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Biomedical subjects

G Johnston

Publications and source records attributed to G Johnston.

At least 55 records · Page 3Linked to original sources
PubMed1991

An evaluation of radiation and dust hazards at a mineral sand processing plant.

This three-part article discusses the results of a 2-y study on radiation and dust hazards in a mineral sand processing plant involving: (1) evaluation of external gamma radiation levels and determination of isotopic composition of the different sand products; (2) evaluation of radiation carried in long-lived radioactive dust (LLRD) particles; (3) evaluation of Rn gas concentrations within the working environs of the plant. Gamma radiation levels had a mean value of approximately 40 nSv h-1, and monazite sand returned the highest activity concentrations of 0.16% and 3.4% for 238U and 232Th, respectively. Low volume gross respirable dust sampling revealed an average long-lived airborne alpha activity concentration of 0.07 +/- 0.02 Bq m-3 and an average dust mass concentration of 3.3 +/- 2 mg m-3. Gamma spectroscopy applied to high-volume air samples showed average airborne 232Th and 238U activities of 0.012 +/- 0.004 Bq m-3 and 0.005 +/- 0.002 Bq m-3, respectively, giving an airborne 232Th: 238U ratio of 2.4:1. Air sampling using a high volume, five-stage cascade impactor indicated an average activity median aerodynamic diameter (AMAD) of 3.2 microns with an associated average geometric standard deviation (GSD) of 2.8. Average radiation dose arising from the inhalation of LLRD was estimated to be 7 mSv per annum. CR-39 (polycarbonate plastic) nuclear track detectors indicated that Rn gas concentrations in the environs of the processing plant dry mill and main product warehouse ranged from 30 Bq m-3 to 220 Bq m-3, with an average value of 100 Bq m-3, which presents a possible inhaled dose from Rn daughters of 1.5 mSv y-1 (assuming an equilibrium ratio of 0.5).

Air Pollutants, Radioactive↗
PubMed1990

Preparation of xenon-133 in a lipid emulsion for tissue perfusion studies.

A simple, inexpensive technique for concentrating xenon-133 in a medium suitable for intravenous use is reported. The method uses a 20% lipid emulsion, standard syringes, an oscillating motor, and xenon-133, which is available commercially. Typically, 43% of the xenon-133 combines with the lipid emulsion and remains stable for more than 24 hours in vitro.

Fat Emulsions, Intravenous↗
PubMed1988

Osteogenesis in two marsupial species, the bandicoot Isoodon macrourus and the possum Trichosurus vulpecula.

Skeletal development of two marsupial species, the bandicoot, Isoodon macrourus and the brushtail possum, Trichosurus vulpecula, has been examined in whole mount preparations using a technique of clearing and differential staining of cartilage and bone. Both marsupials possess a complete cartilaginous skeleton at birth and ossification begins in the maxilla, mandible and certain bones of the forelimb soon after birth. The general pattern of ossification in these marsupials is similar to that in eutherians but the long bones of the forelimbs, and the thoracic vertebrae, have a precocious development when compared with that of eutherian mammals. This difference may be due to the requirement of the marsupial forearms for the passage of the young from the cloaca to the pouch. Accelerated rib development occurs, and is possibly related to respiratory movements which are initiated at a very much earlier stage than in eutherian mammals.

Aging↗
PubMed1987

Selection of an animal model for resurfacing hip arthroplasty.

This study was done to determine whether sheep provide a better model of resurfacing hip arthroplasty than dogs. Eighteen sheep were subjected to unilateral resurfacing arthroplasty. Fifty-eight percent developed femoral loosening by 10 months. This reflects the clinical situation in humans: loosening has been the leading cause of failure. By contrast, reports of experiments with dogs describe very low loosening rates. Sheep provide a more stringent test of hip arthroplasty than dogs. The critical difference appears to be activity level. Sheep allowed free activity on a farm more closely simulate the situation of active patients than do dogs housed in small enclosures in conventional research facilities. New techniques of prosthetic hip arthroplasty that lend themselves to animal models should be studied in sheep before being studied in humans.

Animals↗
PubMed1987

Sodium-dependent D-glucose transport in brush-border membrane vesicles from isolated rat small intestinal villus and crypt epithelial cells.

Differentiation and maturation of enterocytes occur with migration from the crypt to villus compartments. To investigate the effect of epithelial cell differentiation on sodium-dependent D-glucose transport, brush-border membrane vesicles were prepared from small intestinal epithelial cell suspensions selectively isolated from villus and crypt populations. Enterocytes were isolated with a morphologically monitored sequential cell dissociation method. Thymidine kinase, sucrase, and alkaline phosphatase activities were measured as differentiation markers of specific cell populations. Brush-border membrane vesicles were purified and their kinetic characteristics defined with a rapid filtration method under conditions of a zero-trans, 100 mM cis-NaSCN gradient. Typical "overshoot" phenomena characteristic of sodium D-glucose cotransport were observed for both villus (five- to eight-fold equilibrium values) and crypt brush-border membrane vesicles (two- to four-fold equilibrium values). Kinetics analyses of the initial D-glucose flux in brush-border membrane vesicles suggested the presence of at least two sodium-dependent D-glucose carriers in the villus and only a single carrier in the crypt compartments. These data indicate that sodium D-glucose cotransport occurs in brush-border membranes of both villus and crypt populations. Moreover, quantitative and qualitative differences between these two membrane populations suggest that epithelial D-glucose transport processes are differentiation dependent and reflect the degree of enterocyte development.

Animals↗
PubMed1987

Boxer's fractures--conservative or operative management?

Sixty-three consecutive patients presented during an 18-month period with isolated closed fractures of the fifth metacarpal neck. Follow-up ranged from 3 to 20 months. Forty were recalled for study and divided into a conservative group (25 patients) and an operative group (15 patients). Both groups were statistically comparable. All patients obtained good results. Subjectively, no patient had long-term pain or dissatisfaction with the functional or cosmetic result. Objectively, all patients regained full joint motion and normal grip strength. Mild rotatory malalignment was present in both groups, but the conservative group had less extensor lag. The main difference between the two groups centered on residual dorsal angulation. This cosmetic deformity was considerably less in the operative group, although the cost of this improvement was significantly longer rehabilitation. Failure to correct dorsal angulation was not associated with functional disability.

Adult↗
PubMed1985

Seasonal variations in plasma testosterone concentrations in the male marsupial bandicoot Isoodon macrourus in captivity.

Although bandicoots in Queensland mate throughout the year, the majority of births occur in late winter and spring. To ascertain whether this seasonality in mating is manifest in the male reproductive system; body weight, testes size, and plasma testosterone concentration were examined in eight bandicoots throughout the year. The size of the testes increased with age in all bandicoots and there was no evidence of seasonal variation. Plasma testosterone concentrations fluctuated from 0.1 to 70.0 ng/ml and a seasonal cycle was observed, with a nadir in concentrations in March and a peak in September. The peak in testosterone concentration coincided with the period of the year when the majority of births occurred. Subsequent statistical analysis suggested that the annual plasma testosterone profile correlated well with the rate of change of day length.

Acclimatization↗
PubMed1984

The uniformity of growth within the litter of the marsupial, Isoodon macrourus.

The amount of information concerning reproduction in eutherian mammals differs markedly with that available for marsupials. There is at present a good understanding of growth in the eutherian litter after birth but the respective information for litter bearing marsupials has still to be obtained. In this study the growth of the young bandicoot after leaving the pouch was examined. Each of the monitored young, 38 females and 12 males, was weighed weekly and a growth rate estimated for the ages 65 to 105 days. Although these growth rates varied from 3.80 to 9.50 g/days and large variations in growth rate were observed between litters, the findings suggest that development within a pouch, in contrast to uterine development, gives rise to a litter which is more uniform in size.

Animals↗
PubMed1984

Recurrent posterior instability (subluxation) of the shoulder.

A retrospective survey of fifty shoulders in thirty-five patients with recurrent posterior instability revealed generally poor results of treatment, particularly of operative treatment. Only eleven of the shoulders had a primary traumatic insult as the event initiating the instability. Although forty-one of the affected shoulders demonstrated voluntary instability, it was the associated involuntary, unintentional instability of these shoulders that prompted the patients to seek medical attention. Pain and functional impairment relating to work and to the activities of daily living were not significant in most of these patients. The results of surgical reconstruction were generally poor, the recurrence rate was 50 per cent (thirteen of twenty-six shoulders), and there were complications in five of the twenty-six shoulders that had been operated on. Attention is drawn to the complication of degenerative osteoarthritis that is associated with posterior glenoid osteotomy. We advise care in the selection of patients for surgical reconstruction.

Activities of Daily Living↗
PubMed1982

Glycyl-L-leucine transport in the rat small intestine.

The uptake of the peptide glycyl-L-leucine across the brush border of the rat small intestinal enterocyte was studied using everted rings. The transfer of leucine from the dipeptide into the enterocyte was greater than the glycine uptake from glycyl-L-leucine. This additional component for leucine transport was found to be abolished by the removal of sodium, by the presence of 10 mM L-alanine beta-naphthylamide, and by excess free leucine. In contrast, the uptake of glycine from glycyl-L-leucine was not sodium-dependent and was not reduced by the presence of excess free leucine. The presence of harmaline over a concentration range up to 10 mM inhibited some of the peptide-bound leucine and glycine uptake. Transport of leucine from glycyl-L-leucine in the presence of 20 mM free leucine was competitively inhibited by glycyl-L-proline, although not completely. It is concluded that, in the rat, the sodium-sensitive component of amino acid uptake from the dipeptide represents free amino acid liberated by superficial hydrolysis, while the transport of the intact peptide is not sodium dependent. In addition, it appears that there are at least two routes of entry for the intact dipeptide glycyl-L-leucine, only one of which is shared with glycyl-L-proline.

Alanine↗
PubMed1980

The role of bone scans in assessing malignant melanoma in patients with stage III disease.

Two hundred abnormal bone scans of patients with a malignant melanoma were reread in a blinded fashion to identify osseous metastases. These findings were compared with serum calcium and alkaline phosphatase levels, skeletal surveys and survival curves of the same patients. Thirty-four of the 38 patients classified as positive for osseous metastases by bone scans ultimately supported that diagnosis. Three patients have probable, but not proved, osseous metastases, and one patient is classified as false-positive. Identification of osseous metastases by skeletal surveys never preceded bone scan identification. Skeletal surveys were most helpful in the identification of a benign condition which caused scan positivity. Serum calcium and alkaline phosphatase levels were never as sensitive or specific as either scans or surveys. In two patients with progressive osseous disease, the levels fell. We believe that radionuclide bone scans should be the first diagnostic procedure for suspected osseous metastases in patients with a malignant melanoma. It appears to be a more sensitive and specific test than skeletal surveys or serum calcium and alkaline phosphatase levels. We believe its use as a first test would save time, money and needless surgical procedures.

Adult↗