Combined prosthetic replacement of the mitral and aortic valves. Preoperative and postoperative hemodynamic studies at rest and the left ventricular response to muscular exercise

Detailed preoperative and postoperative hemodynamic studies were carried out in 12 patients with severe aortic and mitral valve disease in whom replacement of both valves with ball-valve prostheses was carried out. Replacement of both valves resulted in restoration to normal, or nearly normal, the resting values of cardiac output, left ventricular end-diastolic pressure (LVEDP), pulmonary arterial pressure, and pulmonary vascular resistance. However, studies of left ventricular function during muscular exercise revealed abnormalities in the relationships between cardiac output and oxygen consumption in six of seven patients, and in no patient was the left ventricular response to exercise normal when assessed by the relation between LVEDP and stroke volume. It appears likely, therefore, that underlying myocardial disease or coronary arterial disease contributed to the preoperative disability in these patients, and may limit complete symptomatic recovery following operation. The residual impairment of myocardial performance observed in these patients appears to be more pronounced than that previously demonstrated in patients in whom isolated replacement of either the mitral or aortic valve had been performed.

The mechanics of left ventricular contraction in acute experimental cardiac failure

The effects of acute cardiac failure induced by pentobarbital or pronethalol on the basic mechanical properties of the intact left ventricle were examined in the dog, and the influence on auxotonic and isovolumic contractions of the increase in end-diastolic volume that usually accompanies cardiac failure was assessed. The right heart bypass preparation was employed, and isovolumic beats were induced by sudden balloon occlusion of the aortic root. The ventricular pressure-volume curve was determined directly, and the mechanical responses of the myocardial fibers and contractile elements were calculated.When end-diastolic pressure was held constant, failure reduced the extent of circumferential fiber shortening, and the tension-velocity relation calculated during isovolumic beats was always shifted, with reductions in both maximal velocity (average decrease 30%) and maximal developed tension (average 23%); in addition, during failure achievement of maximal contractile element velocity and maximal tension was delayed, whereas the total duration of contraction was always prolonged. Acetylstrophanthidin tended to reverse all of these changes. When end-diastolic volume was augmented during failure at a constant stroke volume, the extent of circumferential fiber shortening was reduced (3.82 cm to 2.02 cm), and during ejection the fiber and contractile element velocities were diminished at wall tensions comparable to control; maximal velocity and velocity at peak tension were also decreased. The tension-velocity relation during isovolumic beats was shifted by failure with consistent reductions in maximal shortening velocity, but changes in maximal tension were small. Maximal instantaneous power was always reduced by failure, and a striking alteration occurred in the relation between work expended in stretching the series elastic component and the external work; the former, "internal work," increased by an average of 90%, the latter diminished by 11%, and the total contractile element work remained essentially unchanged. These findings are discussed within the framework of a three dimensional model that included fiber length, wall tension, and contractile element velocity. The experimental techniques employed appear to permit a more complete definition of the abnormalities of the ventricular myocardium in experimental failure. They are potentially applicable in the closed-chest animal and allow quantitative determinations of the contractile properties of the left ventricle.

Alterations in resting length-tension relations of cardiac muscle induced by changes in contractile force

Effects of sustained postextrasystolic potentiation (P.S.), norepinephrine (NE), and calcium on resting length-tension relations of heart muscle were studied in the cat papillary muscle and isovolumic dog ventricle. In papillary muscles, P.S., calcium or NE produced no change in diastolic compliance when the muscles were freely isotonic, or afterloaded, and force remained constant. However, under isometric conditions, P.S. induced a small fall in diastolic tension while systolic force rose. Similar decrements in diastolic tension were observed when force of contraction was augmented by simply increasing afterload from a constant initial muscle length.

In the isovolumic ventricle, P.S., NE, and calcium each induced substantial increments in developed pressure, accompanied by small decreases in end-diastolic pressure. The latter was reduced or abolished by augmenting the initial contractile state with calcium or NE, so that the super-imposition of P.S. induced only trivial increments in developed pressure.

It is concluded that P.S., calcium, or NE do not induce changes in the resting length-tension relations of heart muscle per se. However, resting length at any given resting tension does increase slightly upon the augmentation of systolic force alone. It is postulated that these findings may be explained by the existence of a series viscous component.

Patterns of brachial arterial blood flow in conscious human subjects with and without cardiac dysfunction

The patterns of phasic and instantaneous mean brachial arterial blood flow at rest, and during various interventions, were studied in 35 conscious human subjects. Flow was measured with an electromagnetic flowmeter applied to the brachial artery (BA) prior to retrograde arterial catheterization of the left ventricle.

The patterns of phasic BA flow in six patients without left-heart disease were compared with those of patients having a variety of cardiac lesions. In three patients with aortic stenosis, a prolonged upslope and a delayed systolic flow peak were noted, while in five patients with severe aortic regurgitation, a progressive decline in flow occurred throughout diastole; retrograde diastolic flow occurred infrequently at end diastole, but was elicited in three patients by inflation of a wrist cuff. Among seven patients with idiopathic hypertrophic subaortic stenosis, those with large pressure gradients across the left ventricular outflow tract exhibited a bifid systolic brachial arterial flow pulse and an abnormal response in brachial arterial flow during the beat following a premature ventricular contraction. In patients with mitral stenosis, the flow pulse was normal, while in three patients with mitral regurgitation, the period during which systolic flow occurred was abbreviated.

Mean brachial arterial blood flow averaged 72.7 ml/min, and neither peak nor mean flow levels bore a relation to the cardiac lesion, the stroke volume, or the cardiac index. All patients exhibited spontaneous variations in resting brachial arterial flow. Usually the fluctuations were in phase with periodic fluctuations in mean arterial pressure, although in some patients periodic fluctuations in arterial pressure and brachial arterial flow occurred in opposite directions, and in other patients random flow changes were observed.

Contractions of the forearm muscles were found to cause striking mechanical limitation of instantaneous brachial arterial flow. During maximal contraction of the forearm muscles, actual cessation of flow occurred.

Prior to investigating the influence of reflex interventions on brachial arterial flow, studies were performed to determine whether or not local anesthesia and surgical exposure of the brachial artery altered resting flow in forearm bed or the reflex connections to the forearm. Plethysmographic determinations of the resting forearm blood flow, and of the response to a cold pressor test, before and after exposure of the brachial artery, indicated that resting flow was unchanged and that reflex activity was essentially intact. Carotid arterial compression in five patients resulted in a prompt increase in forearm vascular resistance (average 53.4%). The response to manual stimulation of the carotid sinus in four patients suggested that reflex forearm vasodilatation was rapidly induced. In six patients studied during the course of a 20-second Valsalva maneuver, marked reflex vasoconstriction occurred approximately 10 seconds after the onset of the maneuver.

The present technique has permitted the first description of the normal pattern of phasic brachial arterial flow in unanesthetized human subjects, as well as the alterations in phasic flow contour accompanying various cardiac lesions. In addition, it has allowed investigation of rapid, transient alterations in peripheral arterial blood flow not previously accessible to measurement.

Studies on digitalis. XVI. Effects on myocardial oxygen consumption

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Left ventricular performance during muscular exercise in patients with and without cardiac dysfunction

The LVEDP, cardiac output, and V o o2 were measured before and during supine muscular exercise in 38 patients. The normal pattern, established in seven patients without left ventricular dysfunction, consisted of an exercise factor [see Equation in PDF File], an LVEDP during exercise of less than 12 mm Hg, and little change or a decrease in LVEDP, which was accompanied in most instances by an increase in the stroke volume. In the majority of 31 patients with various cardiac lesions, but without valvular regurgitation, measurement of the LVEDP before and during exercise permitted the definition of normal or abnormal left ventricular function when the status of the left ventricle could not have been ascertained from other measurements. Thus, in most of the patients with mitral stenosis and abnormal resting hemodynamics, the pattern of left ventricular function during exercise was considered to be normal. Among the patients with aortic stenosis or left ventricular myocardial disease and elevated resting LVEDP, two types of abnormal performance of the left ventricle were identified. In some patients, an increase in LVEDP was accompanied by an increase in stroke volume, and this response was termed "abnormal left ventricular dynamics"; in the remaining patients, an increase in LVEDP and no change or a fall in stroke volume occurred and this response was termed "depressed left ventricular function." It is concluded that determination of the LVEDP before and during exercise adds importantly to measurements of the changes in cardiac output and O 2 consumption in characterizing left ventricular performance. The method employs standard catheterization techniques and appears to provide a practical and useful means for evaluating the functional status of the left ventricle in patients with and without myocardial dysfunction.

Considerations regarding the technique for transseptal left heart catheterization

Improvements in the equipment and technique for transseptal left heart catheterization appear to have largely overcome the major problems and complications that have been encountered in recent years with this procedure. Improvements in equipment have included the addition of a stylet for the needle, modifications in the design of the catheter, and the use of a catheter tip occluder both for manipulation of the catheter within the left heart and to close the end hole during selective angiography. The steps employed for insertion of the catheter and needle were described in detail, and the use of landmarks such as the left main-stem bronchus, the spine, the left atrial shadow, and the aortic bulge was discussed. The indications for, and relative contraindications to, transseptal catheterization currently applied in this laboratory were also described. The relative contraindications consist of (1) a giant right atrium, (2) severe rotational anomalies of the heart or great vessels, and kyphoscoliosis; (3) marked dilation of the ascending aorta; (4) anticoagulant therapy, and (5) a history of recent systemic arterial embolization. Since the introduction of these technical changes and precautions, with the exception of one nonfatal aortic puncture, the problems previously encountered during transseptal catheterizations have been avoided in more than 350 consecutive transseptal left heart studies in this laboratory.

Comparison of the force-velocity relation and the ventricular function curve as measures of the contractile state of the intact heart

The contractile state of the intact canine left ventricle was investigated by determining the instantaneous relations between tension and contractile element velocity (V CE ) during the course of single, isovolumic beats produced by balloon occlusion of the aorta. The relative sensitivity of this relation was compared with that of the ventricular function curve (VFC) by exerting small inotropic influences. In seven experiments, low doses of norepinephrine always shifted the isovolumic force-velocity (FV) relation, increases occurring in maximum V CE (32.7%) and maximum tension (P 0 ) (16.9%). The VFC was unchanged in four of the seven dogs. Moderate hypothermia (average 30.8°C) in four dogs increased P 0 (average 28%), with no change, or a fall, in maximum VCE; the VFC during hypothermia was shifted upward and to the left in two experiments and unchanged in two. Moderate increases in heart rate always produced increases in maximum V CE (average 13.5%) but no change in the VFC was observed. Thus, the isovolumic FV relation proved more sensitive than the VFC in detecting changes in myocardial contractile state and allowed more complete definition of these alterations by providing separation of changes in shortening velocity from alterations in the strength of myocardial contraction.

Left ventricular function following replacement of the aortic valve. Hemodynamic responses to muscular exercise

Evaluations of left ventricular myocardial function were carried out in 14 patients 4 to 16 months after stenotic or regurgitant malformations of the aortic valve had been corrected by valve replacement. The circulatory responses to exercise, judged by the increases in cardiac output in relation to the increases in oxygen consumption, were normal or only mildly reduced in 12 patients. In five patients, the relationships between the change in the left ventricular end-diastolic pressure and the alteration in the stroke volume were also normal, a fall or an increase in left ventricular end-diastolic pressure of less than 3 mm. Hg being accompanied by an increase in stroke volume. In eight patients, however, abnormal increases in the left ventricular end-diastolic pressure occurred during exercise, and in four the left ventricular end-diastolic pressure was increased to levels above 12 mm. Hg. Variable alterations in the stroke volume accompanied these increases in end-diastolic pressure. It is suggested that in the three patients who exhibited simultaneous increases in left ventricular end-diastolic pressure and stroke volume, the changes were either a manifestation of the Frank-Starling mechanism, or primarily the result of a positive inotropic influence. In the five patients who exhibited increases in left ventricular end-diastolic pressure, but no change or a fall in stroke volume, it is proposed that a distinct depression of left ventricular performance was present. Thus, while the cardiac output response was adequate to meet the stress of exercise in the majority of the patients studied following aortic valve replacement, determination of the relationship between the left ventricular end-diastolic pressure and the stroke volume permitted the detection of abnormalities in the function of the left ventricle.

Oxygen cost of electrical activation of the heart

The present study was undertaken to define the O 2 requirements of electrical activation of the heart. Thirteen isolated canine hearts were perfused with whole blood from which calcium had been removed with an exchange resin and to which the disodium salt of ethylenediaminetetraacetic acid had been added. Spontaneous depolarizations were suppressed by raising the plasma potassium to an average concentration of 7.5 mEq/liter, and the right ventricle was stimulated electrically at controlled frequencies. Although the stimuli produced propagated depolarizations, neither high-sensitivity strain gauge arches sutured to both ventricles, nor careful visual observation, showed any evidence of associated contractile activity. Ten of the hearts were studied with repetitive single stimuli applied in the conventional fashion, while the remaining three hearts were subjected to paired electrical stimulation. Changes of myocardial O 2 consumption (MV · O 2 ) were measured at a constant coronary blood flow and arterial O 2 content by determining changes of venous O 2 content from a continuous recording of venous PO 2 . Increases of the frequency of depolarization were uniformly accompanied by small increases of MV · O 2 , averaging 0.40 ± 0.04 (SEM) µliter/activation/100 g. The increases were of the same order of magnitude in the hearts subjected to paired electrical stimulation as in the hearts studied with single stimulation, suggesting that the altered frequency and rhythm of depolarization in paired electrical stimulation cannot account for the marked increase of MV · O 2 which this intervention produces in the intact heart. It is concluded that the amount of O 2 required for electrical activation of the heart is less than 1% of the total O 2 consumption of the normally working heart.

Effective closure of the mitral valve without atrial systole

There has been considerable dispute concerning the role of atrial contraction in the closure of the atrioventricular valves. Selective angiocardiograms with left ventricular [see figure in the PDF file] opacification in 43 patients having a variety of arrhythmias that resulted in the absence of atrial systole, or in an abnormal temporal relationship between atrial and ventricular contractions, revealed no evidence of mitral regurgitation. From this observation it is concluded that a properly timed atrial contraction is not always essential for effective closure of the mitral valve in man.

Effects of changes in body position on the severity of obstruction to left ventricular outflow in idiopathic hypertrophic subaortic stenosis

The circulatory responses to alterations in posture were determined in 10 patients with idiopathic hypertrophic subaortic stenosis. Tilting to a 45° head-up position augmented the subaortic gradient by an average of 35 mm Hg and intensified the obstruction to left ventricular outflow. In addition, the post-extrasystolic decrease of the arterial pulse pressure became more prominent. Tilting to a 20° head-down position reduced the gradient by an average of 11 mm Hg and tended to reduce the severity of the obstruction. Elevation of the lower extremities also resulted in a reduction of the intraventricular systolic pressure gradient, the reduction averaging 28 mm Hg, and apparently increased the dimensions of the obstructing orifice.

It is postulated that these effects on the obstruction to outflow induced by changes in posture result primarily from alterations in left ventricular volume secondary to changes in venous return. As a consequence, in the upright position, the size of the left ventricular outflow tract is reduced and the intraventricular pressure gradient is augmented while the cardiac output is reduced, resulting in an intensification of the obstruction. The opposite changes occur during the head-down tilt or during elevation of the legs.

These hemodynamic findings provide an explanation for the intensification of symptoms commonly experienced by patients with idiopathic hypertrophic subaortic stenosis in the erect position, and for the discrepancies between the symptoms and the severity of obstruction determined by cardiac catheterization carried out in the supine position. Assumption of the head-down, legs-up position is suggested as an emergency therapeutic maneuver for patients with hypertrophic subaortic stenosis.

Mechanism of increase of myocardial oxygen uptake produced by catecholamines

The relative roles of augmented hemodynamic performance and direct stimulation of oxidative metabolism in mediating the increase of myocardial oxygen uptake (MVo2) produced by catecholamines have been examined in an isolated canine heart preparation. The responses of MVo2 to graded doses of isoproterenol, norepinephrine, or epinephrine were determined before and after the induction of cardiac arrest with potassium. Although increases of MVo2 occurred in the arrested state with the larger doses of the amines, they constituted only a small fraction, generally between 5 and 20%, of the increases produced by the same doses of amines when the hearts were beating. It is concluded that while large doses of catecholamines can increase oxidative metabolism of the nonbeating heart by a small amount, the increases of MVo2 produced by catecholamines in the beating heart are due in large part to the hemodynamic alterations which the amines induce.

Velocity of contraction as a determinant of myocardial oxygen consumption

In 12 dogs on right-heart bypass with heart rate, stroke volume, and aortic pressure constant, the velocity of contraction was augmented comparably by three fundamentally distinct interventions in the same heart: 1) sustained postextrasystolic potentiation produced by paired, electrical stimulation; 2) norepinephrine infusion; and 3) calcium infusion. In each instance the correlation between velocity of contraction and MVo2 was striking. During paired stimulation, maximum rate of left ventricular ejection increased by an average of 50.3% ± 3.8% (se of mean) above control, MVo2 increased by 1.96 ± 0.10 ml/100 g per min (39.8% ± 1.6% above control), while the tension-time index (TTI) fell 12.4% ± 1.1%. With norepinephrine, and with calcium, left ventricular ejection rates were increased 52.9 ± 3.2% and 55.1 ± 3.2%, respectively, and MVo2 was augmented 2.03 ± 0.08 ml/100 g per min and 1.87 ± 0.04 ml/100 g per min, while the TTI decreased 15.9 ± 0.6% and 12.4 ± 2.4%. Since MVo2 always increased substantially while TTI fell, tension cannot be considered to be the sole determinant of MVo2. Since comparable increases in velocity of contraction produced by different interventions were associated with similar large augmentations of MVo2, it appears that the velocity of contraction is an important determinant of MVo2. Furthermore, it is likely that the so-called O2 wasting effect exerted by norepinephrine on myocardial metabolism may be explained largely by an increased velocity of contraction.

Effects of changing heart rate in man by electrical stimulation of the right atrium. studies at rest, during exercise, and with isoproterenol

A technic is described for controlling the heart rate in patients with normal atrioventricular conduction by means of an electrical pacemaker catheter that stimulated the right atrium. When the heart rates of 17 patients in the resting state were elevated from an average of 80 to 121 beats/min., the cardiac indices remained virtually unchanged and averaged 3.67 and 3.72 L./min./M. 2 , respectively. Further increases in the heart rates resulted in small reductions in the cardiac indices to an average value of 3.21 L./min./M. 2 at 148 beats/min. The stroke volumes, ejection periods, and mean rates of ejection decreased as heart rate was increased.

The role of heart rate in the circulatory response to exercise was examined in seven patients. When the heart rates were controlled by electrical stimulation at rates comparable to those previously achieved spontaneously during exercise, it was observed that cardiac output rose normally with exercise and that this rise was accomplished entirely through an increase in the stroke volume. In five patients the effects of isoproterenol infusion were also studied before and during control of the heart rate at the level reached spontaneously during isoproterenol administration. Again, when the heart rate was not permitted to rise, the increases in cardiac output with isoproterenol were mediated through increases in the stroke volume. These studies indicate that in the absence of augmented metabolic requirements, homeostatic mechanisms maintain cardiac output relatively constant despite large induced changes in the heart rate. However, when metabolic demands are increased by muscular exercise, or the circulation is stimulated by catecholamines, cardiac output can rise through an increase in stroke volume, even when alterations in the heart rate are prevented.

Three cognitive dimensions

A logical space developed by Oppenheim to differentiate and locate publications was used to construct a self-report questionnaire. Factor analysis of responses to the questionnaire gave reason to suppose that Oppenheim's dimensional scheme may provide a basis for cognitive styles each corresponding to a different dimension.

Left atrial and left ventricular pressures in subjects without cardiovascular disease: observations in eighteen patients studied by transseptal left heart catheterization

Transseptal left heart catheterizations were carried out in 18 patients without apparent evidence of organic cardiovascular disease. These studies have permitted delineation of the pressures that exist in the left side of the heart in normal subjects studied in a basal physiologic state.