title: Ambient pollution and heart rate variability.
abstract: BACKGROUND
  We investigated associations between ambient pollution levels and cardiovascular function in a repeated measures study including 163 observations on twenty-one 53- to 87-year-old active Boston residents observed up to 12 times from June to September 1997. Particles with aerodynamic diameter </=2.5 microm (PM(2.5)) were measured continuously using a tapered element oscillating microbalance.
  
  
  RESULTS
  The protocol involved 25 minutes per week of continuous Holter ECG monitoring, including 5 minutes of rest, 5 minutes of standing, 5 minutes of exercise outdoors, 5 minutes of recovery, and 20 cycles of slow breathing. Heart rate variability (HRV) was assessed through time domain variables: the standard deviation of normal RR intervals (SDNN) and the square root of the mean of the squared differences between adjacent normal RR intervals (r-MSSD). Mean 4-hour PM(2.5) levels ranged from 3 to 49 microg/m(3); 1-hour ozone levels ranged from 1 to 77 ppb. In multivariate analyses, significantly less HRV (SDNN and r-MSSD) was associated with elevated PM(2.5). During slow breathing, a reduction in r-MSSD of 6.1 ms was associated with an interquartile (14.3 microg/m(3)) increase in PM(2.5) during the hour of and the 3 hours previous to the Holter session (P=0.006). During slow breathing, a multiple pollution model was associated with a reduction in r-MSSD of 5.4 ms (P=0.02) and 5.5 ms (P=0.03) for interquartile changes in PM(2.5) and ozone, respectively, resulting in a combined effect equivalent to a 33% reduction in the mean r-MSSD.
  
  
  CONCLUSIONS
  Particle and ozone exposure may decrease vagal tone, resulting in reduced HRV.
authors.affiliation: Channing Laboratory, Brigham and Women's Hospital and the Harvard Medical School, Boston, MA 02115-5804, USA. redrg@gauss.bwh.harvard.edu
authors.forename: D R
authors.initials: DR
authors.lastname: Gold
authors.forename: A
authors.initials: A
authors.lastname: Litonjua
authors.forename: J
authors.initials: J
authors.lastname: Schwartz
authors.forename: E
authors.initials: E
authors.lastname: Lovett
authors.forename: A
authors.initials: A
authors.lastname: Larson
authors.forename: B
authors.initials: B
authors.lastname: Nearing
authors.forename: G
authors.initials: G
authors.lastname: Allen
authors.forename: M
authors.initials: M
authors.lastname: Verrier
authors.forename: R
authors.initials: R
authors.lastname: Cherry
authors.forename: R
authors.initials: R
authors.lastname: Verrier
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000397:Air Pollution; D015716:Electrocardiography, Ambulatory; D015444:Exercise / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010126:Ozone / Q000032:analysis; D010316:Particle Size; D012016:Reference Values; D012119:Respiration; D013997:Time Factors
chemical_list: D010126:Ozone