Keith M. Diaz

Fitbit®: An accurate and reliable device for wireless physical activity tracking.

Background: A smart accelerometer named the Fitbit has recently been introduced in the consumer market as a physical activity monitor that can interface wirelessly with mobile phones and a manufacturer-established website to allow consumers to track their physical activity in real-time. The purpose of this study was to examine the validity and reliability of the Fitbit for measuring energy expenditure during treadmill walking and running relative to energy expenditure assessed by indirect calorimetry. Methods: A total of 23 healthy adults (10 males, mean age: 30.6 ± 7.9 years; mean BMI: 24.7 ± 3.0 kg/m2) completed a four-phase treadmill exercise protocol (6 min/phase) under laboratory conditions. The protocol consisted of walking at slow (1.9 mph), moderate (3.0 mph), and brisk (4.0 mph) paces; and jogging (5.2 mph). Participants were fitted with three hip-based Fitbit One devices (two on right, one on left hip) and two wrist-based Fitbit Flex devices (one on right and left wrist). Energy expenditure was ...

Visit-to-Visit Variability of Blood Pressure and Cardiovascular Disease and All-Cause Mortality A Systematic Review and Meta-Analysis

Visit-to-visit variability of blood pressure (BP) has been associated with cardiovascular disease (CVD) and mortality in some but not all studies. We conducted a systematic review and meta-analysis to examine the association between visit-to-visit variability of BP and CVD and all-cause mortality. Medical databases were searched through June 4, 2014, for studies meeting the following eligibility criteria: adult participants; BP measurements at ≥3 visits; follow-up for CVD, coronary heart disease, stroke, or mortality outcomes; events confirmed via database, death certificate, or event ascertainment committee; and adjustment for confounders. Data were extracted by 2 reviewers and pooled using a random-effects model. Overall, 8870 abstracts were identified of which 37 studies, representing 41 separate cohorts, met inclusion criteria. Across studies, visit-to-visit variability of systolic BP and diastolic BP showed significant associations with outcomes in 181 of 312 (58.0%) and 61 of 188 (32.4%) analyses, respectively. Few studies provided sufficient data for pooling risk estimates. For each 5 mm Hg higher SD of systolic BP, the pooled hazard ratio for stroke across 7 cohorts was 1.17 (95% confidence interval [CI], 1.07–1.28), for coronary heart disease across 4 cohorts was 1.27 (95% CI, 1.07–1.51), for CVD across 5 cohorts was 1.12 (95% CI, 0.98–1.28), for CVD mortality across 5 cohorts was 1.22 (95% CI, 1.09–1.35), and for all-cause mortality across 4 cohorts was 1.20 (95% CI, 1.05–1.36). In summary, modest associations between visit-to-visit variability of BP and CVD and all-cause mortality are present in published studies. However, these findings are limited by the small amount of data available for meta-analysis.

Relationship of visit-to-visit and ambulatory blood pressure variability to vascular function in African Americans.

Visit-to-visit clinic blood pressure variability (BPV) and 24-h BPV have both been identified as independent risk factors for cardiovascular (CV) morbidity and mortality; however, the mechanisms contributing to the increased CV risk as yet are unclear. The purpose of this study was to assess the relationship between BPV and endothelial function in a cohort of putatively healthy African Americans. A total of 36 African Americans who were sedentary, non-diabetic, non-smoking, free of CV and renal disease and not on antihypertensive medication followed an American Heart Association low fat, low salt diet for 6 weeks. Upon completion of the 6-week dietary stabilization period, participants underwent 24-h ambulatory BP monitoring and had their office blood pressure (BP) measured on 3 separate days. Right brachial artery diameter was assessed at rest, during reactive hyperemia (flow-mediated vasodilation: FMD), and after nitroglycerin administration (nitroglycerin-mediated vasodilation: NMD). Participants classified as having decreased endothelial function according to either %FMD or the FMD/NMD ratio had significantly higher 24-h BPV and a trend for higher visit-to-visit BPV when compared with participants with normal endothelial function. Continuous variable analyses revealed a significant positive association between NMD and 24-h diastolic BPV (DBPV). Visit-to-visit systolic BPV (SBPV), 24-h SBPV and 24-h DBPV were all negatively associated with the FMD/NMD ratio. All relationships remained significant after adjustment for age, body mass index and mean BP levels. These results may suggest that BPV is increased in African Americans with decreased endothelial function and is associated with the vascular smooth muscle response to nitric oxide.

Unmasking masked hypertension: prevalence, clinical implications, diagnosis, correlates and future directions

‘Masked hypertension’ is defined as having non-elevated clinic blood pressure (BP) with elevated out-of-clinic average BP, typically determined by ambulatory BP monitoring. Approximately 15–30% of adults with non-elevated clinic BP have masked hypertension. Masked hypertension is associated with increased risks of cardiovascular morbidity and mortality compared with sustained normotension (non-elevated clinic and ambulatory BP), which is similar to or approaching the risk associated with sustained hypertension (elevated clinic and ambulatory BP). The confluence of increased cardiovascular risk and a failure to be diagnosed by the conventional approach of clinic BP measurement makes masked hypertension a significant public health concern. However, many important questions remain. First, the definition of masked hypertension varies across studies. Further, the best approach in the clinical setting to exclude masked hypertension also remains unknown. It is unclear whether home BP monitoring is an adequate substitute for ambulatory BP monitoring in identifying masked hypertension. Few studies have examined the mechanistic pathways that may explain masked hypertension. Finally, scarce data are available on the best approach to treating individuals with masked hypertension. Herein, we review the current literature on masked hypertension including definition, prevalence, clinical implications, special patient populations, correlates, issues related to diagnosis, treatment and areas for future research.

Endothelial activation microparticles and inflammation status improve with exercise training in African Americans

African Americans have the highest prevalence of hypertension in the world which may emanate from their predisposition to heightened endothelial inflammation. The purpose of this study was to determine the effects of a 6-month aerobic exercise training (AEXT) intervention on the inflammatory biomarkers interleukin-10 (IL-10), interleukin-6 (IL-6), and endothelial microparticle (EMP) CD62E+ and endothelial function assessed by flow-mediated dilation (FMD) in African Americans. A secondary purpose was to evaluate whether changes in IL-10, IL-6, or CD62E+ EMPs predicted the change in FMD following the 6-month AEXT intervention. A pre-post design was employed with baseline evaluation including office blood pressure, FMD, fasting blood sampling, and graded exercise testing. Participants engaged in 6 months of AEXT. Following the AEXT intervention, all baseline tests were repeated. FMD significantly increased, CD62E+ EMPs and IL-6 significantly decreased, and IL-10 increased but not significantly following AEXT. Changes in inflammatory biomarkers did not significantly predict the change in FMD. The change in VO2 max significantly predicted the change in IL-10. Based on these results, AEXT may be a viable, nonpharmacological method to improve inflammation status and endothelial function and thereby contribute to risk reduction for cardiovascular disease in African Americans.

Racial Differences in Abnormal Ambulatory Blood Pressure Monitoring Measures: Results From the Coronary Artery Risk Development in Young Adults (CARDIA) Study

BACKGROUND Several ambulatory blood pressure monitoring (ABPM) measures have been associated with increased cardiovascular disease risk independent of clinic blood pressure (BP). African Americans have higher clinic BP compared with Whites but few data are available on racial differences in ABPM measures. METHODS We compared ABPM measures between African American (n = 178) and White (n = 103) participants at the Year 5 Coronary Artery Risk Development in Young Adults study visit. BP was measured during a study visit and the second and third measurements were averaged. ABPM was conducted over the following 24 hours. RESULTS Mean ± SD age of participants was 29.8 ± 3.8 years and 30.8 ± 3.5 years for African Americans and Whites, respectively. Mean daytime systolic BP (SBP) was 3.90 (SD 1.18) mm Hg higher among African Americans compared with Whites (P < 0.001) after age-gender adjustment and 1.71 (SD 1.03) mm Hg higher after multivariable adjustment including mean clinic SBP (P = 0.10). After multivariable adjustment including mean clinic SBP, nighttime SBP was 4.83 (SD 1.11) mm Hg higher among African Americans compared with Whites (P < 0.001). After multivariable adjustment, the African Americans were more likely than Whites to have nocturnal hypertension (prevalence ratio: 2.44, 95% CI: 0.99-6.05) and nondipping (prevalence ratio: 2.50, 95% CI: 1.39-4.48). The prevalence of masked hypertension among African Americans and Whites was 4.4% and 2.1%, respectively, (P = 0.49) and white coat hypertension was 3.3% and 3.9%, respectively (P = 0.99). Twenty-four hour BP variability on ABPM was higher among African Americans compared with Whites. CONCLUSIONS These data suggest racial differences in several ABPM measures exist.

Physical Activity and the Prevention of Hypertension

As the worldwide prevalence of hypertension continues to increase, the primary prevention of hypertension has become an important global public health initiative. Physical activity is commonly recommended as an important lifestyle modification that may aid in the prevention of hypertension. Recent epidemiologic evidence has demonstrated a consistent, temporal, and dose-dependent relationship between physical activity and the development of hypertension. Experimental evidence from interventional studies has further confirmed a relationship between physical activity and hypertension as the favorable effects of exercise on blood pressure reduction have been well characterized in recent years. Despite the available evidence strongly supporting a role for physical activity in the prevention of hypertension, many unanswered questions regarding the protective benefits of physical activity in high-risk individuals, the factors that may moderate the relationship between physical activity and hypertension, and the optimal prescription for hypertension prevention remain. We review the most recent evidence for the role of physical activity in the prevention of hypertension and discuss recent studies that have sought to address these unanswered questions.

Prevalence, Determinants, and Clinical Significance of Masked Hypertension in a Population-Based Sample of African Americans: The Jackson Heart Study.

BACKGROUND The disproportionate rates of cardiovascular disease in African Americans may, in part, be due to suboptimal assessment of blood pressure (BP) with clinic BP measurements alone. To date, however, the prevalence of masked hypertension in African Americans has not been fully delineated. The purpose of this study was to evaluate masked hypertension prevalence in a large population-based sample of African Americans and examine its determinants and association with indices of target organ damage (TOD). METHODS Clinic and 24-hour ambulatory BP monitoring were conducted in 972 African Americans enrolled in the Jackson Heart Study. Common carotid artery intima-media thickness, left ventricular mass index, and the urinary albumin:creatinine excretion ratio were evaluated as indices of TOD. RESULTS Masked hypertension prevalence was 25.9% in the overall sample and 34.4% in participants with normal clinic BP. All indices of TOD were significantly higher in masked hypertensives compared to sustained normotensives and were similar between masked hypertensives and sustained hypertensives. Male gender, smoking, diabetes, and antihypertensive medication use were independent determinants of masked hypertension in multivariate analyses. CONCLUSIONS In this population-based cohort of African Americans, approximately one-third of participants with presumably normal clinic BP had masked hypertension when BP was assessed in their daily environment. Masked hypertension was accompanied by a greater degree of TOD in this cohort.

Endothelial-Dependent Flow-Mediated Dilation in African Americans With Masked-Hypertension

BACKGROUND Office-blood pressure (BP) measurements alone overlook a significant number of individuals with masked-hypertension (office-BP: 120/80-139/89 mm Hg and 24-h ambulatory BP monitoring (ABPM) daytime ≥135/85 mm Hg or night-time ≥120/70 mm Hg). Diminished endothelial function contributes to the pathogenesis of hypertension. To better understand the pathophysiology involved in the increased cardiovascular (CV) disease risk associated with masked-hypertension, we estimated the occurrence, assessed the endothelial function, compared plasma levels of inflammatory markers, white blood cell count (WBC count), tumor necrosis factor-α (TNF-α), and high sensitivity C-reactive protein (hsCRP) and examined the possible relationship between endothelial function and inflammatory markers in apparently healthy prehypertensive (office-BP: 120/80-139/89 mm Hg) African Americans. METHODS Fifty African Americans who were sedentary, nondiabetic, nonsmoking, devoid of CV disease were recruited. Office-BP was measured according to JNC-7 guidelines to identify prehypertensives in whom ABPM was then assessed. Fasting plasma samples were assayed for inflammatory markers. Brachial artery flow-mediated dilation (FMD) at rest and during reactive hyperemia was measured in a subset of prehypertensives. RESULTS Subjects in the masked-hypertension sub-group had a higher hsCRP (P = 0.04) and diminished endothelial function (P = 0.03) compared to the true-prehypertensive sub-group (office-BP: 120/80-139/89 mm Hg and ABPM: daytime <135/85 mm Hg or night-time <120/70 mm Hg). Regression analysis showed that endothelial function was inversely related to hsCRP amongst the masked-hypertensive sub-group (R(2) = 0.160; P = 0.04). CONCLUSIONS Masked-hypertension was identified in 58% of African Americans which suggests that a masking phenomenon may exist in a sub-group of prehypertensives who also seem to have a diminished endothelial function that could be mediated by an elevated subclinical inflammation leading to the increased CV disease.

Patterns of Sedentary Behavior in US Middle-Age and Older Adults: The REGARDS Study.

PURPOSE The purposes of this study were to examine patterns of objectively measured sedentary behavior in a national cohort of US middle-age and older adults and to determine factors that influence prolonged sedentary behavior. METHODS We studied 8096 participants from the REasons for Geographic and Racial Differences in Stroke (REGARDS) Study, a population-based study of black and white adults 45 yr or older. Seven-day accelerometry was conducted. Prolonged sedentary behavior was defined as accumulating 50% or more of total sedentary time in bouts of 30 min or greater. RESULTS The number of sedentary bouts greater than or equal to 20, 30, 60, and 90 min were 8.8 ± 2.3, 5.5 ± 1.9, 1.9 ± 1.1, and 0.8 ± 0.7 bouts per day, respectively. Sedentary bouts greater than or equal to 20, 30, 60, and 90 min accounted for 60.0% ± 13.9%, 48.0% ± 15.5%, 26.0% ± 15.4%, and 14.2% ± 12.9% of total sedentary time, respectively. Several factors were associated with prolonged sedentary behavior in multivariate-adjusted models (odds ratio [95% confidence interval]): older age (65-74 yr: 1.99 [1.55-2.57]; 75 yr or older: 4.68 [3.61-6.07] vs 45-54 yr), male sex (1.41 [1.28-1.56] vs female), residence in nonstroke belt/buckle region of the United States (stroke belt: 0.87 [0.77-0.98]; stroke buckle: 0.86 [0.77-0.95] vs non-belt/buckle), body mass index (BMI) (overweight: 1.33 [1.18-1.51]; obese: 2.15 [1.89-2.44] vs normal weight), winter (1.18 [1.03-1.35] vs summer), and low amounts of moderate-to-vigorous physical activity (MVPA) [0 min·wk: 2.00 [1.66-2.40] vs ≥150 min·wk). CONCLUSIONS In this sample of US middle-age and older adults, a large proportion of total sedentary time was accumulated in prolonged, uninterrupted bouts of sedentary behavior as almost one-half was accumulated in sedentary bouts greater than or equal to 30 min. Several sociodemographic (age, sex, and BMI), behavioral (MVPA), environmental (region), and seasonal factors are associated with patterns of prolonged sedentary behavior.