Showing papers on "Cardiac cycle published in 1967"

The Architecture of the Heart in Systole and Diastole Technique Of Rapid Fixation And Analysis Of Left Ventricular Geometry

Abstract: Techniques for rapid fixation of the canine left ventricle in systole or diastole that have permitted analysis of ventricular geometry under known hemodynamic conditions are described. Six ventricles were arrested at and diastole, 7 at end ejection, and 7 in diastole following acute ventricular overdistension. The architecture of the ventricles was analyzed from measurements of the fixed ventricles and silicone-rubber casts of the ventricular cavities. In ventricles of matched weights, the average reduction, from end diastole to end ejection, of the apex to mitral valve distance was 4.6%, while that from apex to aortic valve was less than 1%. The minor internal equator was reduced by 26%, the midwall radius by 16%, and the outer radius by 8.5%. The ratio of the average end-diastolic volume minus end-systolic volume to the end-diastolic volume (analogous to stroke volume/end-diastolic volume) averaged 59%. The average wall thickness was 28% greater in systolic than in diastolic ventricles. The papillary muscle volume averaged 5.0%e of ventricular volume at end diastole and 14.7% at end systole. The area of the mitral valve orifice averaged 28% less at end systole than at end diastole; this area was 39% more in the hearts subjected to over-transfusion than in those with normal filling pressures. These data provide a framework for construction of a geometric model suitable for use in analyses of the mechanics of left ventricular contraction. Moreover, the methods described offer the possibility of correlating ventricular geometry and ultrastructure with cardiac function in normal and in abnormal hearts.

Factors Determining Vulnerability to Ventricular Fibrillation Induced by 60-CPS Alternating Current

Abstract: Very weak, 60-cps alternating current applied directly to the heart can cause ventricular fibrillation; greater current strength is required to induce ventricular fibrillation with a single shock delivered during the vulnerable period of the cardiac cycle. The present experiments were designed to examine the basis of this difference. The studies were performed in anesthetized open-chest dogs. The current strength required to induce ventricular fibrillation was 0.52 ± 0.16 ma with 60 cps for 5 sec, and 15.0 ± 4.3 ma with a single square-wave pulse of 10 msec. However, when the duration of 60 cps was reduced to produce only 4, 3, 2, or 1 ventricular response, the threshold for ventricular fibrillation after the last response was 0.4, 2, 18, or 24 ma respectively. After any given number of successive premature ventricular responses, the fibrillation threshold was comparable with either 60 cps or a single pulse. We concluded that, if an accelerating ventricular tachycardia that is produced by 60-cps stimulation is of sufficient duration (5 or 6 beats), the VF threshold is reduced progressively after each premature ventricular response, thus making it possible to induce VF with very weak current.

A study of the period of isovolumic relaxation in normal subjects and in patients with heart disease.

Abstract: 1. 1. Measurements of isovolumic relaxation time from simultaneous recording of the apex cardiogram, carotid tracing and phonocardiogram were obtained in 64 normal subjects and in 60 patients with compensated heart disease. This time interval was measured from the second heart sound of the phonocardiogram to the O point of the apex cardiogram. The range for normal values was 50 to 140 milliseconds, with a mean of 103 ± 22 milliseconds. In the patients with compensated heart disease this interval ranged from 58 to 175, with a mean of 102 ± 26 milliseconds. The standard error of the measurement was 4 per cent of the mean. 2. 2. Age itself did not influence the duration of isovolumic relaxation time. Heart rate, exercise and the administration of isoproterenol significantly decreased the isovolumic relaxation time. 3. 3. Digitalis significantly increased the duration of the isovolumic relaxation time, which may prove to be the basis for a useful and simple method of evaluating digitalization in man. 4. 4. Since this period of the cardiac cycle may be altered by pharmacologic means and by disease states, it may be a useful avenue to the study of the condition of ventricular function in man.

Intracardiac Pressure-Flow Dynamics in Isolated Ventricular Septal Defects

Abstract: This study was conducted to determine the nature of intracardiac shunting in 50 patients between the ages of 3 and 15 years with isolated ventricular septal defects. Simultaneous right and left ventricular pressures and biplane cineangiocardiography were utilized to study the timing and the direction of flow across the defect. Patients with low to moderately elevated right ventricular pressures demonstrated left-to-right shunting across the defect throughout the cardiac cycle. When pressure in the right ventricle approximated that of the left, right-to-left shunting occurred across the defect into the left ventricle during isovolumic relaxation. All patients shared in common the following: (1) a predominant left-to-right gradient and shunt across the defect into the body of the right ventricle during diastole; and, (2) augmentation of the left-to-right gradient with resultant increase of the shunt into the right ventricle during isovolumic contraction immediately preceding opening of the aortic valve. In comparing patients with and without pulmonary hypertension, the major variations in the cardiac cycle occurred during the periods of ventricular ejection and isovolumic relaxation. These two periods are primarily affected by the changing relationships of the size of the defect, ratio of pulmonary to systemic resistance, and magnitude of net shunts.

Effects of induced ventricular fibrillation on ventricular performance and cardiac metabolism.

Abstract: The effects of induced ventricular fibrillation on ventricular performance and cardiac metabolism were studied in dogs. When ventricular fibrillation was induced by a brief 7.5-v a-c stimulus and allowed to persist spontaneously for one hour, no significant effects on subsequent cardiac function were apparent. An increase in myocardial oxygen consumption and a decrease in coronary vascular resistance occurred during the period of fibrillation. When ventricular fibrillation was maintained by constant a-c stimulation, however, immediate and significantly deleterious effects on cardiac performance resulted. Coronary vascular resistance rose; myocardial oxygen consumption increased, but the increase was significantly less than in animals in which fibrillation persisted without electrical stimulation. Anerobic glycolysis ensued, leading to lactate accumulation in coronary venous blood. The small a-c current used to maintain ventricular fibrillation impairs oxygen utilization, interferes with oxygen availability, and has a markedly deleterious effect on cardiac performance. A more satisfactory method of dependably maintaining the heart in ventricular fibrillation is needed before induced ventricular fibrillation can be safely employed to arrest cardiac contraction for prolonged periods during open cardiac operations.

Electrical Stimulation and Digitalis Drugs Repetitive Response in Diastole.

Abstract: SummaryIn the nondigitalized animal, a unipolar stimulus to the endocardium or myocardium discharged during diastole resulted in a single response unless energies greater than 5 J were used. During digitalization employing ouabain, the diastolic threshold energy for a repetitive ventricula response (RVR) was reduced by 6 orders of magnitude. RVR was first noted after 70% of the toxic dose of ouabain had been given and consisted of 2 ventricular ectopic beats. With advancing degrees of digitalization, a single stimulus evoked paroxysms of ventricular tachycardia. The most sensitive part of the cardiac cycle followed immediately after inscription of the T wave. As toxicity was approached, the zone of lowered threshold extended throughout most of the diastolic interval.

The Dominant Pacemaker of the Human Heart Antegrade and Retrograde Activation of the Heart

Abstract: In 25 cases at open heart surgery, atrial and ventricular close bipolar electrograms, an atrial unipolar electrogram, and a lead-II electrocardiogram were simultaneously monitored throughout each procedure In six cases the ventricles or atria, or both, were paced by electrical stimulation Although atrial activity could frequently not be clearly delineated on the lead II electrocardiogram, the time relationship between atrial and ventricular depolarization could at all times be determined from the electrograms During ventricular premature beats and ventricular rhythms, retrograde A-V conduction and retrograde activation of the atria were common, and unidirectional retrograde A-V block was infrequent In spontaneous and induced cardiac arrhythmias the fastest pacemaker of the heart, atrial, His bundle, or ventricular, usually activated the entire heart

Ventricular augmentor fibers in the cervical vagosympathetic trunk.

Abstract: SummaryThe existence of ventricular augmentor fibers in the cervical vago-sympathetic trunk of the dog has been established by electrical stimulation after atropine. These fibers are distributed directly to both right and left ventricles, although preliminary evidence indicates disproportionate supply to the right ventricle. Augmentation in atrial systole during vagal stimulation after atropine also indicates significant innervation of atrial musculature, but these influences may often be subordinate to alterations in mean atrial pressure. Cardioaccel-erator responses may or may not accompany the augmentor changes in intraventricular pressure, and are usually more characteristic of right vagal stimulation.

The myelinated fibers in the aortic nerve of the swine.

Abstract: The aortic nerves of 24 Chester White swine were identified electrophysiologically by the synchronization of the recorded action potentials with the cardiac cycle; and the occurrence of the maximum firing rates observed on the oscilloscope during systole. The aortic nerve, thus identified, was traced to the aortic arch in two preparations. The left aortic nerve was a separate bundle in 15 of 24 (62.5%) swine investigated. In the remaining 37.5% of the swine the nerve was dissected from within the vagus after identification at the level of the nodose ganglion. At this level the aortic nerve leaves the ganglion with the superior laryngeal nerve, runs caudomedially with it a short distance, then loops back laterally into the vagus to run caudally to the arch of the aorta. An aortic nerve was not observed in the right vagus nor in the sympathetic trunk of either side. The myelinated fibers counted from six aortic nerves were less than 10 μ in diameter with the majority in the 2–6 μ range, and averaged 542 in number.

Another look at echocardiography. Concepts in biomedical engineering.

Abstract: The ultrasonic waveform representing the motion of the anterior leaflet of the mitral valve provides precise timing for opening and closing of the mitral valve and for the opening snap. The largest amount of acoustic power in the cardiac cycle is generated from aortic valve opening and closing. Analysis of pulse-by-pulse echoes provides more accurate information. Pulse-by-pulse echoes provide a simple method for detecting turbulence at the mitral valve in patients with mitral regurgitation. The motion of the prosthetic ball and cage can be separated only by pulse-by-pulse analysis. Analysis of the echocardiogram may provide a simple, safe and painless technic for measuring stroke volume and cardiac output in patients with implanted prosthetic valves. The linear assumption of flow is known to be false, but the degree of nonlinearity is unknown. The pulse-by-pulse technic described here shows promise in terms of resolving the nonlinear flow.

Heart sounds in atrial flutter-fibrillation.

Abstract: Two cases of audible atrial sounds occurring during atrial flutter-fibrillation are reported. In the first case, the atrial sounds were recorded at roughly half the rate of the atrial flutter-fibrillation waves; this is in contrast to the usual 1:1 relation of all previously reported cases of atrial flutter. In the second case, the atrial sounds increased abruptly in intensity during ventricular systole and early diastole up to the opening snap. It is suggested that the atrial sounds in the present cases were produced by a rapid tensing of the atrial wall during atrial contraction. Such audible atrial activity is probably more common than is generally appreciated.

Effect of Decreasing the Force of Right Atrial Contraction on Right Ventricular Stroke Volume

Abstract: The effect of reducing the force of right atrial contraction on right ventricular stroke volume was determined in anesthetized open-chest dogs. Atrial contractile force, measured directly with a strain-gauge arch, was decreased by electrical stimulation of the right vagus nerve; right ventricular stroke volume was measured with an electro-magnetic flowmeter. Heart rate was maintained constant by electrical stimulation of the right atrium. Vagal stimulation decreased atrial contractile force by an average of 47±2.6 (SEM)% of the control, and stroke volume fell by 4.0±0.9%. During vagal stimulation, no change was observed in right ventricular contractile force. In addition, no consistent change was noted in mean right atrial or right ventricular pressures. The relation between the decrease in atrial force and stroke volume was not altered significantly by the rate of right atrial pacing. In 7 of 10 experiments, increasing the inhibition of atrial force produced a further decrease in stroke volume. Since neural, mechanical, and humoral factors modify atrial contractile force in the intact animal, the present study provides more definitive evidence that the ability to alter atrial force represents another adaptive mechanism in the regulation of cardiac performance.

The Precordial Movements in Adults with Pulmonic Stenosis

Abstract: The precordial movements were studied in 24 adults with pulmonic stenosis. All patients were studied by cardiac catheterization. Normal kinetocardiographic criteria were applied to the patients with pulmonic stenosis. These provided a measure of the magnitude of atrial movements and relative amplitude and duration of movements associated with ventricular systole. Twenty-two patients had abnormal ventricular systolic movements by these criteria. These increased systolic movements are attributed to right ventricular overload. However, the location of these movements was frequently in areas generally considered as reflecting left ventricular activity. Possible explanations for this apparent paradox are discussed. There was a predictable relation between the motions associated with atrial contraction and the right ventricular pressure.

Certain aspects of the heart as a pump

Abstract: Two aspects of the heart as a pump, largely dealing with factors molding the flow and pressure dynamics across the heart valves are presented These areas of cardiac dynamics included (1) the function of the atrium and (2) the dynamics of ventricular ejection Atrial systole was shown to consist of a wavelike contraction which propagates a pressure front toward the ventricle When the pressure front reaches the ventricle, the A-V valve is closed and there is a rise in ventricular end-diastolic size which causes an atrial-induced augmentation of the next ventricular contraction During the ventricular ejection, ventricular pressure was shown to exceed aortic pressure for 37 per cent of the ejection period and coincided with the period of blood acceleration During deceleration, but still forward flow, there was a negative gradient across the aortic valve At zero blood flow an abrupt aortic backflow coinciding with the incisura of aortic pressure indicated aortic valve closure It was shown that inertiance dominates flow dynamics across the aortic valve

Changes in the structure of left ventricular systole during cooling

Abstract: Although the act ion of hypothermia on the body and, in p a r t i c u l a r , on the hear t has been widely inves t iga ted , insuff ic ient at tention has been paid to the study of changes in the s t r u c t u r e of left v e n t r i c u l a r sys to le under the influence of cooling. The c o m p a r a t i v e l y few pape r s on this subjec t a r e incomplete and contain con t r ad i c to ry informat ion [10, 11].

The systolic murmur of combined pulmonary stenosis and infundibular stenosis

Abstract: This report describes a patient with severe valvular and functional subvalvular pulmonic stenosis in whom phonocardiograms, right heart catheterization and angiocardiograms demonstrate that the early part of the systolic murmur is due to flow through the pulmonary valves, and the late accentuation due to flow through both infundibulum and pulmonary valves. The importance of the late contraction of the infundibulum, as well as the persistence of a gradient between the inflow and outflow tracts, is emphasized. The late peak of the murmur reflects the higher velocity of the blood flow at the end of right ventricular systole. A presystolic murmur due to right atrial contraction and relative tricuspid stenosis is described.