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Biomedical subjects

R D Feldman

Publications and source records attributed to R D Feldman.

84 records · Page 5Linked to original sources
PubMed1984

The risk ratio is insufficient for clinical decisions. The case of prophylactic cholecystectomy.

The medical literature contains studies that recommend both for and against prophylactic cholecystectomy when cholelithiasis is present. To investigate whether differing analytic techniques contribute to these disparate recommendations, we analyzed the decision to "wait and see" or "operate now," using both risk ratio and life expectancy analysis on the same data base. With intermediate symptom incidence estimates the risk ratio strongly favored an "operate now" approach, because it lessened the risk of death from gallbladder disease by up to 19-fold. In the group most favored by immediate surgery, 25-year-old men, risking death with immediate surgery increased life expectancy by only one percent (168 days). The risk ratio increased to over 30 for this group with the low incidence estimates, but the difference in life expectancy decreased to 120 days. With the high incidence estimates, the risk ratio declined to 16.4 and the life expectancy difference increased to 186 days. These data demonstrate that (1) the risk ratio can imply a course of action that is different from that implied by life expectancy analysis, and (2) the maximum expected return on the risk of immediate death with elective surgery for silent gallstones is only a one percent increase in life expectancy. This analysis suggests that single measures of effect such as the risk ratio and life expectancy do not capture all the information necessary to make an informed decision.

Adult↗
PubMed1983

Effects of teaching on hospital costs.

This study estimates effects of undergraduate and graduate medical education on hospital costs, using a national sample of 367 U.S. community hospitals observed in 1974 and 1977. Data on other cost determinants, such as casemix, allow us to isolate the influence of teaching with greater precision than most previous studies. Non-physician expense in major teaching hospitals is at most 20 percent higher than in non-teaching hospitals; the teaching effect is about half this for hospitals with more limited teaching programs. Results for ancillary service departments are consistent with those for the hospital as a whole.

Costs and Cost Analysis↗
PubMed1983

Dynamic regulation of leukocyte beta adrenergic receptor-agonist interactions by physiological changes in circulating catecholamines.

beta-Adrenergic receptors on human mononuclear leukocytes were assessed using [125I]iodohydroxybenzylpindolol binding. Subjects were studied supine and after being ambulatory, a maneuver that increases plasma catecholamines approximately two-fold. beta-Receptor affinity for agonists, measured by the competition of [125I]iodohydroxybenzylpindolol binding by (-)isoproterenol was significantly reduced with ambulation and this reduction was associated with a reduction in the proportion of beta-receptors binding agonist with a high affinity from a mean (+/- SEM) of 42 +/- 5 to 24 +/- 2% (P less than 0.01). In a parallel series, beta-adrenergic-stimulated adenylate cyclase activity was also reduced with postural change from 4.6 +/- 1.1 to 2.4 +/- 0.6 pmol [32P]cAMP/min per mg protein (P less than 0.05) after ambulation. Similar reductions in the proportion of receptors binding agonist with a high affinity were seen after infusion of norepinephrine. We conclude that the maneuver of ambulation reduces leukocyte beta-receptor responsiveness and affinity for agonists, probably by the effect of increased plasma catecholamines mediating an uncoupling of the beta-receptor-adenylate cyclase complex.

Adenylyl Cyclases↗
PubMed1982

Differential competition by L-alpha-methyldopa metabolites for adrenergic receptors in rat forebrain.

The capacity of a series of intraneuronal metabolites of L-alpha-methyldopa to compete for alpha-1 ([3H]prazosin, alpha-2([3H]clonidine and beta ([3H]dihydroalprenolol) receptor binding in rat forebrain was studied. Each metabolite studied had a unique order of activity at each receptor. These data show that (-)-erythro-alpha-methylnorepinephrine and (-)-erythro-alpha-methylepinephrine compete with high affinity for alpha-2 receptors, thereby supporting the suggestion that alpha-2 receptors mediate hypotensive effects of L-alpha-methyldopa . Furthermore, these metabolites of L-alpha-methyldopa competed with high potency for beta-1 receptors in forebrain and (-)-erythro-alpha-methylepinephrine was more potent than (-)-epinephrine, (-)-norepinephrine and (-)-erythro-alpha-methylnorepinephrine in competing for beta-2 receptors on human lymphocytes. These data suggest that beta receptor stimulation may be important in determining the net effects of L-alpha-methyldopa. L-alpha-Methyldopa metabolites were much less potent than (-)-epinephrine and (-)-norepinephrine in competition for alpha-1 receptors. (+/-)-alpha-Methyldopamine was less potent than other l-alpha-methyldopa metabolites at all three receptors, suggesting that it is unlikely to be an important hypotensive metabolite of L-alpha-methyldopa.

Animals↗
PubMed1978

High renal plasma flow lability in the kidneys of hypertensive patients.

The spontaneous changes in renal plasma flow (RPF) were determined by sodium paraamino hippurate clearance (CPAH) in the individual kidneys of 71 patients with essential and secondary hypertension. These changes were expressed as changes in CPAH and as changes in CPAH per 100 ml Glomerular Filtration Rate (GFR = inulin clearance) for every individual kidney. Sixteen normal subjects were used as control. The RPF changes were measured between two consecutive 10 minute clearance periods during separated kidney function tests. In all the hypertensive groups studied, when RPF variability was expressed per 100 ml GFR, the variability was found to be two to five times greater than in normals. This findings suggests that in the hypertensive state the blood flow changes in the kidney are more labile than in normals. The high lability of renal blood flow could reflect and abnormality in renal vascular tone. This abnormality could be an important factor in the pathogenesis and maintenance of high blood pressure.

Adult↗
PubMedDate not supplied

A comparison of zidovudine, didanosine, zalcitabine and no antiretroviral therapy in patients with advanced HIV disease.

Three nucleoside analogues, zidovudine (AZT), didanosine (ddI), and zalcitabine (ddC), are approved for use in the treatment of patients with HIV infection. This retrospective study compares the 3 drugs and examines the overall utility of antiretroviral therapy by way of comparisons to a no treatment (No Rx) group in patients with advanced HIV disease. Patients with advanced HIV disease were enrolled in didanosine (August 1989-December 1990) or zalcitabine (October 1990-February 1992) expanded access programmes; continued on zidovudine treatment despite fulfilling criteria for zidovudine failure or intolerance; or maintained on no antiretroviral treatment. Statistical analysis revealed that patients on nucleoside analogue therapy had fewer opportunistic infections (P = 0.001) than those who received no antiretroviral treatment. The Kaplan-Meier 12-month estimate of survival was significantly longer among patients who switched from zidovudine to zalcitabine but not among patients who switched to didanosine, when compared to the other 2 groups (P = 0.05).

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

Simulation of a health insurance market with adverse selection.

A health insurance market is examined in which individuals with a history of high utilization of health care services tend to select fee-for-service (FFS) insurance when offered a choice between FFS and health maintenance organizations (HMOs). In addition, HMOs are assumed to practice community rating of employee groups. Based on these observations and health plan enrollment and premium data from Minneapolis-St. Paul, a deterministic simulation model is constructed to predict equilibrium market shares and premiums for HMO and FFS insurers within a firm. Despite the fact that favorable selection enhances their ability to compete with FFS insurers, the model predicts that HMOs maximize profits at less than 100% market share, and at a lower share than they could conceivably capture. That is, HMOs would not find it to their advantage to drive FFS insurers from the market even if they could. In all cases, however, the profit-maximizing HMO premium is greater than the experience-rated premium and, thus, the average health insurance premium per employee in firms offering both HMOs and FFS insurance is predicted to be greater than in firms offering one experience-rated plan. The model may be used to simulate the effects of varying the employer's method of contributing to health insurance premiums. Several contribution methods are compared. Employers who offer FFS and HMO insurance and pay the full cost of the lowest-cost plan are predicted to have lower average total premiums (employer plus employee contributions) than employers who pay any level percent of the cost of each plan.

Actuarial Analysis↗
PubMedDate not supplied

Which types of hospital mergers save consumers money?

This study analyzes the changes in costs and prices from 1986 to 1994 for more than 3,500 U.S. short-term general hospitals, including 122 horizontal mergers. These mergers were generally financially beneficial to consumers, providing average price reductions of approximately 7 percent. Merger-related price reductions were considerably less in market areas with higher market concentration levels. Merger-related price reductions in areas with higher penetration by health maintenance organizations (HMOs) were approximately twice those in areas with lower HMO penetration. Merger-related price reductions were greater for low-occupancy hospitals, nonteaching hospitals, nonsystem hospitals, similar-size hospitals, and hospitals with greater premerger service duplication.

American Hospital Association↗
PubMedDate not supplied

HMO consolidations: how national mergers affect local markets.

The health maintenance organization (HMO) industry has undergone a wave of national consolidations in recent years. The most notable among these were between United HealthCare and MetraHealth (1995), PacifiCare Health Systems and FHP International (1996), Aetna Life and Casualty and U.S. Healthcare (1996), and Aetna and Prudential's health care unit (1999). This paper examines HMO consolidation from 1994 to 1997, looking first at concentration at the national level and then at the consequences of national consolidations for local markets. Whereas earlier mergers may have caused only a small increase in the type of local market concentration that may increase prices, later and currently proposed mergers may be motivated by considerations of increasing local market concentration. However, the concentration-increasing effect of national mergers was offset by the concentration-decreasing effect of HMO entry and growth. The analyses suggest that antitrust policy still has a role to play in ensuring that HMO markets remain open to new entry and in evaluating the effect of national mergers on local market concentration.

Antitrust Laws↗