Biomedical subjects

H X Barnhart

Publications and source records attributed to H X Barnhart.

10 recordsLinked to original sources

PubMed1998

Goodness-of-fit tests for GEE modeling with binary responses.

Analysis of data with repeated measures is often accomplished through the use of generalized estimating equations (GEE) methodology. Although methods exist for assessing the adequacy of the fitted models for uncorrelated data with likelihood methods, it is not appropriate to use these methods for models fitted with GEE methodology. We propose model-based and robust (empirically corrected) goodness-of-fit tests for GEE modeling with binary responses based on partitioning the space of covariates into distinct regions and forming score statistics that are asymptotically distributed as chi-square random variables with the appropriate degrees of freedom. The null distribution and the statistical power of the proposed goodness-of-fit tests were assessed using simulated data. The proposed goodness-of-fit tests are illustrated by two examples using data from clinical studies.

Antidepressive Agents↗

PubMed1997

Angioplasty or surgery for multivessel coronary artery disease: comparison of eligible registry and randomized patients in the EAST trial and influence of treatment selection on outcomes. Emory Angioplasty versus Surgery Trial Investigators.

The Emory Angioplasty versus Surgery Trial (EAST) showed that multivessel patients eligible for both percutaneous transluminal coronary angioplasty (PTCA) and coronary bypass surgery (CABG) had equivalent 3-year outcomes regarding survival, myocardial infarction, and major myocardial ischemia. Patients eligible for the trial who were not randomized because of physician or patient refusal were followed in a registry. This study compares the outcomes of the randomized and registry patients. Of the 842 eligible patients, 450 did not enter the trial. Their baseline features closely resembled those of the randomized patients and follow up was performed using the same methods. In the registry there was a bias toward selecting CABG in patients with 3-vessel disease (84%) and PTCA in patients with 2-vessel disease (54%). Three-year survival for the registry patients was 96.4%, which was better than the randomized patients, 93.4% (p = 0.044). Angina relief in the registry was equal for CABG and PTCA patients and was better for the PTCA registry (12.4%) than PTCA randomized patients (19.6%) (p = 0.079). Thus, the registry confirms that EAST is representative of all eligible patients and does not represent a low-risk subgroup. Since baseline differences were small, improved survival in the registry may be due to treatment selection. Physician judgment, even in patients judged appropriate for clinical trials, remains a potentially important predictor of outcomes.

Aged↗

PubMed1997

The effect of Tai Chi Quan and computerized balance training on postural stability in older subjects. Atlanta FICSIT Group. Frailty and Injuries: Cooperative Studies on Intervention Techniques.

BACKGROUND AND PURPOSE: This study explored whether two exercise programs would affect the ability to minimize postural sway of 72 relatively inactive, older subjects who participated in the Atlanta FICSIT trial. SUBJECTS: Subjects were randomly assigned to (1) a computerized balance training group, (2) a tai chi group, or (3) an educational group serving as a control for exercise. Each group consisted of 24 members. METHODS: All subjects were evaluated under four postural conditions before, immediately after, and 4 months following their respective interventions, each of which was given over 15 weeks. RESULTS: Platform balance measures revealed greater stability after training among subjects in the balance training group but little change in stability among subjects in the tai chi and educational group. Subjects in the tai chi group were less afraid of falling after training compared with subjects in other groups with similar covariates. CONCLUSION AND DISCUSSION: Unlike computerized balance training, tai chi does not improve measures of postural stability. Because tai chi delayed onset to first or multiple falls in older individuals, this effect does not appear to be associated with measures of enhanced postural stability. Tai chi may gain its success, in part, from promoting confidence without reducing sway rather than primarily facilitating a reduction in sway-based measures.

Accidental Falls↗

PubMed1997

A generalized estimating equation approach for modeling random length binary vector data.

A common measure in clinical trials and epidemiologic studies is the number of events such as seizures, hospitalizations, or bouts of disease. Frequently, a binary measure of severity for each event is available but is not incorporated in the analysis. This paper proposes methodology for jointly modeling the number of events and the vector of correlated binary severity measures. Our formulation exploits the notion that a given covariate may affect both outcomes in a similar way. We functionally link the regression parameters for the counts and binary means and discuss a generalized estimating equation (GEE) approach for parameter estimation. We discuss conditions under which the proposed joint modeling approach provides marked gains in efficiency relative to the common procedure of simply modeling the counts, and we illustrate the methodology with epilepsy clinical trial data.

Anticonvulsants↗

PubMed1996

Effectiveness of revascularization in the Emory angioplasty versus surgery trial. A randomized comparison of coronary angioplasty with bypass surgery.

BACKGROUND: The Emory Angioplasty Versus Surgery Trial (EAST) was designed to determine whether percutaneous transluminal coronary angioplasty (PTCA) is as effective as coronary artery bypass graft surgery (CABG) in restoring arterial perfusion capacity in eligible patients with multivessel disease. METHODS AND RESULTS: Of 392 patients in EAST, 198 were randomized to PTCA and 194 to CABG. Index lesions (2.7 +/- 1.0 per patient) were those with > or = 50% stenosis judged treatable by both angioplasty and surgery. Coronary segments jeopardized by these index lesions were designated as index segments (4.4 +/- 1.4 per patient). Percent stenosis was measured by quantitative angiography at the point of greatest obstruction in the main perfusion path of each index segment. The EAST primary arteriographic end point was the percent of a patient's index segments with < 50% stenosis in the main perfusion pathways at 1 and 3 years. At baseline, the percent of index segments for which revascularization was attempted was 85% for PTCA and 98% for CABG (P < .0001). At 1 year, PTCA patients had a smaller percentage of successfully revascularized index segments than CABG patients (59% versus 88%, P < .001). At 3 years, the findings were similar but less striking (70% versus 87%, P < .001). When only "high-priority" index segments (2.1 +/- 1.6 per patient) were considered, baseline attempts were comparable (96% versus 99%, P = NS); despite this, CABG remained more successful at 1 (64% versus 93%, P < .001) and 3 (76% versus 89%, P < .01) years. However, the mean percent of index segments free of severe stenosis (> or = 70%) did not differ between PTCA and CABG patients at 3 years (93% versus 95%, P = NS). Furthermore, the frequency of patients with all index segments free of severe stenosis did not differ between the two groups at 1 (76% versus 83%, P = NS) or 3 (82% for both PTCA and CABG) years. CONCLUSIONS: In patients with multivessel disease, index segment revascularization was more complete with CABG than PTCA at both 1 and 3 years. However, when the physiological priority of the target lesion and the measured severity of the residual stenosis are taken into account, the advantage of CABG becomes less significant or nonsignificant. This may, in part, explain why these two strategies did not differ in terms of the EAST primary clinical end points over 3 years.

Aged↗

PubMed1996

Reducing frailty and falls in older persons: an investigation of Tai Chi and computerized balance training. Atlanta FICSIT Group. Frailty and Injuries: Cooperative Studies of Intervention Techniques.

OBJECTIVE: To evaluate the effects of two exercise approaches, Tai Chi (TC) and computerized balance training (BT), on specified primary outcomes (biomedical, functional, and psychosocial indicators of frailty) and secondary outcomes (occurrence of falls). DESIGN: The Atlanta FICSIT (Frailty and Injuries: Cooperative Studies of Intervention Techniques), a prospective, randomized, controlled clinical trial with three arms (TC, BT, and education [ED]. Intervention length was 15 weeks, with primary outcomes measured before and after intervention and at 4-month follow-up. Falls were monitored continuously throughout the study. SETTING: Persons aged 70 and older living in the community. PARTICIPANTS: A total of 200 participants, 162 women and 38 men; mean age was 76.2. MEASUREMENTS: Biomedical (strength, flexibility, cardiovascular endurance, body composition), functional (IADL), and psychosocial well-being (CES-D scale, fear of falling questionnaire, self-perception of present and future health, mastery index, perceived quality of sleep, and intrusiveness) variables. RESULTS: Grip strength declined in all groups, and lower extremity range of motion showed limited but statistically significant changes. Lowered blood pressure before and after a 12-minute walk was seen following TC participation. Fear of falling responses and intrusiveness responses were reduced after the TC intervention compared with the ED group (P = .046 and P = .058, respectively). After adjusting for fall risk factors, TC was found to reduce the risk of multiple falls by 47.5%. CONCLUSIONS: A moderate TC intervention can impact favorably on defined biomedical and psychosocial indices of frailty. This intervention can also have favorable effects upon the occurrence of falls. Tai Chi warrants further study as an exercise treatment to improve the health of older people.

Accidental Falls↗

PubMed1996

Natural history of human immunodeficiency virus disease in perinatally infected children: an analysis from the Pediatric Spectrum of Disease Project.

OBJECTIVE: To describe the progression of human immunodeficiency virus (HIV) disease through clinical stages from birth to death among a large number of perinatally infected children. METHODS: The Pediatric Spectrum of Disease (PSD) project, coordinated by the Centers for Disease Control and Prevention (CDC), has conducted active surveillance for HIV disease since 1988 in seven geographic regions. PSD data are collected from medical and social service records every 6 months through practitioners at each participating hospital clinic. We analyzed data from perinatally HIV-infected children born between 1982 and 1993. The natural history of HIV disease was divided into five progressive stages using the clinical categories in the CDC 1994 pediatric HIV classification system: stage N, no signs or symptoms; stage A, mild signs or symptoms; stage B, moderate signs or symptoms; stage C, severe signs or symptoms; and stage D, death. A five-stage Markov model was fitted to the PSD data. To compare the estimates from the PSD project with the published estimates, we also fitted an alternative Markov model using acquired immunodeficiency syndrome (AIDS; 1987 case definition) in place of stage C and also calculated standard Kaplan-Meier estimates. RESULTS: A total of 2148 perinatally HIV-infected children were included in the analysis. The estimated mean times spent in each stage were: N, 10 months; A, 4 months; B, 65 months; and C, 34 months. We estimated that a child born with HIV infection has a 50% (95% confidence interval [CI], 40%-60%) chance of severe signs or symptoms developing by 5 years of age and a 75% (95% CI, 68%-82%) chance of surviving to 5 years of age. For a child in stage B, there is a 60% (95% CI, 49%-71%) chance of severe signs or symptoms developing within the next 5 years and a 65% (95% CI, 56%-73%) chance of surviving 5 more years. The estimated mean time from birth to stage C was 6.6 (95% CI, 5.7-7.5) years, and the estimated mean survival time from birth was 9.4 (95% CI, 8.1-10.7) years. From the alternative Markov model, the estimated mean time from birth to AIDS was 4.8 (95% CI, 4.5-5.2) years. CONCLUSION: Markov modeling using the revised pediatric classification system allowed us to describe the natural history of HIV disease in children before diagnosis of AIDS. On average, children progress to moderate symptoms in the second year of life and then remain moderately symptomatic for more than half of their expected lives, underscoring their need for clinical care before the onset of AIDS. The results from the Markov model are useful in family counseling, health care planning, and clinical trial designs.

Acquired Immunodeficiency Syndrome↗

PubMed1995

Emory Angioplasty Versus Surgery Trial (EAST): design, recruitment, and baseline description of patients.

In patients with multivessel coronary artery disease who require revascularization there is uncertainty as to the selection of the appropriate patients for percutaneous transluminal coronary angioplasty (PTCA) as opposed to coronary artery bypass grafting (CABG). To define the relative roles of PTCA and CABG for multivessel disease, 392 patients were randomly assigned to revascularization by PTCA or CABG and followed for 3 years. This is a single-center randomized study in which individual group assignment was known but grouped data remained blinded until a full 3 years of follow-up was complete on all patients. The patients were randomized in 4 strata: (1) 2-vessel disease with 1 lesion per vessel; (2) 2-vessel disease with multiple lesions in at least 1 vessel; (3) 3-vessel disease with 1 lesion per vessel; and (4) 3-vessel disease with multiple lesions in at least 1 vessel. All data were collected on study-specific forms and sent to an independent biostatistical coordinating center for entry into a computerized database. All data will be analyzed by intention-to-treat. The primary endpoint of the trial is the composite of death of any cause, Q-wave myocardial infarction within 3 years, or a large reversible thallium defect at 3 years. Multiple secondary endpoints will include each of the components of the primary endpoint, the need for additional procedures, angiographic status at 1 and 3 years measured by an independent quantitative coronary arteriography laboratory, and measures of quality of life. A total of 5,118 patients were screened, of whom 3,371 were excluded for angiographic reasons, 191 because the angioplasty operators or surgeons believed that the patients were anatomically unsuitable, and 714 for clinical exclusions, leaving 842 eligible patients, of whom 392 were randomized. Of these, 40% had triple-vessel disease and 60% had double-vessel disease. There was no baseline difference between the 2 treatment arms for any clinical or major angiographic variable. This randomized trial will permit an in-depth comparison of coronary angioplasty and coronary surgery in comparable patients suitable for either procedure. Clinical, angiographic, and quality-of-life comparisons will be made and should be helpful in medical decision making between the 2 procedures.

Adult↗

PubMed1995

Multiple population models for multivariate random length data--with applications in clinical trials.

This paper focuses on the development and study of multiple population models for multivariate random length data, of the type often encountered in clinical trials. If experimental outcomes per subject consist of multiple measurements of a quantitative variable and the number of these measurements, then a multivariate random length vector is observed. For this type of data, the experimental treatment is likely to affect both the quantitative measurements and the number of these measurements. One example of such data is from the National Heart, Lung and Blood Institute Type II coronary intervention study (Brensike et al. (1982; Controlled Clinical Trials 3, 91-111; 1984, Circulation 69, 313-324)). The outcome data consist of vectors of lesion sizes with lengths determined by the number of underlying lesions assessed from the patients' angiograms, where both the numbers and the lesion sizes depend on patients' overall disease status. We propose models which can realistically describe the relationships between the quantitative variables and the number of responses. The asymptotic covariance of the maximum likelihood estimators is obtained. Data from the Type II study are analyzed using this multiple population model.

Biometry↗

PubMed1994

A randomized trial comparing coronary angioplasty with coronary bypass surgery. Emory Angioplasty versus Surgery Trial (EAST)

BACKGROUND: The clinical benefit of percutaneous transluminal coronary angioplasty (PTCA) as compared with coronary-artery bypass grafting (CABG) for patients with multivessel coronary artery disease has not been established. To determine the outcomes of these treatments in patients referred for the first time for coronary revascularization, we conducted a three-year prospective, randomized trial comparing the two procedures. METHODS: Revascularization was performed by accepted methods. Follow-up clinical information was collected every six months, and coronary arteriography and thallium stress scanning were performed at one and three years. The primary end point was a composite of death, Q-wave myocardial infarction, and a large ischemic defect identified on thallium scanning at three years. Secondary end points included clinical and angiographic status and the need for additional revascularization procedures. Data were analyzed according to the intention-to-treat principle. RESULTS: Of the 5118 patients screened for the trial, 842 (16.5 percent) were eligible for enrollment, and 392 (7.7 percent) agreed to participate. A total of 194 patients were randomly assigned to the CABG group, and 198 to the PTCA group. The primary end point occurred in 27.3 percent of the CABG group and 28.8 percent of the PTCA group (P = 0.81). Death occurred in 6.2 percent of the CABG group and 7.1 percent of the PTCA group (P = 0.73 by log-rank test). At three years, the proportions of patients in the CABG group who required repeated bypass surgery (1 percent) or angioplasty (13 percent) were significantly lower than the proportions in the PTCA group (22 and 41 percent, respectively; P < 0.001). Angiographic studies at three years showed a greater degree of revascularization in the CABG group. Angina was more frequent in the PTCA group (20 percent) than in the CABG group (12 percent). CONCLUSIONS: We found that CABG and PTCA did not differ significantly with respect to the occurrence of the composite primary end point. Consequently, the selection of one procedure over the other should be guided by patients' preferences regarding the quality of life and the possible need for subsequent procedures.

Angioplasty, Balloon, Coronary↗