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Biomedical subjects

L E Chambless

Publications and source records attributed to L E Chambless.

At least 91 records · Page 5Linked to original sources
PubMed1994

Cytomegalovirus/herpesvirus and carotid atherosclerosis: the ARIC Study.

Ubiquitous viruses such as members of the human herpes virus group, particularly cytomegalovirus (CMV), have been proposed to be clinically important agents in the initiation and progression of atherosclerosis. Antibodies to CMV and herpes simplex virus type 1 (HSV1) and type 2 (HSV2) were determined in 340 matched case-control pairs from the Atherosclerosis Risk in Communities (ARIC) Study. Cases were defined by B-mode ultrasonography as persons with thickened carotid artery walls consistent with early atherosclerosis but without a history of cardiovascular disease. Controls were defined as persons without thickened walls or history of cardiovascular disease. The case-control odds ratio for CMV antibodies was 1.55 (P = .03), for HSV 1.41 (P = .07), and for HSV2 0.91 (P = .63). When adjustment was made for potential confounders, the odds ratios were 1.36 for CMV (P = .24), 1.21 for HSV1 (P = .45), and 0.61 (P = .05) for HSV2. These results suggest a modest association between CMV and asymptomatic carotid wall thickening consistent with early atherosclerosis.

Antibodies, Viral↗
PubMed1994

Lipoprotein(a) as a correlate of stroke and transient ischemic attack prevalence in a biracial cohort: the ARIC Study. Atherosclerosis Risk in Communities.

Although both mean lipoprotein(a) [Lp(a)] concentration and national stroke prevalence estimates are consistently higher in American blacks than in whites, no information exists on the relationship of Lp(a) and stroke prevalence in African-Americans. Associations of Lp(a) with stroke or transient ischemic attack (TIA) are addressed in this report for 15,160 participants--4160 blacks and 11,000 whites--in the Atherosclerosis Risk in Communities (ARIC) Study. Lp(a) was measured in ARIC as its total protein component by double-antibody enzyme-linked immunosorbent assay (ELISA) for apo(a) detection. Self-reported stroke/TIA history was assessed as part of a standardized questionnaire, and resulted in age-adjusted stroke/TIA prevalences of 3.0% in blacks (n = 120) and 2.0% in whites (n = 222). Overall, mean Lp(a) protein levels were markedly higher for blacks than for whites (160.5 versus 81.6 micrograms/mL, respectively), and were statistically significantly higher among individuals reporting stroke/TIA history for both races (191.3 versus 159.6 micrograms/mL in blacks; 100.6 versus 81.2 micrograms/mL in whites). Multivariable logistic regression analysis for the association of Lp(a) protein with stroke/TIA status yielded a prevalence odds ratio (OR) (95% confidence intervals) of 1.17 (1.05, 1.30) overall (based on one standard deviation difference, 108.2 micrograms/mL, in Lp[a] protein). Race-specific ORs, after adjustment for the same covariates, were equivalent for blacks [OR = 1.17 (0.99, 1.39)] and whites [OR = 1.19 (1.04, 1.36)]. These data suggest that Lp(a) is an independent risk factor for stroke/TIA in both blacks and whites, and that the relative risk of stroke/TIA associated with Lp(a) protein does not vary by race.(ABSTRACT TRUNCATED AT 250 WORDS)

Black or African American↗
PubMed1994

Relation of carotid artery wall thickness to diabetes mellitus, fasting glucose and insulin, body size, and physical activity. Atherosclerosis Risk in Communities (ARIC) Study Investigators.

BACKGROUND AND PURPOSE: We tested the hypothesis that body mass, waist-to-hip circumference ratio, physical inactivity, diabetes, hyperglycemia, and fasting insulin are each positively associated with asymptomatic carotid artery wall thickness. METHODS: Average intimal-medial carotid wall thickness (an indicator of atherosclerosis) was measured noninvasively by B-mode ultrasonography in cross-sectional samples of 45- to 64-year-old adults, both blacks and whites, free of symptomatic cardiovascular disease, in four US communities. RESULTS: Sample mean carotid wall thickness was approximately 0.7 mm in women (n = 7956) and 0.8 mm in men (n = 6474). Body mass, waist-to-hip ratio, work physical activity, diabetes, and fasting insulin were associated (P < .05) with carotid wall thickness in the hypothesized direction. Adjusted for age, race, smoking, body mass index, artery depth, and Atherosclerosis Risk in Communities field center, mean wall thickness was greater by 0.02 mm in women and 0.03 mm in men for a 0.07-unit (one SD) larger waist-to-hip ratio. Adjusted mean wall thickness was about 0.07 mm thicker in participants with diabetes mellitus and 0.02 mm thicker in participants with hyperglycemia (fasting glucose 6.4 to 7.7 mmol/L) than in subjects with fasting glucose < 6.4 mmol/L. Adjusted mean wall thickness increased by about 0.02 mm with an increase of 100 mmol/L in fasting serum insulin. CONCLUSIONS: Abdominal adiposity, physical inactivity, and abnormal glucose metabolism are associated positively with carotid intimal-medial wall thickness, suggesting these factors contribute to atherogenesis.

Aging↗
PubMed1994

Short-term, within-person variability in clinical chemistry test results. Experience from the Atherosclerosis Risk in Communities Study.

We report the within-person, between-person, and methodological variances of a number of chemical analytes for free-living, middle-aged adults who participated in the Atherosclerosis Risk in Communities Study's Intraindividual Variability Study. The Atherosclerosis Risk in Communities Study is a National Institutes of Health-sponsored multicenter study of atherosclerotic risk factors. In the Atherosclerosis Risk in Communities Study and its Intraindividual Variability Study, concentrations of the following 12 chemical analytes were measured in serum from fasting individuals: sodium, calcium, potassium, creatinine, albumin, total protein, magnesium, phosphorus, urea, insulin, glucose, and urate. The analytes are listed in order of the increasing reliability coefficient (ie, the fraction that between-person variance represents of the total observed population variance), which ranged from .59 for sodium to .91 for urate. The reliability coefficient is a strong predictor of the possibility of finding statistical correlations between measured analyte concentrations and disease occurrence in an epidemiological study like the Atherosclerosis Risk in Communities Study. The within-person variance and methodological variance are also useful in computing confidence intervals for sequential laboratory test results in patients and evaluating limits for internal quality control and proficiency testing programs.

Aged↗
PubMed1993

ARIC hemostasis study--III. Quality control. Atherosclerosis Risk in Communities.

Methods and results from the quality assurance program of the Atherosclerosis Risk in Communities (ARIC) Study regarding hemostasis variables are presented, following up previous reports in this journal on standardized procedures for blood collection and processing (7) and an organized plan for the performance of those procedures (8). Efforts were made to control for and assess all sources of variability, from venipuncture to laboratory analysis, including also local field center processing and sample shipping. The quality control program included (a) a standardized protocol for blood collection and processing; (b) training, certification, and annual recertification of field center personnel for blood collection and processing; (c) monitoring of fasting times, phlebotomy times, processing times, and shipping problems; (d) hemostatic laboratory internal quality control; (e) a replicate blood sample program; (f) an intraindividual variability study; and (g) continual monitoring of quality control and study participants' data. This paper focused on items (c), (d), and (e). Measures of variation, generally standard deviations and coefficients of variation, are estimated for replicate blood sampling and internal quality control data, for activated partial thromboplastin time, fibrinogen, factor VII and VIII activity, von Willebrand factor, antithrombin-III, and protein C. The results demonstrate that it is possible to reliably measure these hemostatic variables in a large multicenter study.

Arteriosclerosis↗
PubMed1993

Methods for assessing difference between groups in change when initial measurements is subject to intra-individual variation.

Statistical analysis of difference between groups in change for some variable, adjusting for initial value, is complicated by the presence of intra-individual variation in that variable. We estimate here the asymptotic bias that results from calculating the adjusted between-group difference by ordinary least squares (OLS) from observed data. We also present explicit formulae that use the OLS estimates, the difference between treatment groups in mean initial values, and a measure of the intra-individual variation to compute a corrected estimator and its variance. Alternatively, we can use OLS on transformed data to obtain unbiased estimates, in which we replace initial observed values by conditional Stein estimates of true values. We illustrate the results with data from an observational study and a clinical trial.

Adrenergic beta-Antagonists↗
PubMed1993

Prevalence of stroke and transient ischemic attacks in the Atherosclerosis Risk in Communities (ARIC) study.

The Atherosclerosis Risk in Communities (ARIC) study is a population-based observational study of randomly sampled, census-based populations in four locations within the United States. The study was designed to determine whether there are regional differences in incidence, prevalence, and mortality rates from cardiovascular and cerebrovascular disease in populations aged 45 to 64 years. Both cohort examinations and community surveillance are included. In addition to a standardized transient ischemic attack (TIA) and stroke questionnaire and algorithm for determination of incidence and prevalence, B-scan ultrasonography is used to quantify the degree of atherosclerotic changes in the carotid artery. Initiated in late 1986, the first cohort evaluation was completed in early 1990. The third, which includes magnetic resonance imaging of the brain, is in progress and will be completed in 1996. Positive responses to the TIA/stroke questionnaire increase by decile of age, are greater in women than men, and are more frequent in African Americans than Caucasians. The baseline study using an algorithm for categorization of patient responses into vascular and other causes of TIA and stroke estimated prevalence of 5.5% in African Americans and 6.3% in Caucasians.

Adult↗
PubMed1993

Carotid artery intimal-medial wall thickening and plasma homocyst(e)ine in asymptomatic adults. The Atherosclerosis Risk in Communities Study.

BACKGROUND: Plasma levels of homocyst(e)ine are elevated in certain patients with occlusive arterial diseases. We extended these findings to asymptomatic adults. METHODS AND RESULTS: We determined plasma homocyst(e)ine levels in 287 pairs of asymptomatic adults. Cases and controls were defined on the basis of intimal-medial thickness of the carotid wall as measured by B-mode ultrasound. Study subjects had no history of atherosclerotic disease and were selected from a probability sample of 15,800 men and women between 45 and 64 years old. Subjects with thickened intimal-medial carotid walls (cases) had higher plasma homocyst(e)ine levels than controls (p < 0.001). The odds ratio for having a thickened carotid artery wall was 3.15 (p < 0.001) for subjects in the top quintile of plasma homocyst(e)ine levels (> 10.5 mumol/L) compared with those in the bottom quintile (< 5.88 mumol/L). CONCLUSIONS: The present study as well as observations on the common occurrence of elevated plasma homocyst(e)ine levels in patients with occlusive arterial diseases suggest that clinical trials should be conducted to determine whether normalization of hyperhomocyst(e)inemia may prevent progression of atherosclerosis.

Arteriosclerosis↗
PubMed1993

Carotid artery intimal-medial thickness distribution in general populations as evaluated by B-mode ultrasound. ARIC Investigators.

BACKGROUND AND PURPOSE: B-mode ultrasound is a widely used technique for the clinical and epidemiological assessment of carotid atherosclerosis. This article provides a description of the distribution of carotid atherosclerosis in the general population. METHODS: Intimal-medial arterial wall thickness was measured by B-mode real-time ultrasound as an index of atherosclerotic involvement in the extracranial carotid arteries as part of the population-based Atherosclerosis Risk in Communities (ARIC) study. The distribution was described by race-sex strata, in which 759 to 4952 individuals were imaged depending on strata and location in the carotid system. RESULTS: Median wall thickness ranged between 0.5 and 1 mm at all ages; fewer than 5% of ARIC participants had values exceeding 2 mm. Individuals tended to have a larger wall thickness in the carotid bifurcation than in the common carotid artery. Internal carotid artery values were more variable, with higher proportions of both large and small wall thicknesses than in the common carotid. The proportion of individuals with a large wall thickness was greatest at the bifurcation and smallest at the common carotid artery. Men had uniformly larger wall thickness than women. Cross-sectional analysis suggests that age-related increases in wall thickness average approximately 0.015 mm/y in women and 0.018 mm/y in men in the carotid bifurcation, 0.010 mm/y for women and 0.014 mm/y for men in the internal carotid artery, and 0.010 mm/y in both sexes in the common carotid artery. CONCLUSIONS: Estimates provided for wall thickness percentiles can serve as "nomograms" by age, race, and sex.

Arteriosclerosis↗
PubMed1992

Short-term intraindividual variability in lipoprotein measurements: the Atherosclerosis Risk in Communities (ARIC) Study.

Much epidemiologic research is based on estimation of an association between a putative risk factor and a health outcome--for example, plasma concentration of lipoproteins and ischemic heart disease. Since the repeatability of a risk factor measurement determines, in part, the ability to ascertain its association in populations, the Atherosclerosis Risk in Communities (ARIC) Intraindividual Variability Study was conducted to estimate various components of variation in analyte data and to estimate the repeatability of these measurements. A total of 40 subjects (17 males and 23 females) from Forsyth County, North Carolina, Minneapolis, Minnesota, Jackson, Mississippi, and Washington County, Maryland, were studied in 1988. Fasting blood was collected three times from each subject, with a 1- to 2-week interval between each visit. The contributions of between-person variability, within-person variability, and processing and assay variability were estimated. From these components, the reliability coefficient, R, the correlation between measures made at repeat visits, was estimated. R was above 0.85 for total cholesterol, high density lipoprotein cholesterol, low density lipoprotein cholesterol, triglycerides, and lipoprotein(a). Low repeatability was obtained for apolipoprotein A-I (R = 0.60). High density lipoprotein subfractions 2 and 3 were intermediate in repeatability. Reliability coefficients from the ARIC Intraindividual Variability Study are generally higher than those found in other studies, and this is related to relative variability in populations studied, to the time between measurements, and to differences in laboratory variability. Only for apolipoprotein A-I would the findings strongly suggest the need to adjust for measurement variability in estimation using one of these analytes as an independent variable.

Cardiovascular Diseases↗
PubMed1992

Postprandial lipemia: reliability in an epidemiologic field study.

Ten subjects from the Forsyth County, North Carolina, and Washington County, Maryland, field centers in the Atherosclerosis Risk in Communities Study had two fat tolerance tests within a 10-day period from September 1988 to February 1989 to determine the reproducibility of markers for postprandial lipemia. No significant differences between visits were found in fasting mean plasma lipids, lipoproteins, and apolipoproteins. Postprandial triglycerides and retinyl palmitate were measured at 3.5 and 9.0 hours after the test meal in whole plasma. There were no significant differences in the mean levels of these analytes between visits. The correlation of triglycerides between repeat visits at 9.0 hours (r = 0.87) was stronger than in fasting samples (r = 0.67) or at 3.5 hours (r = 0.69). The mean plasma retinyl palmitate level at 3.5 hours was 15% higher than at the 9.0-hour level. The correlation of repeat measures of retinyl palmitate at 9.0 hours (r = 0.94) was much stronger than at 3.5 hours (r = 0.79). In conclusion, estimates of reliability in postprandial measurements of 9.0-hour triglycerides and retinyl palmitate levels were as strong as fasting lipid measurements of total cholesterol, high density lipoprotein cholesterol, low density lipoprotein cholesterol, and high density lipoprotein cholesterol, and both postprandial triglyceride measurements exceeded that of fasting triglyceride (r = 0.67).

Apolipoproteins↗
PubMed1992

Short-term intraindividual variability in hemostasis factors. The ARIC Study. Atherosclerosis Risk in Communities Intraindividual Variability Study.

Recent epidemiologic studies found that there is a strong association of hemostatic factors with ischemic heart disease. The Atherosclerosis Risk in Communities (ARIC) Intraindividual Variability (IIV) Study was conducted to estimate the various components of variation in hemostasis factors measured in the ARIC Study and to estimate the measures of repeatability of these factors. A total of 39 subjects (16 men, 23 women) were studied. Each had blood collected three times, with a 1- to 2-week interval between each visit. The contributions of between-person variability, within-person (biologic) variability, and processing and assay variability were estimated. Then the reliability coefficient R was estimated as the proportion of total variance accounted for by between-person variance. The reliability coefficient can be interpreted as the correlation between measures made at repeat visits. Among the various analytes, the reliability coefficients were quite high for activated partial thromboplastin time and plasma factor VIII (R = 0.92, 0.86, respectively). Low repeatability was obtained for antithrombin III activity and protein C (R = 0.42, 0.56, respectively). The lack of repeatability for these variables derives mostly from the processing (field center and laboratory) variation. Other analytes--fibrinogen, plasma factor VII, and von Willebrand factor--were intermediate in repeatability. In comparing the analyte-specific high-level to low-level groups, no substantial difference of within-person plus method coefficient of variation between the two groups was found for any analyte except for factor VIII, whereas the corresponding variance components for most analytes were higher for the higher analyte level. Reliability coefficients from this ARIC IIV study are generally higher than those found in other studies, and this is related to the relative variations in populations studied and to the time between measurements.

Antithrombin III↗
PubMed1992

Measuring ankle systolic blood pressure: validation of the Dinamap 1846 SX.

Clinical and epidemiologic situations requiring repeated measurements of blood pressure in the lower extremity are increasingly incorporating automated measurement devices; however, no device has been validated adequately for ankle blood pressure. This study evaluates the Dinamap 1846 SX against Doppler ultrasound in determining ankle systolic blood pressure (SBP) and compares a parallel with contour wrapping technique for applying the blood pressure cuff. Ankle SBP was measured on 71 adult volunteers by both devices simultaneously, for each cuff wrap. Averages of three readings were compared to evaluate Dinamap versus Doppler SBP estimates and to assess any cuff wrap effect. Multiple linear regression was used to assess potential effect modifiers. Instrument differences (Dinamap minus Doppler) for the parallel wrap (95% confidence intervals in parenthesis) were -1.5 mmHg (-3.1, 0.0) and -3.9 mmHg (-5.6, -2.2) for the contour wrap. Wrap effect differences (contour minus parallel) for the Doppler were -4.9 mmHg (-6.3, -3.5) and -7.2 mmHg (-8.7, -5.8) for the Dinamap. Degree of ankle taper was a strong modifier of cuff effect for the Dinamap but not for the Doppler: adjusted cuff effect with the Dinamap ranged from -3 to -10 mmHg. Measurement precision (within-person reproducibility, measured by within-person standard deviation [sigma 2] and reliability coefficient [R]) was higher for the Dinamap than the Doppler technique, lowest for the parallel wrap and Doppler configuration (sigma 2 = 5.4 mmHg, R = 0.88) and greatest for the contour wrap and Dinamap (sigma 2 = 4.0 mmHg, R = 0.94). In conclusion, cuff-wrapping technique can generate SBP differences of greater magnitude than instrument differences. Conditional on the use of the contour wrap, and by virtue of its high repeatability and ease of operation, the Dinamap is a useful tool for epidemiologic study and the clinical assessment of peripheral arterial disease.

Adult↗
PubMed1991

Effects of chromium supplementation on serum high-density lipoprotein cholesterol levels in men taking beta-blockers. A randomized, controlled trial.

OBJECTIVE: To determine the efficacy of glucose tolerance factor (GTF)-chromium for increasing serum levels of high-density lipoprotein (HDL) cholesterol in patients taking beta-blockers. DESIGN: Randomized, double-blind, placebo-controlled trial. SETTING: Mixed primary and referral-based outpatient clinic at a university-affiliated VA Medical Center. PATIENTS: Referred sample of 72 men receiving beta-blockers, mainly for hypertension. Sixty-three patients (88%) completed the study. INTERVENTIONS: Current medications, including beta-blockers, were continued. During the 8-week treatment phase, patients in the chromium group received a total daily dose of 600 micrograms of biologically active chromium divided into three equal doses; control patients received a placebo of identical appearance and taste. MEASUREMENTS: Serum levels of total cholesterol and HDL cholesterol were measured. MAIN RESULTS: Mean baseline levels of HDL and total cholesterol (+/- SD) were 0.93 +/- 0.28 mmol/L and 6.0 +/- 1.0 mmol/L (36 +/- 11.1 mg/dL and 232 +/- 38.5 mg/dL), respectively. The difference between groups in adjusted mean change in HDL cholesterol levels, accounting for baseline HDL cholesterol levels, age, weight change, and baseline total cholesterol levels, was 0.15 mmol/L (5.8 mg/dL) (P = 0.01) with a 95% Cl showing that the treatment effect was greater than +0.04 mmol/L (+1.4 mg/dL). Mean total cholesterol, triglycerides and body weight did not change significantly during treatment for either group. Compliance as measured by pill count was 85%, and few side effects were reported. Two months after the end of treatment, the between-group difference in adjusted mean change from baseline to end of post-treatment follow-up was -0.003 mmol/L (-0.1 mg/dL). CONCLUSION: Two months of chromium supplementation resulted in a clinically useful increase in HDL cholesterol levels in men taking beta-blockers.

Adrenergic beta-Antagonists↗
PubMed1991

Carotid atherosclerosis measured by B-mode ultrasound in populations: associations with cardiovascular risk factors in the ARIC study.

To assess whether carotid atherosclerosis measured by B-mode ultrasound is related to cardiovascular risk factors, 386 cases with carotid artery wall thickening and an equal number of controls free of arterial intima-media thickening were drawn from the cohort of the Atherosclerosis Risk in Communities (ARIC) Study examined in four communities in the United States between 1988 and 1990. Cases and controls were individually matched on sex, race, age group, study center, and date of examination. The mean values of total cholesterol, low density lipoprotein (LDL) cholesterol, total triglyceride, blood pressure, and pack-years of cigarette smoking were higher in cases than controls. Mean high density lipoprotein (HDL) cholesterol was lower in cases than controls. Case-control differences were all statistically significant. Multivariable-adjusted odds ratios point to differences of considerable magnitude in the risk of carotid atherosclerosis between groups defined by clinical and public health-oriented risk factor cut-points.

Arteriosclerosis↗
PubMed1990

On the use of a logistic risk score in predicting risk of coronary heart disease.

Many studies over the last 20 years have used logistic regression to model the relationship between the risk of developing coronary heart disease (CHD) and the levels of risk factors such as high blood pressure, high serum cholesterol, and cigarette smoking. Subsequently, several investigators have proposed the use of some of the published estimated logistic risk functions to predict risk in new populations. Because of great variation in definition of event, duration of follow-up, population characteristics, definition of risk variables, and selection of other variables in the logistic functions, direct use of such established functions would generally not have validity for the prediction of absolute risk levels. A review of fifteen of these studies indicates on the one hand generally similar results in direction and order of magnitude of effects of the major risk factors, confirming the importance of these risk factors of CHD. On the other hand the reviews indicate sufficient variation to suggest that extrapolation to new populations even to predict relative risk is not justified.

Age Factors↗
PubMed1990

The association of corneal arcus with coronary heart disease and cardiovascular disease mortality in the Lipid Research Clinics Mortality Follow-up Study.

The relationship between corneal arcus (arcus senilis) and mortality from coronary heart disease (CHD) and cardiovascular disease (CVD) is examined in a prospective study of White men (n = 3,930) and women non-hormone users (n = 2,139), ages 30-69, followed for an average of 8.4 years as part of the Lipid Research Clinics Mortality Follow-up Study. After excluding those with clinically manifest CHD at baseline, corneal arcus was strongly associated with CHD and CVD mortality only in hyperlipidemic men ages 30-49 years, for whom the relative risk for CHD and CVD death was 3.7 and 4.0, respectively, after adjusting for age, total cholesterol, HDL cholesterol, and smoking status using a Cox proportional hazards model. Among 30-49 year old males, corneal arcus appears to be a prognostic factor for CHD, independent of its association with hyperlipidemia in this age-group, of about the same magnitude as other common risk factors, underscoring the usefulness of corneal arcus as a prognostic factor to the practicing clinician.

Adult↗