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Biomedical subjects

B S Lewis

Publications and source records attributed to B S Lewis.

35 records · Page 2Linked to original sources
PubMed1978

Selective coronary angiography in patients with conduction disturbances of the heart.

Selective coronary angiography and left ventriculography was performed in 14 patients with conduction disturbances of the heart or chronic complete heart block. Occlusive coronary arterial diseas was present in 3 patients: 2 of these had had extensive previous myocardial infarction and 1 complained of angina pectoris. The other patients gave no history of coronary artery disease and conduction abnormalities were the consequence of idiopathic fibrosis of the conducting system. The coronary arteries were normal or dilated and were remarkably free of atheroma in this group of older patients. Left ventricular function, as measured by ejection fraction, was normal except in the 2 patients who had had previous myocardial infarction.

Adult↗
PubMed1978

Computer prediction of left ventricular complicance throughout diastole in normal patients.

This study deals with the development of a computer program to predict instantaneous left ventricular complicance, as defined by the tangent modulus E, throughout diastole. Diastole is divided into discrete time intervals according to the major events which occur: the start of isovolumic relaxation (aortic valve closure), mitral valve opening, the point of minimum left ventricular pressure, the junction of the rapid and slow filling phases, the start of atrial systole, and the peak of the 'a' wave. Each interval is separated into subintervals. Over each subinterval two mechanisms are assumed to operate: myocardial relaxation or contraction producing a pressure change without an accompanying volume change, followed by explansion of the left ventricle at constant pressure. Although these mechanisms occur simultaneously in the intact heart, they are treated sequentially in a multistage computer program that employs the finite element technique to determine the displacements within a thick-walled ellipsoidal shell. The smaller the time interval between successive stages, the closer is the approximation to the actual continous process of myocardial relaxation, contraction, and distension. Diastolic determinants revealed in this investigation are the mechanical properties of the myocardium, the state variables of pressure and volume, and the control variables of wall thickness and cavity size. In isovolumic relaxation, the myocardium relaxes and the ventricular wall thickens to reduce intracavitary pressure. The relaxation process continues and intraventricular pressure falls to a minimum (0-point) while ventricular volume increases after mitral valve opening. In the succeeding phases, excluding atrial systole, ventricular filling pursues, the properties of the myocardium change, there is an increase in tone (possibly due to myocardial contraction), the wall thins and intraventricular pressure rises. Computer prediction shows that at the start of diastole the tangent modulus is approximately 6 times the enddiastolic value, and is nearly 0 at the onset of the slow filling phase. Tangant modulus is a useful index by which to distinguish normal from abnormal patients provided the characteristics of E as a function of time are recognized and compared throughout diastole.

Compliance↗
PubMed1978

Left ventricular wall thickness during the isovolumic relaxation period.

Left ventricular (LV) wall thickness was measured by echocardiography at the onset and at the end of the isovolumic relaxation period (IRP) in a group of normal young subjects. Measured LV minor diameter was constant during the IRP in these patients and there was no change in interventricular septal thickness. Posterior LV wall thickness increased by 12 +/- 6 (SD)% (P less than 0.001) and mean LV wall thickness by 6 +/- 4% (P less than 0.01). An increase in LV wall thickness during the IRP is consistent with simple fluid dynamic principles.

Adolescent↗
PubMed1978

Echocardiographic left ventricular function in mitral stenosis.

Left ventricular function was measured by echocardiography in 22 patients with pure mitral stenosis. Thirteen patients underwent closed transventricular mitral valvulotomy and nine underwent open mitral valvulotomy using cardiopulmonary bypass. Preoperative left ventricular function was normal in most patients but was depressed in older subjects (P less than 0.05) and in those undergoing a second operation on the mitral valve (P less than 0.001). The decrease in left ventricular function was probably related to the duration of mitral valve disease, with fibrosis and rigidity of the subvalvar apparatus and posterobasal left ventricular wall. There was no change in ventricular dimensions or in left ventricular function as measured by percentage shortening of the left ventricular diameter and ejection fraction 7 to 12 days after open or closed mitral valvulotomy.

Adult↗
PubMed1977

Deanol in minimal brain dysfunction.

The literature on minimal brain dysfunction is confused, confusing and controversial. The statements that the condition exists, needs treatment, and that treatment may be pharmacological, are more expressions of faith than accepted fact. We believe they are true (within limits not discussed in the article). Furthermore, there is evidence that some patients with MBD are hypo-aroused, while others are not. The role of deanol in the treatment of MBD is still unclear, because of the complexities of identifying appropriate patients in terms of levels of arousal, as well as identifying appropriate measures of response. There is sufficient support for an effect of deanol in the literature to justify further investigation. Further studies should attend to important methodological problems as discussed.

Attention Deficit Disorder with Hyperactivity↗
PubMed1977

Echocardiographic left ventricular function in aortic and mitral incompetence and the effect of valve replacement.

Left ventricular (LV) function was studied by echocardiography in 28 patients with volume overload of the LV before and after valve replacement. Of the 28 subjects, 19 had mitral valve disease (eight with mitral incompetence and 11 with mitral incompetence and stenosis) and nine patients had aortic incompetence. Patients with chronic mitral and aortic incompetence had marked LV enlargement with normal or slightly depressed systolic function; in those with acute mitral incompetence the degree of cardiomegaly was less and the state of LV function depended on the underlying cause of valvular incompetence. Valve replacement was followed by a decrease in LV end-diastolic volume and this occurred in the first week after operation. There was a gradual improvement in LV function in some patients, as measured by normalized mean velocity of posterior LV wall motion. Paradoxical septal motion occurred in many patients after operation but improved in the late postoperative period.

Adolescent↗
PubMed1976

Pulsus paradoxus in the bedside assessment of patients with bronchial asthma.

Pulsus paradoxus (PP) was measured in 35 patients with bronchial asthma. The presence and degree of PP correlated well with the clinical conditions of the patient and with peak expiratory flow rate (PEF). PP and PEF are useful bedside measurements in the assessment and management of patients with bronchial asthma. Although the degree of PP is usually directly related to the severity of the attack of asthma, it was absent in the one patient who remained severly ill with unreleived bronchospam when he became exhausted. Our experience with this patient, and with previous patients who are not included in the present analysis, emphasises the fact that PP must not be considered in isolation but in conjunction with the patient's clinical state and with other indices of the severity of the astmatic attack.

Acute Disease↗
PubMed1976

Ocular reaction to oxprenolol. A case report.

A case is presented of a patient who developed ocular symptoms and a skin rash after treatment with oxprenolol (Trasicor) for 2 months. The lesions improved on withdrawal of the drug and her eye symptoms became worse when she was again treated with oxprenolol. Patients who receive beta-adrenergic blocking drugs must be watched carefully for side-effects.

Drug Eruptions↗
PubMed1976

Left ventricular diastolic pressure-volume relations in man.

Diastolic function of the left ventricle was analysed in patients with different cardiac diseases: acute and chronic volume overload (in aortic and mitral incompetence), pressure overload and inappropriate ventricular hypertrophy (aortic stenosis and hypertrophic cardiomyopathy), congestive cardiomyopathy, and constrictive pericarditis. Most patients were receiving digitalis therapy at the time of study. A constant exponential relation between pressure and volume was assumed, and pressure-volume curves were constructed from two points: the instantaneous pressure-volume relation at beginning-diastole and at end-diastole. The determinants of left ventricular end-diastolic pressure were studied. Left ventricular end-diastolic pressure depended on the beginning-diastolic pressure and volume (O point), the slope of the pressure-volume curve (m), and the volume which distended the ventricle in diastole. In chronic volume loading and in congestive cardiomyopathy the curves were flatter than normal, so that left ventricular end-diastolic pressure was only slightly increased despite the large volume filling the ventricle. In pressure overload and in constrictive pericarditis the curves were steeper than normal. Acute changes in volume were accomplished by a shift up or down the pressure-volume curve but in these patients the slope was not altered: the ventricle had not had time to adapt and end-diastolic pressure was greatly increased.

Aortic Valve Insufficiency↗
PubMed1976

Left ventricular function in chronic renal failure.

Left ventricular function was studied in 14 patients with end-stage chronic renal failure using non-invasive methods (echocardiography and systolic time intervals). Patients were divided into 3 groups. Group 1 consisted of 5 patients who were normotensive at the time of study and group 2 of 7 patients who were hypertensive when studied. Group 3 consisted of 2 patients: one was receiving propranolol and the other, studied 302 days after renal transplantation, was receiving digitalis for recurrent episodes of cardiac failure. All except the patient receiving propranolol had normal left ventricular function in systole with normal measurements of fractional fibre shortening (% delta S, EF) and normal measurements relating to the velocity of ventricular contraction (mean Vcf, mean velocity of posterior wall motion). Stroke volume and cardiac output were normal in some patients but were increased in patients with fluid overload. Early diastolic compliance of the left ventricle seemed to be normal except in the patient with recurrent cardiac failure. The study provided no evidence for the existence of a specific uraemic cardiomyopathy.

Adult↗
PubMed1975

Maximal rate of fall of left ventricular pressure in cardiomyopathy and constrictive pericarditis.

The maximal rate of fall of left ventricular pressure (peak negative dp/dt) was measured in 4 patients with congestive cardiomyopathy (primary myocardial disease), in 5 patients with constrictive pericarditis and in 3 controls. Measurements were made at rest, with leg raising, after a bolus of 6 mug intravenous isoprenaline, and in patients with constrictive pericarditis during pulsus paradoxus. Peak negative dp/dt was 1810 +/- 234 mmHg/sec in controls; it was reduced in patients with constrictive pericarditis (1337 +/- 514 mmHg/sec) and greatly decreased in patients with congestive cardiomyopathy (812 +/- 190 mmHg/sec). There was close linear correlation between resting peak positive and peak negative dp/dt and there was little change with leg raising. Isoprenaline caused an increase in peak positive dp/dt, but there was only a small change in peak negative dp/dt. In patients with constrictive pericarditis, peak negative dp/dt varied during pulsus paradoxus: the linear relationship to peak positive dp/dt was maintained throughout the respiratory cycle. Peak negative dp/dt may be a useful index of myocardial function.

Adolescent↗
PubMed1975

Velocity of contractile element shortening in constrictive pericarditis and the effect of pulsus paradoxus.

Force-velocity curves were constructed in nine patients with CP from a high-fidelity LV pressure tracing and its simultaneously recorded first derivative. Vmax and peak Vce (Vpm) were calculated using the 2-element (Hill) or Voigt model; the curves were also constructed and Vmax measured using the 3-element Maxwell model. The measurements were compared with those in a group of four patients with CMO and with two control subjects. Measurements of the celerity of ventricular contraction--peak LVdp/dt, Max d/IP and Vmax (2-element model)--were reduced in CP and greatly reduced in CMO. The effect of beat-to-beat variations in preload during pulsus paradoxus on the indices of ventricular celerity was studied. Peak LVdp/dt and Vpm varied with the change in LVEDP: the change in Vmax was negligible using the 2-element (Hill) or Voigt model. The 3-element (Maxwell) model failed to discriminate between the three groups of patients and seems to be invalid at high LV end-diastolic pressures.

Adolescent↗
PubMed1975

Immediate haemodynamic effects of verapamil in man.

The effect of the antiarrhythmic drug verapamil (Isoptin) on circulatory dynamics and myocardial contractility was studied in six patients in sinus rhythm: three patients were control subjects and three had underlying rheumatic valvular disease. The drug was given as an intravenous bolus (10 mg) and measurements made in the control state and repeated 1, 3, 5 and 10 min after administration of verapamil. Left ventricular (LV) systolic pressure fell by 18% 1 min after intravenous verapamil (p less than 0.01) and returned twoards the range of normal after 10 min. Heart rate increased and cardiac and stroke index were not altered 5 and 10 min after administration of the drug. Peak LVdp/dt and Vmax were reduced while LV end-diastolic pressure increased reflecting a decrease in LV contractility. The hemodynamic effects were similar in digitalised and nondigitalised patients.

Adult↗
PubMed1975

Left ventricular function in systole and diastole in aortic incompetence.

Left ventricular pressure-volume relationships were studied in 30 patients with aortic incompetence: six with an acute lesion, 21 with chronic disease and three patients in whom a cusp perforation was superimposed on chronic disease. In acute aortic incompetence, systolic function was depressed and in diastole an unprepared ventricle with a normal modulus of elasticity and a normal rate of change of instantaneous stiffness of the pressure-volume relationship was unable to tolerate the volume load, so that the early diastolic and end-diastolic pressures were elevated. Compliance was greatly reduced at these volumes because the ventricle was operating on the steep portion of its pressure-volume curve. In chronic aortic imcompetence, systolic function was, however, normal but adaptive processes allowed the ventricle to operate with a smaller rate of change of instantaneous stiffness and a flatter pressure-volume curve, so that the volume load could be accommodated at a lower end-diastolic pressure. In patients with an acute phase superimposed on chronic disease, the sudden additional volume overload shifted the position of the diastolic pressure of the patient from the adaptive pressure-volume curve of chronic aortic incompetence, so that although the rate of change of instantaneous stiffness was low, the lowest diastolic pressure recorded and the left ventricular end-diastolic pressures were elevated.

Acute Disease↗
PubMed1975

Cardiac hypertrophy and left ventricular end-diastolic stress.

Equatorial and longitudinal left ventricular wall stress were calculated at end-diastole in a group of 66 patients in sinus rhythm. Thirty-one patients had volume overload of the left ventricle: six with acute and 21 with chronic aortic incompetence, and four with chronic mitral incompetence. Another six patients had aortic stenosis and 25 had congestive cardiomyopathy. Four patients served as controls. Stress was calculated using a thick-walled ellipsoid model. In patients with volume overload and congestive cardiomyopathy, ventricular dilatation was accompanied by an appropriate increase in wall thickness so that the "stress conversion factor" (the factor relating pressure to stress) was normal and absolute stress depended on end-diastolic pressure. In pressure overload of the left ventricle (aortic stenosis), the increase in wall mass reduced the stress conversion factor so that aboslute fiber stress was normal. These data support the hypothesis that muscle fiber stress may be an important determinant of left ventricular hypertrophy.

Angiocardiography↗
PubMedDate not supplied

The hyperacute phase of true posterior infarction.

The hyperacute phase of true posterior myocardial infarction is described in detail. This electrocardiographic manifestation, hitherto unnamed as such, presents with slope-depression of the S-T segments with relatively wide and deep T-waves in the right precordial Leads V1 to V4. The condition then progresses to the well-recognized fully evoked phase of acute true posterior wall myocardial infarction.

Acute Disease↗