Biomedical subjects

Virginie Rondeau

Publications and source records attributed to Virginie Rondeau.

7 recordsLinked to original sources

PubMed2006

Effects of particulate air pollution on systolic blood pressure: A population-based approach.

Given the hypothesis that particulate air pollution is associated with systolic blood pressure, the effect of daily concentrations of air pollution on blood pressure was assessed in 2612 elderly subjects in the urban area of Bordeaux, France. Blood pressure was measured by a digital monitor. Particle concentrations (PM10) were obtained from the AIRAQ association that operates a local monitoring network of the air quality. To represent the ambient urban air pollution, stations had to be sufficiently correlated (i.e., correlation >0.70) and to have sufficiently similar mean levels of pollution. Linear regression was used to model the association between concentrations of particles (PM10) and systolic blood pressure. We observed associations between the fifth lag hour and systolic blood pressure for an increase of 10 microg/m3 of PM10 (beta = -1.12, 95% confidence interval: [-1.90; -0.30]). Despite contradictory results, fine particles must be considered nowadays as a major component of atmospheric air pollution in which everything must be put into practice in terms of public health actions in order to protect the general population and particularly the elderly group.

Aged↗

PubMed2006

Survival analysis to estimate association between short-term mortality and air pollution.

BACKGROUND: Ecologic studies are commonly used to report associations between short-term air pollution and mortality. In such studies, the unit of observation is the day rather than the individual. Moreover, individual data on the subjects are rarely available, which limits the assessment of individual risk factors. These associations can also be investigated using case-crossover studies. However, by definition, individual risk factors are not studied, and such studies analyze only dead subjects, which limits the statistical power. OBJECTIVE: We suggest that the survival analysis is more suitable when cohorts are examined with a time-dependent ecologic exposure. To our knowledge, to date this type of analysis has never been proposed. DESIGN, PARTICIPANTS, MEASUREMENTS: In the present study we used a Cox proportional hazards model to investigate the distribution over time of the short-term effect of black smoke and sulfur dioxide in 439 nonaccidental and 158 cardiorespiratory deaths among the 1,469 subjects of the Personnes Agées QUID (PAQUID) cohort in Bordeaux, France. The model has a delayed entry and a polynomial distributed lag from 0 to 5 days. Results are adjusted for individual risk factors, temperature, relative humidity, weekday, season, influenza epidemics, and a time function to control temporal trends. RESULTS: We identified a positive and significant association between cardiorespiratory mortality and black smoke, with a 24% increase in deaths 3 days after a 10-microg/m3 increase in black smoke (95% confidence interval, 4-47%). CONCLUSIONS: We conclude that the Cox proportional hazards model with time-dependent covariates is very suitable to investigate simultaneously the short-term effect of air pollution on health and the effect of individual risk factors on a cohort study.

Aged↗

PubMed2005

frailtypack: a computer program for the analysis of correlated failure time data using penalized likelihood estimation.

Correlated survival outcomes occur quite frequently in the biomedical research. Available software is limited, particularly if we wish to obtain smoothed estimate of the baseline hazard function in the context of random effects model for correlated data. The main objective of this paper is to describe an R package called frailtypack that can be used for estimating the parameters in a shared gamma frailty model with possibly right-censored, left-truncated stratified survival data using penalized likelihood estimation. Time-dependent structure for the explanatory variables and/or extension of the Cox regression model to recurrent events are also allowed. This program can also be used simply to obtain directly a smooth estimate of the baseline hazard function. To illustrate the program we used two data sets, one with clustered survival times, the other one with recurrent events, i.e., the rehospitalizations of patients diagnosed with colorectal cancer. We show how to fit the model with recurrent events and time-dependent covariates using Andersen-Gill approach.

Cluster Analysis↗

PubMed2005

A three-level model for binary time-series data: the effects of air pollution on school absences in the Southern California Children's Health Study.

A three-level model is proposed to simultaneously examine the effects of daily exposure to air pollution and individual risk factors on health outcomes without aggregating over subjects or time. We used a logistic transition model with random effects to take into account heterogeneity and overdispersion of the observations. A distributed lag structure for pollution has been included, assuming that the event on day t for a subject depends on the levels of air pollution for several preceding days. We illustrate this proposed model via detailed analysis of the effect of air pollution on school absenteeism based on data from the Southern California Children's Health Study.

Absenteeism↗

PubMed2004

Do subject characteristics modify the effects of particulate air pollution on daily mortality among the elderly?

OBJECTIVE: Studies have reported associations between mortality and air pollution, but questions subsist on the identification of susceptible subgroups in the population. We studied individual characteristics that modify the relationship between particulate air pollution and mortality among elderly. METHOD: We examined 527 nonaccidental deaths (197 cardiorespiratory deaths) among the 1469 subjects from the Personnes Agees QUID cohort in Bordeaux between 1988 and 1997. Air pollution was measured as black smoke by urban monitoring background stations. We used a case crossover approach and calculated odds ratio by conditional logistic regression models. RESULTS: We observed associations between the third lag day and cardiorespiratory mortality for an increase of 10 microg/m3 of black smoke (odds ratio = 1.30, 95% confidence interval: 1.01-1.68). CONCLUSIONS: Our results provide insight into factors possibly conferring susceptibility to the acute effect of urban air pollution.

Aged↗

PubMed2003

Maximum penalized likelihood estimation in a gamma-frailty model.

The shared frailty models allow for unobserved heterogeneity or for statistical dependence between observed survival data. The most commonly used estimation procedure in frailty models is the EM algorithm, but this approach yields a discrete estimator of the distribution and consequently does not allow direct estimation of the hazard function. We show how maximum penalized likelihood estimation can be applied to nonparametric estimation of a continuous hazard function in a shared gamma-frailty model withright-censored and left-truncated data. We examine the problem of obtaining variance estimators for regression coefficients, the frailty parameter and baseline hazard functions. Some simulations for the proposed estimation procedure are presented. A prospective cohort (Paquid) with grouped survival data serves to illustrate the method which was used to analyze the relationship between environmental factors and the risk of dementia.

Algorithms↗

PubMedDate not supplied

A review of epidemiologic studies on aluminum and silica in relation to Alzheimer's disease and associated disorders.

Although the neurotoxicity of aluminum is well established, the association between the metal and dementia or associated disorders remains a subject of debate. In this article, we present a review of articles published on epidemiologic studies of this subject. Different sources of exposure are considered (occupational exposure, aluminum-containing products), with emphasis on drinking water. We separate the various health effects of aluminum into three categories: neurological disorders (other than cognitive decline or AD); cognitive decline; and dementia or Alzheimer's disease. Furthermore, we present the results obtained on silicon in drinking water, a chemical constituent that interacts with aluminum. We conclude that not enough epidemiological evidence supports a link between aluminum in drinking water and AD. The role of silica in drinking water has been less studied, and clear results have not yet emerged.

Aluminum↗