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Biomedical subjects

J H Ware

Publications and source records attributed to J H Ware.

At least 91 records · Page 5Linked to original sources
PubMed1982

Comparison of medical and surgical management of coronary artery disease: methodologic issues.

Coronary artery bypass surgery has been recommended for patients with a wide variety of signs, symptoms, and medical histories. Investigators have used historically controlled studies, registries and randomized clinical trials to compare the efficacy of medical and surgical management of coronary artery disease in well-defined patient groups. Historically controlled studies offer a weak basis for inference because of rapid changes in medical practice and in the prognosis for patients with coronary artery disease. Randomized trials are the ideal method for comparing therapies, but only a few trials, in highly selected patients, have been completed. Thus, registry studies provide an important part of the currently available evidence. In this paper, the strengths of randomized and registry studies are compared and the need for "meta-analyses" that integrate the evidence from both types of study is discussed. The institutional variation in surgical mortality and its implication for treatment strategy are also discussed.

Clinical Trials as Topic↗
PubMed1982

Random-effects models for longitudinal data.

Models for the analysis of longitudinal data must recognize the relationship between serial observations on the same unit. Multivariate models with general covariance structure are often difficult to apply to highly unbalanced data, whereas two-stage random-effects models can be used easily. In two-stage models, the probability distributions for the response vectors of different individuals belong to a single family, but some random-effects parameters vary across individuals, with a distribution specified at the second stage. A general family of models is discussed, which includes both growth models and repeated-measures models as special cases. A unified approach to fitting these models, based on a combination of empirical Bayes and maximum likelihood estimation of model parameters and using the EM algorithm, is discussed. Two examples are taken from a current epidemiological study of the health effects of air pollution.

Air Pollution↗
PubMed1981

Assessment of the health effects of atmospheric sulfur oxides and particulate matter: evidence from observational studies.

Steadily rising energy costs have increased the need for reliable information on the health effects of atmospheric sulfur oxides and particulate matter. Because ethical and practical considerations limit studies of this question under controlled conditions, observational studies provide an important part of the relevant information. This paper examines the currently available epidemiologic evidence from population studies of the health effects of these pollutants. Nonexperimental studies also have important limitations, including the inability to measure accurately the exposure burden of free living individuals, and the potential for serious confounding by other factors affecting health. We begin with a discussion of some of these methodologic issues. The evidence is then reviewed, first in association with fluctuations in 24 hr mean concentration of sulfur oxides and particulate matter, and then in association with differences in mean annual concentration. In the last section, this evidence is summarized and used to approximate the exposure-response relationship linking pollutant concentrations with mortality and morbidity levels.

Air Pollutants↗
PubMed1980

Observations on the optimum time for operative intervention for aortic regurgitation. I. Evaluation of the results of aortic valve replacement in symptomatic patients.

Fifty consecutive patients undergoing aortic valve replacement for isolated aortic regurgitation were studied prospectively by echocardiography, electrocardiography and cardiac catheterization. Good quality echocardiograms were obtained in 49 of the 50 patients. Left ventricular (LV) dilatation was present in all 49 patients. LV systolic function, as assessed by echocardiographic percent fractional shortening, was normal in many patients but was moderately to severely reduced (less than 25%) in 14 patients (29%). Echocardiographic studies 6 months postoperatively revealed significant reductions in LV end-diastolic dimension (73.8 mm vs 58.7 mm; p less than 0.01), and serial echocardiographic studies early and late after operation revealed that the decrease in LV size had occurred by the time of the early study (8-22 days postoperatively), with little additional change thereafter. Operative deaths occurred in three of the 49 patients (6%). Eight of the 49 patients (16%) died of congestive heart failure (CHF) after hospital discharge at times ranging from 5-43 months after operation. Preoperative echocardiographic measurements of the LV end-systolic dimension and percent fractional shortening were strongly associated (p less than 0.01) with these late CHF deaths. Preoperative LV end-systolic dimension greater than 55 mm and fractional shortening less than 25% identified the high-risk group: nine of 13 patients (69%) in this group died either at operation or subsequently from CHF. In contrast, of 32 patients with LV end-systolic dimension less than 55 mm, only one died at operation and one died late from CHF. Thus, the population at high risk of late death from CHF was identified before operation by echocardiography.

Adult↗
PubMed1980

Evaluation of aortic valve replacement in patients with valvular aortic stenosis.

Echocardiographic and hemodynamic studies were obtained in 42 consecutive patients undergoing aortic valve replacement for isolated aortic stenosis. Concentric left ventricular (LV) wall thickening, the most common preoperative abnormality, occurred in 95% of patients. LV dilation with reduced fractional shortening was noted in approximately 25% of patients but was severe in only one patient. Six months after operation, LV wall thickness had decreased on average but had not returned to normal and fractional shortening was unchanged. Repeat measurements in 13 patients an average of 37 months after operation were unchanged compared with measurements made 6 months after operation. When patients were subdivided into those with LV dilatation and those without, we found that patients with dilated ventricles preoperatively had a greater decrease in LV internal dimension and mass than those without preoperative dilatation. The patient data also were examined for possible association with mortality. One operative (2%) and five late cardiac (13%) deaths occurred. No preoperative or 6-month postoperative echocardiographic or hemodynamic measurement was strongly associated with these deaths, nor were any late deaths due to congestive heart failure. Compared with preoperative measurements in symptomatic patients who were operated for isolated aortic regurgitation, patients with aortic stenosis had smaller left ventricles with less depression of systolic function, as well as less aortic root and left atrial dilatation. Our data do not support the concept that the aortic valve should be replaced before the onset of symptoms to prevent irreversible LV damage in patients with isolated aortic stenosis.

Adult↗
PubMed1980

Echocardiographic measurements in normal subjects from infancy to old age.

Echocardiographic data from 92 younger normal subjects (1 month to 23 years of age) and 136 older normal subjects (20-97 years of age) were pooled and analyzed to obtain prediction equations for normal echocardiographic values. Using a bivariate regression model with the assumption that variability is constant as a percentage of the expected value, we developed regression equation and graphs that allow calculation of a 95% prediction interval for several echocardiographic measurements as a function of the subject's age and either body weight or body surface area. Body weight could be substituted for body surface area with no loss of precision. Further, examination of residuals showed that the linear prediction model fit well for all ages and all echocardiographic measurements studied. The measurements were obtained using the recently published standards recommended by the American Society of Echocardiography.

Adolescent↗
PubMed1979

Echocardiographic measurements in normal subjects: evaluation of an adult population without clinically apparent heart disease.

In order to determine normal echocardiographic values for older subjects, we studied 136 adults (78 men and 58 women, 20 to 97 years of age) without evidence of cardiovascular disease. When patients were subdivided into six age groups, progressive changes were found in mean normal values for various parameters. Specifically, when the oldest group (over 70 years) was compared with the youngest group (21-30 years), significant (p less than 0.01) increases in aortic root (22 percent) and left atrial (16 percent) dimensions, in ventricular septal (20 percent) and left ventricular free-wall (18 percent) thicknesses, and in estimated left ventricular mass (15 percent) were noted. In addition, a significant (p less than 0.01) decrease in mean mitral E-F slope (43 percent) and slight decreases in mean left ventricular systolic and diastolic internal dimensions (5 and 6 percent, respectively; p less than 0.05) were noted. Left ventricular ejection fraction and percentage fractional shortening were found to be independent of age. These data have been used to derive regression equations that are related to both age and body surface area. The regression equations can be used to calculate mean normal values and 95 percent prediction intervals for echocardiographic measurements in adults.

Adult↗
PubMed1979

Echocardiographic assessment of cardiac anatomy and function in hypertensive subjects.

Cardiovascular complications are a major source of morbidity and mortality in hypertensive patients. To assess the prevalence of anatomic and functional abnormalities of the heart in such patients, we studied 234 asymptomatic subjects with mild-to-moderate systemic hypertension by echocardiography. After adjusting the echocardiographic values for age and body surface area, we found abnormally increased ventricular septal and/or posterobasal free-wall thickness in 61% of the hypertensive subjects. We found increased left atrial, aortic root, and left ventricular internal dimension (at end-diastole) in 5-7%, and decreased mitral valve closing velocity (E-F slope) and left ventricular ejection fraction were noted in six and 15% of the subjects, respectively. Four percent of the patients had disproportionate septal thickening (i.e., ventricular septal-to-left ventricular free-wall thickness ratio greater than or equal to 1.3). In contrast to the high prevalence of cardiac abnormalities detected by echocardiography, less than 10% of the hypertensive subjects had abnormal 12-lead ECGs or abnormal chest x-rays. These findings demonstrate a high prevalence of cardiac abnormalities in a population of asymptomatic hypertensive subjects. These abnormalities can be detected by echocardiography before they are otherwise apparent.

Adult↗
PubMed1977

Urinary excretion of immunoreactive prostaglandin E: a circadian rhythm and the effect of posture.

The excretion of urinary immunoreactive prostaglandin E (iPGE), sodium, potassium, creatinine and volume was studied in 4 hr collections in normal women at normal activity. iPGE exhibited a circadian rhythm with an amplitude of 29% and peak excretion at 4:55 P. M. There were also significant circadian rhythms for sodium, potassium, creatinine, and volume, all peaking in late afternoon. There were no significant changes either in the total excretion or in the circadian rhythms of iPGE, potassium, or creatinine excretion when the subjects remained in bed for an entire day while the circadian rhythms of sodium and volume were significantly modified in amplitude and phase, respectively. Urinary aldosterone excretion decreased significantly when the subjects were at bed rest. iPGE excretion increased 33% when subjects were first recumbent and then erect for consecutive 4 hr period on the same day (but when subjects were erect 1 day for a 4 hr period, iPGE excretion was lower by 32% than for the same 4 hr period the preceding day when they were recumbent). These data indicate that: 1) the sympathetic nervous system and renin-angiotensin-aldosterone system do not affect the circadian rhythms of urinary iPGE, and 2) short-term experiments of prostaglandin E excretion must be designed to avoid misleading results due to the circadian rhythm.

Adult↗
PubMed1977

A new method for quantifying ventricular regularization during atrial fibrillation.

Atrial fibrillation (AF) characteristically results in random variation of the intervals between successive ventricular depolarizations. However, when a patient with AF is treated with excessive amounts of digitalis, regular junctional rhythms may occur. The detection of "regularization" of the ventricular rhythm in patients with AF may signal early digitalis toxicity. In this paper, we describe a new method for quantifying the extent of ventricular regularization by the statistical analysis of the intervals between successive ventricular depolarizations (R-R intervals). This method yields a single index (Z score) which reflects the degree to which a sequence of R-R intervals deviates from a random distribution. Simulation studies demonstrate that our method is sensitive to "regularization" of as little as two to four percent of R-R intervals, even when equal intervals occur in small groups that might easily escape detection by visual electrocardiographic interpretation. Analysis of records from six nondigitalized subjects in AF shows that the sequence of R-R intervals is usually random, or very nearly so. Records obtained from the same patients when digitalized often demonstrate more regularized activity, reflected by an index (Z score) which is higher than expected from chance deviation if a random process is assumed. Preliminary data also suggeest that exercise is associated with substantial regularization of ventricular depolarization.

Atrial Fibrillation↗
PubMed1977

Serum immunoglobulins: methods for the determination of normal values in international units.

This paper describes the proper statistical methods for the determination of the range of normal values of serum immunoglobulins in any population and for the conversion of those ranges, or any serum immunoglobulin value, from mg per ml to World Health Organization International Units. In determining the normal range, it is argued that the analysis should be based upon the logarithms of the serum immunoglobulin values and that the range of normal values about the mean should be determined by the application of tolerance limits, rather than the more familar but incorrect confidence limits. For converting normal ranges from mg per ml to International Units, methods of parallel line bioassay (for IgG and IgA) and non-linear bioassay (for IgM and IgD) are used. For both bioassay methods, graphical techniques are described.

Humans↗
PubMed1977

Circadian rhythm analysis when output is collected at intervals.

It has long been recognized that many physiological and biochemical parameters show a repeating pattern of variation over 24 hours, i.e., a circadian rhythm. Halberg, Tong and Johnson (1965) used the sinusoidal model with 24-hour cycle to describe this variation. Tong (1976) described the polar coordinate transformation by which the sinusoidal regression problem can be treated as a linear regression problem. When the output of a system following diurnal variation, e.g. the human kidney, is collected at regular intervals and assayed, the expected quantity of substance present corresponds to the integral of the underlying output function. This paper shows that the polar coordinate transformation also linearizes this regression problem. More importantly, the covariance structure of Halberg et al. does not include interindividual variation. An alternative and more general model is proposed here based upon Rao's (1959) growth curve analyses. The latter method allows testing for adequacy of the sinusoidal model and leads to inferences about population parameters. An example is given.

Circadian Rhythm↗
PubMed1976

Randomized clinical trials. Perspectives on some recent ideas.

In spite of the controversy over the role of randomized clinical trials in medical research, the rationale underlying such trials remains persuasive as compared to recent suggestions for alternative non-randomized studies such as those relying on the use of historical controls and adjustment technics. Others have suggested that recent statistical innovations for improving clinical trials, including adaptive allocation of treatment to patients and sequential stopping procedures, are underutilized. These innovations, though theoretically interesting, are not easily adapted to large-scale, complex medical trials in which there may be multiple end points and delayed response times. Ethical considerations suggest that randomized trials are more suitable than uncontrolled experimentation in protecting the interests of patients. Randomized clinical trials remain the most reliable method for evaluating the efficacy of therapies.

Biometry↗
PubMed1976

Reanalysis of some baboon descent data.

Wagner and Altmann [1973] recently reported an analysis of a set of baboon descent times, some of which were left censored due to varying arrival times at the observation site. Any transformation of the data which reverses order produced a set of right censored observations. In this way, the Kaplan-Meier [1958] estimate of the descent time distribution can be computed. Estimates of the mean and variance of the distribution are given, as well as the standard error of the estimate of the mean.

Animals↗