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Biomedical subjects

M R Stephens

Publications and source records attributed to M R Stephens.

30 records · Page 2Linked to original sources
PubMed1979

Carotid sinus hypersensitivity in patients presenting with syncope.

In 23 patients (ages 44 to 81) presenting with syncope, vertigo, or transient amnesia, carotid sinus massage produced a significant bradycardia in association with symptoms. The 10 most severely symptomatic patients were studied electrophysiologically, including measurement of intracardiac conduction times and corrected sinus node recovery times, as well as with carotid sinus massage before and after atropine. The only detectable abnormality in five of this group was asystole produced by carotid sinus massage; the other five had, in addition, evidence of either sinuatrial disease or an intracardiac conduction defect. Cardiac pacing in these 10 patients completely abolished their symptoms. In a control group of 52 asymptomatic patients (ages 36 to 87), an abnormal response to carotid sinus massage was uncommon (2%).

Adult↗
PubMed1979

The relationship of a decline in myofibrillar ATP-ase activity to the development of severe left ventricular hypertrophy in the rat.

Abdominal aortic coarctation in the rat led to a modest degree of cardiac hypertrophy associated with normal ATPase activity of myofibrills. The addition of aortic incompetence was accompanied by the development of severe hypertrophy (approx. 75 %). During the course of this latter increase in heart weight, the Ca++ ATPase of myofibrils progressively declined to a level 36% below controls. This occurred at a time when protein synthesis was stimulated as evidenced by increased incorporation of H3 lysine into myofibrils. Results are compatible with the hypothesis that the abnormal ATPase activity reflects the synthesis of an abnormal myosin molecule.

Animals↗
PubMed1978

Left anterior hemiblock in adult Africans.

A total of 4,000 consecutive electrocardiograms covering an 8-yr period was studied and all cases with pure left anterior hemiblock reviewed on the basis of clinical diagnosis and subsequent follow-ups. There were 66 cases in all, representing 1.6% of the total series with an age range of 30--81 and a mean of 53.4 yr; 43 males to 23 females--a ratio of approximately 2 : 1. 34 cases (51.5%) were hypertensives all with a minimum diastolic pressure of 120 mm Hg before treatment. Congestive cardiomyopathy accounted for 16 cases (24.3%) and diabetes mellitus unassociated with other ailments for another 6 cases (9.1%). Other causes included mixed aortic valve disease with 2 cases (3%), endomyocardial fibrosis with 2 cases (3%). In 6 patients (9.1%), all above the age of 70, who had been admitted for minor surgical operations, no cause could be found. This etiological pattern differs from that seen in white populations where ischemic heart disease is by far the commonest cause. The extreme rarity to left anterior hemiblock in rheumatic mitral valve disease is considered of help in separating cases of lone rheumatic regurgitation from those of mitral regurgitation complicating congestive cardiomyopathy if and when diagnostic difficulty arises.

Adult↗
PubMed1978

Portal hypertension in vinyl chloride monomer workers. A hemodynamic study.

Hemodynamic studies were performed in 5 vinyl chloride monomer workers in whom splenomegaly or thrombocytopenia was detected during a screening program at major chemical plant. Three patients had portal hypertension and collateral venous circulations, with intrasplenic pressures between 20 and 29 mm Hg and normal wedged hepatic venous pressures, but the gradient between the wedged and free hepatic vein pressures was also increased. Splenic blood flows were increased in both hypertensive and normotensive patients. There was no correlation between the splenic blood flow and the portal pressure or the presence of portal fibrosis. The portal hypertension associated with vinyl chloride exposure is mainly presinusoidal in type, and may be attributed to an abnormality of the portal vein radicles, or hepatic sinusoids.

Adult↗
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

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↗
PubMedDate not supplied

An audit of cardiac arrest management by extended trained ambulance crew.

OBJECTIVE: To audit the use of extended skills by South Glamorgan Ambulance crew in attempted resuscitations from out-of-hospital cardio-respiratory arrest, in terms of successful discharge of patients from hospital and the accuracy with which agreed protocols were applied. Design-Retrospective analysis of ambulance report forms, electrocardiograph rhythm strips, casualty cards and discharge summaries during 26 months (1st May 1987-30th June 1989). SETTING: A mixed urban and semi-rural area of 187 square miles with a population of 396,000. RESULTS: There were 274 attempted resuscitations. Seven patients (2.5%) were managed for primary respiratory arrest and 3 were discharged. In 98 patients (35.8%) the initial resuscitation protocol was for ventricular fibrillation: 26 were admitted and 17 were discharged. In 169 patients (61.7%) the initial resuscitation protocol was for asystole or electromechanical dissociation: 11 were admitted and 1 discharged. The majority of patients who were successfully discharged from hospital were those in ventricular fibrillation who responded to defibrillation alone (13 survivors). Drug administration may have played a role in the successful resuscitation of the remainder. Endotracheal intubation was successful in 94.7% and vein cannulation in 87.7% of attempts. There were deviations from the ventricular fibrillation protocol in 27 cases (27.5%) and from the asystole protocol in 27 cases (16.0%). CONCLUSION: Survival rates for ventricular fibrillation managed by these personnel were satisfactory with early defibrillation. Defibrillation alone was responsible for the majority of successful resuscitations. The additional benefit of drug administration appears small, though potentially important. The majority of patients were in asystole by the time the ambulance arrived. IMPLICATIONS: Extended trained crews use their skills effectively. The most important skill is defibrillation. Further studies are required to explain the high proportion of patients found in asystole. The performance of individual ambulance personnel should be assessed prospectively, because agreed resuscitation protocols are not always followed.

Ambulances↗