9 results on '"LaValley, Michael P."'
Search Results
2. Design of the WHIP-PD study: a phase II, twelve-month, dual-site, randomized controlled trial evaluating the effects of a cognitive-behavioral approach for promoting enhanced walking activity using mobile health technology in people with Parkinson-disease
- Author
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Rawson, Kerri S., Cavanaugh, James T., Colon-Semenza, Cristina, DeAngelis, Tami, Duncan, Ryan P., Fulford, Daniel, LaValley, Michael P., Mazzoni, Pietro, Nordahl, Timothy, Quintiliani, Lisa M., Saint-Hilaire, Marie, Thomas, Cathi A., Earhart, Gammon M., and Ellis, Terry D.
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- 2020
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3. The ACR20 and defining a threshold for response in rheumatic diseases: too much of a good thing
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Felson, David T and LaValley, Michael P
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- 2014
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4. Development of a clinical prediction algorithm for knee osteoarthritis structural progression in a cohort study: value of adding measurement of subchondral bone density.
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LaValley, Michael P., Lo, Grace H., Price, Lori Lyn, Driban, Jeffrey B., Eaton, Charles B., and McAlindon, Timothy E.
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- 2017
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- View/download PDF
5. A comparison of time dependent Cox regression, pooled logistic regression and cross sectional pooling with simulations and an application to the Framingham Heart Study.
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Ngwa, Julius S., Cabral, Howard J., Cheng, Debbie M., Pencina, Michael J., Gagnon, David R., LaValley, Michael P., and Cupples, L. Adrienne
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LOGISTIC regression analysis ,HEART disease diagnosis ,HEART diseases ,THERAPEUTICS ,LIPID metabolism ,MYOCARDIAL infarction diagnosis ,MEDICAL research - Abstract
Background: Typical survival studies follow individuals to an event and measure explanatory variables for that event, sometimes repeatedly over the course of follow up. The Cox regression model has been used widely in the analyses of time to diagnosis or death from disease. The associations between the survival outcome and time dependent measures may be biased unless they are modeled appropriately. Methods: In this paper we explore the Time Dependent Cox Regression Model (TDCM), which quantifies the effect of repeated measures of covariates in the analysis of time to event data. This model is commonly used in biomedical research but sometimes does not explicitly adjust for the times at which time dependent explanatory variables are measured. This approach can yield different estimates of association compared to a model that adjusts for these times. In order to address the question of how different these estimates are from a statistical perspective, we compare the TDCM to Pooled Logistic Regression (PLR) and Cross Sectional Pooling (CSP), considering models that adjust and do not adjust for time in PLR and CSP. Results: In a series of simulations we found that time adjusted CSP provided identical results to the TDCM while the PLR showed larger parameter estimates compared to the time adjusted CSP and the TDCM in scenarios with high event rates. We also observed upwardly biased estimates in the unadjusted CSP and unadjusted PLR methods. The time adjusted PLR had a positive bias in the time dependent Age effect with reduced bias when the event rate is low. The PLR methods showed a negative bias in the Sex effect, a subject level covariate, when compared to the other methods. The Cox models yielded reliable estimates for the Sex effect in all scenarios considered. Conclusions: We conclude that survival analyses that explicitly account in the statistical model for the times at which time dependent covariates are measured provide more reliable estimates compared to unadjusted analyses. We present results from the Framingham Heart Study in which lipid measurements and myocardial infarction data events were collected over a period of 26 years. [ABSTRACT FROM AUTHOR]
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- 2016
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6. Impact of misspecifying the distribution of a prognostic factor on power and sample size for testing treatment interactions in clinical trials.
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Reichmann, William M., LaValley, Michael P., Gagnon, David R., and Losina, Elena
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SAMPLE size (Statistics) , *CLINICAL trials , *TIME-varying systems , *HEALTH outcome assessment , *COMPUTER simulation , *PROGNOSTIC tests , *DISTRIBUTION (Probability theory) , *TREATMENT effectiveness - Abstract
Background: Interaction in clinical trials presents challenges for design and appropriate sample size estimation. Here we considered interaction between treatment assignment and a dichotomous prognostic factor with a continuous outcome. Our objectives were to describe differences in power and sample size requirements across alternative distributions of a prognostic factor and magnitudes of the interaction effect, describe the effect of misspecification of the distribution of the prognostic factor on the power to detect an interaction effect, and discuss and compare three methods of handling the misspecification of the prognostic factor distribution. Methods: We examined the impact of the distribution of the dichotomous prognostic factor on power and sample size for the interaction effect using traditional one-stage sample size calculation. We varied the magnitude of the interaction effect, the distribution of the prognostic factor, and the magnitude and direction of the misspecification of the distribution of the prognostic factor. We compared quota sampling, modified quota sampling, and sample size re-estimation using conditional power as three strategies for ensuring adequate power and type I error in the presence of a misspecification of the prognostic factor distribution. Results: The sample size required to detect an interaction effect with 80% power increases as the distribution of the prognostic factor becomes less balanced. Misspecification such that the actual distribution of the prognostic factor was more skewed than planned led to a decrease in power with the greatest loss in power seen as the distribution of the prognostic factor became less balanced. Quota sampling was able to maintain the empirical power at 80% and the empirical type I error at 5%. The performance of the modified quota sampling procedure was related to the percentage of trials switching the quota sampling scheme. Sample size re-estimation using conditional power was able to improve the empirical power under negative misspecifications (i.e. skewed distributions) but it was not able to reach the target of 80% in all situations. Conclusions: Misspecifying the distribution of a dichotomous prognostic factor can greatly impact power to detect an interaction effect. Modified quota sampling and sample size re-estimation using conditional power improve the power when the distribution of the prognostic factor is misspecified. Quota sampling is simple and can prevent misspecification of the prognostic factor, while maintaining power and type I error. [ABSTRACT FROM AUTHOR]
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- 2013
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7. The influence of pericardial fat upon left ventricular function in obese females: evidence of a site-specific effect.
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Ning Hua, Zhongjing Chen, Phinikaridou, Alkystis, Pham, Tuan, Ye Qiao, LaValley, Michael P., Bigornia, Sherman J., Ruth, Megan R., Apovian, Caroline M., Ruberg, Frederick L., and Hamilton, James A.
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MAGNETIC resonance imaging , *ADIPOSE tissues , *STATISTICAL correlation , *LEFT heart ventricle , *HEART physiology , *RIGHT heart ventricle , *OBESITY , *PERICARDIUM , *REGRESSION analysis , *STATISTICS , *T-test (Statistics) , *BODY mass index , *INTER-observer reliability , *DESCRIPTIVE statistics - Abstract
Background Although increased volume of pericardial fat has been associated with decreased cardiac function, it is unclear whether this association is mediated by systemic overall obesity or direct regional fat interactions. We hypothesized that if local effects dominate, left ventricular (LV) function would be most strongly associated with pericardial fat that surrounds the left rather than the right ventricle (RV). Methods Female obese subjects (n = 60) had cardiovascular magnetic resonance (CMR) scans to obtain measures of LV function and pericardial fat volumes. LV function was obtained using the cine steady state free precession imaging in short axis orientation. The amount of pericardial fat was determined volumetrically by the cardiac gated T1 black blood imaging and normalized to body surface area. Results In this study cohort, LV fat correlated with several LV hemodynamic measurements including cardiac output (r = -0.41, p = 0.001) and stroke volume (r = -0.26, p = 0.05), as well as diastolic functional parameters including peak-early-filling rate (r = -0.38, p = 0.01), early late filling ratio (r = -0.34, p = 0.03), and time to peak-early-filling (r = 0.34, p = 0.03). These correlations remained significant even after adjusting for the body mass index and the blood pressure. However, similar correlations became weakened or even disappeared between RV fat and LV function. LV function was not correlated with systemic plasma factors, such as C-reactive protein (CRP), B-type natriuretic peptide (BNP), Interleukin-6 (IL-6), resistin and adiponectin (all p > 0.05). Conclusions LV hemodynamic and diastolic function was associated more with LV fat as compared to RV or total pericardial fat, but not with systemic inflammatory markers or adipokines. The correlations between LV function and pericardial fat remained significant even after adjusting for systemic factors. These findings suggest a site-specific influence of pericardial fat on LV function, which could imply local secretion of molecules into the underlying tissue or an anatomic effect, both mechanisms meriting future evaluation. [ABSTRACT FROM AUTHOR]
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- 2014
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8. Comparative analysis of the growth and biological activity of a respiratory and atheroma isolate of Chlamydia pneumoniae reveals strain-dependent differences in inflammatory activity and innate immune evasion.
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He X, Liang Y, LaValley MP, Lai J, and Ingalls RR
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- Animals, Cells, Cultured, Chlamydophila Infections microbiology, Chlamydophila pneumoniae classification, Chlamydophila pneumoniae growth & development, Chlamydophila pneumoniae immunology, Disease Models, Animal, Fibroblasts immunology, Fibroblasts microbiology, Humans, Macrophages microbiology, Mice, Inbred C57BL, Chlamydophila Infections pathology, Chlamydophila pneumoniae isolation & purification, Immune Evasion, Immunity, Innate, Macrophages immunology, Plaque, Atherosclerotic microbiology, Respiratory System microbiology
- Abstract
Background: Chlamydia pneumoniae is a common human pathogen that is associated with upper and lower respiratory tract infections. It has also been suggested that C. pneumoniae infection can trigger or promote a number of chronic inflammatory conditions, including asthma and atherosclerosis. Several strains of C. pneumoniae have been isolated from humans and animals, and sequence data demonstrates marked genetic conservation, leaving unanswered the question as to why chronic inflammatory conditions may occur following some respiratory-acquired infections., Methods: C. pneumoniae strains AR39 and AO3 were used in vitro to infect murine bone marrow derived macrophages and L929 fibroblasts, or in vivo to infect C57BL/6 mice via the intranasal route., Results: We undertook a comparative study of a respiratory isolate, AR39, and an atheroma isolate, AO3, to determine if bacterial growth and host responses to infection varied between these two strains. We observed differential growth depending on the host cell type and the growth temperature; however both strains were capable of forming plaques in vitro. The host response to the respiratory isolate was found to be more inflammatory both in vitro, in terms of inflammatory cytokine induction, and in vivo, as measured by clinical response and lung inflammatory markers using a mouse model of respiratory infection., Conclusions: Our data demonstrates that a subset of C. pneumoniae strains is capable of evading host innate immune defenses during the acute respiratory infection. Further studies on the genetic basis for these differences on both the host and pathogen side could enhance our understanding how C. pneumoniae contributes to the development chronic inflammation at local and distant sites.
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- 2015
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9. The influence of pericardial fat upon left ventricular function in obese females: evidence of a site-specific effect.
- Author
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Hua N, Chen Z, Phinikaridou A, Pham T, Qiao Y, LaValley MP, Bigornia SJ, Ruth MR, Apovian CM, Ruberg FL, and Hamilton JA
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- Adipokines blood, Adipose Tissue pathology, Adult, Biomarkers blood, Body Mass Index, Female, Hemodynamics, Humans, Inflammation Mediators blood, Magnetic Resonance Imaging, Cine, Middle Aged, Obesity blood, Obesity diagnosis, Obesity physiopathology, Pericardium pathology, Risk Factors, Ventricular Dysfunction, Left blood, Ventricular Dysfunction, Left diagnosis, Ventricular Dysfunction, Left physiopathology, Ventricular Function, Right, Young Adult, Adipose Tissue physiopathology, Adiposity, Obesity complications, Pericardium physiopathology, Ventricular Dysfunction, Left etiology, Ventricular Function, Left
- Abstract
Background: Although increased volume of pericardial fat has been associated with decreased cardiac function, it is unclear whether this association is mediated by systemic overall obesity or direct regional fat interactions. We hypothesized that if local effects dominate, left ventricular (LV) function would be most strongly associated with pericardial fat that surrounds the left rather than the right ventricle (RV)., Methods: Female obese subjects (n = 60) had cardiovascular magnetic resonance (CMR) scans to obtain measures of LV function and pericardial fat volumes. LV function was obtained using the cine steady state free precession imaging in short axis orientation. The amount of pericardial fat was determined volumetrically by the cardiac gated T1 black blood imaging and normalized to body surface area., Results: In this study cohort, LV fat correlated with several LV hemodynamic measurements including cardiac output (r = -0.41, p = 0.001) and stroke volume (r = -0.26, p = 0.05), as well as diastolic functional parameters including peak-early-filling rate (r = -0.38, p = 0.01), early late filling ratio (r = -0.34, p = 0.03), and time to peak-early-filling (r = 0.34, p = 0.03). These correlations remained significant even after adjusting for the body mass index and the blood pressure. However, similar correlations became weakened or even disappeared between RV fat and LV function. LV function was not correlated with systemic plasma factors, such as C-reactive protein (CRP), B-type natriuretic peptide (BNP), Interleukin-6 (IL-6), resistin and adiponectin (all p > 0.05)., Conclusions: LV hemodynamic and diastolic function was associated more with LV fat as compared to RV or total pericardial fat, but not with systemic inflammatory markers or adipokines. The correlations between LV function and pericardial fat remained significant even after adjusting for systemic factors. These findings suggest a site-specific influence of pericardial fat on LV function, which could imply local secretion of molecules into the underlying tissue or an anatomic effect, both mechanisms meriting future evaluation.
- Published
- 2014
- Full Text
- View/download PDF
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