Biomedical subjects
Publications and source records attributed to A T Johnson.
A system for obtaining respiratory flow rate waveforms, tidal volume, minute volume, respiration rate, inhalation time and exhalation time is described. The system is based on a microcomputer with analog-to-digital converter board. System software allows calibration, data acquisition and data analysis. Data can be obtained automatically at fixed time intervals. The system is inexpensive and reliable.
Forty-six subjects were required to perform a console-monitoring and two hand-eye coordination tasks while wearing masks with lenses clouded to give seven levels of visual acuity. The console-monitoring task performance was found to be the most sensitive to visual acuity, followed by the random hand-eye coordination task. These results can be used to help predict performance degradation when lenses become clouded due to condensation or particulate deposition.
The purpose of this investigation was to determine performance decrement due to altered vision while wearing a respiratory face mask. Lenses clouded to visual acuities of 20/64, 20/38, 20/34, 20/28, 20/23, 20/20, and 20/15 were applied to each mask while subjects performed a battery of vision tests involving tracking and hand-eye coordination skills. Generally, performance decrement followed a significant curvilinear pattern as visual acuity worsened. These findings warrant the need to investigate the transfer of this performance decrement to skills that are inherent to military-type tasks.
A large Caucasian family is presented, in which a juvenile-onset form of open-angle glaucoma is transmitted in an autosomal dominant fashion. Sixteen affected family members were identified from 31 at-risk individuals descended from the affected founder. Affected patients developed high intraocular pressures (sometimes > 40 mm Hg) within the first 2 decades of life. Linkage analysis between the disease phenotype and 12 microsatellite repeat markers located on chromosome 1q gave a maximum lod score of 8.38 at a recombination fraction of zero for marker D1S210. Analysis of recombinant haplotypes suggests a total inclusion region of about 14 cM between markers D1S194 and D1S218 at 1q21-q31. This represents the second juvenile-glaucoma family, in which the disease has been mapped to the long arm of chromosome 1.
BACKGROUND: Juvenile glaucoma is an uncommon form of open-angle glaucoma that is usually recognized during childhood or early adulthood and which often has a strong family history. METHODS: The authors clinically characterized a large multigeneration family with autosomal-dominant, juvenile-onset, open-angle glaucoma. Linkage analysis with short tandem repeat polymorphisms was used to evaluate the Rieger's syndrome locus as the site of the disease-causing mutation. RESULTS: Forty members of a family with a five-generation history of open-angle glaucoma were examined. Clinical data were available from an additional five individuals, three of whom were decreased. Older family members provided limited information about the visual history of five other deceased individuals in the first three generations. Fifty-nine people were at 50% risk of harboring the disease-causing mutation; and of these, 30 were affected with glaucoma by examination or by family history. All affected patients had an affected parent. The average age at diagnosis was 18 years (range, 8-30 years). Affected family members tended to be myopic but lacked other ocular or systemic abnormalities. The intraocular pressures (IOPs) of affected individuals were commonly more than 50 mmHg when they were first examined. Gonioscopy showed the angles to be open, with no abnormal pigmentation, iris processes, or embryonic tissue. Topical medications were initially effective in controlling IOP, but surgery was usually required for long-term pressure control. The Rieger's syndrome locus on chromosome 4q25 was excluded as the site of the disease-causing mutation. CONCLUSION: Juvenile open-angle glaucoma can occur as an autosomal dominant trait with high penetrance. Genetic linkage analysis of the family reported here has the potential to identify the chromosomal location of a glaucoma-causing gene. This gene is genetically distinct from the chromosome 4 locus that was recently associated with Rieger's syndrome.
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Glaucoma is a significant cause of blindness world wide. There is evidence to suggest that at least a subset of the disease is determined genetically. We studied 37 members of a family affected with an autosomal dominant form of juvenile open angle glaucoma and 22 were found to be affected. Linkage analysis using short tandem repeat markers mapped the disease-causing gene to chromosome 1q21-q31. Eight markers were significantly linked (Zmax > 3.0) to the disease, with the highest lod score 6.5 (theta = 0), provided by D1S212. The atrial natriuretic peptide (ANP)/receptor system has been proposed to have a role in glaucoma and one of the ANP receptor genes maps to chromosome 1q.
The respirator performance rating table (PRT) scheme has been offered as a way to organize physiological information to be useful for mask design. Designers do not usually deal exclusively with one kind or another of mask physiological effect. This paper presents normal mask design modules and how they relate to mask physiological effects as given in the PRT.
The rate of work expended to move air in the respiratory system has been determined for five different airflow waveshapes, a non-linear respiratory model and five exercise levels. As expected, the rectangular waveshape was the most efficient. Model conditions were then changed one a time: (i) starting lung volume was allowed to vary, (ii) exhalation flow limitation was added, (iii) respiration was considered to be a metabolic burden determining part of the ventilation requirement and (iv) a respirator mask was added. Although there is no direct work advantage to varying initial lung volume, such volume changes appear to be dictated by the asymmetry of lung recoil pressure about the lung relaxation volume; allowing the work of respiration to become a metabolic burden clearly shows why respiratory waveforms change from rest to exercise; and, adding a respirator imposes a severe respiratory burden on the wearer engaging in moderate, heavy and very heavy exercise.
The Performance Rating Table (PRT) is introduced as a means to separate mask-wearer performance by causative factors. The PRT shows which mask factors require design attention and how the mask affects different users.
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.
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.
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.
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.
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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.
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This paper describes a closed-loop control system for controlling the irradiance and spectral quality generated by fluorescent lamps in a controlled environment chamber. The 400 to 800 nm irradiance and the ratio of the red waveband (600 to 700 nm) to the far-red waveband (700 to 800 nm) were independently controlled and varied as functions of time. A suggested application is to investigate the possibility of synergistic effects of changing irradiance levels and changing spectral distributions on photoperiodism and photomorphogenesis.