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Biomedical subjects

C A Johnson

Publications and source records attributed to C A Johnson.

At least 181 records · Page 10Linked to original sources
PubMed1995

The television, school, and family smoking prevention and cessation project. VIII. Student outcomes and mediating variables.

BACKGROUND: This paper presents the student outcomes of a large-scale, social-influences-based, school and media-based tobacco use prevention and cessation project in Southern California. METHODS: The study provided an experimental comparison of classroom delivery with television delivery and the combination of the two in a 2 x 2 plus 1 design. Schools were randomly assigned to conditions. Control groups included "treatment as usual" and an "attention control" with the same outcome expectancies as the treatment conditions. Students were surveyed twice in grade 7 and once in each of grades 8 and 9. The interventions occurred during grade 7. RESULTS: We observed significant effects on mediating variables such as knowledge and prevalence estimates, and coping effort. The knowledge and prevalence estimates effects decayed partially but remained significant up to a 2-year follow-up. The coping effort effect did not persist at follow-ups. There were significant main effects of both classroom training and TV programming on knowledge and prevalence estimates and significant interactions of classroom and TV programming on knowledge (negative), disapproval of parental smoking, and coping effort. There were no consistent program effects on refusal/self-efficacy, smoking intentions, or behavior. CONCLUSIONS: Previous reports demonstrated successful development and pilot testing of program components and measures and high acceptance of the program by students and parents. The lack of behavioral effects may have been the result of imperfect program implementation or low base rates of intentions and behavior.

Child↗
PubMed1995

Recognition and liking of tobacco and alcohol advertisements among adolescents: relationships with susceptibility to substance use.

BACKGROUND: Exposure to tobacco and alcohol advertising has been associated with adolescent substance use. However, it is not clear whether favorable reactions to advertising are an antecedent to or a consequence of substance use. This study investigated relationships between adolescents' levels of susceptibility to substance use and their recognition and liking of tobacco and alcohol advertising. METHOD: Eighth-grade students viewed pictures of tobacco and alcohol advertisements with brand names and identifying information obscured, attempted to identify the brand name and type of product being advertised, and rated their liking of the advertisements. Subjects were divided into three substance use status groups: nonsusceptible nonusers (have never used and do not intend to do so), susceptible nonusers (have not used but have not made a firm commitment not to experiment in the future), and users (have tried the substance). RESULTS: Susceptible nonusers liked the tobacco advertisements at a level that was significantly greater than that of the nonsusceptible nonsmokers and comparable to that of the users. Liking of the alcohol advertisements generally increased with alcohol use status. CONCLUSIONS: These results suggest that tobacco advertisements ostensibly targeted to adult smokers may have the effect of recruiting new adolescent smokers.

Adolescent↗
PubMed1995

Prenatal predictors of cesarean section due to labor arrest.

Cesarean section due to labor arrest occurs because the fetus is too large for the maternal outlet tract. If these women could be identified prior to labor, patient management could be optimized for both the clinician and the woman. A case-control study was designed to identify predictors of Cesarean section due to labor arrest. A five year retrospective review identified 32 cases and 329 controls with complete data for the prenatal maternal variables. Both cases and controls were considered for the stepwise logistic regression model. The prenatal variables predicting Cesarean section due to labor arrest are parity, history of past macrosomia, maternal age, term fundal height and maternal height. This model can be considered a pilot model that can be tested in a large international/inter-ethnic population.

Adolescent↗
PubMed1995

The effect of flicker on foveal and peripheral thresholds for oscillatory motion.

This study evaluated the influence of superimposed luminance flicker on the detection of oscillatory motion. Thresholds for oscillatory motion were determined in the fovea and at 2, 6 and 25 deg in the right field for a small luminous target with and without sinusoidal luminance flicker. At the fovea, flicker modulation up to 80% at frequencies from 1.5 to 9 Hz had no effect on motion detection, except for oscillatory motion at a frequency of 8 Hz, for which thresholds were elevated by about 0.2 log units. In the periphery, flicker elevated motion thresholds up to 0.3-0.4 log units at low and moderate frequencies of oscillation at all locations tested. However, both foveal and peripheral motion thresholds were unaffected by flicker when the luminance of the target was reduced. The absence of a robust effect of target flicker on motion thresholds may be accounted for in part by the comparison of activity across a large population of motion-detecting neurons with different direction preferences. Another contributing factor may be the existence of foveal velocity- and position-detecting mechanisms with similar sensitivities.

Female↗
PubMed1995

Aging effects for opponent mechanisms in the central visual field.

Visual field sensitivity measures were obtained for normal observers between the ages of 20 and 83 years, using test conditions in which detection has been shown to be mediated by opponent (chromatic) mechanisms (Size V target, 620 nm stimulus, 31.5 asb [10 cd/m2] white background). Average visual field sensitivity for opponent mechanisms decreased by approximately 0.6 dB per decade. This age-related sensitivity loss was smallest for the central 10 degrees visual field (0.5 dB per decade) and increased as a function of stimulus eccentricity (0.66 dB per decade for 20 to 30 degrees eccentricity), although the differences in aging effects for various eccentricities were not statistically significant. There were negligible differences in age-related sensitivity losses for opponent mechanisms in various quadrants of the visual field. These findings are generally similar to those obtained for standard automated perimetry, which uses a small white target on a white background. By comparison, short wave-length-sensitive mechanisms exhibit age-related losses that are more than twice as large, even after lenticular transmission losses are taken into account. These data provide a basis for distinguishing early disease-related losses from those related to normal aging.

Adult↗
PubMed1995

The Glenn A. Fry Award Lecture. Early losses of visual function in glaucoma.

Getting back to the questions raised by Dr. Enoch 12 years ago, I believe that we have made significant progress in the early psychophysical detection of glaucoma and that we are either on the right track or considerably closer to it. The continuing progress in conventional automated perimetry has improved the overall quality of visual field testing in the ophthalmic community, as well as providing standardization and state-of-the-art analysis procedures for everyone. We have certainly not solved the problem of early detection of glaucoma, but we now have more sensitive procedures that are available for existing clinical instrumentation. SWAP has clearly shown that it is able to detect glaucomatous losses several years before they are evident by conventional automated perimetry, and results from the other test procedures mentioned earlier are also very encouraging. Thus, although we may not yet have the pot of gold, we have been able to pick up a few valuable nuggets along the way. This leads me to believe that the current approaches are on the right track. However, Dr. Enoch's message should also serve to remind us that there are few panaceas for early detection of functional loss in glaucoma. Our progress to date has been influenced by our greater understanding of the properties of visual mechanisms and the pathophysiology of glaucoma. It has also been driven by clever and innovative approaches and new test procedures, as well as advances in technology. However, it has also been based on a considerable amount of research effort in the form of long-term prospective longitudinal studies of large populations of normal observers, patients with various stages of glaucomatous damage, and patients at risk of developing glaucoma. Answers to all of the issues pertaining to the ultimate clinical value of psychophysical procedures for early detection of glaucoma do not come quickly, but they are of vital importance to ocular health care. I hope that my brief discussion of new developments in psychophysical detection of glaucoma has convinced you that significant progress has been made, and that some of you will be motivated to join in this important research endeavor.

Awards and Prizes↗
PubMed1995

Effects of luminance, contrast, and blur on visual acuity.

Although previous investigations have reported that changes in background luminance, stimulus contrast, and dioptric blur can each affect visual acuity independently, it has not been shown how these three variables interact to influence visual acuity. This is a particularly important issue if one is interested in predicting how individuals with different refractive characteristics will be able to perform acuity-based tasks in degraded visual environments with low background lighting and contrast levels. To investigate these relations, we conducted a series of experiments in which measurements of visual acuity were obtained for four subjects using Landolt C targets of varying contrast at several background luminances for levels of blur between 0 and 8 diopters (D). Our results show that visual acuity is significantly affected by all three factors, and that their effects are essentially additive. At all luminance and contrast levels, the reduction in visual acuity is greatest for dioptric blur up to 2.0 D, with a more gradual reduction in visual acuity for dioptric blur of greater than 2.0 D. At all blur and luminance levels, visual acuity decreases gradually for contrast levels down to 20%, and decreases sharply for lower contrast levels. Over the range of background luminances we tested (75.0 to 0.075 cd/m2), visual acuity decreases linearly with reductions in luminance. The additive effects of dioptric blur, contrast, and luminance provide a basis for predicting visual acuity-related task performance for individuals in different visual environments. For example, an individual with 6/6 (20/20) visual acuity under high luminance-high contrast conditions will fall to 6/18 (20/60) acuity for low luminance conditions and 6/30 (20/100) for low luminance-low contrast conditions. Similarly, an individual with an uncorrected visual acuity of 6/30 (20/100) under optimal conditions will fall to approximately 6/120 (20/400) under low luminance conditions and 6/240 (20/800) under low luminance-low contrast conditions.

Adult↗
PubMed1995

Continuation high schools: youth at risk for drug abuse.

Students at alternative high schools may be at substantial risk for drug abuse. The present article provides a general overview of the drug use-related context of continuation high schools in southern California. A total of 144 students and ninety-six staff were interviewed from twenty continuation high schools. The interview data revealed that continuation school students show high levels of substance use. However, only 20 percent of the students report that they received any drug abuse prevention programming. Also, students at continuation high schools aspired to a productive life after high school including continued education. Thus, these youth may still be amenable to preventive educational interventions which deter them from drug use and help them to fulfill their future goals.

Adolescent↗
PubMed1995

Explaining exercise behavior and satisfaction with social exchange theory.

This study tested the hypothesis that the variables specified by social exchange theory (perceived rewards of exercising, perceived costs of exercising, social and tangible investments, and available alternative activities) are associated with exercise behavior and satisfaction. 190 health club members completed a questionnaire assessing attitudes toward exercise, exercise behavior, and demographic information. Exercise frequency and satisfaction were regressed on the social exchange theory variables and demographic covariates. Exercise satisfaction, the number of investments in exercise, and the number of available alternative activities were significantly related to exercise frequency, and the number of perceived rewards of exercise and the number of investments were significantly related to exercise satisfaction. These results suggest that social exchange theory is useful for explaining exercise behavior.

Adult↗
PubMed1995

Recombinant human DNase I in cystic fibrosis patients with severe pulmonary disease: a short-term, double-blind study followed by six months open-label treatment.

Chronic pulmonary infection is the major cause of morbidity and mortality in cystic fibrosis (CF). Recombinant human deoxyribonuclease (rhDNase) in vitro has been shown to dramatically reduce the viscoelasticity of the sputum from CF patients. Phase II and III clinical trials have shown the drug to be safe, and that patients with a forced vital capacity (FVC) of > 40% predicted show an improvement in pulmonary function when receiving rhDNase. The current study evaluates the safety and efficacy of rhDNase in the most severly ill CF patients (FVC < 40% predicted). A double-blind, randomized, placebo-controlled trial in which patients received either 2.5 mg rhDNase twice daily or placebo for a period of 14 days followed by a 6 month open extension period (OEP) is reported. Seventy patients were recruited for the double-blind study, and 64 entered the OEP of whom 38 completed. During the OEP, all patients received 2.5 mg rhDNase twice daily. In both the double-blind period and the OEP the drug appeared to be safe. During the double-blind study, forced expiratory volume in one second (FEV1) and FVC improved in both groups but there was no statistically significant difference between the groups. In the OEP, there was mean improvement in percentage predicted FEV1 and FVC, 9 and 18%, respectively, for all patients participating. In conclusion, DNase is safe when administered in conjunction with a rigorous regimen of chest physiotherapy to severely ill patients (FVC < 40% predicted) with CF. The double-blind, 14 day study showed no significant improvement in pulmonary function but some patients may have improved after longer administration of rhDNase.

Administration, Inhalation↗
PubMed1995

Serum advanced glycosylation end-products in patients on hemodialysis and CAPD.

OBJECTIVES: Part I: To evaluate the long-term effects of daily glucose absorption from the peritoneal dialysis fluid on the formation of low-molecular-weight advanced glycosylation end-products (AGE-peptides) in nondiabetic continuous ambulatory peritoneal dialysis (CAPD) patients. Part II: To determine the acute effect of CAPD on serum AGE-peptide concentrations. DESIGN: Part I: Noninterventional, parallel, cross-sectional clinical trial. Part II: Crossover clinical trial. SETTING: A university-based hospital, and clinics. PATIENTS: Part I: Sixty nondiabetic subjects recruited into three age-matched (+/- 5 years) groups, as follows: 20 healthy volunteers (controls); 20 hemodialysis patients; and 20 CAPD patients. Part II: Eight patients with diabetes mellitus (type I or II) and chronic renal failure who were about to undergo CAPD. INTERVENTION: Part I: None. Part II: Uninterrupted CAPD, as medically required. MEASUREMENTS: Part I: To determine serum AGE-peptide concentrations blood samples were obtained randomly from controls and CAPD patients, and predialysis from hemodialysis patients. Hemoglobin A1c was also measured in all subjects. Part II: To determine serum AGE-peptide concentrations, blood samples were collected within one month prior to initiation of CAPD (predialysis) and, again, one week after initiation of uninterrupted CAPD (postdialysis). Hemoglobin A1c was measured predialysis. RESULTS: Part I: Mean hemoglobin A1c values for all groups were within the normal range; however, the mean value for CAPD patients was significantly higher than for both hemodialysis patients and healthy controls (controls, 5.21% +/- 0.6%; hemodialysis, 5.12% +/- 0.5%; CAPD, 5.78% +/- 0.6%; p < 0.01). The dialysis patients had a significantly higher mean serum AGE-peptide concentration than the control subjects (controls, 7.02 +/- 3.4 units/mL; hemodialysis, 11.9 +/- 3.6 units/mL; CAPD, 11.1 +/- 4.5 units/mL; p < 0.01). There was no difference in the mean serum AGE-peptide concentration of patients in the hemodialysis and CAPD groups. Part II: The mean hemoglobin A1c value in the diabetic predialysis patients was 9.2% +/- 1.9%. There was no difference between the predialysis and postdialysis serum AGE-peptide concentrations (predialysis, 16.9 +/- 9.6 units/mL; postdialysis, 16.0 +/- 2.9 units/mL; p = 0.78). CONCLUSIONS: Despite the increased glucose load and the higher hemoglobin A1c values, indicating poor glycemic control, nondiabetic CAPD patients did not have higher serum AGE-peptide concentrations than the nondiabetic hemodialysis patients. In diabetic patients, CAPD did not further increase the serum concentrations of AGE-peptides.

Blood Glucose↗
PubMed1995

Subungual melanoma.

Twenty (1.5%) of 1,350 patients with malignant melanoma treated during a 17-year period had their primary lesion in the nail bed. The thumb (5 patients) and big toe (7) were the most commonly involved digits. Mean delay before diagnosis was 1.4 years. Thirteen patients were black and 7 white. Eight patients (40%) were initially misdiagnosed as having traumatic, infective or benign lesions. Four patients presented with recurrent local disease after inappropriate nail excision or inadequate nail biopsy, while 2 patients had regional nodal spread and 2 had systemic metastases. Mean Breslow depth was 5.7 mm. The histogenetic subtypes were acral lentiginous melanoma (12 patients) and nodular melanoma (4 patients); 4 lesions were unclassifiable. All patients underwent amputation of the involved digit and 12 required node dissection (therapeutic in 11, prophylactic in 1). Five patients (25%) are alive (mean 52 months, range 29-99 months); 4 are disease-free and 1 has brain metastases. Overall median survival was 32 months with a 26% 5-year survival rate. Delayed diagnosis and advanced disease at presentation contributed to the poor prognosis in nail bed melanoma.

Adult↗
PubMed1994

Parallel computing in biomedical research.

Scalable parallel computer architectures provide the computational performance needed for advanced biomedical computing problems. The National Institutes of Health have developed a number of parallel algorithms and techniques useful in determining biological structure and function. These applications include processing electron micrographs to determine the three-dimensional structure of viruses, calculating the solvent-accessible surface area of proteins to help predict the three-dimensional conformation of these molecules from their primary structures, and searching for homologous DNA or amino acid sequences in large biological databases. Timing results demonstrate substantial performance improvements with parallel implementations compared with conventional sequential systems.

Algorithms↗
PubMed1994

Visual field profile of optic neuritis. One-year follow-up in the Optic Neuritis Treatment Trial.

PURPOSE: The purpose of this present study was to evaluate longitudinal visual field information for 448 patients over their first year of follow-up in the Optic Neuritis Treatment Trial. METHODS: We reviewed 6536 automated static visual fields performed on a visual field analyzer (Humphrey Visual Field Analyzer) at nine visits within the 1-year period for each of the patients. RESULTS: The median values of the mean deviations for affected eyes were as follows: -22.88 dB at baseline, -1.94 dB at 6 months, and -1.62 dB at 1 year. At 6 months, 51% of affected eye visual fields were normal, and at 1 year 55.9% were normal. Approximately two thirds (68.8%) of the fellow eyes were classified as abnormal at baseline, although the defects were generally slight. One third (33.2%) were abnormal at 6 months, and approximately one third were still abnormal at 1 year. More than 87% of those abnormal at 6 months and at 1 year had been abnormal at baseline. Binocular analysis revealed that 13.2% of patients showed a chiasmal or retrochiasmal type of field defect at least once during the year (5.1% bitemporal; 8.9% homonymous). Of the patients who showed a retrochiasmal visual field defect, 75.7% had an abnormal magnetic resonance imaging scan at baseline compared with 46% of the rest of the patients in the Optic Neuritis Treatment Trial (chi 2 = 10.73, df = 1, P < .002). CONCLUSION: Over the first year of follow-up, the majority of patients with visual field defects from acute optic neuritis returned to normal, as measured by automated static perimetry. Many fields showed variation in the pattern and location of the sensitivity loss. Chiasmal and retrochiasmal defects occurred more commonly than previously reported.

Acute Disease↗
PubMed1994

Pharmacokinetics of tazobactam M1 metabolite after administration of piperacillin/tazobactam in subjects with renal impairment.

Tazobactam is a new derivative of penicillinic acid sulfone, which functions as an irreversible inhibitor of many beta-lactamases. The disposition of tazobactam M1 metabolite after intravenous (i.v.) infusion of 3 g of piperacillin/0.375 g of tazobactam was evaluated in 26 subjects with various degrees of renal impairment. Participants in the study were 18 subjects with creatinine clearances (ClCR) ranging from 7.4-41.8 mL/min, 4 subjects maintained on continuous ambulatory peritoneal dialysis (CAPD), and 4 subjects undergoing chronic hemodialysis (HD). The pharmacokinetic parameters of piperacillin and tazobactam were evaluated and were similar to previous reports. Tazobactam M1 metabolite maximum plasma concentration increased as renal function declined. The terminal elimination half-life and area under the plasma concentration-time curve of the tazobactam M1 metabolite increased as renal function declined. The mean rate of recovery of the tazobactam M1 metabolite in hemodialysate during a 3- to 4.2-hour HD session 1 hour after the i.v. infusion of piperacillin/tazobactam was 25.3%. However, when HD was performed at 36-48 hours after the i.v. infusion, 57.6% of the tazobactam dose was recovered as M1 metabolite, suggesting further conversion of tazobactam to M1 metabolite. Peritoneal dialysis removed 15.8% (n = 2) of the tazobactam dose as the M1 metabolite. Using a dose of 3 g of piperacillin/0.375 g of tazobactam, the predicted maximum steady-state plasma concentrations of the tazobactam M1 metabolite are 14.6 micrograms/mL, 34.8 micrograms/mL, and 48.8 micrograms/mL for subjects with ClCR 20-40 mL/min (every 6 hour dosing), ClCR < 20 mL/min (every 8 hour dosing), and on CAPD (every 12 hour dosing), respectively.

Adult↗
PubMed1994

Chest pain self-management training for patients with coronary artery disease.

This study was designed to evaluate the efficacy of a brief, structured pain management program to improve control over chest pain episodes in patients diagnosed with coronary artery disease. Twenty-six male veterans who attended the three-session program were compared with twenty-six matched controls. Results indicated significant short-term reductions in self-report of number of chest pain episodes in treated subjects. Self-report of pretreatment daily physical activity level moderated treatment outcome, as individuals reporting lower levels of physical activity derived greater benefit than their high-activity counterparts. These results suggest the potential utility of incorporating chest pain control strategies into comprehensive cardiac rehabilitation programs.

Adult↗
PubMed1994

Reproductive manifestations of thyroid disease.

Thyroid function and reproductive function have many interactions, the scope and mechanism of which are not fully understood. These functions are of greatest clinical importance for veterinarians working with breeders of purebred dogs. Thyroid dysfunction does not always result in clinical signs of reproductive disorders or in subfertility. It seems that animals with overt thyroid dysfunction are those most likely to manifest reproduction problems.

Animals↗