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Estimation of the maximum flow-mediated brachial artery response using local regression methods.

Authors
Andrew-ME; Li-S; Fekedulegn-D; Dorn-J; Joseph-PN; Violanti-J; Burchfiel-CM
Source
Physiol Meas 2007 Oct; 28(10):1213-1224
NIOSHTIC No.
20032835
Abstract
We consider methods for estimating the maximum from a sequence of measurements of flow-mediated diameter of the brachial artery. Flow-mediated vasodilation (FMD) is represented using the maximum change from a baseline diameter measurement after the release of a blood pressure cuff that has been inflated to reduce flow in the brachial artery. The influence of the measurement error on the maximum diameter from raw data can lead to overestimation of the average maximum change from the baseline for a sample of individuals. Nonparametric regression models provide a potential means for dealing with this problem. When using this approach, it is necessary to make a judicious choice of regression methods and smoothing parameters to avoid overestimation or underestimation of FMD. This study presents results from simulation studies using kernel-based local linear regression methods that characterize the relationship between the measurement error, smoothing and bias in estimates of FMD. Comparisons between fixed or constant smoothing and automated smoothing parameter selection using the generalized cross validation (GCV) statistic are made, and it is shown that GCV-optimized smoothing may over-smooth or under-smooth depending on the heart rate, measurement error and measurement frequency. We also present an example using measured data from the Buffalo Cardio-Metabolic Occupational Police Stress (BCOPS) pilot study. In this example, smoothing resulted in lower estimates of FMD and there was no clear evidence of an optimal smoothing level. The choice to use smoothing and the appropriate smoothing level to use may depend on the application.
Keywords
Psychological-factors; Statistical-analysis; Analytical-processes; Time-weighted-average-exposure; Blood-pressure; Cardiac-function; Stress; Cardiovascular-function; Cardiovascular-system-disorders
Contact
ME Andrew, Biostatistics and Epidemiology Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevent, MS 4050, 1095 Willowdale Rd, Morgantown, WV 26505-2888
CODEN
PMEAE3
Publication Date
20071001
Document Type
Journal Article
Fiscal Year
2008
NTIS Accession No.
NTIS Price
Issue of Publication
10
ISSN
0967-3334
NIOSH Division
HELD
Priority Area
Services: Public Safety
Source Name
Physiological Measurement
State
WV; NY
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