Central adiposity and subclinical cardiovascular disease in police officers

Given the associations between obesity and cardiovascular disease (CVD), we evaluated a related but less well-established association between waist circumference and brachial artery reactivity (BAR), a functional measurement of subclinical CVD, where lower levels indicate dysfunction. Regression models examined trends in mean BAR across waist circumference tertiles in police officers, a high-stress occupational group with increased risk for CVD. Mean BAR decreased across increasing waist tertiles among men, but not women, and this association was stronger among officers who consumed more alcohol. Larger waist circumference may be associated with lower BAR, providing an opportunity for intervention prior to disease development.

Cortisol patterns and brachial artery reactivity in a high stress environment

Chronic stress can result in frequent or persistent challenges of the hypothalamic-pituitary-adrenal (HPA) axis resulting in abnormal cortisol patterns and increased risk for cardiovascular disease (CVD). Police work is an environment replete with stress. The present article describes associations between cortisol, a biomarker of stress, and brachial artery flow mediated dilation (FMD) in police officers. A random sample stratified on gender (n=100, 33% women) was generated from officers in a mid-sized urban department. Four salivary cortisol parameters were derived: after awakening, following a standardized high protein meal challenge, during the entire day, and after a dexamethasone suppression test. Continuous scan B-Mode ultrasound was used to measure percent change in brachial artery FMD following occlusion and release. Elevated cortisol secretion after awakening was significantly associated with impaired FMD in women, reflected by an inverse trend. Adjustment for age, smoking, and alcohol consumption did not appreciably alter this trend. A similar result was not evident among male officers. Responses of other cortisol challenges to the HPA axis were not associated with FMD. In conclusion, increased cortisol secretion after awakening was independently associated with impaired FMD in female police officers only, indicating a possible link between HPA axis stress response and subclinical CVD. However, because associations were not found with other cortisol parameters and were not evident in male officers, replication of these findings with a prospective study design may be warranted.

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

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.