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Biomedical subjects

A M Stewart

Publications and source records attributed to A M Stewart.

At least 19 recordsLinked to original sources
PubMed1991

Evaluation of delayed effects of ionizing radiation: an historical perspective.

It is widely assumed that after the bombing of Hiroshima and Nagasaki there were no lasting effects of the acute injuries (which included extensive damage to blood forming tissues by the radiation) or the massively high death rate (which was caused by environmental effects of the blast as well as personal injuries). However, close inspection of the dose response curves for non-cancer deaths has shown that this could be a false impression caused by one effect of marrow aplasia being confused with leukemia (defective erythropoiesis) and a second effect being confused with early selection in favor of general fitness (defective immune responses). Possible consequences of such confusion (for cancer risk coefficients) are discussed in relation to what is known about late effects of prenatal x-rays and occupational exposures to radiation.

History, 20th Century↗
PubMed1991

Changing interactions between astrocytes and neurons during CNS maturation.

The environments of the developing brain and injured adult brain differ in their abilities to support axonal growth. To determine if astrocytes contribute to this difference, neurons were plated onto astrocytes cultured from the neonatal rat cortex and from the injured adult brain. Two patterns of neurite growth were observed in these two astrocyte culture systems. Neurons contacting the neonatal astrocytes had neurites that were twice as long as those contacting the injured adult astrocytes. Furthermore, in cultures with neonatal astrocytes, neurites faithfully followed the astrocytic processes, maximizing their contact, while in cultures of injured adult astrocytes, the neurites had a tendency to cross the processes orthogonally, minimizing their interaction with the astrocytes. When neurons were grown suspended over either neonatal or injured adult astrocytes, no difference in neurite length or the pattern of neurite growth was observed, indicating that neurite growth was not differentially affected by soluble factors released from the two populations of astrocytes. The addition of fetal calf serum, which is known to contain protease inhibitors, did not alter neurite growth when compared to serum-free medium, suggesting that a substantial difference in protease activity does not account for the variations in neurite length observed. Based on these results, it appears that the molecular components of the external surface of injured adult astrocytes do not support neurite growth to the same extent as those found on neonatal astrocytes. The differing abilities of these two populations of cultured astrocytes to support neurite growth in culture may reflect a change in the functional role of these cells that occurs during the development of the central nervous system.

Age Factors↗
PubMed1991

A randomised study of outcomes in a defined group of acutely ill elderly patients managed in a geriatric assessment unit or a general medical unit.

The aim of this study was to identify differences in the medical management and clinical outcome in a group of elderly patients admitted to a designated geriatric assessment unit (GAU) or to two general medical units (GMUs). A prospective randomised controlled trial was undertaken in 267 patients aged 70 years and over (mean age = 78.3 years). Following discharge from hospital, patients were followed up at three monthly intervals for a total of 12 months. At the time of discharge, no significant differences were found in inpatient management, length of stay, mortality rates, discharge rates to institutional care or utilisation of community services in patients admitted to the GAU and the GMUs. Similarly, no significant differences were found at three, six, nine, and 12 month follow up in case fatality, activities of daily living indices, mental health status, rates of institutional referral and the level of community service support in patients admitted to the GAU and the GMUs studied. These findings do not show any advantage for the unselected 70+ acutely ill elderly patient who is admitted to a designated geriatric assessment unit rather than to a general medical unit. Therefore, an admission policy to GAU, based solely on age 70+ is medically inappropriate and cost-inefficient. Evidence from other sources suggests that an age cohort of acutely admitted patients beyond 80 years may well have returned more optimistic findings for the GAU. In future, GAUs will require a more selective admission policy to maximise the benefits of their rehabilitative and interdisciplinary approach.

Acute Disease↗
PubMed1990

A-bomb radiation and evidence of late effects other than cancer.

Cancer risk coefficients for ionizing radiation are currently based on the assumption that, after the bombing of Hiroshima and Nagasaki, there were no late effects of early selection (survival of the fittest) or acute marrow damage. These negative findings were the result of applying a linear model of relative risk to the deaths of 5-y survivors. By applying a linear-quadratic model to these deaths (i.e., a model with more than one degree of freedom), we have obtained evidence of longstanding competition between selection effects of the early deaths and other radiation effects, and also evidence that late effects of radiation include marrow damage as well as cancer. Consequently, the present method of risk estimation--by linear extrapolation of high dose effects--should no longer be used for estimating the cancer effects of occupational exposures or background radiation.

Humans↗
PubMed1978

Pre-cancers and liability to other diseases.

Data of 10,556 case-control pairs from the Oxford Survey of Childhood Cancers and related sources have shown that when cancers originate in the reticuloendothelial system (RES neoplasms) they are liable to cause loss of immunological competence before they are clinically recognizable. Since these early effects may have lethal consequences, the true prevalence of RES neoplasms is difficult to identify, especially in infection-sensitive age groups and populations with high death rates from infection. An inevitable consequence of a nuclear holocaust is a high infection death rate. Therefore, a population of A-bomb survivors is a totally unsuitable one for studying the precise nature of the association between ionizing radiation and human cancers.

Adolescent↗
PubMed1977

Diffuse xanthogranulomatous pyelonephritis in children: an unrecognized variant.

Xanthogranulomatous pyelonephritis in childhood has been thought to exist only in focal form. We encountered 2 cases of diffuse xanthogranulomatous pyelonephritis in children and have found 3 others reported in the literature, making it necessary to change this concept. The essential radiologic and pathologic differences between focal and diffuse xanthogranulomatous pyelonephritis are reviewed.

Child, Preschool↗
PubMed1977

Age variation in the cancer risks from foetal irradiation.

A modified Mantel-Haenszel analysis of data from the Oxford Survey of Childhood Cancers has shown that cases associated with foetal irradiation (X-rayed cases) accounted for a higher proportion of deaths between 5 and 10 years than of earlier or later deaths. This finding is compatible with somewhat later origins for the cancers actually caused by the radiation exposures (radiogenic cases) than for other (idiopathic) cases which proved fatal before 10 years of age. Therefore the usual time for incurring congenital anomalies (or the first trimester of foetal life) could be the commonest time for initiating childhood cancers. The theoretical implications of this and other findings of the Oxford Survey are discussed within the framework of a theory which assumes that all mutant cells have cancer potentialities and that defects in the immune surveillance mechanism favour multiplication of these cells (or endogenous sources of self-replicating foreign proteins) as well as live pathogens (or exogenous sources of self-replicating foreign proteins).

Age Factors↗
PubMed1977

Congenital oesophageal stenosis.

A case of congenital oesophageal stenosis presenting shortly after birth is reported. Treatment by daily dilatation with a bead on a continuous thread loop was carried on at home over several months. This proved to be a simple, safe, and effective treatment.

Dilatation↗