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Biomedical subjects

J C Hershey

Publications and source records attributed to J C Hershey.

At least 19 recordsLinked to original sources
PubMed1992

Effect of ibuprofen upon denervated skeletal muscle resistance and compliance vessels during endotoxemia.

The primary aim of these studies was to specifically evaluate the non-neural role of the cyclooxygenase products on the peripheral vascular decompensation associated with endotoxemia. The constant-flow perfused, vascularly isolated, denervated double-canine gracilis muscle preparation in which one muscle is used as a control for the contralateral side was employed. The experimental muscle (GMi) received ibuprofen while the control (GMc) was infused with the vehicle. The results of these studies suggest that endotoxin increases the arterial conductance (i.e., arterial dilation) by 100% and venous compliance (i.e., venoconstriction) by 40%. These observations, which are consistent with venous pooling, were not significantly altered by the continuous intra-arterial infusion of ibuprofen at a peripheral blood concentration of 160 microM. Ibuprofen caused a small but statistically significant increase in the conductance/compliance ratio at 60, 75, and 90 min post endotoxin, suggesting that cyclooxygenase products may play a minor role in the non-neural regulation of capillary fluid dynamics during endotoxemia. Consequently, these studies do not provide convincing evidence that would support a non-neural cyclooxygenase role in the peripheral vascular decompensation reported to occur during systemic endotoxemia.

Animals↗
PubMed1991

Influence of histaminergic receptors on denervated canine gracilis muscle vascular tone during endotoxemia.

The purpose of this study was to determine if endogenously released histamine and its non-neural interaction with the H1- and H2-histaminergic receptors in the peripheral vasculature can account for the decompensatory loss of peripheral vascular tone associated with the hypotension occurring during endotoxemia. A denervated in situ constant flow double canine gracilis muscle preparation that permitted one muscle to serve as a control (GMc) for the contralateral experimental muscle (GMe) was used. Endotoxemia was induced by intravenous infusion of 2 mg.kg-1.30 min-1 endotoxin. The specific H1 and H2 antagonists diphen-hydramine and cimetidine were infused either together or separately in both high and low dosages into the GMe. Blockades were validated by intra-arterial injection of histamine or the specific agonists betahistine for H1 and dimaprit for H2 receptors. The results suggest that the high-dose diphenhydramine produced a nonspecific dilation not seen with the lower dose. Because both the blocked and unblocked vascular beds exhibited the same degree of vasodilation after endotoxin, these studies do not support the hypothesis that endogenously released histamine is responsible for the loss of vascular tone. These studies do verify, however, that a nonneurally mediated loss of skeletal muscle vascular tone is an important factor to consider in the overall cardiovascular hypotension occurring during endotoxin shock.

Adenosine↗
PubMed1988

Outcome bias in decision evaluation.

In 5 studies, undergraduate subjects were given descriptions and outcomes of decisions made by others under conditions of uncertainty. Decisions concerned either medical matters or monetary gambles. Subjects rated the quality of thinking of the decisions, the competence of the decision maker, or their willingness to let the decision maker decide on their behalf. Subjects understood that they had all relevant information available to the decision maker. Subjects rated the thinking as better, rated the decision maker as more competent, or indicated greater willingness to yield the decision when the outcome was favorable than when it was unfavorable. In monetary gambles, subjects rated the thinking as better when the outcome of the option not chosen turned out poorly than when it turned out well. Although subjects who were asked felt that they should not consider outcomes in making these evaluations, they did so. This effect of outcome knowledge on evaluation may be explained partly in terms of its effect on the salience of arguments for each side of the choice. Implications for the theory of rationality and for practical situations are discussed.

Decision Making↗
PubMed1988

Measuring the economic impact of perioperative total parenteral nutrition: principles and design.

Although the use of total parenteral nutrition (TPN) has been increasing in recent years, few studies have been performed on both its costs and its effectiveness or benefits. This paper provides a general review of the methods of cost-effectiveness and cost-benefit analysis, summarizes briefly the existing cost-analysis studies of TPN, and outlines the authors' proposed study design for their economic assessment of TPN.

Clinical Trials as Topic↗
PubMed1986

Comparing aggregate estimates of derived thresholds for clinical decisions.

Thresholds for medical decision making are the probabilities of disease at which clinicians choose to initiate testing or therapy. A descriptive analysis of clinicians' decision making can derive their test and test-treatment thresholds and has the potential to explain variations in test utilization. A previously described method summarizes thresholds for a group of clinicians by determining the range of probability which includes the maximum number of clinicians' individual thresholds. However, there is no statistical procedure to compare the summary measure of thresholds that is derived from the distribution of clinicians' thresholds. We describe two alternative methods of developing a summary measure of the thresholds for a group of clinicians. These alternative methods enable the analyst to apply standard statistical tests when analyzing the decision-making behavior of groups of clinicians. For the "Unweighted Mean of the Midpoints" method, confidence limits of means and standard t-tests can be used to compare different groups. For the "Weighted Mean of the Midpoints" method, a weighted standard error of the mean can be calculated to determine confidence intervals, and a weighted t-test or weighted regression can be used to compare weighted means of the midpoints of threshold ranges.

Angiography↗
PubMed1979

A re-appraisal of the productivity potential and economic benefits of physician's assistants.

A combined optimization-simulation model is used to examine the extent of productivity and economic benefits to be gained from adding a physician's assistant to a one-physician ambulatory health care practice. It is shown that previous models (which have predicted productivity gains as large as 90 per cent) have overstated these benefits by ignoring offsetting changes in patients' waiting time, waiting room congestion, practice hours, and supervisory requirements. When all these factors are considered, the productivity gain may be as small as 20 per cent, and the increase in net income may be negligible. The sensitivity of productivity and net income to changes in supervisory requirements is also examined. This paper suggests that a rational explanation exists for the reluctance of physicians to adopt physician's assistants in their practices. The economic benefits derived from adding a physician's assistant may well have been overstated in the existing literature.

Ambulatory Care↗
PubMed1978

The productivity potential of physicians' assistants: an integrated approach to analysis.

Although many previous analytical studies indicate that physicians' assistants can substantially increase productivity and reduce costs, the utilization of physicians' assistants in ambulatory health care settings has grown at a disappointing rate. This apparent discrepancy may be explained in part through close examination of the models used in the analytical studies. This paper describes the limitations of previous studies and shows how analysis can be improved through the use of a combined optimization-simulation model. The model is applied to a hypothetical example to demonstrate how productivity and income benefits can be overstated, and to test the sensitivity of such benefits to a range of management policies for the ambulatory care practice regarding patient load, physical resources, appointment scheduling, and more flexible assignment of providers to patients.

Computers↗
PubMed1976

Factors affecting the use of physician services in a rural community.

This paper examines the relative importance of various independent variables for predicting five separate measures of physician utilization in a rural community. The independent variables include socioeconomic, demographic, attitudinal, and health status factors. The results are comparable to those of national studies which find that health status is the primary determinant of utilization. Income, price measures, and travel time are notable for their relative unimportance in this rural area. This suggests that resources are more likely to be allocated on the basis of medical need within a given health care market than across a number of market areas.

Adolescent↗
PubMed1975

The use of an information system for community health services planning and management.

The challenge of delivering health care on a more cost-effective and equitable basis has led to the formation of new kinds of organizations, which in turn require new kinds of management information systems. The system described in this article is used for planning resource allocation and monitoring the overall performance of Livingston Community Health Services, Inc., a rural community-owned health service designed to provide comprehensive care to a geographically defined target population. The Health Services Data System processes information on performance and productivity, effectiveness with respect to the target population, and billing and financial activities. Input consists of the results of a community census and two household surveys, patient registrations and patient services operating data, and financial data. Besides billing patients automatically, the system integrates financial, demographic, and health services utilization data to generate monthly summaries for the administrators, medical director, and community board. The article discusses several examples of these summaries, stratifying utilization by geographic location of residence, age, income, and race.

Accounting↗
PubMed1975

Making sense out of utilization data.

Health care utilization studies often reach conflicting conclusions about the appropriate measures of utilization and the relationships between such measures and the explanatory variables. The purpose of this paper is to demonstrate why such ambiguities exist, provide empirical tests of different models, and suggest an appropriate analytical framework. A household survey of a rural California community was used to collect both family and individual data on utilization, "need," accessibility, attitudes, and demographics. A number of possible utilization models are presented, each containing alternative sets of dependent and independent variables. Multiple regression analysis is applied to each model, providing considerable insight into the roles of specific independent variables in explaining alternative utilization measures. The omission of certain variables, such as health status (or "need"), can result in an incorrect interpretation of the results.

Adult↗
PubMedDate not supplied

Clinical guidelines for using two dichotomous tests.

Building on the threshold model developed by Pauker and Kassirer for a single test, the authors describe a decision analytic model for two tests with dichotomous outcomes. The model includes ten decision strategies that differ depending on which tests are performed, whether the tests are performed together or in sequence, and the definition of a positivity criterion used to make the treatment decision when the test results disagree. Formulas derived from the model are used to compute the preferred option as a function of disease probability and to calculate test and test-treatment thresholds. General guidelines developed from the model can be used without calculation to identify relative preferences for alternative options and to predict threshold effects.

Diagnosis↗
PubMedDate not supplied

Multiple test analyzer (MTA): a microcomputer program for determining preferred strategies with two diagnostic tests.

There are ten distinct management strategies in clinical situations that involve two diagnostic tests with dichotomous outcomes. The authors describe a microcomputer program, based on a previously described model, that can be used to identify test and test-treatment thresholds and to compute preferred strategies. The program provides tables and graphs of the results, which can be viewed or printed, and there is an optimization routine that facilitates comprehensive analysis. It can be used by decision-analytic researchers and policy analysts, medical educators who teach decision analysis, and clinicians who use decision analysis in their practices.

Computers↗
PubMedDate not supplied

Clinical reasoning and cognitive processes.

Expected utility theory, and the Bayesian probability theory on which it is based, form the normative basis of most work in medical decision analysis. Recent work in the psychology of judgments and decisions indicates that people do not conform to the axioms of this theory and that these deviations occur in clinical reasoning as well as in the psychology laboratory. At issue is what to do now. The authors argue that the important next steps lie at the interface between descriptive, prescriptive, and normative accounts, all of which affect each other. They point to examples in which the simplest application of supposedly normative theory seems inappropriate, and suggest ways in which the tension between normative and descriptive models may be resolved.

Cognition↗
PubMedDate not supplied

The importance of considering single testing when two tests are available.

When considering two dichotomous tests in combination for reaching a treatment decision, the choice between single and multiple testing depends, in part, on the pretest probability of disease. The authors show that two tests are never preferred to a single test for all disease probabilities, regardless of whether the two tests are performed in parallel or in series.

Decision Making↗
PubMedDate not supplied

The single-cutoff trap: implications for Bayesian analysis of stress electrocardiograms.

Quantitative analysis of exercise electrocardiograms has been emphasized by many investigators. Specific problems have been found when a single cutoff is used to define a positive or a negative test: a single cutoff does not distinguish stress electrocardiography results that are slightly positive from those that are markedly positive. This may lead clinicians to underweigh strong evidence for or against coronary artery disease. This study evaluated clinicians' quantitative analysis of stress electrocardiograms. Two hundred and thirty-five physicians interpreted the results of mildly positive (1.2 mm ST-segment depression) and strongly positive (2.2 mm ST-segment depression) stress electrocardiograms. Their posttest probability estimates were too high for a mildly positive test (0.62 +/- 0.02 versus actual of 0.38; p less than 0.001) and too low for a strongly positive test (0.77 +/- 0.01 versus actual of 0.98; p less than 0.001). Physicians should understand decision aids and should use multiple rather than single cutoffs to interpret the results of stress electrocardiography.

Bayes Theorem↗
PubMedDate not supplied

Knowing for the sake of knowing: the value of prognostic information.

In evaluating diagnostic tests, traditional methods in decision analysis often emphasize how the results of the test will or will not affect patient management. Clinicians are advised to avoid testing if the results will not alter treatment strategy or other management plans. But patients may be interested in the prognostic information that testing provides even if it is not used to guide treatment. The authors present a model that defines this prognostic information as the expected deviation from the prior probability of disease. The model generates utility functions that are curvilinear over prior probabilities. Whereas the traditional threshold approach to medical decision making produces at most three zones of management strategy (withhold, test, and treat), the incorporation of prognostic information into threshold analysis produces two additional zones (test but withhold anyway, and test but treat anyway). Conditions under which one or both of these additional zones will appear are described. The model justifies the practice of performing tests that cannot alter management plans; it explains the unwillingness of some patients to undergo diagnostic testing when they fear unwanted results; and it provides a method for quantifying the sensitive nature of confidential tests. The model is illustrated using the antibody test for the Smith antigen. This test has a high specificity but a low sensitivity for lupus erythematosus. Clinicians may use the test because a positive result will support their prior suspicion of disease even though they may not change their management strategy if the test result is negative. The advantage of testing in this setting lies in the test's potential for establishing with virtual certainty that the disease is present. Thus, the test is valued for the prognostic information it provides apart from its effect on patient management.

Decision Trees↗