue 6June 1967Pages 1512-1514 Copyright & PermissionsCopyright © 1967 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1967.212.6.1512PubMed4952141History Published online 1 June 1967 Published in print 1 June 1967 Metrics

Direct Evidence of Nonuniform Distribution of Vagal Effects on Dog Atria

The duration of the monophasic action potential (APD), the interval between atrial beats and the delay time between excitation of the right and left atria of dogs were measured, using coaxial suction electrodes, before and during vagal stimulation. The effect of vagal stimulation on the degree of shortening of APD varied at different recording sites in the atrium, the shortening being more pronounced in the right than in the left atrium. Threshold and rate of recovery after cessation of stimulation varied throughout the atrium. The results indicate that the vagal effect is nonuniformly distributed over the atrium. The time difference between excitation of the right and left atria increased with vagal stimulation under the present experimental condition, suggesting that a reduction of synchrony of excitation occurred in the atrial myocardial fibers as a whole. The same conclusion was derived from analysis of the pattern of the P wave before and during vagal stimulation.

Repolarization Phase at Various Sites of the Right Atrium

By means of a suction electrode method, the time course of depolarization and repolarization was observed in the in situ exposed right atrium of dogs. Under normal conditions the end of repolarization at various sites on the atrium occurred after the QRS spikes, and therefore, the T a wave should be inscribed after and not during the QRS spikes. The concentric spread of activation originating from the S-A node has been confirmed. The region of inital excitation does not become the initial focus of repolarization. The initial focus of repolarization is different from animal to animal, and this focus cannot be associated with any special cardiac tissue. The process of repolarization occurs concentrically from an initial focus that is not limited to any specific region of the atrium.

Intracardic thrombosis on implants of graphite cloth and of gold-plated polyurethane

Summary Acid-absorbing and electroconductive woven graphite cloth pretreated with heparin solution and suspended between the right atrium and right ventricle of dogs failed to decrease the the extent of thrombosis that was seen on other materials with “rough” surfaces. The electro-conductivity of gold-plated, smooth, intracardiac implants of polyurethane did not alter or delay the thrombus formation either, the size and quality of thrombi being the same as on smooth and nonconductive plastics. The earlier conclusions that the “rough” materials in heart chambers are covered with thrombus by direct deposition from the blood stream, and that the smooth plastic stays free from thrombi when it is not in the contact with the suture lines, are supported with data from these experiments.

Clearance of Rb86 from Coronary Blood by the Atria of Dogs.

The rate of clearance of Rb86 from blood by several areas of the atria was studied in 18 dogs because of evidence that Rb86 uptake and rate of coronary blood flow are closely related. Mean rates of clearance averaged 0.40 ml blood/g/min. These were not significantly different in the right atrium, left atrium and interatrial septum. Rb86 uptake by the atria formed a larger portion of total myocardial uptake when cardiac output was low. Frequently the clearance per gram of tissue exceeded that found simultaneously in the ventricles. Finally, this indicates that atrial flow is better maintained when the animal is in poor condition than is flow to the ventricles.

Effects of changes in intraluminal pressure on inotropic and chronotropic responses of isolated mammalian hearts.

The effect of increasing the intraluminal pressure in the right heart on the activity of isolated perfused dog hearts and the effect of increasing the intraluminal pressure on the activity of isolated right atria of dogs, rabbits, guinea pigs and albino rats have been studied. It has been observed that there is a direct relationship between the magnitude of intraluminal right atrial pressure and the inotropic and chronotropic responses of the whole heart and right atrium up to certain critical pressures (5–15 mm Hg). Some modifications in this behavior of the hearts due to repeated changes in the intraluminal pressure have also been described. It has been suggested that stretch of the cardiac tissue due to increased intraluminal pressure may cause alterations in membrane metabolism at the pacemaker.

Temperature changes in the blood of the pulmonary artery and left atrium of dogs during exposure to extreme cold.

Polyethylene cannulae were surgically placed in the pulmonary artery and left atrium of dogs; thermistors mounted in polyethylene tubing and hypodermic needles, were passed through these cannulae and the temperature changes of the blood and rectum were recorded photographically. Continuous recordings of these temperature changes in unanesthetized dogs were made when the experimental animals were suddenly exposed to an ambient temperature of –35°C for 30 minutes. Shivering began immediately after exposure to cold; blood and rectal temperatures increased 0.4–0.5°C during the 30 minutes of exposure. It was found that the rectal temperature exceeded the left atrial blood temperatures from 0.2 to 0.3°C, and that in all experiments except one, the left atrial blood temperature exceeded that of the pulmonary artery from 0.01 to 0.15°C. Increased metabolism, along with cutaneous vasoconstriction probably explains the rise in blood and rectal temperatures during exposure to cold. Thermodynamic considerations of carbon dioxide and oxygen exchanges in the lungs lend support to the findings regarding the pulmonary artery-left atrial blood temperature gradient.

Acute dynamic effects of a shunt between a systemic artery and the left atrium.

A communication was established between the left subclavian artery and left atrium in dogs to assess the acute dynamic effects of a diastolic input load on the left heart. Sudden diastolic pressure loading, produced by opening the shunt abruptly was followed by acute ventricular dilatation and fibrillation, and pulmonary congestion and edema. Gradual opening of the shunt provided time for cardiac adjustments to the increased ventricular output, and acute failure did not occur. These data suggest that adjustments in myocardial function can take place quickly in response to a markedly enhanced input load. On opening the shunt the aortic pressure fell in consonance with the decreased total peripheral resistance, while the left atrial pressure increased sharply. The pulmonary arterial pressure remained unchanged. Systemic vasoconstriction produced by adrenalin, strophanthin or asphyxia enhanced the flow through the shunt.