Biomedical subjects

B Rosner

Publications and source records attributed to B Rosner.

391 records · Page 22Linked to original sources

PubMedDate not supplied

Autoregressive modelling for the analysis of longitudinal data with unequally spaced examinations.

Missing and/or unequally spaced examinations are often present in longitudinal studies. An autoregressive model is presented for the analysis of such data for continuous outcome variables. The fitting of the model can be accomplished by weighted non-linear regression methods available in standard statistical packages. Some features of the model include consideration of both time-dependent and fixed covariates, assessment of the relationships between changes in outcome and exposure over short periods of time, and use of all available person-time for an individual. An illustration looking at the role of personal cigarette smoking on changes in pulmonary function in children is included.

Adolescent↗

PubMedDate not supplied

Multivariate methods for binary longitudinal data with heterogeneous correlation over time.

Clustered binary data occur frequently in biostatistical work. One particular application is in binary longitudinal data, where several visits are available for the same individual. Several approaches have been proposed for the analysis of clustered binary data. In Rosner, a polychotomous logistic regression model was proposed which is a generalization of the beta-binomial distribution and allows for person- and visit-specific covariates, while controlling for clustering effects. One assumption of this model is that all pairs of visits within an individual are equally correlated, which may be inappropriate if several visits are available over a long follow-up period. In this paper, this approach is extended to allow for heterogeneous correlation over time. The total time period is divided into subintervals and a beta-binomial mixture model is introduced to estimate odds ratios relating outcomes for pairs of visits both within a subinterval as well as in different subintervals. To include covariates, an extension of the polychotomous logistic regression model is proposed, which allows one to estimate effects of person-, subinterval-, and visit-specific covariates, while controlling for clustering using the beta-binomial mixture model. This model is applied to the analysis of respiratory symptom data in children collected over a 14-year period in East Boston, MA, in relation to maternal and child smoking, where the unit is the child and symptom history is divided into early-adolescent and late-adolescent symptom experience.

Humans↗

PubMedDate not supplied

The influence of cigarette smoking and age on bone loss in men.

Hand X-rays were examined among 341 healthy male participants (age 40-80 yr) of the Normative Aging Study who had two successive X-rays 3 to 5 yr apart. Bone density was estimated at midshaft of the second metacarpal as percent cortical area. As expected, cross-sectional analysis revealed a decrease in percent cortical area with age. Current smokers tended to have slightly lower percent cortical areas than "never" smokers. When participants were followed longitudinally over a 3 to 5 year period, a trend toward greater bone loss with increasing age was generally observed in both smoking status groups, although smokers' rate of loss after age 55 yr deviated slightly from this pattern. Current smokers under age 55 yr consistently showed greater bone loss than never smokers.

Adult↗

PubMedDate not supplied

Randomized trials of aminoglycoside antibiotics: quantitative overview.

Individual randomized trials comparing aminoglycosides have usually involved a sample size inadequate for reliable detection of small to moderate differences. In a search for overall effects that might not be apparent from any single trial, a quantitative overview of all randomized studies comparing amikacin, gentamicin, netilmicin, sisomicin, and tobramycin was performed. These aminoglycosides appeared equally efficacious, except that tobramycin seemed less effective than sisomicin. Patients given gentamicin or sisomicin seemed to run a higher risk of nephrotoxicity than those given amikacin; the risk for patients receiving tobramycin was lower than that for patients given gentamicin but higher than that for those given netilmicin. The only statistically significant difference with regard to auditory toxicity was a lower risk among patients receiving netilmicin than among those given amikacin or tobramycin. Meaningful differences in toxicity may exist for individual aminoglycosides given in efficacious doses. Future trials must include sample sizes sufficient to detect differences of the magnitudes observed in this overview. In the absence of such data, the overview may guide clinicians in determining the risk-to-benefit ratio for a particular aminoglycoside, especially for patients at high risk of toxicity.

Aminoglycosides↗

PubMedDate not supplied

Effect of hydrogen ion and protein concentrations on the activity of beta-lactam antibiotics.

The susceptibility of 50 isolates of Staphylococcus aureus to seven beta-lactam antibiotics was measured under four conditions, involving two pH values and the presence or absence of serum protein. Multiple linear regression analysis was used to determine the effect of pH, protein, and antibiotic on the minimal inhibitory concentrations (MICs). Each of these factors as well as their interactions had significant effects on the MIC. The effects of pH and protein did not bear a predictable relationship to the extent of binding of antibiotic to serum proteins. All MICs were higher in the presence of protein at both pH values. For some antibiotics, the protein effect at pH 6.0 was larger than that at pH 7.4; for others the protein effect was smaller at pH 6.0. These data indicate that pH and protein effects must be determined individually for beta-lactam antibiotics.

Anti-Bacterial Agents↗

PubMedDate not supplied

Vaginal colonization with mycoplasma hominis and ureaplasma urealyticum.

Vaginal cultures obtained from unselected young women who consulted the gynecologist in a student health service were examined for Ureaplasma urealyticum and Mycoplasma hominis. Each participant completed a confidential questionnaire. Multiple logistic regression analysis was used to determine which variables, of a large number ascertained, were associated with mycoplasmal colonization. U. urealyticum was isolated from 273 (56.8%) of 481 participants. The following variables were significantly predictive of colonization with U. urealyticum: black race, absence of antibiotic use, cigarette smoking, and number of sexual partners during the last year. Lifetime number of sexual partners was significantly predictive only in women who used nonbarrier methods of contraception. M. hominis was isolated from 85 (17.7%) of the 481 participants. Independent variables that were significantly predictive of colonization with M. hominis included black race, young age, and, for users of nonbarrier methods of contraception, lifetime number of sexual partners.

Black or African American↗

PubMedDate not supplied

An evaluation of the Vita-Stat automatic blood pressure measuring device.

Four Vita-Stat (VS) automatic, coin-operated, blood pressure measuring devices were evaluated for accuracy and precision. Under field conditions, 342 adults had two blood pressure measurements with both the VS device and with the Random-Zero (RZ) device. Two of the VS machines gave significantly higher systolic (SBP) and diastolic blood pressure (DBP) values, compared to the RZ values. The mean difference between these two units and the RZ device were clinically important (14.0 and 6.9 mm Hg SBP; 7.5 and 6.8 mm Hg DBP), and resulted in the misclassification of 23% of normotensives as hypertensives. We observed a significant order effect on SBP with the VS device, with a mean decrement of 4.9 mm Hg between the first and second SBP values, compared to 0.6 mm Hg with the RZ device. Even after adjusting for this bias, all four VS devices gave significantly more variable SBP readings than the RZ unit; two of the four also gave more variable DBP values. These data suggest that the VS device is neither accurate nor precise enough at the present time to be recommended for widespread use. These findings also raise questions concerning the monitoring of performance of this and similar devices in the field.

Adult↗

PubMedDate not supplied

A prospective study of aspirin use and primary prevention of cardiovascular disease in women.

OBJECTIVE: The aim of the study was to examine prospectively the association between regular aspirin use and the risk of a first myocardial infarction and other cardiovascular events in women. DESIGN: Prospective cohort study including 6 years of follow-up. SETTING: Registered nurses residing in 11 US states. PARTICIPANTS: US registered nurses (n = 87,678) aged 34 to 65 years and free of diagnosed coronary heart disease, stroke, and cancer at baseline. Followup was 96.7% of total potential person-years of follow-up. MAIN OUTCOME MEASURES: Incidence of myocardial infarction, stroke, cardiovascular death, and all important vascular events. RESULTS: During 475,265 person-years of follow-up, we documented 240 nonfatal myocardial infarctions, 146 nonfatal strokes, and 130 deaths due to cardiovascular disease (total, 516 important vascular events). Among women who reported taking one through six aspirin per week, the age-adjusted relative risk (RR) of a first myocardial infarction was 0.68 (95% confidence interval [CI], 0.52 to 0.89; P = .005), as compared with those women who took no aspirin. After simultaneous adjustment for risk factors for coronary disease, the RR was 0.75 (95% CI, 0.58 to 0.99; P = .04). For women aged 50 years and older, the age-adjusted RR was 0.61 (95% CI, 0.45 to 0.84; P = .002) and the multivariate RR was 0.68 (95% CI, 0.50 to 0.93; P = .02). We observed no alteration in the risk of stroke (multivariate RR = 0.99; P = .94). The multivariate RR of cardiovascular death was 0.89 (P = .56) and of important vascular events was 0.85 (P = .12). When examined separately, the results were nearly identical for the subgroups who took one through three and four through six aspirin per week. Among women who took seven or more aspirin per week, there were no apparent reductions in risk. CONCLUSIONS: The use of one through six aspirin per week appears to be associated with a reduced risk of a first myocardial infarction among women. A randomized trial in women is necessary, however, to provide conclusive data on the role of aspirin in the primary prevention of cardiovascular disease in women.

Adult↗

PubMedDate not supplied

Statistical methods for the analysis of the association between bronchial responsiveness and pulmonary function changes.

An autoregressive model for the analysis of longitudinal data was applied in the context of investigating the effect of bronchial responsiveness on the growth of pulmonary function in children. In the model used, the correlation between pulmonary function values within an individual decreases exponentially as the time between visits increases. The model incorporates both fixed and time-dependent covariates in a unified fashion and does not require complete data in all visits for each individual. Furthermore, the change in pulmonary function is not assumed to be linear over time. Using response to cold air data as a measure of bronchial responsiveness, we found that children who responded to cold air have a slower rate of growth in pulmonary function. In addition, the data suggested that the effect of cigarette smoking may be greater as the response to cold air increases. Extensions of the autoregressive approach to other correlation structures and to the case of unequidistant observations are discussed.

Adolescent↗

PubMedDate not supplied

Significance of blood pressure in infancy. Familial aggregation and predictive effect on later blood pressure.

Blood pressure was measured in 730 infants and their mothers within 5 days of birth. Paternal blood pressures were obtained where possible, and follow-up measurements were made on participants at 1 week and 1, 6, 12, 18, and 24 months. Infant blood pressures were adjusted for such variables as age, observer, cuff size, and sleep/activity status. Infant blood pressure correlated with maternal blood pressure corrected for age and observer shortly after birth (r = 0.138, p less than 0.001 for systolic pressure; r = 0.169, p less than 0.001 for diastolic pressure). Father-infant correlations were significant only at 1 month after birth (r = 0.179, p = 0.031; r = 0.250, p = 0.002 for systolic and diastolic pressures respectively), and sibling correlations were significant from 6 months after birth (r = 0.173, p = 0.011 for systolic pressure; r = 0.265, p less than 0.001 for diastolic pressure). Blood pressures of infants before 6 months after birth were not consistently predictive of later pressures, but systolic and diastolic blood pressures 6 and 12 months after birth were significantly and positively related to pressures at later ages (for systolic pressures at 6 and 12 months, r = 0.147, p = 0.003; 6 and 18 months, r = 0.218, p less than 0.001; 6 and 24 months, r = 0.212, p less than 0.001). These results indicate that the familial aggregation of blood pressure and blood pressure tracking can be detected early in life.

Adult↗

PubMedDate not supplied

Lack of an effect of dietary saturated fat and cholesterol on blood pressure in normotensives.

The effect on blood pressure (BP) levels of modifying the saturated fat and cholesterol content in the diet was studied in two separate protocols in normotensive volunteers. For 3 months, 19 men and women, aged 14 to 54 years, adhered to a diet that eliminated meat, poultry, eggs, and dairy fat from the subjects' customary nonvegetarian diet, which had included 71 g/day (35%) of dietary fat. The experimental diet reduced the consumption of saturated fat from 21 to 10 g, dietary cholesterol was lowered from 398 to 69 mg per day, but consumption of polyunsaturated fatty acids, carbohydrates, and dietary fiber was unchanged. Body weight and urinary sodium and potassium excretion were not significantly altered. Mean BP before and after the low fat diet was 116/74 and 115/74 mm Hg, respectively. A second double-blind study tested the effect on BP of dietary cholesterol at levels of 155 and 471 mg/day. Seventeen semivegetarian college students consumed one egg per day concealed in desserts for 3 weeks, and identical desserts containing no eggs for an additional 3 weeks. Mean BP at the end of the egg and eggless periods was 108/69 and 107/69 mm Hg, respectively. Thus, in short-term nutritional studies, dietary saturated fat and cholesterol at low-to-moderate levels of intake have no significant effects on BP in normotensive adults.

Adolescent↗

PubMedDate not supplied

Factors affecting blood pressures in newborn infants.

Blood pressure (BP) was measured in 837 newborn infants ranging in age from 1-6 days and their mothers in Boston, Massachusetts, and Providence, Rhode Island. The BP increased significantly with age in days, birth weight, weight on day of measurement, arm circumference, and ponderal index. There was no relation of sex, race, pulse rate, type of feeding, or Apgar scores to BP in the neonatal period. Significant correlation was found between maternal and infant BP (r = 0.196 for systolic (SBP) and 0.157 for diastolic (DBP) pressures, p < 0.001). Preliminary analysis shows a trend for resemblance of 1-month and newborn BP.

Age Factors↗

PubMedDate not supplied

Cardiovascular risk factors among children of men with premature myocardial infarction.

The possible association between fasting glucose, cholesterol, triglyceride, blood pressure, and body weight in children and the early occurrence of paternal myocardial infarction (MI) was explored by examination of 91 children of 38 fathers who had experienced MI before they were 50 years old and 86 children of 39 healthy father. The only variables significantly associated with paternal MI were childhood cholesterol (P = .003) and glucose (P = .006). The results are consistent with the hypothesis that elevated childhood cholesterol levels offer a mechanism whereby family history predicts future risk of coronary heart disease.

Adult↗