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Biomedical subjects

J R Muir

Publications and source records attributed to J R Muir.

At least 19 recordsLinked to original sources
PubMed1979

Haemodynamic and electrocardiographic effects of intravenous disopyramide (rythmodan) following acute myocardial infarction.

1 The haemodynamic and electrocardiographic effects of intravenous disopyramide were studied in fifteen patients with acute myocardial infarction. 2 Five minutes after drug injection a rise in heart rate, aortic mean and diastolic pressures and systemic vascular resistence was noted which persisted for at least 30 min. A small increase in pulmonary arterial diastolic pressure (mean = 1.5 mm Hg) occurred at 5 min only and no significant change of cardiac output was found throughout the period of the study (1 h). 3 Surface electrocardiograms revealed transient prolongation of the P-R interval and a sustained increase in the QTc interval. 4 The haemodynamic changes suggest an anticholinergic effect of the drug. There was no definite evidence of a negative inotropic effect in this study, however, these peripheral haemodynamic measurements might not have revealed a modest negative inotropic effect. 5 The electrocardiographic changes are similar to those previously reported in normals and in patients without acute myocardial infarction.

Adult↗
PubMed1979

Estimation of myocardial infarct size in man using 99m Tc polyphosphate.

We have critically evaluated the use of 99m Tc polyphosphate to estimate myocardial infarct size. Optimum conditions were first defined with respect to infarct edge definition, and relative activity over infarct and bone and in blood pool. The scintigrams of 53 patients with acute transmural myocardial infarction were recorded under these defined constant conditions and analysed in various ways. Visual grading of infarct area or intensity correlated poorly with other indices of infarct severity. Computer-assisted measurements of above-background infarct uptake area or of total farct activity correlated well with clinical, electrocardiographic, and enzymatic measurements of infarct severity.

Adult↗
PubMed1977

The vectorcardiographic estimation of left ventricular filling pressure following acute myocardial infarction.

High gain vectorcardiograms, in the "timed" mode, have been recorded in 50 patients hospitalized with noncardiac complaints, and in 32 previously well patients following acute myocardial infarction. The terminal component of the atrial vector loop has been analysed in the horizontal, frontal and sagittal planes in all the cases. A technique is described by which the three variables, magnitude, direction and depolarization time of the terminal atrial vector in each plane can be summated to give a numerical value for the total displacement of left atrial activity. This figure is referred to as the "total vector value". In the 32 postinfarction patients the "P-terminal force" was also measured from lead V1 of the scalar electrocardiogram. In these patients both the total vector value and the "P-terminal force" was correlated with the pulmonary diastolic pressure, as an indirect assessment of left ventricular filling pressure. In the immediate postinfarction period the correlation between the total vector value and the pulmonary diastolic pressure was good (r = 0.92), but that between the "P-terminal force" and the pulmonary diastolic pressure was poor (r = 0.11). Alterations in atrial electrical activity recorded by either method correlated poorly with changes in the pulmonary arterial pressure occurring more than 36 h after acute infarction. The "total vector value" provides an accurate noninvasive method for the detection of a rise in the left ventricular enddiastolic pressure within the first 36 h following an acute myocardial infarction. It is superior in this respect to the "P-terminal force" measured from the standard scalar electrocardiogram.

Adult↗
PubMed1977

The electrophysiological evaluation of intravenous acebutolol, a beta-blocking drug.

The electrophysiological effects of acebutolol were studied in 12 patients. Heart rate and systemic arterial pressure were monitored. Plasma acebutolol levels were estimated. The first 6 patients (group A) received 0.3 mg/kg body weight I.V. The subsequent 6 patients (group B) received 0.5 mg/kg body weight I.V. Acebutolol delayed both antegrade and retrograde conduction through the AV node. The effect was greater in group B patients. Effective and functional refractory periods of the AV node were also increased after acebutolol. Intraatrial and intraventricular conduction and the effective refractory periods of the atrium and ventricle were not affected. Acebutolol did not alter significantly the sinus node recovery time or the QTc interval. Heart rate fell, especially where initial rates were fast. Systolic arterial pressure was lowered in group B patients. Peak mean levels of acebutolol were reached 5 min after injection of the drug. In the doses used, acebutolol, although well tolerated, failed to demonstrate electrophysiological evidence of a membrane-stabilizing effect and is therefore unlikely to add to the areas of success achieved by other beta-blocking drugs in the management of arrhythmias.

Acebutolol↗
PubMed1976

A study of the acute electrophysiological and cardiovascular action of disopyramide in man.

The acute electrophysiological and hemodynamic effects of intravenous disopyramide (1.5 mg/kg body weight) were studied in 12 patients with suspected coronary artery disease. Plasma levels of disopyramide were monitored. Disopyramide delayed conduction within the His-Purkinje system and increased the effective refractory period of the atrium. Conduction within the AV node and its refractory period, however, was not significantly altered by the drug. The corrected Q-T interval was significantly increased. Disopyramide increased systemic arterial pressure and slightly raised the left ventricular end diastolic pressure. Heart rate, cardiac and stroke index were unaltered. Peak mean levels of disopyramide were reached 5 minutes after the injection of the drug.

Adult↗
PubMed1975

A simplified technique for the production of experimental aortic regurgitation.

A simple and effective method for the production of aortic incompetence in dogs is described. The instrument used in the procedure can be made easily and is robust. Controlled rupture of one or more of the three aortic valve cusps can be achieved without thoracotomy. There was no immediate operative mortality in the study and the time required to complete the procedure averaged 30 min. No evidence of healing of the cusp rupture could be found at necropsy even in dogs sacrificed 480 days after operation.

Animals↗
PubMed1975

Ruptured sinus of Valsalva aneurysm with aortic-left atrial fistula.

We report the case of a previously healthy 56-year-old male who suddenly developed severe chest pain and pulmonary edema. Cardiac catheterization and angiography revealed an aneurysm of the noncoronary sinus of Valsalva which had ruptured into the left atrium. This was confirmed at operation and it was noted that there were no signs of bacterial infection or rheumatic valve disease. We therefore concluded that the aneurysm was of congential origin. A successful repair of the defect was carried out and the patient made a satisfactory recovery. There are only 3 other reported cases of rupture of a congenital sinus of Valsalva aneurysm into the left atrium, and in only one case did the aneurysm originate from the noncoronary sinus and this patient had associated rheumatic aortic and mitral valve disease. We have received the classification of sinus of Valsalva aneurysms, the associated congenital and acquired defects and the presenting features of unruptured and ruptured aneurysms.

Aortic Aneurysm↗
PubMed1975

The clinical features and significance of bifascicular block complicating acute myocardial infarction.

Two series of patients with anterior myocardial infarction complicated by right bundle branch block with either left anterior hemiblock (RBBB+LAH) or left posterior hemiblock (RBBB+LPH), have been studied. The first was a retrospective analysis taken from a time when prophylactic pacing wires were not inserted, and the second was a prospective series in whom pacing wires were inserted as soon as the condition defect was seen. The overall prevalence of RBBB+LAH was 3.3% compared to 1.6% for RBBB+LPH, and complete atrioventricular block was seen in 36% of the former and 66% of the latter. From the retrospective data it was apparent that hospital death was usually associated with massive myocardial infarction, although 3 of the 25 patients in this series died in hospital from sudden development of complete atrioventricular block. If the defect was transitory (1-3 days) then the prognosis was that of acute anterior infarction uncomplicated by fascicular block. The policy of prophylactic pacing failed to show any overall change in hospital mortality, and only 3 patients survived long enough to have permanent pacemakers inserted. This procedure has been of benefit to only one of these cases.

Bundle-Branch Block↗
PubMed1975

Calcium uptake and ATPase activity of microsomes from heterotopically transplanted rabbit heart.

Heterotopic cardiac transplantation was performed in rabbits. The calcium uptake and ATPase activities of microsomal fraction were studied in three groups (group I, normal controls; group II, early transplants; group III, late transplants) during severe rejection as characterized histologically and electrocardiographically. Group III showed a significant decrease in calcium uptake but no difference in ATPase activity compared with groups I or II. The results demonstrate that in the rejecting transplanted hearts there is an uncoupling of microsomal calcium uptake from this ATP splitting function.

Adenosine Triphosphatases↗
PubMed1975

The effects of iron deficiency on rat liver enzymes.

The effect of iron deficiency on a number or iron containing enzymes in rat liver has been examined. In addition, 6-phosphogluconate dehydrogenase and glucose 6-phosphate dehydrogenase have been assayed. Of the mitochondrial electron transport reactions only succinate-cytochrome C reductase activity was decreased in iron deficient animals. Microsomal reductase enzymes associated with the NADPH-oxidase system were also markedly decreased although cytochrome P450 concentrations were unaffected. Both 6-phosphogluconate dehydrogenase and glucose 6-phosphate dehydrogenase were reduced in young iron deficient rats but the former had returned to control levels at the age of 14 weeks.

Age Factors↗
PubMed1975

Observations on the interaction of calcium and hydrogen ions on ATP hydrolysis by the contractile elements of cardiac muscle.

The ability of cardiac myosin, actomyosin, and myofibrils to hydrolyze ATP has been studied at varying hydrogen and calcium ion concentrations. The ATPase activity of dog cardiac myofibrils was measured over the pH range of 6.5-7.4, as the calcium ion concentration was varied from 0-1.5 X 10(-4) M. The ATPase of these myofibrils, and of rabbit cardiac myosin and actomyosin was also measured in the absence of ionic calcium over the pH range 6-9. The Km of MgATP of cardiac myofibrils was studied over the pH range 6.5-7.4. In the absence of calcium ions, myofibrillar, myosin, and actomyosin ATPase activities are maximal at pH 8.0. At any given calcium ion concentration, the myofibrillar ATPase is depressed by lowering pH. The results suggest that the influence of hydrogen ions on the ability of myofibrils to hydrolyze ATP is complex, and may not only be the result of a simple competition between hydrogen and calcium ions for binding sites on troponin.

Actomyosin↗