title: Ambient temperature and biomarkers of heart failure: a repeated measures analysis.
abstract: BACKGROUND
  Extreme temperatures have been associated with hospitalization and death among individuals with heart failure, but few studies have explored the underlying mechanisms.
  
  
  OBJECTIVE
  We hypothesized that outdoor temperature in the Boston, Massachusetts, area (1- to 4-day moving averages) would be associated with higher levels of biomarkers of inflammation and myocyte injury in a repeated-measures study of individuals with stable heart failure.
  
  
  METHODS
  We analyzed data from a completed clinical trial that randomized 100 patients to 12 weeks of tai chi classes or to time-matched education control. B-type natriuretic peptide (BNP), C-reactive protein (CRP), and tumor necrosis factor (TNF) were measured at baseline, 6 weeks, and 12 weeks. Endothelin-1 was measured at baseline and 12 weeks. We used fixed effects models to evaluate associations with measures of temperature that were adjusted for time-varying covariates.
  
  
  RESULTS
  Higher apparent temperature was associated with higher levels of BNP beginning with 2-day moving averages and reached statistical significance for 3- and 4-day moving averages. CRP results followed a similar pattern but were delayed by 1 day. A 5°C change in 3- and 4-day moving averages of apparent temperature was associated with 11.3% [95% confidence interval (CI): 1.1, 22.5; p = 0.03) and 11.4% (95% CI: 1.2, 22.5; p = 0.03) higher BNP. A 5°C change in the 4-day moving average of apparent temperature was associated with 21.6% (95% CI: 2.5, 44.2; p = 0.03) higher CRP. No clear associations with TNF or endothelin-1 were observed.
  
  
  CONCLUSIONS
  Among patients undergoing treatment for heart failure, we observed positive associations between temperature and both BNP and CRP-predictors of heart failure prognosis and severity.
authors.affiliation: Cardiovascular Epidemiology Research Unit, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215, USA. ewilker@bidmc.harvard.edu
authors.forename: Elissa H
authors.initials: EH
authors.lastname: Wilker
authors.forename: Gloria
authors.initials: G
authors.lastname: Yeh
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Wellenius
authors.forename: Roger B
authors.initials: RB
authors.lastname: Davis
authors.forename: Russell S
authors.initials: RS
authors.lastname: Phillips
authors.forename: Murray A
authors.initials: MA
authors.lastname: Mittleman
mesh_terms: D000368:Aged; D015415:Biomarkers / Q000378:metabolism; D001900:Boston; D002097:C-Reactive Protein / Q000378:metabolism*; D016022:Case-Control Studies; D005260:Female; D006333:Heart Failure / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D020097:Natriuretic Peptide, Brain / Q000097:blood*; D026302:Tai Ji; D013696:Temperature; D014409:Tumor Necrosis Factor-alpha / Q000097:blood*
chemical_list: D015415:Biomarkers; D014409:Tumor Necrosis Factor-alpha; D020097:Natriuretic Peptide, Brain; D002097:C-Reactive Protein