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Biomedical subjects

N Duan

Publications and source records attributed to N Duan.

At least 55 records · Page 3Linked to original sources
PubMed1996

The impact of zidovudine compared with didanosine on health status and functioning in persons with advanced HIV infection and a varying duration of prior zidovudine therapy. AIDS Clinical Trials Group 116/117 Study Group.

The objective of this study was to compare the effects of zidovudine and didanosine on health-related quality of life in persons with advanced HIV infection and varying duration of prior zidovudine exposure. It was designed as a substudy nested in two similar placebo-controlled active-control-arm randomized trials, using sites of the AIDS Clinical Trials Group participating in the randomized trials of zidovudine versus didanosine (ACTG 116 and 117). The patients comprised 356 participants enrolled in ACTG 116 and 117. All had HIV infection and either a CD4 count of <200 cells/mm3, or a CD4 count of <300 cells/mm3 plus symptoms of HIV disease. Participants were randomized equally within strata defined by duration of prior zidovudine therapy, to receive didanosine sachets at a dose of 500 mg daily (334 mg in subjects weighing <60 kg) or 750 mg daily (500 mg in subjects weighting <60 kg) plus inactive capsules resembling zidovudine, or to receive zidovudine capsules at a dose of 600 mg daily plus inactive sachets resembling didanosine. The main outcome measures were self-reported health-related quality of life, healthcare utilization, disability, work and symptom impact. The results showed no differences in reported symptom impact or healthcare utilization, and most measures of disability were similar. In the group with more than 8 weeks of prior zidovudine therapy, several of the health status scale scores for ongoing participants were significantly better for didanosine recipients, but average differences were small. Use of several different approaches to combining health status and survival showed no differences in the overall quality-time experiences between the treatment groups. Individuals taking zidovudine, low-dose didanosine and high-dose didanosine experienced 33, 34 and 35 weeks, respectively, in at least the typical health state if they had fewer than 8 weeks of previous zidovudine therapy, and had 23, 23 and 26 weeks, respectively, if they had more than 8 weeks previous use of zidovudine. Results did not differ when data were analysed within strata ofpatients who had any versus no prior exposure to zidovudine, or AIDS versus non-AIDS status. In conclusion, functional status and health-related quality of life were substantially similar among persons receiving either zidovudine or didanosine, regardless of the duration of prior zidovudine treatment.

Adult↗
PubMed1995

Effects of kappa-opioid receptor agonists on stimulated phosphoinositide hydrolysis in rat kidney.

To determine the effects of kappa-opioid receptor agonists on phosphoinositide metabolism in rat renal cortex, tissue slices labelled with [3H]inositol were stimulated with norepinephrine or carbachol alone or in combination with the kappa-opioid receptor agonists, ethylketocyclazocine, trans-3,4-dichloro-N-methyl-N-[2-(pyrrolindinyl)-cyclohexyl)- benzeneacetamide (U50,488) and nalorphine. Both norepinephrine and carbachol stimulated phosphoinositide hydrolysis (measured in a LiCl buffer) concentration- and time-dependently. The EC50 and maximal stimulation of phosphoinositide hydrolysis for norepinephrine and carbachol were approximately 3 microM and 0.15 dpm released/dpm incorporated, respectively. Concentrations up to 1 mM of ethylketocyclazocine, U50,488 or nalorphine alone did not affect phosphoinositide hydrolysis. However, ethylketocyclazocine and U50,488 decreased 10 microM norepinephrine-stimulated phosphonositide hydrolysis concentration-dependently, each with an approximate IC50 of 30 microM. In contrast, nalorphine had no effect on norepinephrine-stimulated phosphoinositide hydrolysis. In addition, concentrations of up to 1 mM ethylketocyclazocine or U50,488 did not alter carbachol-stimulated phosphoinositide hydrolysis. The inhibitory effect of U50,488 and ethylketocyclazocine on norepinephrine-stimulated phosphoinositide hydrolysis was blocked by the selective kappa-opioid receptor antagonist, nor-binaltorphimine. These results indicate that kappa 1-opioid receptor stimulation may affect phosphoinositide metabolism in rat renal cortex by modulating the subcellular effects of renal alpha 1-adrenoceptor activation.

Animals↗
PubMed1995

Health status and function with zidovudine or zalcitabine as initial therapy for AIDS. A randomized controlled trial. Roche 3300/ACTG 114 Study Group.

OBJECTIVE: To evaluate the functional and health status implications of prescribing zalcitabine or zidovudine for initial therapy of acquired immunodeficiency syndrome (AIDS). DESIGN: A substudy of a randomized controlled trial. SETTING: Private and public clinics and referral centers. PATIENTS: Had human immunodeficiency virus (HIV) infection, less than 0.20 x 10(9)/L (200 microliters) CD4+ cells, and either a history of Pneumocystis carinii pneumonia or symptoms of HIV infection. Fifty-eight percent (338/668) of main study enrollees representing 90% of enrollees at participating sites were included in this substudy. INTERVENTIONS: Either zalcitabine at 0.75 mg every 8 hours plus inactive capsules identical in appearance to zidovudine or zidovudine at 200 mg (later 100 mg) every 4 hours plus inactive tablets identical in appearance to zalcitabine. MAIN OUTCOME MEASURES: Results of a periodically completed self-report survey instrument containing specific questions about symptom impact, disability, work, functioning, and utilization as well as nine health and functioning scales adapted from the Medical Outcomes Study (MOS). RESULTS: Zalcitabine recipients were twice as likely to undergo an invasive procedure (P = .004) or be admitted to hospital (P = .01). Zalcitabine recipients reported greater than 40% more symptoms that interfered with activity (P = .001) and greater than 50% more disability days (P < .01). They also had a 7% lower employment rate and a 35% lower monthly income. Average observed health status scores were lower in zalcitabine recipients overall, but especially in the early portion of the study. New methods for combining survival and health status data showed that, over 76 weeks of study, a typical zidovudine recipient spent about 4 (10%) more weeks with at least the typical health state than did a typical zalcitabine recipient. CONCLUSIONS: Zidovudine has substantial advantages over zalcitabine in initial monotherapy of AIDS in terms of functional outcomes such as symptoms impact, disability, work, utilization, and health status. In this case, the differences in functional outcomes presaged differences in physiological and clinical measures. The inclusion of functional outcomes can greatly improve the information available from a clinical trial.

Acquired Immunodeficiency Syndrome↗
PubMed1995

Factors related to immunization status among inner-city Latino and African-American preschoolers.

OBJECTIVE: To identify factors associated with undervaccination at 3 months and 24 months among low-income, inner-city Latino and African-American preschool children. DESIGN: Interviews with a representative sample of inner-city families using a cross-sectional, multi-stage, cluster-sample design combined with a replicated quota sampling approach. SETTING: South Central and East Los Angeles areas in inner-city Los Angeles. POPULATION: Eight hundred seventeen Latino and 387 African-American families with children between 12 and 36 months of age. MAIN OUTCOME VARIABLES: Being fully immunized or up-to-date (UTD) at 3 months (1 diphtheria-tetanus-pertussis vaccine and 1 oral polio vaccine) and 24 months of age (4 diphtheria-tetanus-pertussis vaccines, 3 oral polio vaccines, and 1 measles-mumps-rubella vaccine). METHODS: Logistic regressions of UTD immunization status at 3 and 24 months by population and health care system factors. RESULTS: Seventy percent of Latino children and 53% of African-American children were UTD at 3 months of age. At 24 months of age, 42% of Latino children and 26% of African-American children were UTD on their immunizations. Receipt of the first immunizations by 3 months was associated with smaller family size, and evidence of connection to prenatal care. Latino children were less likely to be UTD at 24 months if they obtained well child care from private providers versus public clinics (odds ratio [OR] = 0.45, 95% confidence interval [CI] = 0.26, 0.79). There was also a trend for Latino children to be less well immunized if they were in health maintenance organizations versus public clinics (0.31, 0.05 < P < .1). African-American children were more likely to be UTD at 24 months if they were UTD at 3 months (OR = 5.56, 95% CI = 1.43, 21.6), had more health visits (OR = 1.13, 95% CI = 1.01, 1.27), and were less likely to be UTD at 24 months if they were on Medicaid versus private insurance (OR = 0.26, 95% CI = 0.08, 0.90). IMPLICATIONS: Both African-American and Latino children in inner-city Los Angeles have low immunization rates at 3 and 24 months. Prenatal care and family size are strongly associated with being UTD by 3 months; however, family and child characteristics are relatively unimportant predictors of being UTD at 24 months of age. Important risk factors for underimmunization at 2 years of age in the inner-city, low-income communities studied include type of health insurance and source of well child care, with the public sector having higher rates than private doctors' offices or health maintenance organization/managed care plans.

Black or African American↗
PubMed1994

Can long-term exposure distributions be predicted from short-term measurements?

A method for estimating long-term distributions of exposure based on repeated short-term measurements within the same population is developed. If the short-term measurements span seasonal variation, and if the distributions are log-normal or nearly so, then long-term distributions can be estimated from as few as two visits to the same population. The method is illustrated using examples drawn from EPA's TEAM Study of exposures to volatile organic compounds.

Air Pollutants↗
PubMed1991

Stochastic microenvironment models for air pollution exposure.

Exposure assessment is a crucial link in air pollution risk assessment and management. With the recent advances in instrumentation, it has become possible to measure air pollution exposures in the vicinity of the individual human subjects, using either personal monitoring or microenvironment monitoring. For many important pollutants such as CO, NO2, and VOC, the air pollution exposure depends crucially on the location and activity of the individual: indoor versus outdoor, smoking versus not smoking, etc. The stochastic microenvironment models were developed to relate air pollution exposure to the location and activity. We review the two major existing models, the Cartesianization method (Duan, 1980, 1982, 1987) and SHAPE (Ott, 1981, 1982, 1984), and compare their assumptions and implications. We also propose a new model, the variance components model, which includes both Cartesianization and SHAPE as special cases. The variance components model considers both long-term average concentrations and short-term fluctuations. The Cartesianization focuses on long-term averages, while SHAPE focuses on short-term fluctuations. We propose to choose among the three models by examining the variance function which relates variability to averaging time. The theory is applied to the data collected from U.S. EPA's Washington CO Study, with the variance function estimated using Carroll and Ruppert's (1984) transform-both-sides regression model and Duan's (1983) smearing estimate. For the microenvironment in transit, both long-term averages and short-term fluctuations are important.

Air Pollution↗
PubMed1987

Health insurance and the demand for medical care: evidence from a randomized experiment.

We estimate how cost sharing, the portion of the bill the patient pays, affects the demand for medical services. The data come from a randomized experiment. A catastrophic insurance plan reduces expenditures 31 percent relative to zero out-of-pocket price. The price elasticity is approximately -0.2. We reject the hypothesis that less favorable coverage of outpatient services increases total expenditure (for example, by deterring preventive care or inducing hospitalization).

Analysis of Variance↗
PubMed1987

Cost-sharing and the use of general medical physicians for outpatient mental health care.

Many patients with emotional disorders receive their mental health care from general medical physicians. In this article, we examine differences in costs and style between mental health care delivered by mental health specialists and that provided by general medical physicians, and the sensitivity to insurance of the patient's choice of mental health care provider. We use data from a randomized trial of cost-sharing, the RAND Health Insurance Experiment. Even when all outpatient mental health care was free (up to 52 visits a year), one-half of the users of outpatient mental health services visited general medical providers only. This half accounted for only 5 percent of outpatient mental health care expenditures, because the treatment delivered by general medical providers was much less intensive than that delivered by mental health specialists. Mental health status, at enrollment, was similar for those who received their mental health care from either provider group. Despite the large difference in cost of care, the choice of provider (mental health specialist versus general medical provider) was not sensitive to the generosity of insurance.

Adult↗
PubMed1986

How cost sharing affects the use of ambulatory mental health services.

The less generous insurance coverage for mental health care has generated some controversy. The major unresolved question is how the demand for outpatient mental health care responds to cost sharing. We used data from a randomized trial of fee-for-service health insurance for the nonelderly to address this question. The study enrolled 5809 persons. The results are based on 19 819 person-years of data. One hundred thirty-three percent more is spent on outpatient psychotherapy when care is free to patients than when they pay 95% of the fee, subject to an annual catastrophic limit. But, the absolute level of expenditure is low on all plans; $32 per person per year with free care. The response to psychotherapy services to cost sharing is insignificantly larger than that for outpatient general medical services. We found no evidence that more generous coverage for outpatient psychotherapy decreases total health expenditures.

Ambulatory Care↗
PubMed1986

Sociodemographic factors and the use of outpatient mental health services.

What are the effects of sociodemographic factors on the use of outpatient mental health services when different demographic groups have identical health insurance coverage? The authors answer this question using data from the Rand Health Insurance Experiment. Health insurance was randomly assigned to families representative of the nonaged, noninstitutionalized civilian population in six U.S. sites. Income has no significant total effect on use when all income groups have the same coverage. When the effects of variables correlated with socioeconomic status are removed, users with higher socioeconomic status are significantly more likely to choose a mental health specialist rather than only general medical providers for their mental health care (P less than 0.05); among those who visit mental health specialists, those with higher socioeconomic status incur significantly greater expenses (P less than 0.10). Women use significantly more mental health services than men (P less than 0.05), who in turn use significantly more mental health services than children (P less than 0.05), even after controlling for demographic factors, health status, and insurance coverage. Similarly, there are large differences (roughly sixfold) by site in outpatient mental health expenses even when all sites have identical coverage.

Adolescent↗
PubMed1986

Use of outpatient mental health services by a general population with health insurance coverage.

Characteristics of use of mental health services by 4,254 persons enrolled in the Rand Health Insurance Study were analyzed in an attempt to predict patterns of use by a general population with assigned insurance coverage. Families in the study, whose members ranged in age from birth through 62 years, were randomly assigned to one of 14 insurance plans covering a wide variety of services by all licensed provider groups. During a one-year period less than 4 percent of the enrollees visited a mental health specialist, and only 7.1 percent saw any provider for mental health care. About half of those receiving outpatient mental health care visited general medical providers only. Annual outpatient mental health expenses per enrollee were about $25 (1983 dollars). The authors compare their findings with those of other studies and discuss their implications for insurance coverage of mental health services.

Ambulatory Care↗
PubMed1986

Dental insurance and the oral health of preschool children.

Using data from the Rand Health Insurance Experiment, the effects of cost-sharing plans on the health of the primary teeth in 264 children aged 3 to 5 years were investigated. From six areas in the United States, families were assigned at random to different dental and medical insurance plans. The plans varied in the amount of required cost sharing. Families participated in the study for 3 (70%) or 5 (30%) years. Children covered by the plan (requiring no cost sharing) had significantly fewer decayed teeth and deft (decayed, extracted, and filled teeth) at the end of the study than did children covered by the cost-sharing plans. No differences existed among plans in the number of extracted and restored teeth. Children of middle- and low-income families benefited most from having access to free dental care.

Child Health Services↗
PubMed1985

Effect of cost-sharing on the use of medical services by children: interim results from a randomized controlled trial.

Health care expenditures of 1,136 children whose families participated in a randomized trial, The Rand Health Insurance Experiment, are reported. Children whose families were assigned to receive 100% reimbursement for health costs spent one third more per capita than children whose families paid 95% of medical expenses up to a family maximum. Outpatient use decreased as cost-sharing rose for a variety of use measures: the probability of seeing a doctor, annual expenditures, number of visits per year, and numbers of outpatient treatment episodes. Hospital expenditures did not vary significantly among children insured with varying levels of cost-sharing. Episodes of treatment for preventive care were as responsive to cost-sharing as episodes for acute or chronic illness. The results give no reason not to insure preventive care as liberally as care for acute illness.

Adolescent↗
PubMed1984

The sensitivity of mental health care use and cost estimates to methods effects.

The authors determined the sensitivity of estimates of the use and cost of outpatient mental health care to two methods effects: the definition of a mental health visit and strategies for allocating mental health care costs. They use data from the Rand Health Insurance Study, which has a random sample of the nonaged noninstitutionalized civilian population in six United States sites. Estimates of the use of mental health specialists are insensitive to alternative methods. However, estimates of the use and cost of the mental health care delivered by nonpsychiatrist physicians (e.g., internists) are quite sensitive to methods effects. Nevertheless, the cost of care from nonpsychiatrist physicians is so low that the total cost of outpatient mental health care is not meaningfully affected by methods effects.

Community Mental Health Services↗