Dog Left Ventricle Research Articles

Distensibility of the dog left ventricle.

Left ventricular diastolic pressure-circumference curves were determined in 13 dogs, during stepwise hemorrhage and transfusion of blood. The linearity and small amount of scatter in the pressure-circumference curves obtained during control circumstances is evidence that elasticity rather than viscosity or inertia is the dominant determinant of the curve. Coincident with the slow infusion of epinephrine the distensibility increased. The importance of viscosity and inertial effects in the myocardial wall may also have increased, as evidenced by the increased scatter of the pressure-circumference graph. The magnitude of the change in distensibility observed was great enough to produce large changes in ventricular performance at a given filling pressure.

Instantaneous Dimensional Changes of the Left Ventricle in Dogs

The cardiac cycle in dogs starts with an isovolumic period in which there is shortening of the base-to-apex length with an increase in cross-sectional area. Total shortening is about one-fourth of that in open-chest dogs. Minimal changes in base-to-apex length occur during the ejection phase, and there is a typical pattern of decrease in cross-sectional area. During isovolumic relaxation, the left ventricular base-to-apex length increases. Rapid filling is characterized by a sudden increase in cross-sectional area and is followed by a diastasis of varying lengths. Atrial systole is associated with a sudden significant increase in cross-sectional area and a decrease in base-to-apex length. The magnitude of change in cross-sectional area about the left ventricle during ejection may be used as an index of stroke volume. Our studies suggest that the ventricle contracts in an "eccentric manner," and relaxes in a "concentric fashion." Simultaneous monitoring of the instantaneous changes in cross-sectional area and circumference about the middle of the left ventricle may be used as an index of its efficiency of contraction in awake, intact dogs.

Glutamic oxaloacetic transaminase activity in different zones of the ventricular muscle of the dog.

OF the tissues of several animal species the myocardium has the highest concentration of glutamic oxaloacetic transaminase (GOT)1–3. Distribution of this enzyme in several zones of the cardiac muscle has received but scant attention in the literature. However, it has been shown that the dog's left ventricle has a higher GOT activity than the right one4, and a similar difference has been described for the concentration of adenosine tri-phosphatase and succinic dehydrbgenase5. On the other hand, Jennings, Kaltenbach and Smetters failed to note significant differences in the left ventricle of the dog between the GOT activity of the posterior papillary muscle, the left ventricle immediately beneath, and the anterior superior septum6. The present observations show that GOT activity of the myocardium is not uniform, and that there are significant differences in dogs among several zones of both ventricles.

Interaction of actomyosin and adenosinetriphosphate as studied with glycerol-extracted cardiac muscle bundles.

Glycerol-extracted muscle bundles were obtained from the right and left ventricles of dogs. Isometric tension developed on addition of adenosinetriphosphate (ATP) and resistance to stretch of the extracted bundles and the rate of ATP hydrolysis of the myofibrillar components of the bundle were studied. Effects of temperature, ionic strength, pH and concentrations of ATP, sodium, magnesium and calcium were evaluated. The results indicated that the contractile phenomenon producing tension is a complex of at least two underlying reactions one of which promotes contraction ( R1) and the other ( R2) relaxation. Which of these reactions limits tension development is determined by the concentration of ATP. The concentration at which the transition takes place between R1 as the limiting reaction to R2 is a function of temperature, ionic strength, pH and the concentration of calcium ions. R1 appears to be associated with the hydrolysis of ATP and this may be the energy-supplying reaction. Certain findings in regard to the effect of concentration of divalent cations on the contractile response and the rate of hydrolysis are difficult to reconcile, however, with the contention that R1 is a reaction in which ATP is hydrolyzed. At very low concentration of Mg and Ca, hydrolysis is strikingly inhibited though contraction takes place. Furthermore, concentrations of Mg of the order of 2 x 10–2 m inhibit enzymatic hydrolysis and promote contraction. Concentrations of Ca of 10–2 m inhibit contraction but accelerate ATP hydrolysis.

Alterations in systemic vascular volume of the dog in response to hexamethonium and norepinephrine.

A diaphragm pump of controlled constant output was substituted for the left ventricle in dogs. Left auricular blood was conducted to a reservoir, from which it was pumped into the thoracic aorta. Left ventricular by-pass was complete. Alterations in total vascular volume were continually monitored by observation of the pump reservoir level. Sympathetic blockade (hexamethonium) increased total vascular volume (mean 15%). This resulted in decreased venous return and decreased right ventricular output. Norepinephrine constricted the total vasculature and decreased vascular volume (mean 12%). This resulted in increased venous return and cardiac output. These experiments demonstrated the complex integrated responses of the total circulation to sympathetic vasomotor activity. The role of the sympathetic nervous system not only in the regulation of arteriolar tone and cardiac activity but also in adjusting total vascular volume and venous return was emphasized. Venous return, and hence cardiac output alterations accompanying systemic vasomotor activity can only be detected by continuous methods of flow measurement.

The excitability cycle of the dog's left ventricle determined by anodal, cathodal, and bipolar stimulation.

Investigations are reported in which the excitability cycle of the dog's heart was tested successively by unipolar anodal and cathodal square wave shocks as well as by bipolar stimulation. The classical view that excitability decreases smoothly during the relative refractory phase was substantiated. The excitability for anodal stimulation reached its maximum of the cardiac cycle immediately after the absolute refractory period and exceeded cathodal excitability at that moment. Evidence is presented that the dip phenomenon described by Orias, Brooks and their associates is due to their arrangement of driving and testing electrodes. The coincidence of the dip phenomenon with the vulnerable period may be related to simultaneous spreading of two fronts of activation from cathode and anode of bipolar electrodes which would create favorable conditions for reentry.

New contributions to the study of the intracavity potential in cases of right bundle branch block in the human heart

1. 1. It is quite probable that in the hearts of normal subjects the upper portion of the interventricular septum is early activated from left to right. In this way it is easy to explain the initial positive deflection of the normal right intraventricular tracing. This deflection has a higher voltage when the exploring electrode is closer to the upper portions of the septum. 2 2. 2. There is no reason to believe that right bundle branch block alters the early activation of the upper portion of the septum. Therefore, one must suspect two different phases in the activation of the interventricular septum in right bundle branch block: the first is an early phase which corresponds to the activation of the upper portions of the septum. The electrocardiographic findings during this phase are the same as those found in normal subjects and are not modified by the presence of the block. Such as early phase of septal activation could explain the inscription of the initial positive deflection of the rsR complex in Lead V 1. The second is a later phase which appears 0.04 to 0.05 second after the beginning of QRS and which is not related to the first R in Lead V 1. During this later phase, activation of the septum below the lesion takes place. 3. 3. In cases of right bundle branch block we were able to register a rapid complex of the rsRS type with a negative T in leads taken from within the right ventricular cavity. The first small positive deflection of the intraventricular tracing coincides with the initial R in Lead V 1. The late positive deflection of the intraventricular tracing coincides with the first portion of the ascending branch of R′ in Lead V 1. It appears that in these intraventricular tracings we recorded the two phases of septal activation. 4. 4. It is possible to recognize in the right precordial leads the two phases of septal activation produced above and below the site of the block. One must not forget that the time of such activations is variable and depends, among other factors, on the thickness of the septum and on the existence of myocardial alterations in this septum. 5. 5. In a patient with coarctation of the aorta and a probable congenital right bundle branch block, we were able to study the left intraventricular potential. The exploring electrode passed through an interauricular communication and reached the left ventricular cavity. The tracing was similar to those which we have registered in the left ventricle of dogs in which the right bundle branch was severed.

Electrocardiograms with large, upright T waves and long Q-T intervals

It is suggested, on the basis of the experimental results of cooling or warming the endocardial surface of the dog's left ventricle, that large, upright T waves in the human electrocardiogram, together with prolongation of the Q-T interval, may oftent be due to ischemic changes preponderantly involving the muscle layers at the endocardial surface of the left ventricle. The best examples of electrocardiograms of this type were obtained from patients with arterial hypertension and symptoms and signs of encephalopathy. Further study is needed before the reason for this association can be suggested.