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Biomedical subjects

A T Johnson

Publications and source records attributed to A T Johnson.

At least 19 recordsLinked to original sources
PubMed1992

Effects of jogging exercise on patients with the pigmentary dispersion syndrome and pigmentary glaucoma.

BACKGROUND: Exercise-induced anterior chamber pigment dispersion with intraocular pressure (IOP) elevation has been reported in patients with the pigmentary dispersion syndrome. Marked pigment dispersion with or without elevation of IOP could predispose these patients to visual field loss. The authors designed this study to evaluate the effects of jogging exercise on anterior chamber pigment and IOP in a group of patients with the pigmentary dispersion syndrome or pigmentary glaucoma. METHODS: Fourteen subjects with the pigmentary dispersion syndrome, 10 subjects with pigmentary glaucoma, and 10 control subjects underwent a 45-minute protocol of jogging exercise. Anterior chamber pigment was graded and IOP was measured before and up to 3 hours after completion of the exercise protocol. RESULTS: Eyes of experimental subjects were significantly more likely to develop exercise-induced pigment dispersion than were eyes of control subjects. In experimental subjects, eyes treated with pilocarpine at the time of the study were significantly less likely to develop exercise-induced pigment dispersion than eyes not treated with pilocarpine. In two experimental subjects, pre-exercise treatment with pilocarpine appeared to inhibit exercise-induced pigment dispersion. CONCLUSIONS: The authors do not believe that all patients with the pigmentary dispersion syndrome or pigmentary glaucoma need to avoid exercise. However, for patients with these disorders who regularly engage in jogging or more strenuous or more jarring types of exercise, they suggest an evaluation before and after the type of exercise in question. If marked exercise-induced pigment dispersion occurs, pilocarpine therapy may be an alternative to avoidance of the exercise.

Anterior Chamber↗
PubMed1992

Respirator performance rating table for mask design.

The ultimate goal for respirator mask designers is computer-aided design. Mask design, however, is a very complex operation, with many different interrelationships. Current knowledge does not allow significant incorporation of physiological information into mask design. Rather, physiological information is usually gathered during mask evaluation, after the design process has been completed. The Performance Rating Table (PRT) is a beginning step to formulating physiological knowledge in a way that can be useful for design. The PRT organizes physiological knowledge to assign performance data to various mask and level of work causes. Best estimates of tabled values were obtained from the literature.

Body Temperature Regulation↗
PubMed1992

Respirator performance rating tables for nontemperate environments.

Respirator performance rating tables have been constructed for hot, humid (29 degrees C, 95% RH); hot, dry (49 degrees C, 30% RH); and cold, dry (-32 degrees C, 70% RH) conditions. These tables convey expected wearer performance percentages compared to unmasked workers for various mask elements and work rates. The hot, humid condition was found to be the most severe overall. Many table entries approach 100%, thus leading to difficulties in correcting mask deficiencies.

Equipment Design↗
PubMed1992

Modelling exercise-induced pulmonary hemorrhage in racing thoroughbreds.

Exercise-induced pulmonary hemorrhage (EIPH) affects a large portion of racing thoroughbred horses. Sites of hemorrhage and causal mechanisms remain unestablished. Our mathematical model was constructed to test the hypothesis that EIPH could be caused by a combination of respiratory and circulatory mechanical factors occurring during exercise. Various physiological data for respiration, blood circulation and exercise were incorporated into the model. Results show that inhalation pressure drops across airway resistances become great enough during exercise to cause rupture of capillaries for both bronchial and pulmonary systems.

Airway Resistance↗
PubMed1990

The pathology of posterior amorphous corneal dystrophy.

The youngest affected member of a family with a five-generation history of posterior amorphous corneal dystrophy underwent penetrating keratoplasty. The corneal button was studied by light and electron microscopy, representing the first pathologic description of this condition. Light microscopy demonstrated fracturing of the most posterior collagen layers of the stroma and focal attenuation of endothelial cells. Electron microscopy showed the collagen fibers in the most posterior stromal lamellae to be disorganized. Descemet's layer was interrupted by a band of collagen fibers resembling stroma, and there was loss of endothelial cells. These findings suggest a developmental abnormality in the formation of the posterior stroma and Descemet's membrane in posterior amorphous corneal dystrophy.

Child, Preschool↗
PubMed1985

Development of the subretinal space in the preterm human eye: ultrastructural and immunocytochemical studies.

To investigate the development of the subretinal space in the human infant, eyes were obtained from 12 live-born, anomaly-free, preterm infants from 20 to 32 weeks gestation and from one 3-month postterm infant. The retinas were studied by light microscopy, electron microscopy, and immunocytochemistry. The immunocytochemical studies utilized rabbit antiserum against purified bovine interstitial retinol binding protein (IRBP). A subretinal space containing IRBP was present in the central retina at 20 weeks and extended further into the periphery (expressed as a percentage of the distance from the optic disc to the ora serrata in the temporal hemisphere) as the retina developed. At 28 weeks, IRBP was absent only from the most peripheral 25% of the retina and reached the temporal ora serrata at 32 weeks. At 3 months postterm, IRBP immunofluorescence outlined fully developed photoreceptors, which were present from the optic disc to the ora serrata. The appearance of IRBP in the subretinal space correlated with the development of the first photoreceptor outer segment discs.

Fluorescent Antibody Technique↗
PubMed1985

Microcomputer program for the design of digital filters.

The program presented here is intended to be a design device and learning tool for digital filters. Digital filters designed with the program can be implemented by incorporation within the data analysis programs of the user. The program is written in BASIC for use with the IBM-PC, is intended to be user-friendly, and includes a great deal of filter assistance not found in other programs. An example of program use shows how one filter can be used to remove noise from respiratory waveform data.

Analog-Digital Conversion↗
PubMed1976

The energetics of mask wear.

Experimental data further defining the region of predominant respiratory stress is presented. Within this region, energy requirements of respiration increase disproportionately to the overall energy expenditure of the body as excercise intensity increases. Addition of a mask accentuates this tendency, especially since no physiological compensation is possible in mask parameters. Mask technology has improved masks to the point where they no longer dominate the man-mask system, but instead contribute resistances and dead volumes approximately equal to those naturally occurring in man. Modeling base on minimization of respiratory energy rate of expenditure in the human is applied to this man-mask system and predictions are made which to this point have been nearly impossible to obtain from experimental data.

Body Temperature↗
PubMed1975

Mask design considerations.

Mask design should be based more strongly on physiological data obtained from working individuals. This paper is a compendium of pertinent information as well as a guide to better design. An indication of the trends of current research is also given.

Adaptation, Physiological↗