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Biomedical subjects

Thomas Lumley

Publications and source records attributed to Thomas Lumley.

48 records · Page 3Linked to original sources
PubMed2003

The association between time since last meal and blood pressure in older adults: the cardiovascular health study.

OBJECTIVES: To demonstrate a postprandial hypotensive (PPH) phenomenon in older adults. DESIGN: Observational, prospective cohort study composed of baseline and nine follow-up visits. SETTING: Cardiovascular Health Study, an epidemiological study of risk factors for cardiovascular disease in older adults. PARTICIPANTS: Five thousand eight hundred eighty-eight community-dwelling adults aged 65 and older. MEASUREMENTS: Blood pressure and time since last meal were recorded synchronously at baseline and at follow-up clinic visits. Generalized estimating equations were used to estimate associations between time since last meal and blood pressure and to adjust variance estimates to account for repeated blood pressure measures within subjects across fasting times. RESULTS: Mean systolic and diastolic blood pressures were lower in the first hour after the last meal and were progressively higher through the fourth hour after the last meal than blood pressures measured immediately after the last meal (0 hour: 133.7/68.8 mmHg; 1st hour: 130.1/66.6 mmHg; 4th hour: 136.5/71.1 mmHg). Changes were significant for systolic and diastolic measures (P <.001 for both). Exploratory analyses suggested that the systolic PPH association was more pronounced in women. Little evidence was found that the degree of systolic or diastolic PPH varied by age, race, prevalent cardiovascular disease, heart rate, ejection fraction, treated hypertension or diabetes mellitus, or body mass index. CONCLUSION: These data support previous observations that there is a significant drop in blood pressure within 1 hour after a meal in older adults. Time since last meal may be an important factor to consider when measuring blood pressure in older adults, and perhaps national standards need to be set.

Aged↗
PubMed2003

Estimating disease prevalence in two-phase studies.

Disease prevalence is ideally estimated using a 'gold standard' to ascertain true disease status on all subjects in a population of interest. In practice, however, the gold standard may be too costly or invasive to be applied to all subjects, in which case a two-phase design is often employed. Phase 1 data consisting of inexpensive and non-invasive screening tests on all study subjects are used to determine the subjects that receive the gold standard in the second phase. Naive estimates of prevalence in two-phase studies can be biased (verification bias). Imputation and re-weighting estimators are often used to avoid this bias. We contrast the forms and attributes of the various prevalence estimators. Distribution theory and simulation studies are used to investigate their bias and efficiency. We conclude that the semiparametric efficient approach is the preferred method for prevalence estimation in two-phase studies. It is more robust and comparable in its efficiency to imputation and other re-weighting estimators. It is also easy to implement. We use this approach to examine the prevalence of depression in adolescents with data from the Great Smoky Mountain Study.

Adolescent↗
PubMed2003

Exposure assessment of particulate matter for susceptible populations in Seattle.

In this article we present results from a 2-year comprehensive exposure assessment study that examined the particulate matter (PM) exposures and health effects in 108 individuals with and without chronic obstructive pulmonary disease (COPD), coronary heart disease (CHD), and asthma. The average personal exposures to PM with aerodynamic diameters < 2.5 microm (PM2.5) were similar to the average outdoor PM2.5 concentrations but significantly higher than the average indoor concentrations. Personal PM2.5 exposures in our study groups were lower than those reported in other panel studies of susceptible populations. Indoor and outdoor PM2.5, PM10 (PM with aerodynamic diameters < 10 microm), and the ratio of PM2.5 to PM10 were significantly higher during the heating season. The increase in outdoor PM10 in winter was primarily due to an increase in the PM2.5 fraction. A similar seasonal variation was found for personal PM2.5. The high-risk subjects in our study engaged in an equal amount of dust-generating activities compared with the healthy elderly subjects. The children in the study experienced the highest indoor PM2.5 and PM10 concentrations. Personal PM2.5 exposures varied by study group, with elderly healthy and CHD subjects having the lowest exposures and asthmatic children having the highest exposures. Within study groups, the PM2.5 exposure varied depending on residence because of different particle infiltration efficiencies. Although we found a wide range of longitudinal correlations between central-site and personal PM2.5 measurements, the longitudinal r is closely related to the particle infiltration efficiency. PM2.5 exposures among the COPD and CHD subjects can be predicted with relatively good power with a microenvironmental model composed of three microenvironments. The prediction power is the lowest for the asthmatic children.

Age Factors↗
PubMed2002

Genetic variants of coagulation factor XIII, postmenopausal estrogen therapy, and risk of nonfatal myocardial infarction.

We hypothesized that possession of either of 2 functional coagulation factor XIII polymorphisms, one within subunit A (Val34Leu) and one within subunit B (His95Arg), might modulate the prothrombotic effects of estrogen and help to explain the variation in incidence of arterial thrombotic events among postmenopausal women using hormone replacement therapy. In a population-based case-control study of 955 postmenopausal women, we assessed the associations of factor XIII genotypes and their interactions with estrogen therapy on risk of nonfatal myocardial infarction (MI). The presence of the factor XIIIA Leu34 allele was associated with a reduced risk of MI (odds ratio [OR] = 0.70, 95% confidence interval [95% CI] = 0.51-0.95). The presence of the factor XIIIB Arg95 allele had little association with MI risk. Neither factor XIII polymorphism alone significantly modified the association between the risk of MI and current estrogen use. In exploratory analyses, however, there was a significant factor XIII subunit gene-gene interaction. Compared to women homozygous for both common factor XIII alleles, the Arg95 variant was associated with a reduced risk of MI in the presence of the Leu34 variant (OR = 0.36, 95% CI = 0.17-0.75) but not in the absence of the Leu34 variant (OR = 1.11, 95% CI = 0.69-1.79). Moreover, among women who had at least 2 copies of the variant factor XIII alleles and were current estrogen users, the risk of MI was reduced by 70% relative to estrogen nonusers with fewer than 2 factor XIII variant alleles (P value for interaction =.03). If confirmed, these findings may permit a better assessment of the cardiovascular risks and benefits associated with postmenopausal estrogen therapy.

Adult↗
PubMed2002

Time trends in high blood pressure control and the use of antihypertensive medications in older adults: the Cardiovascular Health Study.

BACKGROUND: Control of high blood pressure (BP) in older adults is an important part of public health efforts at prevention. OBJECTIVE: To assess recent time trends in the awareness, treatment, and control of high BP and in the use of medications to treat high BP. METHODS: In the Cardiovascular Health Study, 5888 adults 65 years and older were recruited from 4 US centers. At baseline, participants underwent an extensive examination that included the measurement of BP, use of medications, and other risk factors. Participants were followed up with annual visits that assessed BP and medication use from baseline in 1989-1990 through the examination in 1998-1999. The primary outcome measures were control of BP to levels lower than than 140/90 mm Hg and the prevalence of use of various classes of antihypertensive medications. RESULTS: The awareness, treatment, and control of high BP improved during the 1990s. The proportions aware and treated were higher among blacks than whites, though control prevalences were similar. For both groups combined, the control of high BP to lower than 140/90 mm Hg increased from 37% at baseline to 49% in 1999. The 51% whose BP was not controlled generally had isolated mild to moderate elevations in systolic BP. Among treated persons, the improvement in control was achieved in part by a mean increase of 0.2 antihypertensive medications per person over the course of 9 years. Improved control was also achieved by increasing the proportion of the entire Cardiovascular Health Study population that was treated for hypertension, from 34.5% in 1990 to 51.1% in 1999. Time trends in antihypertensive drug use were pronounced. Among those without coronary disease, the use of low-dose diuretics and beta-blockers decreased, while the use of newer agents, such as calcium channel blockers, angiotensin-converting enzyme inhibitors, and alpha-blockers increased. CONCLUSIONS: While control of high BP improved in the 1990s, about half the participants with hypertension had uncontrolled BP, primarily mild to moderate elevations in systolic BP. Low-dose diuretics and beta-blockers--the preferred agents since 1993 according to the recommendations of the Joint National Committee on the Detection, Evaluation and Treatment of High Blood Pressure--remained underused. More widespread use of these agents will be an important intervention to prevent the devastating complications of hypertension, including stroke, myocardial infarction, and heart failure.

Age Factors↗
PubMed2002

Network meta-analysis for indirect treatment comparisons.

I present methods for assessing the relative effectiveness of two treatments when they have not been compared directly in a randomized trial but have each been compared to other treatments. These network meta-analysis techniques allow estimation of both heterogeneity in the effect of any given treatment and inconsistency ('incoherence') in the evidence from different pairs of treatments. A simple estimation procedure using linear mixed models is given and used in a meta-analysis of treatments for acute myocardial infarction.

Angioplasty↗
PubMed2002

Civil protection orders and risk of subsequent police-reported violence.

CONTEXT: Approximately 1.5 million US women experience intimate partner violence annually. Approximately 20% of these women obtain civil protection orders, but the effectiveness of such orders in preventing future violence is unclear. OBJECTIVE: To assess associations between obtaining a protection order and risk of subsequent police-reported intimate partner violence. DESIGN, SETTING, AND SUBJECTS: Retrospective cohort study of 2691 adult female residents of Seattle, Wash, with an incident of male intimate partner violence reported to the Seattle Police Department between August 1, 1998, and December 31, 1999. MAIN OUTCOME MEASURE: Relative risk (RR) of police-reported physical and psychological abuse in the 12 months following the index incident according to protection order status (temporary protection order, usually in effect for 2 weeks; permanent protection order, usually in effect for 12 months; or no protection order). RESULTS: Overall rates of police-reported physical and psychological abuse in the 12 months of follow-up were 13.5 per 100 person-years and 12.3 per 100 person-years, respectively. After controlling for cohabitation at time of index incident and index incident offense type, women with temporary protection orders in effect were more likely than women without protection orders to be psychologically abused (RR in the first 6 months after the index incident, 4.0; 95% confidence interval [CI], 2.2-7.2; RR in the entire 12 months after the index incident, 4.9; 95% CI, 2.8-8.6), while women with permanent protection orders in effect were less likely than those without orders to be physically abused (RR in the first 6 months, 0.4; 95% CI, 0.1-1.1; RR in the entire 12 months, 0.2; 95% CI, 0.1-0.8). CONCLUSIONS: Permanent, but not temporary, protection orders are associated with a significant decrease in risk of police-reported violence against women by their male intimate partners.

Adult↗
PubMed2002

Diuretic therapy, the alpha-adducin gene variant, and the risk of myocardial infarction or stroke in persons with treated hypertension.

CONTEXT: A genetic variant in alpha-adducin has been associated with renal sodium reabsorption and salt-sensitive hypertension. Whether this genetic variant modifies the effect of diuretic therapy on the incidence of myocardial infarction (MI) and stroke is unknown. OBJECTIVES: To estimate the interaction between alpha-adducin and diuretic therapy on the risk of MI or stroke. Specifically, we hypothesized that in participants with treated hypertension, the risk of MI or stroke associated with diuretic use would be lower in carriers of the adducin variant than in carriers of the adducin wild-type genotype. DESIGN, SETTING, AND PARTICIPANTS: Population-based case-control study of patients enrolled in a health maintenance organization, treated pharmacologically for hypertension, and genotyped as homozygous carriers of the adducin wild-type genotype or carriers of 1 or 2 copies of the Trp460 variant allele. Cases had a first nonfatal MI (n = 206) or stroke (n = 117) between January 1995 and December 1998. Controls (n = 715) were a stratified random sample of pharmacologically treated hypertensive patients who were matched to MI cases by age, sex, and calendar year. MAIN OUTCOME MEASURE: Risk of the combined outcome of first nonfatal MI or stroke. RESULTS: The adducin variant was present in more than one third of the participants. Among the 653 carriers of the adducin wild-type genotype, diuretic therapy was not associated with the risk of MI or stroke (odds ratio [OR], 1.09; 95% confidence interval [CI], 0.78-1.52). Among the 385 carriers of the adducin variant allele, diuretic therapy was associated with a lower risk of the combined outcome of MI and stroke than other antihypertensive therapies (OR, 0.49; 95% CI, 0.32-0.77). The OR in carriers of the adducin variant was less than half of the OR in carriers of the wild-type genotype (P =.005). The case-control synergy index (SI) was 0.45 (95% CI, 0.26-0.79) for the combined outcome of MI and stroke. The point estimates of the diuretic-adducin interaction were similar in separate analyses of MI (SI, 0.41; 95% CI, 0.21-0.80) and stroke (SI, 0.53; 95% CI, 0.24-1.19). The diuretic-adducin interaction was not confounded by traditional cardiovascular risk factors, was specific to diuretic therapy but not present for other major antihypertensive drug classes, and did not differ substantially between subgroups defined by age, sex, race, diabetes, and history of cardiovascular disease. CONCLUSIONS: In carriers of the adducin variant, diuretic therapy was associated with a lower risk of combined MI or stroke than other antihypertensive therapies. If these findings are confirmed in other studies, this large subgroup of the hypertensive population may be especially likely to benefit from low-dose diuretic therapy.

Aged↗
PubMed2002

A stroke prediction score in the elderly: validation and Web-based application.

The objective of this study was to construct a prediction model for predicting stroke in an elderly U.S. population, and to assess the accuracy in this population of other previously published prediction models. The subjects were participants in the Cardiovascular Health Study: 2,495 men and 3,393 women age 65 years and older at baseline, and followed for 6.3 years. Among 5,711 participants free of baseline stroke, 399 strokes occurred. Sex-specific prediction equations were constructed using study variables that were most importantly related to incident stroke: age, systolic blood pressure, diabetes, ECG diagnosis of atrial fibrillation or left ventricular hypertrophy, confirmed history of cardiovascular disease, diabetes, time to walk 15 ft, and serum creatinine. The prediction rule was implemented as a risk score and in a Web-based interactive Java applet. Overall, the model predicted 5-year stroke risks ranging from less than 1 to 59%. The 20% of subjects in the highest predicted risk group had a 5-year actual stroke incidence rate of 15%, while the 20% lowest risk group had a 1% incidence. Risk scores from two other studies performed well in these study participants. Effective discrimination between low and high stroke risk in the elderly was possible in this cohort with data that are easy to obtain. Evaluation of the generalizability and clinical usefulness of this prediction model requires further research.

Aged↗
PubMed2002

Spatial characteristics of fine particulate matter: identifying representative monitoring locations in Seattle, Washington.

This study investigates how PM2.5 varies spatially and how these spatial characteristics can be used to identify potential monitoring sites that are most representative of the overall ambient exposures to PM2.5 among susceptible populations in the Seattle, WA, area. Data collected at outdoor sites at the homes of participants of a large exposure assessment study were used in this study. Harvard impactors (HIs) were used at 40 outdoor sites throughout the Seattle metropolitan area. Up to six sites at a time were monitored for 10 consecutive 24-hr average periods. A fixed-effect analysis of variance (ANOVA) model that included date and location effects was used to analyze the spatial variability of outdoor PM2.5 concentrations. Both date and location effects were shown to be highly significant, explaining 92% of the variability in outdoor PM2.5 measurements. The day-to-day variability was 10 times higher than the spatial variability between sites. The site mean square was more than twice the error mean square, showing that differences between sites, while modest, are potentially an important contribution to measurement error. Variances of the model residuals and site effects were examined against spatial characteristics of the monitoring sites. The spatial characteristics included elevation, distance from arterials, and distance from major PM2.5 point sources. Results showed that the most representative PM2.5 sites were located at elevations of 80-120 m above sea level, and at distances of 100-300 m from the nearest arterial road. Location relative to industrial PM2.5 sources is not a significant predictor of residential outdoor PM2.5 measurements. Additionally, for sites to be representative of the average population exposures to PM2.5 among those highly susceptible to the health effects of PM2.5, areas of high elderly population density were considered. These representative spatial characteristics were used as multiple, overlapping criteria in a Geographic Information System (GIS) analysis to determine where the most representative sites are located.

Air Pollutants↗
PubMed2001

The importance of the normality assumption in large public health data sets.

It is widely but incorrectly believed that the t-test and linear regression are valid only for Normally distributed outcomes. The t-test and linear regression compare the mean of an outcome variable for different subjects. While these are valid even in very small samples if the outcome variable is Normally distributed, their major usefulness comes from the fact that in large samples they are valid for any distribution. We demonstrate this validity by simulation in extremely non-Normal data. We discuss situations in which in other methods such as the Wilcoxon rank sum test and ordinal logistic regression (proportional odds model) have been recommended, and conclude that the t-test and linear regression often provide a convenient and practical alternative. The major limitation on the t-test and linear regression for inference about associations is not a distributional one, but whether detecting and estimating a difference in the mean of the outcome answers the scientific question at hand.

Data Collection↗