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Biomedical subjects

W D Johnson

Publications and source records attributed to W D Johnson.

At least 91 records · Page 5Linked to original sources
PubMed1994

Vitamin C concentration in gastric juice before and after anti-Helicobacter pylori treatment.

OBJECTIVES: To investigate the change of vitamin C concentration (ascorbic and dehydroascorbic acid) in gastric juice after anti-Helicobacter pylori treatment, and to relate any observed change to gastric pH, inflammatory compromise of the gastric mucosa, plasma vitamin C concentration, and smoking habits. METHODS: Plasma and gastric juice vitamin C, fasting gastric juice pH, gastric histology, and smoking status were studied in 70 patients with H. pylori-associated gastritis before and after therapy. RESULTS: Gastric juice ascorbic acid increased significantly after H. pylori clearance. For the most part, this change was confined to patients who experienced reduction of gastric pH. It was also related to improvement of the compromise of the gastric epithelium, reduction of the proportion of vitamin C composed by dehydroascorbic acid, and increase of the gastric juice/plasma vitamin C concentration gradient. Smokers had lower vitamin C concentrations in plasma and gastric juice before and after H. pylori clearance than nonsmokers. CONCLUSIONS: The findings are consistent with a causal association between H. pylori infection and low ascorbic acid levels in gastric juice, and support two mechanisms for this association: increased oxidation and a decreased secretion of ascorbic acid.

Amoxicillin↗
PubMed1994

Flexion and extension gap measurements in total knee arthroplasty after sacrifice of posterior cruciate ligament.

Twenty-three patients had 25 total knee arthroplasties. The flexion and extension gaps were measured before and after resection of the posterior cruciate ligament. The extension gap increased 2.0 +/- 0.2 mm in the medial compartment and 1.9 +/- 0.3 mm in the lateral compartment. The flexion gap increased 1.4 +/- 0.2 mm in the medial compartment and 2.3 +/- 0.3 mm in the lateral compartment. All increases were statistically significant.

Arthritis, Rheumatoid↗
PubMed1993

Effect of isoniazid prophylaxis on incidence of active tuberculosis and progression of HIV infection.

Tuberculosis occurring with human immunodeficiency virus (HIV) infection is a serious and growing public health problem. We have carried out a randomised clinical trial of a 12-month course of isoniazid plus vitamin B6 versus vitamin B6 alone in Port-au-Prince, Haiti, to assess the efficacy of isoniazid in preventing active tuberculosis in symptom-free HIV-infected individuals. The effect of prophylaxis on the development of HIV disease, AIDS, and death was also investigated. 118 subjects were assigned treatment with isoniazid plus B6 (n = 58) or B6 alone (n = 60) between 1986 and 1989. The treatment groups were similar at study entry in demographic, clinical, and immunological characteristics. Interim analysis in 1990 revealed no significant difference in tuberculosis outcome measures. Follow-up was continued until 1992, at which time significant protection by isoniazid against the development of tuberculosis was apparent, both for the whole study population and for subjects positive for purified protein derivative of tuberculin (PPD). The incidence of tuberculosis was lower in isoniazid recipients than in patients who received B6 alone (2.2 vs 7.5 per 100 person-years). The relative risk of tuberculosis was 3.4 (95% CI 1.1-10.6) for B6 alone versus isoniazid plus B6 (p < 0.05). Isoniazid also delayed progression to HIV disease and AIDS and death. Thus isoniazid effectively decreases the incidence of tuberculosis and delays the onset of HIV-related disease in symptom-free HIV-seropositive individuals. Isoniazid prophylaxis should be considered for HIV-seropositive, PPD-positive subjects, and may also be appropriate for PPD-negative patients in areas where tuberculosis is highly endemic.

AIDS-Related Opportunistic Infections↗
PubMed1993

Analysis of crossover designs with multivariate response.

Crossover designs involve observing the same response variate under different experimental conditions for each subject. Univariate methods are commonly used for analysis of data arising in these designs, but multivariate procedures offer a more general approach. The general multivariate linear model provides a natural framework for the simplest data structure as well as more complex settings with two or more response variates and measurements repeated over time. Multivariate models for crossover designs provide a unified approach that clarifies specification of hypotheses, assumptions required, and testing procedures in a wide class of applications that include longitudinal data as a special case. We focus on the 2 x 2 crossover design, but also describe models for analysing more complex crossover designs.

Adolescent↗
PubMed1993

MULTPERM: a computer package for the analysis of multivariate data using permutation procedures.

MULTPERM is a user-friendly C program using an exact permutation test for comparing groups when the data involve one or more response variables. The program computes the average within group distance based on a generalized distance function. Statistical significance of group differences is assessed by comparing the average distance for the observed data to the distribution of distances generated by all permutations of subjects to groups. This procedure is nonparametric and is especially appropriate if the assumptions underlying more traditional methods are not satisfied. The program was developed for personal computers and compiled using Borland's Turbo C 2.0. It should be easily ported to other platforms. An approximate test based on the beta distribution is incorporated for large samples.

Child↗
PubMed1993

A computer package for the multivariate nonparametric rank test in completely randomized experimental designs.

When research data are measured on at least an ordinal scale and the assumptions required in the theory underlying parametric statistical methods are in question, nonparameteric procedures based on the ranks provide a sound approach to statistical analysis. Biomedical investigations, especially clinical trials, typically involve multivariate response and therefore multivariate statistical methods are called for in the interpretation of results. We discuss applications of the nonparametric multivariate rank test for completely randomized designs. Large sample theory can be used to support these statistical methods for assessing group differences in location. In small samples, randomization tests provide a basis for inferences. The execution of the procedure is facilitated by a computer program developed by the authors.

Algorithms↗
PubMed1993

Evaluation of short research experiences in cancer.

For the past 5 years, the Cancer Education Committee of Louisiana State University Medical School (LSUMS) has selected premedical and medical students to participate in cancer research during the summer months. The students' participation is funded through a NCI R-25 training grant. Each year, LSUMS faculty from both the clinical and basic science departments provide opportunities for the students to participate in cancer research. The students also attend weekly seminars on cancer-related topics and biweekly multi-disciplinary Tumor Conferences. At the end of the summer, the students are required to submit and present a summary of their research project and to complete an evaluation form of the program. The overall evaluation of this experience has been favorable. Seventy-nine percent of the students agreed that the experience exceeded their expectations, and 83% responded that they would be willing to repeat the program. However, when asked if they planned to pursue a career in cancer research or medical oncology, 84 and 62%, respectively, were undecided. These findings raise the following questions: (1) When is the most appropriate time period in the student's education for this experience to take place? and (2) How can students' future career decisions be influenced?

Career Choice↗
PubMed1993

Multivariate nonparametric analysis for the two-period crossover design with application in clinical trials.

Nonparametric methods are presented for the analysis of the two-treatment, two-period crossover design with multivariate response. After forming within-subject sums and differences, the usual tests, including those for carry-over effects and direct treatment effects, can be constructed using a multivariate analysis of variance. When the assumptions relevant to traditional analysis are in question, multivariate nonparametric tests based on ranks provide a realistic alternative. However, multivariate response gives rise to a wider class of hypotheses than is seen in crossover designs with univariate response. We discuss these hypotheses and formulate nonparametric tests for associated analyses.

Clinical Trials as Topic↗
PubMed1993

The likelihood ratio for comparing means when a portion of the subjects fail to respond.

Results of clinical studies are often obscured by the fact that some of the subjects improve with treatment while others do not. As a consequence, for example, we may obtain a contaminated distribution in a treatment group, having one component similar to the entire distribution for a control group and the other shifted by the treatment effect. Maximum-likelihood estimation and the likelihood ratio test for investigating the proportion of responders together with the treatment effect are based on asymptotic theory and use iterative maximization techniques. We investigate the sampling distribution of the estimates and the test and demonstrate their use in statistical inference. Our results suggest that the chi-square distribution with 1.4 degrees of freedom provides a useful test criterion even when the sample sizes are as small as 10. Only in obvious testing situations is the t-test adequate.

Clinical Trials as Topic↗
PubMed1993

Analysis of the 2 x 2 crossover design with subsampling.

Subsampling can be used in experimental design to investigate extraneous sources of variability. One useful strategy is to make independent replicate measurements of the response variate. This can be achieved in clinical studies, for example, by dividing a blood or urine specimen from each of a sample of subjects into aliquots and processing these through a chemistry laboratory in such a way that the replicate determinations are independent. This procedure can be used to increase design efficiency. This paper addresses considerations in the design and analysis of the 2 x 2 crossover plan with this type of subsampling.

Analysis of Variance↗
PubMed1993

The analysis of small-sample multivariate data with applications in clinical trials.

This article discusses statistical methods for the analysis of multivariate data arising in clinical trials involving a small number of subjects randomly assigned to one of several treatment groups. Possible violations of traditional assumptions such as variance homogeneity and normality of errors are often dealt with by carrying out the statistical analysis using strategies such as transforming the data or applying nonparametric procedures. Multivariate nonparametric tests provide a realistic alternative for analyzing such data. We present a permutation procedure for analyzing data arising in randomized experiments.

Clinical Trials as Topic↗
PubMed1993

AIDS in Haiti: 1982-1992.

Haiti was one of the first countries where AIDS was recognized, a burden that led to the stigmatization of an entire nation resulting in serious long-term economic, social, and psychological consequences. Sixty percent of urban hospital beds are now occupied by patients infected with human immunodeficiency virus (HIV). AIDS is the leading cause of death in sexually active adults and increasingly has become a disease of women and children. AIDS threatens to reverse the decrease in infant mortality achieved during the past decade. In spite of educational efforts, the "silent epidemic" continues in all parts of the country and within all strata of society. The current HIV seroprevalence is 10% in urban areas and 5% in rural areas. AIDS is known but not understood; counseling modifies behavior in only 10%-20% of at-risk persons. This distressing situation is likely to worsen in view of the ongoing political crisis since almost all AIDS-education programs are dependent on foreign support.

AIDS-Related Opportunistic Infections↗
PubMed1993

The role of interferon-gamma in the treatment of visceral and diffuse cutaneous leishmaniasis.

Traditionally, the mainstay of visceral and diffuse cutaneous leishmaniasis therapy has been pentavalent antimony, with pentamidine and amphotericin B reserved for refractory cases. Interferon-gamma (IFN-gamma) in combination with pentavalent antimony has been used successfully in treating patients refractory to pentavalent antimony and in patients with previously untreated visceral leishmaniasis (39 total). In addition, 6 patients with diffuse cutaneous leishmaniasis have been treated with combination IFN-gamma and antimony therapy. Preliminary experience with these patients indicates that IFN-gamma is a useful adjunct therapy for severe or refractory cases of visceral leishmaniasis; however, the potential of IFN-gamma in treating diffuse cutaneous leishmaniasis cannot be assessed as current clinical experience is too limited.

Antimony↗
PubMed1993

Isolation of Mycobacterium avium complex from bone marrow aspirates of AIDS patients in Brazil.

Mycobacterium avium complex (MAC) infection has not been reported as a major opportunistic infection among patients with AIDS in Latin America or Africa. In this study, 125 AIDS patients who had persistent fever, anemia, and leukopenia were examined among 2628 AIDS patients admitted to Instituto de Infectologia Emilio Ribas between May 1990 and April 1992. From the bone marrow aspirates of the 125 patients, MAC was isolated from 23 (18.4%) and Mycobacterium tuberculosis was isolated from 9 (7.2%). Between 1985 and 1990, only 11 MAC isolations among 60,000 cultures obtained from human immunodeficiency virus-seronegative patients were documented in São Paulo. Hence, the minimal estimated rate of MAC infection in AIDS patients in this city was 23/2628, or 0.88%. These findings suggest that MAC infection is an important opportunistic infection, especially among a subset of patients with AIDS in Brazil who have clinical characteristics and risk activities similar to those associated with MAC infections in North America and Europe.

AIDS-Related Opportunistic Infections↗
PubMed1993

Anatomical basis of syringomyelia occurring with hindbrain lesions.

Hindbrain lesions that distort or compress the cervicomedullary junction are commonly associated with syringomyelia. As a basis for discussing pathogenetic mechanisms, the upper end of the central canal of the spinal cord was examined histologically in six aborted fetuses and 14 adults dying of natural causes; the results were correlated with magnetic resonance images in 40 normal subjects. The central canal of the medulla, which extends from the cervicomedullary junction to the fourth ventricle, was found to migrate dorsally, elongate in dorsoventral diameter, and dilate beneath the tip of the obex to form a large, everted aperture. This opening communicates directly with the subarachnoid space through the foramen of Magendie and is indirectly continuous with the main body of the fourth ventricle. In adults, the aperture of the central canal is located approximately 1.0 cm below the tela choroidea inferior and 3.5 cm below the midpoint of the fourth ventricle. Analysis of magnetic resonance imaging scans in 45 patients with syringomyelia and simple hindbrain lesions revealed two patterns of cavity formation: 1) lesions that obstructed the upper end of the central canal or its continuity with the subarachnoid space produced a noncommunicating type of syringomyelia; and 2) lesions that obstructed the basilar cisterns or the foraminal outlets of the fourth ventricle produced a communicating type of syringomyelia (hydromyelia) in association with hydrocephalus. Evidence is presented that syrinxes occurring with hindbrain lesions are not caused by a caudal flow of cerebrospinal fluid from the fourth ventricle into the central canal of the spinal cord.

Aged↗
PubMed1993

Characteristics of the acquired immunodeficiency syndrome in Brazil.

The clinical and epidemiologic characteristics of the acquired immunodeficiency syndrome (AIDS) were studied in a tropical area of Brazil. During an 18-month period (July 1989-January 1991), 111 consecutive AIDS patients (102 men and nine women) were evaluated. Patients reported homosexual/bisexual activities (60%), intravenous drug use (19%), or both (6%), heterosexual activities (11%), blood transfusions (2%), and 2% belonged to an undetermined category. Weight loss, fever, oral thrush, and diarrhea were present in > or = 70% of the patients at presentation. An unexpected high frequency of hepatomegaly (49%) was detected, and found to be significantly associated with tuberculosis (P < 0.0001). Although the epidemiologic features of human immunodeficiency virus transmission were comparable to the United States/European pattern, the clinical spectrum of opportunistic infections more closely resembled that reported in Africa and Haiti, with a greater frequency of fungal and mycobacterial infections than Pneumocystis carinii pneumonia and viral infections.

AIDS-Related Opportunistic Infections↗
PubMed1993

Serologic validation of HIV infection in a tropical area.

We have defined human immunodeficiency virus type 1 (HIV-1) serologic reactivity in Brazilians living in an area endemic for tropical diseases. Enzyme-linked immunosorbent assay (ELISA) and Western blot (WB) analyses were performed on 342 patients with diseases including Chagas' disease, schistosomiasis, typhoid fever, helminthiasis, and cutaneous and visceral leishmaniasis. Nine percent of the visceral leishmaniasis patients' sera reacted in the HIV-1 ELISA but all were WB negative. All other sera from these patients were HIV negative. A total of 224 HIV-1 ELISA repeatedly positive sera also were HIV-1 WB tested. They were drawn from a total population of 19,230 individuals, including AIDS patients, blood donors, homosexual men, intravenous drug users, pregnant women, individuals with hemophiliac, and tuberculosis and sexually transmitted disease patients. The WB results were analyzed using five different interpretive criteria for WB positivity. The Centers for Disease Control (CDC) and the World Health Organization (WHO) criteria were the most sensitive and specific for identifying HIV-1-infected individuals. The WB pattern was similar to that seen in the United States. Envelope (ENV) protein antibodies were highly predictive of HIV-1 infection; none of the AIDS patients lacked ENV protein reactivity. We conclude that among the tropical diseases studied, only visceral leishmaniasis is associated with false-positive HIV-1 ELISA tests. Current CDC and WHO criteria for interpretation of HIV-1 WB tests are appropriate for Brazil.

Acquired Immunodeficiency Syndrome↗