Ambient pollution and heart rate variability

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

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.

Particle and ozone exposure may decrease vagal tone, resulting in reduced HRV.