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Biomedical subjects

D Follmann

Publications and source records attributed to D Follmann.

14 recordsLinked to original sources
PubMed1999

Beta-blocker use and survival in patients with ventricular fibrillation or symptomatic ventricular tachycardia: the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial.

OBJECTIVES: To evaluate whether use of beta-adrenergic blocking agents, alone or in combination with specific antiarrhythmic therapy, is associated with improved survival in persons with ventricular fibrillation (VF) or symptomatic ventricular tachycardia (VT). BACKGROUND: The ability of beta-blockers to alter the mortality of patients with VF or VT receiving contemporary medical management is not well defined. METHODS: Survival of 1,016 randomized and 2,101 eligible, nonrandomized patients with VF or symptomatic VT followed in the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial through December 31, 1996 was assessed using Cox proportional hazards analysis. RESULTS: The 817 (28%) patients discharged from hospital receiving beta-blockers had less ventricular dysfunction, fewer symptoms of heart failure and a different pattern of medication use compared with patients not receiving beta-blockers. Before adjustment for important prognostic variables, beta-blockade was not significantly associated with survival in randomized or in eligible, nonrandomized patients treated with specific antiarrhythmic therapy. After adjustment, beta-blockade remained unrelated to survival in randomized or in eligible, nonrandomized patients treated with amiodarone alone (n = 1142; adjusted relative risk [RR] = 0.96; 95% confidence interval [CI] 0.64-1.45; p = 0.85) or a defibrillator alone (n = 1347; adjusted RR = 0.88; 95% CI 0.55 to 1.40; p = 0.58). In contrast, beta-blockade was independently associated with improved survival in eligible, nonrandomized patients who were not treated with specific antiarrhythmic therapy (n = 412; adjusted RR = 0.47; 95% CI 0.25 to 0.88; p = 0.018). CONCLUSIONS: Beta-blocker use was independently associated with improved survival in patients with VF or symptomatic VT who were not treated with specific antiarrhythmic therapy, but a protective effect was not prominent in patients already receiving amiodarone or a defibrillator.

Adrenergic beta-Antagonists↗
PubMed1998

Prevention and Treatment of Hypertension Study (PATHS): effects of an alcohol treatment program on blood pressure.

OBJECTIVE: To determine whether blood pressure is reduced for at least 6 months with an intervention to lower alcohol intake in moderate to heavy drinkers with above optimal to slightly elevated diastolic blood pressure, and whether reduction of alcohol intake can be maintained for 2 years. DESIGN: A randomized controlled trial. METHODS: Six hundred forty-one outpatient veterans with an average intake of 3 or more alcoholic drinks per day in the 6 months before entry into the study and with diastolic blood pressure 80 to 99 mm Hg were randomly assigned to a cognitive-behavioral alcohol reduction intervention program or a control observation group for 15 to 24 months. The goal of the intervention was the lower of 2 or fewer drinks daily or a 50% reduction in intake. A subgroup with hypertension was defined as having a diastolic blood pressure of 90 to 99 mm Hg, or 80 to 99 mm Hg if recently taking medication for hypertension. RESULTS: Reduction in average weekly self-reported alcohol intake was significantly greater (P<.001) at every assessment from 3 to 24 months in the intervention group vs the control group: levels declined from 432 g/wk at baseline by 202 g/wk in the intervention group and from 445 g/wk by 78 g/wk in the control group in the first 6 months, with similar reductions after 24 months. The intervention group had a 1.2/0.7-mm Hg greater reduction in blood pressure than the control group (for each, P = .17 and P = .18) for the 6-month primary end point; for the hypertensive stratum the difference was 0.9/0.7 mm Hg (for each, P = .58 and P = .44). CONCLUSIONS: The 1.3 drinks per day average difference between changes in self-reported alcohol intake observed in this trial produced only small nonsignificant effects on blood pressure. The results from the Prevention and Treatment of Hypertension Study (PATHS) do not provide strong support for reducing alcohol consumption in nondependent moderate drinkers as a sole method for the prevention or treatment of hypertension.

Adult↗
PubMed1997

Effects of oral potassium on blood pressure. Meta-analysis of randomized controlled clinical trials.

OBJECTIVE: To assess the effects of supplementation with oral potassium on blood pressure in humans. DESIGN: Meta-analysis of randomized controlled trials. DATA SOURCES: English-language articles published before July 1995. STUDY SELECTION: Thirty-three randomized controlled trials (2609 participants) in which potassium supplementation was the only difference between the intervention and control conditions. DATA EXTRACTION: Using a standardized protocol, 2 of us independently abstracted information on sample size, duration, study design, potassium dose, participant characteristics, and treatment results. RESULTS: By means of a random-effects model, findings from individual trials were pooled, after results for each trial were weighted by the inverse of its variance. An extreme effect of potassium in lowering blood pressure was noted in 1 trial. After exclusion of this trial, potassium supplementation was associated with a significant reduction in mean (95% confidence interval) systolic and diastolic blood pressure of -3.11 mm Hg (-1.91 to -4.31 mm Hg) and -1.97 mm Hg (-0.52 to -3.42 mm Hg), respectively. Effects of treatment appeared to be enhanced in studies in which participants were concurrently exposed to a high intake of sodium. CONCLUSIONS: Our results support the premise that low potassium intake may play an important role in the genesis of high blood pressure. Increased potassium intake should be considered as a recommendation for prevention and treatment of hypertension, especially in those who are unable to reduce their intake of sodium.

Administration, Oral↗
PubMed1997

Randomized trials of sodium reduction: an overview.

We updated a previously published overview of randomized clinical trials testing the effects of reducing sodium intake. We excluded trials that had confounded designs, enrolled preadolescent study populations, tested intakes outside the usual range for the US population, or reported neither systolic nor diastolic blood pressure. Thirty-two trials with outcome data for 2635 subjects were included. Two reviewers abstracted information independently and differences were reconciled. Pooled blood pressure differences between treated and control groups were highly significant for all trials combined and for trials in hypertensive and normotensive subjects pooled separately. The effects on blood pressure of lowering sodium in hypertensive and normotensive subjects, respectively (each trial weighted according to sample size), were -4.8/-2.5 and -1.9/-1.1 mm Hg (systolic/diastolic). Median differences in sodium excretion between sodium-reduction and control groups in these subgroups were -77 and -76 mmol/24 h, respectively. Weighted linear-regression analyses across the trials showed dose responses, which were more consistent for trials in normotensive subjects. These associations were, per 100 mmol Na/24 h, -5.8/-2.5 and -2.3/-1.4 mm Hg in hypertensive and normotensive subjects, respectively. There is no evidence that sodium reduction as achieved in these trials presents any safety hazards. The blood pressure reduction that would result from a substantial lowering of dietary sodium in the US population could reduce cardiovascular morbidity and mortality.

Blood Pressure↗
PubMed1996

Dietary calcium and blood pressure: a meta-analysis of randomized clinical trials.

PURPOSE: To assess the effect of dietary calcium supplementation on blood pressure. DATA SOURCES: Published reports of trials studying the effect of dietary calcium supplementation on blood pressure were identified by a search of previous reviews, a MEDLINE search, a manual review of journal articles, and a review of abstracts from scientific meetings. STUDY SELECTION: Randomized clinical trials in which dietary calcium intake varied by intervention group were selected. Multifactorial trials were not included. DATA SYNTHESIS: Data from 28 active treatment arms or strata from 22 randomized clinical trials were pooled using a weighted average method, with weights proportional to the inverse of the variance of the treatment effect. The total sample comprised 1231 persons. Because trials of both normotensive and hypertensive persons were included, subgroup analyses could be done. Pooled estimates of the effect of calcium supplementation on blood pressure were -0.18 mm Hg for diastolic blood pressure (95% CI, -0.75 to 0.40 mm Hg) and -0.89 mm Hg for systolic blood pressure (CI, -1.74 to -0.05 mm Hg). Pooled estimates for systolic blood pressure were -0.53 mm Hg (CI, -1.56 to 0.49 mm Hg) for trials of normotensive persons and -1.68 mm Hg (CI, -3.18 to -0.18 mm Hg) for trials of hypertensive persons. Diastolic blood pressure was not significantly affected in either subgroup. CONCLUSION: The pooled estimate shows a statistically significant decrease of systolic blood pressure with calcium supplementation, both for hypertensive persons and for the overall sample. However, the effect is too small to support the use of calcium supplementation for preventing or treating hypertension.

Adult↗
PubMed1995

Multivariate tests for multiple endpoints in clinical trials.

Clinical trials frequently lack a single definitive endpoint that completely describes treatment efficacy. When a treatment affects a disease in a multitude of ways, several endpoints are necessary to describe efficacy. There is a variety of statistical procedures to provide a single p-value when a treatment affects several endpoints. This paper reviews several procedures including Hotelling's T2 test, an approximate likelihood ratio test (Tang et al.), the weighted version of O'Brien's test, tests involving the maximum of several test statistics, and a test based on the average of the maximum of several endpoints (Wittes). I propose a risk score test whose rejection boundary corresponds to a contour of constant risk. Calculations and simulation studies help to compare the different tests with an emphasis on the effect of non-standard alternatives, and on identifying settings where some tests may lack clinical relevance.

Bias↗
PubMed1995

An approximate generalized linear model with random effects for informative missing data.

This paper develops a class of models to deal with missing data from longitudinal studies. We assume that separate models for the primary response and missingness (e.g., number of missed visits) are linked by a common random parameter. Such models have been developed in the econometrics (Heckman, 1979, Econometrica 47, 153-161) and biostatistics (Wu and Carroll, 1988, Biometrics 44, 175-188) literature for a Gaussian primary response. We allow the primary response, conditional on the random parameter, to follow a generalized linear model and approximate the generalized linear model by conditioning on the data that describes missingness. The resultant approximation is a mixed generalized linear model with possibly heterogeneous random effects. An example is given to illustrate the approximate approach, and simulations are performed to critique the adequacy of the approximation for repeated binary data.

Bayes Theorem↗
PubMed1993

Gender differences in the psychosocial variance of Framingham and Bortner Type A measures.

The object of the present study was to determine whether the non-genetic variance of a Type A scale composed of Framingham and Bortner items had gender specific psychosocial components. The study was performed on a group of Swedish twins so that variance explained by heritability for Type A could first be removed from the equation. The overall Type A score had been found to relate to self-reported CHD in this population. The dependent variable was the standardized score residual remaining after removing the genetic variance (i.e., that explained by co-twin score and zygosity). Multiple regression analyses revealed that there were differences in the psychosocial components of the Type A residual in men and women. These results are discussed in terms of culturally accepted gender roles and their possible implications for health endpoints.

Adoption↗
PubMed1992

The use of subjective rankings in clinical trials with an application to cardiovascular disease.

Evaluating a clinical trial can be problematic if the studied treatments affect patients in many ways. A possible method for evaluating treatments is to have raters rank all the patients' trial experiences and then test whether the distribution of ranks differ between treatments. Before one can advocate such a procedure, however, one would like to be assured that raters agree fairly well with one another. As a first step in examining whether raters tend to agree, we conducted a small study with 20 raters evaluating 43 trial experiences from an imaginary cardiovascular clinical trial. Raters showed a high degree of consensus. Moreover, the average ranks agreed fairly well with two quantitative ranking rules. On the other hand, the average ranks did not agree very well with weightings usually selected in cardiovascular trials. These results suggest ranking may be a feasible approach to analysing certain clinical trials with multiple outcomes.

Cardiovascular Diseases↗
PubMed1992

Variance imputation for overviews of clinical trials with continuous response.

Overviews of clinical trials are an efficient and important means of summarizing information about a particular scientific area. When the outcome is a continuous variable, both treatment effect and variance estimates are required to construct a confidence interval for the overall treatment effect. Often, only partial information about the variance is provided in the publication of the clinical trial. This paper provides heuristic suggestions for variance imputation based on partial variance information. Both pretest-posttest (parallel groups) and crossover designs are considered. A key idea is to use separate sources of incomplete information to help choose a better variance estimate. The imputation suggestions are illustrated with a data set.

Analysis of Variance↗
PubMed1991

An overview of randomized trials of sodium reduction and blood pressure.

To test for effects on systolic and diastolic blood pressure and to provide precise estimates of their magnitude, we conducted an overview of randomized clinical trials that aimed to reduce the intake of sodium in human subjects. We excluded from pooled analyses trials with confounded designs, those that compared intake levels beyond the usual range in the population, and those without published reports. Two reviewers abstracted information in duplicate and differences were reconciled. Twenty-three trials with outcome data from an aggregate of 1,536 subjects were included. Data were pooled both separately for hypertensive and normotensive subjects and for all trials combined. With the use of sample size weighting, blood pressure reductions (net of controls) were 4.9 +/- 1.3/2.6 +/- 0.8 mm Hg (systolic and diastolic, respectively, with 95% confidence limits) in hypertensive subjects and 1.7 +/- 1.0/1.0 +/- 0.7 mm Hg in normotensive subjects. The combined blood pressure reductions were 2.9 +/- 0.8/1.6 +/- 0.5 mm Hg. These changes were associated with mean reduction of urinary sodium excretion ranging from 16 to 171 mmol/24 hr for individual trials. A dose-response relation across trials was found, both in normotensive and in hypertensive subjects. These results indicate that sodium reduction lowers mean blood pressure in both hypertensive and normotensive individuals for periods of at least several months. The findings are highly consistent with results of observational epidemiological studies and have implications for preventive strategies of blood pressure control.

Blood Pressure↗
PubMed1985

Longitudinal analysis of categorical epidemiological data: a study of Three Mile Island.

The accident at the Three Mile Island nuclear power plant in 1979 led to an unprecedented set of events with potentially life threatening implications. This paper focusses on the analysis of a longitudinal study of the psychological well-being of the mothers of young children living within 10 miles of the plant. The initial analyses of the data utilize loglinear/logit model techniques from the contingency table literature, and involve the fitting of a sequence of logit models. The inadequancies of these analyses are noted, and a new class of mixture models for logistic response structures is introduced to overcome the noted shortcomings. The paper includes a brief outline of the methodology relevant for the fitting of these models using the method of maximum likelihood, and then the model is applied to the TMI data. The paper concludes with a discussion of some of the substantive implications of the mixture model analysis.

Accidents↗
PubMedDate not supplied

Modelling transitional and joint marginal distributions in repeated categorical data.

When a repeated measures endpoint classifies people into several categories, marginal and transitional models provide two distinct approaches for data analysis. Marginal models estimate the probabilities of being in different categories over time. Transitional models estimate the probability of changing between any two given states during follow-up visits. This paper develops transitional and marginal models and applies them to a clinical trial of treatments of opiate addiction. The primary outcome was the presence or absence of opiates in a thrice weekly urine test, administered for 17 weeks. Subjects frequently miss visits, however, and in effect respond in one of three ways to a visit: missing, opiates present or opiates absent. Thus we have three possible states. Our transitional model conditions on the current state and models the transition from state k to one of the other (0, ..., K-1) states using a mutinomial logit model. This model generalizes previous work of Muenz and Rubinstein. Significant covariates in this model are predictive of state changes. Our marginal model views the state at each time point, rather than the transitions, as the primary response. Here we model the probability of being in state k with a multinomial logit model. Correlation within individuals over visits can be handled by applying the approach of Zeger and Liang or the bootstrap. Significant covariates in this model can include more 'global' summaries of a person such as extent of previous opiate use. Both marginal and transitional models are needed to provide a complete description of an individual's behaviour over time since global summaries might not affect transitions. Of particular substantive interest is how the opiate treatments affect both the marginal and transition probabilities.

Buprenorphine↗