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Biomedical subjects

A M Johnson

Publications and source records attributed to A M Johnson.

At least 325 records · Page 18Linked to original sources
PubMed1986

A preliminary study of the transmission dynamics of the human immunodeficiency virus (HIV), the causative agent of AIDS.

The paper describes some preliminary attempts to formulate simple mathematical models of the transmission dynamics of HIV infection in homosexual communities. In conjunction with a survey of the available epidemiological data on HIV infection and the incidence of AIDS, the models are used to assess how various processes influence the course of the initial epidemic following the introduction of the virus. Models of the early stages of viral spread provide crude methods for estimating the basic reproductive rate of the virus, given a knowledge of the incubation period of the disease (AIDS) and the initial doubling time of the epidemic. More complex models are formulated to assess the influence of variation in the incubation period and heterogeneity in sexual activity. The latter factor is shown to have a major effect on the predicted pattern of the epidemic; high levels of heterogeneity decrease its magnitude. Areas of biological uncertainty, future research needs, and public health implications are discussed.

Acquired Immunodeficiency Syndrome↗
PubMed1986

Bronchopulmonary foregut malformations. The spectrum of anomalies.

Ventral anomalies of accessory pulmonary tissue have been classified as "bronchopulmonary foregut malformations." Between July 1, 1981, and May 31, 1985, 10 children with bronchopulmonary malformations have been cared for on the Pediatric Surgical Service at the University of Virginia. Six patients had bronchogenic cysts, one in an extrathoracic location and one associated with a pulmonary sequestration. Diagnosis was suspected in each case by plain chest radiographs and confirmed by computed tomography scans and ultrasound. Four patients had pulmonary sequestrations, two in association with diaphragmatic hernias. One patient had accessory pulmonary tissue, best classified as a tracheal lobe. Diagnosis in this patient was confirmed by bronchography. Nine patients underwent excision of the malformation without event. In one patient, a bronchogenic cyst was treated successfully by thoracoscopy. Review of the anatomy of these malformations leads to the conclusion that three embryologic events are cardinal in determining their ultimate form: (1) investment of the anomalous pulmonary tissue by the pulmonary artery; (2) the degree of involution of the original foregut communication; and (3) the stage of development leading to pleural investment.

Bronchial Diseases↗
PubMed1986

Evaluation of postoperative flow reserve in internal mammary artery bypass grafts.

The internal mammary artery has been advocated for use in bypass grafting owing to its superior long-term patency when compared to saphenous vein grafts. Concern exists that the flow through the internal mammary artery may be inadequate during periods of peak myocardial demand. This flow was investigated in 24 consecutive patients with a mean proximal left anterior descending artery stenosis of 87.5% who were selected for coronary bypass using the internal mammary artery. Within 8 weeks of operation, all were evaluated by exercise thallium 201 scintigraphy. Thallium activity, expressed as a ratio of anteroseptal activity to posterolateral wall activity (or inferior wall activity if the posterolateral wall was deemed abnormal), was 0.97 +/- 0.15. A second group of 25 patients, with normal coronary arteries, was similarly evaluated. The mean septal to posterolateral wall thallium activity ratio for these control patients was 1.0 +/- 0.15. A third group of 26 patients who underwent single-vessel percutaneous transluminal coronary angioplasty of the left anterior descending artery and a fourth group of 28 saphenous vein graft recipients were compared by stress thallium scintigraphy. Thallium 201 activity for the vein graft group (0.96 +/- 0.19) was not significantly different from that for the mammary artery group, whereas the flows obtained with a single attempt at angioplasty were significantly inferior (p less than 0.05). The internal mammary artery provides excellent coronary flow at peak myocardial demand and compares favorably to angioplasty and saphenous vein grafting.

Angioplasty, Balloon↗
PubMed1985

Left ventricular aneurysm. The Wessex experience.

One hundred patients with left ventricular aneurysms were operated on between February 1973 and January 1983. The principal indications for operation were left ventricular failure in 58, angina in 23, both in 17, with arrhythmia and systemic emboli accounting for one case each. Eighty five had had anterior infarction causing 82 anteroapical and three lateral aneurysms, while the remainder had had inferior infarcts resulting in 14 inferior aneurysms and one lateral aneurysm. Coronary angiography detected a single coronary lesion in 46%. Three patients had aneurysmal plication and the remainder had aneurysmectomy. Eleven mitral valve replacements were performed. Forty patients underwent coronary artery bypass grafting with a mean number of grafts per patients of 1.4. The early mortality was 7% with no early deaths since 1978. The actuarial five year survival was 68%, and 82% of survivors are in New York Heart Association class I or II (mean follow up three years). Left ventricular aneurysmectomy may be performed with a low operative mortality and good long term results.

Coronary Artery Bypass↗
PubMed1985

The antigenic structure of Toxoplasma gondii: a review.

Even though T. gondii is ubiquitous in the animal kingdom, definitive information on its antigenic structure has only become available over the last few years, largely as a result of recent advances in immunology and biochemistry. New knowledge in this area will enable the immune response to the parasite to be studied in greater detail and may lead to the development of newer, more meaningful diagnostic tests for toxoplasmosis, and possibly a vaccine against it. This paper reviews knowledge on the antigenic structure of this extremely widespread and important protozoan parasite.

Animals↗
PubMed1985

Detection of Toxoplasma-specific IgM in cord blood sera by antibody-class capture enzyme-linked immunosorbent assay.

An antibody class capture (ACC) enzyme-linked immunosorbent assay (ELISA) utilizing an F(ab)2 conjugate was established and its specificity and reproducibility were determined. The test was further validated by comparing its results with those obtained by 2 overseas reference laboratories which used the indirect immunofluorescence antibody test (IIFT) for Toxoplasma-specific IgM. It was found that the F(ab)2ACC-ELISA was not affected by the presence of rheumatoid and antinuclear factor in serum, that it was reproducible (coefficients of variation less than 10.0%), and that it compared well with tests currently used overseas. ELISA was then used to test for the presence of Toxoplasma-specific IgM in cord blood sera. The results obtained to date are consistent with the hypothesis that the prevalence of congenital toxoplasmosis in the population of Adelaide is less than 1/2,000.

Antigens, Protozoan↗
PubMed1985

Detection of Toxoplasma cysts and oocysts in an urban environment in a developed country.

Feces of 115 stray or unwanted cats were screened for Toxoplasma oocysts by sucrose density centrifugation and inoculation into mice. None of the feces examined contained detectable levels of viable oocysts. Using a laboratory infected cat, the sensitivity of this detection technique was found to be about 250 oocysts/g of feces by microscopic analysis and about 2 oocysts by mouse inoculation. Samples of pork and lamb chops bought from suburban butcher shops were screened for Toxoplasma cysts by pepsin digestion and mouse inoculation. One of the 30 pork and none of the 30 lamb chops contained viable cysts. Experimental studies determined that the sensitivity of this method of detection was about 1 cyst/100 g of tissue. The relative likelihood of each route of Toxoplasma infection for members of an urban community in a developed country is discussed.

Animals↗
PubMed1985

Primary small bowel malignancies.

Fifty-five patients with primary small bowel malignancies were evaluated from 1955 to 1983. Twenty-seven patients (49%) had carcinoid tumors, 16 (29%) had adenocarcinomas, and 12 (22%) had leiomyosarcomas. The average age at presentation was 68 years (range: carcinoids, 27-82; leiomyosarcomas, 36-75; adenocarcinomas, 40-83). Carcinoids and leiomyosarcomas were 1.7 and 2.0 times, respectively, more common in men; adenocarcinomas showed no sex predominance. Eighty-nine per cent of all patients had symptoms: abdominal pain in 65 per cent, obstruction in 23 per cent, bleeding in 8 per cent, and palpable mass in 5 per cent. Although 27 per cent of carcinoid patients were asymptomatic, 40 per cent exhibited the carcinoid syndrome. Symptoms were longstanding in the majority of cases, and, at the time of diagnosis, 49 per cent of the carcinomas were metastatic. Fifty-five per cent of the tumors were in the ileum, 24 per cent in the jejunum, and 21 per cent in the duodenum. Fifty-five patients (89%) underwent resection for palliation or cure. Five adenocarcinoma patients (32%) survived 1 year, and one (6%) lived 10 years. Twenty-five per cent of leiomyosarcoma patients survived for 10 years. Eighty-seven per cent of patients with carcinoids survived for 1 year, 39 per cent for 5 years, and 22 per cent for 10 years. Previous reports have documented the difficulty of diagnosing these lesions, as does the present study. A higher degree of physician awareness and a more aggressive investigation of referable symptoms should lead to earlier treatment and better long-term results.

Adenocarcinoma↗
PubMed1984

Enhancement of [3H]flunitrazepam binding by mianserin, in vivo.

Mianserin (5-20 mg/kg), like chlordiazepoxide (2.5-10 mg/kg), inhibits the shock-induced suppression of drinking (SSD) in rats. However, in contrast to chlordiazepoxide, the effect of mianserin is not blocked by the benzodiazepine antagonist, Ro 15-1788 (10 mg/kg). Although mianserin does not inhibit [3H]diazepam binding in vitro it has now been found to enhance [3H]flunitrazepam binding to mouse whole brain in vivo at 10-100 mg/kg p.o. These results suggest that mianserin does influence central benzodiazepine receptors, but the mechanism by which it does so differs from that of chlordiazepoxide.

Animals↗
PubMed1984

Strain-dependent, route of challenge-dependent, murine susceptibility to toxoplasmosis.

The response to an intraperitoneal (i.p.) parasite challenge was compared with that caused by an oral challenge, in five different strains of mice. The results are consistent with the hypothesis that murine susceptibility to toxoplasmosis is route of challenge-dependent as well as strain-dependent. The phenomenon occurs in both sexes and appears to be a recessive trait. The finding that the susceptibility of C57BL/6j mice to oral or i.p. challenge is almost the reverse of that of LACA mice, and that BALB/c mice are resistant to challenge by either route, offers an excellent laboratory model for studies on susceptibility to toxoplasmosis.

Animals↗
PubMed1984

Specificity of the enzyme-linked immunosorbent assay (ELISA) for Toxoplasma IgG antibody.

An ELISA developed for Toxoplasma IgG antibody was demonstrated to be more sensitive than the current reference tests, the indirect haemagglutination antibody test (IHAT) and the indirect immunofluorescence test (IIFT). No additional cross reactions were found in the ELISA with sera from patients with other parasitic infections, and there was no interference due to the presence of either rheumatoid factor or antinuclear antibodies.

Cross Reactions↗
PubMed1984

Esophageal atresia with double fistula: the missed anomaly.

Of the various anatomical types of atresia, that of esophageal atresia and double fistula is said to be the least common. In most series, frequency is less than 1%. Seventy-eight patients with esophageal atresia were treated at the University of Virginia Medical Center between 1955 and 1983. Six of them had esophageal atresia and double fistula, and in 5 of these 6, this anomaly was not diagnosed preoperatively and was not detected intraoperatively. Our experience suggests that proximal "pouchograms" are essential in the preoperative evaluation of these patients to detect the presence of esophageal atresia and double fistula. The morbidity and mortality occasioned by overlooking this anomaly far exceed the risk of the contrast study.

Barium Sulfate↗
PubMed1984

Acquired aorto-pulmonary fistula--case report.

Two reports of the rare condition, acquired aorto-pulmonary fistula, are presented, one the result of acute aortic dissection, the other, giant cell aortitis. The presentation, diagnosis, and management are discussed and the literature reviewed.

Aortic Dissection↗
PubMed1984

Looking for a business partner? Shake hands with the medical staff.

During these days of increased competition and dramatic changes in payment systems, pursuing business opportunities in cooperation with local physicians is becoming increasingly important. This articles describes the efforts of Health Central System, Minneapolis, to promote new partnerships with its hospitals' medical staffs at both the local hospital and the corporate level.

Governing Board↗
PubMed1984

Visual problems in children: detection and referral.

A study was made of 151 children referred to orthoptic clinics for suspected squint or suspected impairment of visual acuity. In only 50 children was there no abnormality. The contribution of different branches of the health service to detection and referral was measured. Parents and general practitioners were found to have an important role in early detection and referral, but there remained an important group of 19 children with squints undetected by their parents.There was some evidence of delay in referral, with less than half of the children with true squint being seen by a specialist within six months, and the reasons for this are discussed in terms of parents' and doctors' understanding of visual problems in children. Delay is discussed in relation to the complexity of services for child health and to recent proposals for the integration of paediatric surveillance in general practice.

Amblyopia↗