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Biomedical subjects

J Tucker

Publications and source records attributed to J Tucker.

At least 109 records · Page 6Linked to original sources
PubMed1986

Modulation dependence of the accommodation response to sinusoidal gratings.

The steady-state, monocular, accommodation response to sinusoidal grating targets (spatial frequencies 0.67, 2.0, 6.0 and 18 c/deg) at effective distances between 0.2 and 1.0 m was measured with a laser optometer, as a function of the grating modulation. In general, only a rather weak dependence of the response on modulation was observed. The results are discussed in terms of the theoretical modulation of the retinal image as a function of defocus. It is argued that the accommodative system usually works to produce a contrast in the grating image which is well above the detection threshold. Considerable inter-subject differences in response were observed, suggesting that a variety of strategies may be employed by different subjects when engaged upon the same voluntary accommodation task.

Accommodation, Ocular↗
PubMed1986

Depth of focus and accommodation for sinusoidal gratings as a function of luminance.

It is well-known that the accommodative response of the visual system to Snellen letters and other targets of wide spatial bandwidth becomes less accurate as the luminance is lowered from photopic to scotopic levels, a constant state of "night myopia" eventually being reached. The present study seeks to understand this behavior in terms of the responses to the single-frequency, sinusoidal grating, Fourier components of such targets, for a constant, 80% object modulation. The focal range over which sinusoidal gratings can be detected is first investigated as a function of grating frequency and luminance; this range diminishes as the luminance is lowered. These data are then related to measurements of the accommodative response to similar gratings in the mesopic luminance range (10(-2.5) to 10 cd/m2). The response is less accurate for gratings of low spatial frequency. It appears that, provided that any grating can be detected, changes in luminance generally have only a relatively small effect on the associated accommodative response. However, low spatial frequency gratings can be detected at much lower luminance levels than higher spatial frequency gratings. The effects observed with targets of wide spatial bandwidth may thus be largely ascribed to the inability of the visual system to use higher spatial frequency information as the luminance is lowered.

Accommodation, Ocular↗
PubMed1986

Effects of 0.1% cyclopentolate or 10% phenylephrine on pupil diameter and accommodation.

The mydriatic and cycloplegic effects of either one drop of 0.1% cyclopentolate or two drops of 10% phenylephrine were studied over a period of up to 6 hours after drug instillation, using 5 subjects aged between 25 and 43 years. The extent of mydriasis was determined from the horizontal diameter of the pupil. Dynamic accommodation responses were monitored with an infra-red, continuously recording optometer. Static measurements of the accommodation response/stimulus curve were made with a laser optometer. With either drug, dilation of the pupil occurred more rapidly than recovery of normal pupil diameter. Both drugs caused alterations in the dynamic and static accommodation responses. Response times were generally slowed, and the slope of the accommodation response/stimulus curve and the amplitude of accommodation were reduced. The time course of these changes was broadly similar to that of the pupil dilation. Cyclopentolate hydrochloride was more efficient as a mydriatic but exercised a greater unwanted cycloplegic effect.

Accommodation, Ocular↗
PubMed1985

Human T-lymphotropic virus type III (HTLV-III) infection in seronegative haemophiliacs after transfusion of factor VIII.

Fifteen haemophiliac patients acquired antibodies to human T-lymphotropic virus type III during 1984. One batch of factor VIII concentrate given to all these patients is presumed to be the cause of the seroconversion. A further eighteen patients who received the same batch did not seroconvert and one other patient became seropositive but had not received this batch. Before transfusion of the implicated batch the patients had low T-helper-cell numbers and T-helper/suppressor ratios; neither changed in those who seroconverted. The probability of seroconversion was independently related to the pre-existing low T-helper/suppressor ratio, the number of vials of the implicated batch transfused, and the total annual factor VIII consumption. Ten other patients received a batch of factor IX concentrate from the same donor plasma; none of these patients seroconverted.

Acquired Immunodeficiency Syndrome↗
PubMed1985

The response of rat alveolar macrophages to chronic inhalation of coal dust and/or diesel exhaust.

The use of diesel-powered equipment in underground mines has raised questions regarding possible synergistic effects of coal dust and diesel emissions. Therefore, the effects of chronic exposure of rats to coal dust and/or diesel exhaust on various properties of alveolar macrophages were investigated. Inhalation exposure of rats was 7 hr/day, 5 days/week for 2 years. Exposure groups were: filtered air controls, 2 mg/m3 coal dust, 2 mg/m3 diesel particulate, and 1 mg/m3 coal dust plus 1 mg/m3 diesel exhaust. Exposure to coal dust and/or diesel exhaust had little effect on oxygen consumption, membrane integrity, lysosomal enzyme activity, or protein content of alveolar macrophages. However, exposure to coal dust increased macrophage yield, enhanced chemiluminescence, and increased the activity of the cell membrane (i.e., increased cellular spreading and surface ruffling). In contrast, diesel emissions depressed chemiluminescence and decreased the ruffling of the cell membrane. Therefore, the data suggest that exposure to coal dust and/or diesel exhaust does not affect the viability of alveolar macrophages. However, coal dust may activate alveolar macrophages while diesel emissions may depress the phagocytic activity of these cells. The combination of exposures to coal dust and diesel exhaust results in a phagocytic activity which is an average of the effects of separate exposures.

Animals↗
PubMed1985

Effects of high infusion pressure and large-bore tubing on intravenous flow rates.

An in vitro study was conducted to determine the maximum flow rates that can be obtained with commercially available intravenous (IV) catheters, when infusion pressure and IV tubing size are modified. Standard tubing (3.2 mm ID) and two sizes of experimental large-bore tubing (5.0 mm and 6.4 mm ID) were tested with tap water and diluted packed cells (hematocrit 45) at 600 mm Hg, 300 mm Hg, and gravity flow infusion pressure. The maximum flow rate obtained was 3,158 ml/min for tap water and 3,000 ml/min for diluted packed cells. The increases in flow rates from gravity to 300 mm Hg and from gravity to 600 mm Hg are significant (P less than 0.05) and provide up to 197% and 341% increases, respectively, for all catheter/tubing combinations tested. Large-bore tubing is most effective when used in conjunction with large-bore catheters. For the 8.5 French catheter, a change from standard (3.2 mm ID) to large-bore (6.4 mm ID) tubing resulted in a statistically significant (P less than 0.05) increase in flow rate of more than 200% regardless of infusion pressure.

Fluid Therapy↗
PubMed1985

Age-related changes in proprioception and sensation of joint position.

With a clinical goniometer we measured the ability of 29 normal women to (a) reproduce the perceived position of each knee with that of the other knee, and (b) reproduce from memory the perceived resting position of each knee following its return to rest. Fifteen subjects were under 30 years old and 14 were over 60. The younger group scored higher in all trials. This study suggests the existence of an age-related change in proprioception and static joint position sensation in women and provides a basis for further investigation of contributory factors of musculoskeletal trauma in the elderly.

Adult↗
PubMed1984

A comparative study using immunological and biological assay of the haemostatic responses to DDAVP infusion venous occlusion and exercise in normal men.

In a group of six normal male volunteers, infusion of DDAVP, venous occlusion and exercise were shown to increase plasma levels of factor VIII and plasminogen activator, activity and antigen, to different extents and at differing rates. Any mechanisms suggested to explain release of these proteins by various stimuli should account for such differences. All three stimuli could also increase plasma levels of prostacyclin metabolites, although this was only significant for high doses of DDAVP. Other potential endothelial markers, such as fibronectin and thrombospondin, showed no specific increase after any of the stimuli.

Arginine Vasopressin↗
PubMed1983

Texas Consortium for Physical Therapy Clinical Education. A model for Interinstitutional Consortium arrangements.

This article describes the Texas Consortium for Physical Therapy Clinical Education, which exemplifies one type of collaborative arrangement among universities. Coordination of physical therapy clinical education among five Texas universities is the major function of the Texas Consortium. Although originally developed from a federally funded project (1977-1980), it currently functions with sole financial support from the participating universities. The collaborative efforts of the Texas Consortium have resulted in 1) developing and implementing a common evaluation tool for students' clinical performance; 2) coordinating development of new clinical education centers, development of clinical instructors, and visits to students at clinical education centers; and 3) developing and using a shared computer program for data on clinical education centers. The successful functioning of the Texas Consortium with a resultant decrease in duplication of time, effort, and costs of clinical education demonstrates that this type of arrangement is feasible and beneficial.

Costs and Cost Analysis↗
PubMed1983

Kaolin and the lung.

Explore the source record for details and available documents.

Environmental Exposure↗
PubMed1983

Inhalation studies of diesel exhaust and coal dust in rats.

The preliminary 12-month data of an ongoing two-year chronic inhalation study into the effects of diesel exhaust and coat dust on rats are reported. The study design consists of four exposure regimens: coal dust, diesel exhaust, coal dust plus diesel exhaust, and filtered air (control). Total respirable particulate is being maintained at 2 mg/m3 in all exposure groups. Animals are being serially sacrificed and subjected to immunologic, biochemical, physiological, microbiological, and pathological evaluations. Extracts of diesel emissions showed marked mutagenic activities in the Ames Salmonella his reversion assay. Mutagenic compounds were not however found in the urine of the exposed animals, nor were sister chromatid exchanges detected in peripheral lymphocytes. No changes were observed in cytochrome P450 enzyme activity in lung microsomes of exposed rats. Physiological tests showed no evidence of pulmonary function impairment in any group. Light microscopic examination of the lungs showed dust deposition with the formation of macules in all exposed groups. The preliminary results revealed few pathological effects of significance and no evidence of synergism between diesel exhaust and coal dust.

Animals↗