Mosuk Chow

Test–retest reliability of pulse amplitude tonometry measures of vascular endothelial function: Implications for clinical trial design

Endothelial dysfunction is an important outcome for assessing vascular health in intervention studies. However, reliability of the standard non-invasive method (flow-mediated dilation) is a significant challenge for clinical applications and multicenter trials. We evaluated the repeatability of pulse amplitude tonometry (PAT) to measure change in pulse wave amplitude during reactive hyperemia (Itamar Medical Ltd, Caesarea, Israel). Twenty healthy adults completed two PAT tests (mean interval = 19.5 days) under standardized conditions. PAT-derived measures of endothelial function (reactive hyperemia index, RHI) and arterial stiffness (augmentation index, AI) showed strong repeatability (intra-class correlations = 0.74 and 0.83, respectively). To guide future research, we also analyzed sample size requirements for a range of effect sizes. A crossover design powered at 0.90 requires 28 participants to detect a 15% change in RHI. Our study is the first to show that PAT measurements are repeatable in adults over an interval greater than 1 week.

Effects of Dairy Products on Intracellular Calcium and Blood Pressure in Adults with Essential Hypertension

Background: Consumption of dairy foods has been associated with lower blood pressure in certain populations. Objective: This study examined the effects of dairy foods on blood pressure (BP) and intracellular calcium ((Ca)i) and the dependence of BP changes on changes in (Ca)i. Design: Twenty-three stage 1 hypertensive adults were fed the following 3 experimental diets (5 wk each) in a randomized cross-over design study; a dairy-rich, high fruits and vegetables diet (D-F&V; 30% fat, 7% saturated fat (SFA), 3.4 servings/d dairy), a high fruits and vegetables diet (F&V; 30% fat, 7% SFA, 0.4 servings/d dairy), and an average Western diet (control; 36% fat, 15% SFA, 0.4 servings/d dairy). Systolic (SBP) and diastolic (DBP) BP, calcium regulatory hormones, and erythrocyte (Ca)i were determined. Results: SBP and DBP were significantly reduced by ∼2 mm Hg following both D-F&V and F&V diets vs. the control (P < 0.05). The D-F&V diet significantly lowered 1,25-dihydroxyvitaminD compared with the F&V and control diets (P < 0.01). Serum calcium, parathyroid hormone, calcitonin, and renin activity were unchanged. The D-F&V diet lowered (Ca)i vs. the other two diets (P < 0.01), and this change correlated with the fall in DBP (r = 0.52, P < 0.05). Subjects who responded to the D-F&V diet by significantly reducing (Ca)i exhibited significantly greater net decreases in DBP on the D-F&V vs. the F&V (−2.8 ± 1.0 mm Hg) and control diets (−5.4 ±1.0 mm Hg; diet × group interaction, P < 0.02). Conclusion: Consumption of dairy foods beneficially affects (Ca)i, resulting in improved BP in a subgroup defined by (Ca)i response.

Responses of lean and obese boys to repeated summer exercise in the heat bouts.

PURPOSE To determine the degree of natural acclimatization and artificially induced acclimation-related changes during repeated exercise in the heat bouts in seven lean and seven obese 9- to 12-yr-old boys during summer months. METHODS Beginning at random times during the summer, subjects underwent a 70-min exercise (30% VO(2max)) in the heat exposure (38 degrees C, 50% relative humidity) on six separate days. RESULTS On day 1, obese children were less naturally acclimatized as indicated by significantly higher baseline core temperatures (T(c)) (obese = 37.62 +/- 0.06 vs lean = 37.41 +/- 0.06; P < 0.004). By day 6 versus day 1, significant reductions in baseline T(c) were evident in both groups (obese = 37.41 +/- 0.04 vs lean = 37.18 +/- 0.04; both P < 0.05). Baseline T(c) in obese subjects by day 6 was similar to that of lean subjects on day 1. Daily reductions in exercise T(c) were evident in both groups (final exercising T(c) day 1 vs day 6: obese = 38.15 +/- 0.05 vs 37.89 +/- 0.05; lean = 38.17 +/- 0.09 vs 37.72 +/- 0.06 degrees C; both P < 0.001), occurring at a significantly slower rate in obese subjects (final exercise T(c) day 6 - day 1: obese vs lean = -0.26 +/- 0.04 vs -0.45 +/- 0.08 degrees C; P < 0.05). Significant reductions in exercising heart rate (HR) occurred in the lean but not the obese subjects by day 6 (final exercising HR day 1 vs day 6: obese = 132 +/- 3 vs 131 +/- 3, P > 0.05; lean = 138 +/- 3 vs 127 +/- 3 bpm; P < 0.001). CONCLUSIONS During summer months, obese children are less naturally heat-acclimatized and subsequently acclimate at a slower rate.

An efficient algorithm for estimating the parameters of superimposed exponential signals

An efficient computational algorithm is proposed for estimating the parameters of undamped exponential signals, when the parameters are complex valued. Such data arise in several areas of applications including telecommunications, radio location of objects, seismic signal processing and computer assisted medical diagnostics. It is observed that the proposed estimators are consistent and the dispersion matrix of these estimators is asymptotically the same as that of the least squares estimators. Moreover, the asymptotic variances of the proposed estimators attain the Cramer-Rao lower bounds, when the errors are Gaussian.

Endothelial function, arterial stiffness and adherence to the 2010 Dietary Guidelines for Americans: a cross-sectional analysis

Endothelial dysfunction and arterial stiffness are early predictors of CVD. Intervention studies have suggested that diet is related to vascular health, but most prior studies have tested individual foods or nutrients and relied on small samples of younger adults. The purpose of the present study was to examine the relationships between adherence to the 2010 Dietary Guidelines for Americans and vascular health in a large cross-sectional analysis. In 5887 adults in the Framingham Heart Study Offspring and Third Generation cohorts, diet quality was quantified with the 2010 Dietary Guidelines Adherence Index (DGAI-2010). Endothelial function was assessed via brachial artery ultrasound and arterial stiffness via arterial tonometry. In age-, sex- and cohort-adjusted analyses, a higher DGAI-2010 score (greater adherence) was modestly associated with a lower resting flow velocity, hyperaemic response, mean arterial pressure, carotid-femoral pulse wave velocity (PWV), and augmentation index, but not associated with resting arterial diameter or flow-mediated dilation (FMD). In multivariable models adjusting for cardiovascular risk factors, only the association of a higher DGAI-2010 score with a lower baseline flow velocity and augmentation index persisted (β = - 0·002, P= 0·003 and β = - 0·05 ± 0·02, P< 0·001, respectively). Age-stratified multivariate-adjusted analyses suggested that the relationship of higher DGAI-2010 scores with lower mean arterial pressure, PWV and augmentation index was more pronounced among adults younger than 50 years. Better adherence to the 2010 Dietary Guidelines for Americans, particularly in younger adults, is associated with a lower peripheral blood flow velocity and arterial wave reflection, but not FMD. The present results suggest a link between adherence to the Dietary Guidelines and favourable vascular health.

Changes in Lumbar Disk Morphology Associated With Prolonged Sitting Assessed by Magnetic Resonance Imaging

To determine what if any changes occur to the lumbar disks in the spine after prolonged sitting with and without intermittent breaks during a 4‐hour period.

An algorithm for efficient estimation of superimposed exponential signals

A computational algorithm is given for obtaining asymptotically efficient estimates of the unknown complex amplitudes and frequencies in a superimposed exponential model for signals. It is shown that the variance covariance matrix of these estimates is asymptotically the same as that for the maximum likelihood estimates, and thus the lower bound can be obtained.<<ETX>>

Selecting the normal population with the best regression value - a Bayesian approach

Abstract For the intra-class regression (multiple slopes) model, much attention has been given to the estimation and hypothesis testing problems concerning the parameters. However, few papers in the literature address the practical question of selecting the population with the largest regression value. The existing classical ranking and selection procedure employs a rule which always selects the population associated with the largest sample regression value computed by the least-squares method. Whereas the rule is reasonable if all variances of the sample estimates are equal, it may not be desirable when some of the variances are different because the rule ignores the unequal variances associated with the estimates. We propose a Bayesian approach to the selection problem by calculating, for a given value of the covariate, the posterior probabilities of each population mean being the largest. In the two examples considered in the paper, it is observed that there are occasions when the two largest sample regression values are close together and the larger one is associated with a larger variance, the population with the smaller sample regression value can be selected as the best population by our Bayesian procedure. Although calculation of the posterior probabilities may involve high dimensional numerical integration, the required computation can be handled efficiently by some Monte Carlo integration methods as described in the paper.

A note on sequential estimation of the size of a population under a general loss function

In estimating the size of a finite population under a sequential sampling scheme where the stopping rule is to stop sampling when a fixed number of marked items are observed, it has been shown that the maximum likelihood estimator (MLE) does not have an explicit expression and is inadmissible under weighted-squared-error loss. This note shows that the MLE is inadmissible under a very general class of loss functions. Also, a class of estimators which dominate the MLE is constructed and given in the article. Finally, an optimal class of estimators for some commonly used loss functions will be derived.

The Challenges in Developing an Online Applied Statistics Program: Lessons Learned at Penn State University

Numerous professional fields have an increasing need for individuals trained in statistics and other quantitative analysis techniques. Today there exists great potential to fulfill this need by providing opportunities through online learning. However, to provide a high-quality education for returning adult professionals seeking advanced degrees in applied statistics online, many challenges need to be overcome. Based on our experience developing Penn State University’s online program in applied statistics, we discuss the evolution of the program’s curriculum, recruitment and development of online faculty, and meeting the requirements of students as important areas that require consideration in the development of an online program. We also highlight program evaluation strategies employed to ensure innovation and improvement in online education as cornerstones to a program’s success.