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Biomedical subjects

J W Mason

Publications and source records attributed to J W Mason.

At least 163 records · Page 9Linked to original sources
PubMed1980

Accumulation of MSMA in the fruit of the blackberry (Rubus sp.).

The organic arsenical herbicide, MSMA, is used extensively for weed control along highway rights of way. Residues of the herbicide in edible crops growing near roadsides are of health concern since these products are accessible year round for harvesting by the unsuspecting public. This study examined the uptake and concentration of MSMA in the fruit of the blackberry during the various stages of maturation following the recommended application of 3.37 kg MSMA/hectare. MSMA-Aso accumulated with uptake being greatest in the earliest stages of fruit development. Arsenic levels consistently increased to concentrations of 25-30 microgram/g during one week following herbicide application to green fruit. Uptake during the later stages of development reached approximately 12.5 microgram/g in red and ripe fruit respectively. At all stages, uptake of herbicide in berries exceeded concentrations applied topically, indicating a major source of arsenic through transport from stems and leaves. Berries also absorbed herbicide following topical application to the fruit which is a significant source of arsenic following application in the later stages of development. The movement of herbicide to ripening fruit can be described by a three compartment model in which arsenic gains access from the surface of the berry and by translocation from stems and leaves. Parameter estimates for the model appear in the text.

Arsenic↗
PubMed1980

Evidence for a unidirectional retrograde communication between distal His bundle and atria.

Intracardiac electrogram recordings are presented suggesting the existence in one patient with recurrent supraventricular tachycardia of a functionally unidirectional retrograde connection between the distal His bundle and the low right atrium. Recordings obtained during junctional rhythm showed a short ventriculoatrial conduction time which did not lengthen during rapid or premature ventricular pacing. During an episode of supraventricular tachycardia induced by a single atrial premature stimulus, an infra-His Wenckebach period occurred during which retrograde ventriculoatrial conduction remained constant until ventricular capture was blocked, but atrial activation persisted with the same retrograde atrial activation sequence seen in the previous beats of supraventricular tachycardia. The findings appear to document participation in supraventricular tachycardia of a type of atrio-His fibre originally described by Brechenmacher.

Arrhythmias, Cardiac↗
PubMed1979

Reliability and reproducibility of interpretation of 99mtechnetium pyrophosphate myocardial scintigrams.

The interpretations of 156 99mtechnetium pyrophosphate myocardial scintigrams by four observers were analyzed in order to determine the reliability and reproducibility of the subjective process of reading scintigrams. The scintigrams were scored on an integral scale from 0 to 4, depending upon the degree of myocardial radionuclide accumulation, and the site and nature of uptake were specified. Exact agreement upon score was generally poor but approximate concurrence of interpretation was good (90.4 and 92.5% inter- and intra-observer agreement, respectively). There was somewhat less agreement on scintigrams with the higher scores of 3 and 4 (83.3 and 78.0%, respectively). A high level of concurrence upon the differentiation between diffuse and localized uptake, and upon the site of uptake, was found. We conclude that only approximate rather than exact agreement of individual readers' interpretations can be expected in this subjective technique, that scintigrams with higher degrees of radionuclide accumulation produce slightly greater observer disagreement, and that variability of interpretation could account for some of the diagnostic inaccuracy of 99mtechnetium pyrophosphate myocardial scintigraphy.

Angina Pectoris↗
PubMed1979

Screening of common bacteria capable of demethylation of methylmercuric chloride.

In summary, 21 bacteria were capable or degrading methylmercury chloride as measured by the disappearance of that species from the soil culture media. Disappearance of the methylated form was also accompanied by loss of total mercury in the culture media--probably as a result of reduction of the initial metabolite to volatile Hgo. The role of bacteria in the reduction step is not clear at this time although several authors (SUMMERS et al. 1972 and 1973; BISOGNI and LAWRENCE 1973 ) have suggested facilitated reduction rates in the presence of microorganisms.

Alkylmercury Compounds↗
PubMed1979

Canine electrophysiology of encainide, a new antiarrhythmic drug.

Encainide, a new benzanilide derivative with high potency and a good therapeutic/toxic ratio, was evaluated with the use of standard His bundle recording techniques to determine its effects on the cardiac conduction system in closed chest animals. Twenty mongrel dogs weighing 18 to 29 kg were anesthetized with 4 percent chloralose and classified into groups: group 1, a control group and groups 2, 3, and 4, which were given 0.3, 0.9 and 2.7 mg/kg body weight, respectively, of encainide in an intravenous infusion over a 15 minute period. Plasma concentration, blood pressure, surface electrocardiogram and atrial and His bundle electrograms were recorded before, during and after drug infusion for a total of 120 minutes. Heart rate, A-H and H-V intervals, the QRS complex and Q-Tc interval were measured every 5 minutes during sinus rhythm and with constant atrial pacing. In addition, sinus nodal recovery time and atrial, atrioventricular (A-V) nodal and left ventricular refractory periods were measured before and immediately after infusion and every 30 minutes for 2 hours. Peak plasma concentration averaged 450 ng/ml in group 2, 1,300 ng/ml in group 3 and 4,000 ng/ml in group 4. Blood pressure was not altered at any dose level throughout the study. The QRS complex and H-V interval were significantly prolonged (P less than 0.005) at doses of 0.9 mg/kg and greater. These effects correlated well with plasma concentration. There was no significant change in heart rate, corrected sinus nodal recovery time, A-H interval, Q-Tc interval atrial, A-V nodal or left ventricular refractory period. It is concluded that, unlike other antiarrhythmic agents, encainide prolongs His-Purkinje system conduction without significantly affecting conduction or refractoriness of other parts of the cardiac conduction system in animals.

Anilides↗
PubMed1979

Small vessel disease of the heart resulting in myocardial necrosis and death despite angiographically normal coronary arteries.

A 46 year old man who had undergone cardiac transplantation 1 year previously had progressive congestive heart failure without evidence of cardiac rejection. Cardiac catheterization and angiography revealed a reduced ejection fraction and cardiac output caused by diffuse left ventricular hypokinesia, but the epicardial coronary arteries were widely patent. The transit time of injected contrast material across the coronary arterial tree was greatly slowed. Within a few days cardiogenic shock and death occurred. The large epicardial coronary vessels were grossly patent at autopsy, although nonstenosing arteriosclerotic plaques were identifiable histologically. However, intramyocardial vessels showed severe arteriosclerotic narrowing, resulting in multiple, diffuse microinfarcts.

Coronary Angiography↗
PubMed1979

Clinical electrophysiologic effects of encainide, a newly developed antiarrhythmic agent.

Encainide is a newly developed antiarrhythmic agent. With the use of intracardiac electrophysiologic techniques, its effects on the cardiac conduction system were examined in 10 patients with coronary artery disease. Five patients received 0.6 and five received 0.9 mg/kg body weight of encainide intravenously over 15 minutes. Plasma concentration, heart rate, blood pressure and conduction intervals (A-H, H-V, QRS and Q-T) were measured before, during and after encainide infusion. In addition, sinus nodal recovery time, Wenckebach cycle length, and atrial, atrioventricular (A-V) nodal and right ventricular refractory periods were measured before and after encainide infusion. The average peak plasma concentration was 0.49 +/- 0.35 microgram/ml (mean +/- standard error of the mean). Encainide significantly prologned H-V and QRS intervals in all patients by an average of 31 +/- 7 and 18 +/- 9 percent (standard deviation) (P less than 0.001), respectively. A minimal increase in the Q-T interval was also observed after encainide infusion (2 +/- 9 percent, P less than 0.01), but no significant changes were noted in heart rate, blood pressure, A-H interval, corrected sinus noal recovery time, Wenckebach cycle length or refractory periods of the atrium, A-V node or right ventricle. It is concluded that encainide significantly prolongs conduction in the His-Purkinje system without affecting conduction or refractoriness of other parts of the cardiac conduction system in man.

Aged↗
PubMed1979

A prospective study of corticosteroid and catecholamine levels in relation to viral respiratory illness.

Urinary 17-OHCS, epinephrine and norepinephrine levels were studied for one week before and one week after the onset of acute, severe Adenovirus 4 respiratory illness in 12 Army recruits during Basic Combat Training. During the pre-illness period, a tendency was frequently noted for all three hormone levels to show "spiking" elevations two to four days before illness onset. There was also a tendency for 17-OHCS levels to rise on the day before fever onset. The possible relationship of these pre-illness hormonal changes to stressful experiences and, in turn, to altered host resistance to infectious illness is discussed. Following onset of respiratory illness, 17-OHCS, epinephrine and norepinephrine levels all showed about 60 percent increases over the early pre-illness period baseline value. Elevations of these hormones persisted for about four to five days, roughly in correlation with fever duration, with only slight differences in configuration and timing of curves from one hormone to the next. The problem of evaluating which of several independent variables operating concurrently during infectious illness may be responsible for stimulating the final common neuroendocrine pathways is discussed.

17-Hydroxycorticosteroids↗
PubMed1978

Electrophysiologic findings in patients with idiopathic hypertrophic subaortic stenosis.

Thirteen patients with catheterization-proved idiopathic hypertrophic subaortic stenosis underwent intracardiac electrophysiologic study. There was a large incidence of arrhythmias and a strikingly large incidence of conduction system abnormalities among these patients. The P-A and A-H intervals were normal in all patients. Atrial pacing resulted in Mobitz type 1 block proximal to the His bundle at an abnormal rate (less than 140/min) in 2 of 12 patients (17 percent). H-V intervals were prolonged (greater than 50 msec) in 10 of 12 patients (83 percent) and were greater than 60 msec in 7 patients (58 percent). The atrial effective refractory period was prolonged in 3 of 12 patients and was markedly prolonged in 1 of them. Effective refractory period of the atrioventricular (A-V) node, determined in five patients, was prolonged in three. Dual responses of the A-V node to atrial extrastimuli were found in seven patients. Dual A-V nodal repsonses were evoked with propranolol in three patients and persisted in the other four patients with dual responses despite propranolol administration.

Adult↗
PubMed1978

Techniques for right and left ventricular endomyocardial biopsy.

Right ventricular endomyocardial biopsy using percutaneous right internal jugular approach proved a safe and easily performed technique in more than 1,300 procedures. Adequate tissue was obtained in more than 98 percent of patients and morbidity rate was remarkably low. Other approaches to the right ventricle may be used, but retrograde left ventricular endomyocardial biopsy appears to be the safest and most reliable alternative to transjugular right ventricular biopsy. The safety and success of the techniques for right and left heart biopsy described depend on meticulous attention to methodologic detail.

Biopsy↗
PubMed1978

Cardiac biopsy evidence for a cardiomyopathy associated with symptomatic mitral valve prolapse.

Right ventricular endomyocardial biopsy was performed in 14 patients with mitral valve prolapse to determine the existence of an associated cardiomyopathic process. All 14 patients had echocardiographic, angiographic or auscultatory evidence of mitral valve prolapse, and all were symptomatic. The group had a high incidence rate of conduction system abnormalities (50 percent) and arrhythmias (64 percent), but only one patient had a significant hemodynamic abnormality. Light microscopy revealed an increase in endocardial and interstitial fibrosis in eight patients (57 percent). Electron microscopy, performed in 11 patients, showed mitochondrial degenerative changes in all 11. Nuclear chromatin clumping, intracell edema and myocyte degeneration were frequently present. It is concluded that endomyocardial and myocardial abnormalities exist in some symptomatic patients with idiopathic mitral valve prolapse.

Adult↗
PubMed1978

Cardiac sarcoidosis. Diagnosis with endomyocardial biopsy and treatment with corticosteroids.

A 27 year old woman was hospitalized for progressive dyspnea, fatigue and retrosternal chest pain. She had progressive cardiac enlargement with clinical and laboratory confirmation of a dilated cardiomyopathy. Transvenous percutaneous right ventricular endomyocardial biopsy yielded a specimen showing a noncaseating granuloma. The patient's dyspnea responded dramatically to steroid therapy with corresponding improvement in radiographic and echographic measures of ventricular performance. This case illustrates the problem of diagnosing cardiac sarcoidosis when there is no apparent evidence of other organ involvement.

Adult↗
PubMed1978

Successful treatment by overdrive pacing of recurrent quinidine syncope due to ventricular tachycardia.

A 54 year old patient who experienced recurrent ventricular tachycardia subsequent to quinidine administration for conversion of atrial fibrillation is described. Over a 10 hour period, 25 sustained episodes of ventricular tachycardia occurred for which electrical cardioversion was required in addition to numerous self-terminating paroxysms. Medical therapy with lidocaine, procainamide and propranolol was unsuccessful in controlling the arrhythmia. However, placement of a transvenous right ventricular pacemaker with overdrive pacing at a rate of 110 beats/min abrupty terminated all further ventricular ectopic activity during the period of quinidine elimination. Temporary overdrive pacing may be the treatment of choice for refractory, recurrent, ventricular tachycardia associated with quinidine therapy.

Atrial Fibrillation↗