Search PubMed⌕ Search

Biomedical subjects

J Marshall

Publications and source records attributed to J Marshall.

At least 433 records · Page 24Linked to original sources
PubMed1985

Fundamental importance of arterial oxygen content in the regulation of cerebral blood flow in man.

The relationships between cerebral blood flow (CBF), arterial oxygen content, whole blood viscosity and the transport of oxygen to the brain have been studied in 54 subjects with variations in arterial oxygen content resulting from alterations in haemoglobin concentration ranging from 5.7 to 19.1 g/dl. A highly significant relationship was found between CBF and arterial oxygen content, CBF altering to maintain the rate of transport of oxygen to the brain within certain limits. No significant effect of changes in blood viscosity was evident. In a multiple regression analysis arterial oxygen content emerged as the major determinant of CBF and after this effect had been taken into account there was no significant influence of blood viscosity, arterial pCO2, age or mean arterial blood pressure. The results imply that the alterations in CBF found in subjects with anaemia and polycythaemia are primarily physiological and not caused by the accompanying alterations in blood viscosity. It is proposed that the response of the cerebral circulation to arterial oxygen content is mediated by a local mechanism sensitive to alterations in local tissue oxygen tension.

Adolescent↗
PubMed1985

Assessing nutrient intake with an abbreviated dietary interview.

There is considerable interest in developing a means of assessing dietary intake of specific nutrients with minimal time and expense in epidemiologic studies. Using data from 1,682 individuals who were interviewed using an extensive food frequency dietary history, the authors examined the question of how many foods might be minimally required in order to estimate specific nutrient intakes for epidemiologic purposes. Nutrient indices were constructed for vitamins A and C, dietary fiber, fat, protein, and total calories based on 128 foods included in the interview. They found that a large fraction of the variability of nutrient intake in this population could be explained by a small number of foods. An abbreviated dietary history ascertaining the intake of as few as 15-20 food items may be all that is required in order to test the association between disease outcome and the intake of a single nutrient.

Age Factors↗
PubMed1985

An inquiry into the epidemiology of melanoma.

The authors conducted a study of 404 melanoma patients and 521 control patients of both sexes at Roswell Park Memorial Institute. As have previous investigators, they found that higher risk attaches to upper socioeconomic status, as measured by occupation and education, lightness of complexion and hair, and amount of blue in the admixture of eye color. The authors also found a higher risk among individuals who reacted to sun exposure by burning, blistering, or freckling rather than by tanning. A particular concern was to measure risk associated with exposure to the sun. As have two other investigators, they found that risk decreased with increasing exposure, suggesting either that individuals continually exposed to the sun have less risk because of tanning, or that susceptibles purposely avoid sun exposure, or both. The fact that melanoma occurs with greater frequency on sites exposed to the sun suggests that sun exposure plays a part. These studies showed a dose-response increase in risk (odds ratios of up to 4 for males and over 6 for females) with increases in number of traits possessed, such as light complexion, and burning or freckling in response to sun exposure. This is consistent with the authors' earlier finding of a strong familial aggregation of melanoma.

Adult↗
PubMed1985

Regional cerebral oxygen utilization, blood flow, and blood volume in benign intracranial hypertension studied by positron emission tomography.

Using PET, we measured regional cerebral oxygen utilization, oxygen extraction, blood flow, and blood volume in five patients with benign intracranial hypertension. No significant differences in regional cerebral function were found between the patients and 15 age-matched normal controls. Cerebral decompression with a lumboperitoneal shunt produced little change in regional cerebral function in one patient studied serially. The raised CSF pressure of benign intracranial hypertension is therefore not associated with any significant deterioration in cerebral oxygen metabolism or hemodynamics.

Adult↗
PubMed1985

Neodymium-YAG laser in ophthalmic practice--principles and early experience.

We show our early experience with the Q Switched Neodymium-YAG Laser. Selected cases from the clinical spectrum of patients treated over nine months are discussed with regard to technique, results and possible complications. We feel that the YAG Laser will make an important contribution to ophthalmic care but further research and assessment are required before its full value and safety are ascertained.

Cataract Extraction↗
PubMed1985

Reparative epiretinal fibrosis after diabetic vitrectomy.

Closed microsurgery for the haemorrhagic and tractional sequelae of proliferative diabetic retinopathy is frequently successful in restoring and maintaining useful vision. Severe complications may arise, however, including the reproliferation of cellular membranes on the retinal surface with subsequent retinal distortion or redetachment. The clinical and histopathological features of such reparative epiretinal fibrosis are presented and methods of prevention are discussed.

Diabetic Retinopathy↗
PubMed1985

The rapid rejection of allogeneic lymphocytes by a non-adaptive, cell-mediated mechanism (NK activity).

The fate of allogeneic lymphocytes (AO or DA) transferred to non-immune PVG recipients was studied in the light of previous evidence (Heslop & McNeilage, 1983; Rolstad & Ford, 1983) that allogeneic lymphocytes can be rapidly destroyed in certain strain combinations of rats and mice by a mechanism that is distinct from either T-cell mediated immunity or an alloantibody response. AO lymphocytes injected into PVG recipients were discriminated from syngeneic lymphocytes within 15-30 min of i.v. injection, as testified by the excess release of 51Cr into the lymph plasma of the recipient. The following experiments were intended to distinguish between natural antibody and natural killer (NK) cells as the mechanism responsible for the allogeneic lymphocyte cytotoxicity (ALC) displayed by PVG rats. Nude rats treated from birth with anti-mu chain serum and shown to be lacking B and T lymphocytes, as well as being profoundly deficient in immunoglobulin, displayed more aggressive ALC than did control nude rats which, in turn, showed stronger ALC than did euthymic rats. Serum from PVG nude rats exerted no inhibitory or destructive effect on allogeneic lymphocytes in an antibody-dependent cellular cytotoxicity system, an assay of graft-versus-host activity, or when injected into 3-4-week-old PVG rats which had not yet developed ALC. Treatment of nude rats with anti-asialo GM 1 antiserum depressed ALC and NK activity in parallel, thus adding to a wide range of circumstances in which ALC and NK activity are closely correlated. In conclusion, ALC is implemented by a non-adaptive, cell-mediated mechanism independent of immunoglobulin, but the precise identity of the effector cell in the recipients' lymphatic tissues remains to be settled.

Animals↗
PubMed1984

Mechanism of polyuria and natriuresis in atrioventricular nodal tachycardia.

A woman with tachycardia associated with polyuria was investigated. Electrophysiological analysis showed that the tachycardia was an atrioventricular nodal re-entrant tachycardia. Programmed stimulation was then used to provoke and sustain the tachycardia for 40 minutes. Polyuria, with an appreciable increase in free water clearance, was observed. This was associated with reduction in plasma and urinary arginine vasopressin concentrations. Appreciable natriuresis also developed. These results support the hypothesis that the polyuria with increased free water clearance and the natriuresis occurring during sustained tachycardia in man are due to inhibition of secretion of vasopressin and the release of natriuretic factor.

Arginine Vasopressin↗
PubMed1984

Survey of reproductive hazards among oil, chemical, and atomic workers exposed to halogenated hydrocarbons.

Several halogenated hydrocarbons are suspected of causing adverse reproductive effects. Because of such concerns, the Oil, Chemical, and Atomic Workers International Union surveyed the reproductive histories of two groups of workers. One group worked at plants engaged in the production or use of halogenated hydrocarbons (exposed) whereas the others had no such opportunity for exposure (nonexposed). Although a low response rate precludes firm conclusions, the 1,280 completed questionnaires provide useful data for generating hypotheses in this developing field of interest. A history of diagnosed cancer was reported more frequently among exposed workers. The infant mortality rate was also significantly elevated among the offspring of exposed workers. No risk gradient was observed for episodes of infertility, fetal loss, congenital defects, or low-birthweight offspring. Concerns with nonresponse, exposure characterization, possible confounding factors, and limited statistical power are addressed. The results provide further suggestions which help to direct studies of occupational reproductive risks.

Abnormalities, Drug-Induced↗
PubMed1984

Plasma protein binding of warfarin: methodological considerations.

Recent theoretical work has suggested that radiochemical impurities can significantly alter the binding results for highly protein-bound drugs. We compared protein binding of warfarin by ultrafiltration and equilibrium dialysis with 98% radiochemically pure [14C]warfarin. Ultrafiltration and equilibrium dialysis were performed at 37 degrees C and pH 7.45 on the plasma of patients receiving chronic warfarin therapy. Binding to plasma from seven patients were measured in duplicate by both a nonspecific radioisotopic technique and a specific HPLC technique. The nonspecific technique gave percentage of free warfarin values of 1.84 +/- 0.11 (mean +/- SD) and 1.59 +/- 0.14 for ultrafiltration and equilibrium dialysis, respectively. The HPLC procedure yielded a percentage of free warfarin by ultrafiltration of 0.969 +/- 0.203 and a value of 0.690 +/- 0.095 by equilibrium dialysis (p less than 0.05). The HPLC procedure for protein binding was performed on plasma samples from 12 additional patients and yielded a percentage of free warfarin of 1.01 +/- 0.69 by ultrafiltration and 0.44 +/- 0.34 by equilibrium dialysis (p less than 0.05). It can be concluded that radiochemical impurities may lead to significant overestimation of the percentage of free warfarin. Ultrafiltration yielded a higher percentage of free warfarin than did equilibrium dialysis, but the ability to distinguish binding differences among patients was similar.

Blood Proteins↗
PubMed1984

Retinitis pigmentosa: a quantitative study of the apical membrane of normal and dystrophic human retinal pigment epithelial cells in tissue culture in relation to phagocytosis.

The phagocytic capabilities of both normal and dystrophic human retinal pigment epithelial cells were assessed by challenging cultures with both non-biological and biological particles. Cells from either source ingested both carbon particles and latex microspheres. Quantification of the phagocytic process in relation to microspheres showed that uptake was linear over an 8 h period and the rate was dose-dependent. All cultures phagocytosed rod outer segments from a variety of species, but excluded bacteria. By using bovine rod outer segments labelled with [H3] choline both normal and dystrophic cells were still accumulating label 24 h subsequent to challenge; however, this technique had significant problems. The introduction of any particulate matter into the culture medium resulted in changes in the apical membrane of the recipient cells. Such responses were quantified in terms of apical projections per unit area. Counts were always greater in cells challenged with biological material even if the material was not engulfed.

Aged↗
PubMed1984

Intravenous urography with low-osmolality contrast agents: theoretical considerations and clinical findings.

There are theoretical reasons for expecting some aspects of image quality in intravenous urography to be modified when low-osmolality, rather than conventional, contrast agents are used. The clinical findings in urography using two of these, the non-ionic agents iohexol (Omnipaque 350, Nyegaard) and iopamidol (Niopam 370, Bracco/Merck), are compared with those using sodium iothalamate (Conray 420, May & Baker Ltd), and are discussed against this theoretical background. The best nephrogram obtained with the new agents often occurred later than with the conventional agent, but quantitative differences in its density were explicable on a total iodine dose basis. The pyelographic density obtained with the new agents was significantly greater than with the conventional agent without any evidence, when abdominal compression was used, of the predicted associated poor distension of the collecting system.

Contrast Media↗
PubMed1984

In vivo measurement of regional cerebral haematocrit using positron emission tomography.

A method is described for measuring the regional cerebral-to-large vessel haematocrit ratio using inhalation of carbon-11-labelled carbon monoxide and the intravenous injection of carbon-11-labelled methyl-albumin in combination with positron emission tomography. The mean value in a series of nine subjects was 0.69. This is approximately 20% lower than the value of 0.85 previously reported. It is concluded that previous measurements of regional cerebral blood volume using a haematocrit ratio of 0.85 will have underestimated the value of regional cerebral blood volume by 20%.

Albumins↗
PubMed1984

Measurement of regional cerebral pH in human subjects using continuous inhalation of 11CO2 and positron emission tomography.

The cerebral pH of four normal human subjects has been measured using continuous inhalation of 11CO2 and positron emission tomography (PET). 11CO2 was administered to each subject at a constant rate for 15 min, during which time serial arterial plasma 11C levels were determined and serial 11C cerebral uptake PET scans were performed at a fixed axial tomographic level. 11C uptake kinetics were analysed using a three-compartment model. Rate constants have been estimated for the free exchange of 11CO2 between plasma and cerebral compartments for each subject, and their cerebral pH calculated. Whole brain pH values ranged from 6.96 to 7.05, and no significant pH difference between regions containing predominantly grey or white matter was noted. Best fits to 11C uptake data were achieved by effectively neglecting the metabolic fixation of 11C by cerebral tissue. The purpose of this study was to test the feasibility of pH measurement using the 11CO2 continuous inhalation technique. It is concluded from the results and the error analysis that continuous 11CO2 inhalation combined with PET is potentially a simple and useful method for determining regional cerebral pH.

Brain↗
PubMed1984

Quantitative measurement of blood-brain barrier permeability using rubidium-82 and positron emission tomography.

In normal brain, the blood-brain barrier (BBB) is highly impermeable to K+ cations, their transport being controlled by ATPases situated in the endothelial cell membranes. 82Rb+ is a positron-emitting analogue of K+ with a half-life of 75 s. Using a steady-state model and positron emission tomography, quantitative extraction data for 82Rb+ transport across the BBB have been obtained both in normal human subjects and in a variety of conditions of cerebral pathology. A mean cerebral Rb extraction of 2.1% was found for normal subjects, corresponding to a mean value of 1.1 x 10(-6) cm s-1 for 82Rb+ cation permeability across the BBB. No increase in cerebral Rb extraction was observed for patients with diffusely raised intracranial pressure secondary to obstructive hydrocephalus and benign intracranial hypertension, or for patients with multiple sclerosis or cerebral systemic lupus erythematosus. Cerebral tumours that were enhanced on computed tomography scanning showed a significant increase in local Rb uptake. No correlation between tumour size, or grade of glioma, and tumour Rb extraction was found. Nonenhancing tumours showed no increase in local Rb extraction, and regions of perifocal tumour oedema also had Rb extraction values in the normal range. It is concluded that increased Rb extraction occurs only where tight junction integrity in the BBB breaks down locally, that is, in the microcirculation of enhancing tumours but not in that of perifocal regions of tumour oedema or nonenhancing tumours.

Adult↗
PubMed1984

Transition from a hunter-gatherer to a settled lifestyle in the !Kung San: effect on iron, folate, and vitamin B12 nutrition.

In 1969 a group of hunter-gatherer San were studied (Am J Clin Nutr 1971;24:229-42). Their state of hematological nutrition was excellent with a negligible incidence of iron, folate, or vitamin B12 deficiency. A genetically and linguistically similar San community who have been settled for the past 15 yr were the subjects of the present study. Anemia, due in the main to iron and/or folate deficiency, has become more common. Alcoholism has become rife in both sexes and all age groups. Our findings show that a settled lifestyle has resulted in a significant deterioration in the San's hematological nutrition.

Adolescent↗