Short-term metal particulate exposures decrease cardiac acceleration and deceleration capacities in welders: a repeated-measures panel study

OBJECTIVE: Acceleration (AC) and deceleration (DC) capacities measure heart rate variability during speeding up and slowing down of the heart, respectively. We investigated associations between AC and DC with occupational short-term metal PM(2.5) exposures. METHODS: A panel of 48 male welders had particulate matter less than 2.5 microns in diameter (PM(2.5)) exposure measurements over 4–6 h repeated over 5 sampling periods between January 2010 and June 2012. We simultaneously obtained continuous recordings of digital ECG using a Holter monitor. We analysed ECG data in the time domain to obtain hourly AC and DC. Linear mixed models were used to assess the associations between hourly PM(2.5) exposure and each of hourly AC and DC, controlling for age, smoking status, active smoking, exposure to secondhand smoke, season/time of day when ECG reading was obtained and baseline AC or DC. We also ran lagged exposure response models for each successive hour up to 3 h after onset of exposure. RESULTS: Mean (SD) shift PM(2.5) exposure during welding was 0.47 (0.43) mg/m(3). Significant exposure–response associations were found for AC and DC with increased PM(2.5) exposure. In our adjusted models without any lag between exposure and response, a 1 mg/m(3) increase of PM(2.5) was associated with a decrease of 1.46 (95% CI 1.00 to 1.92) ms in AC and a decrease of 1.00 (95% CI 0.53 to 1.46) ms in DC. The effect of PM(2.5) on AC and DC was maximal immediately postexposure and lasted 1 h following exposure. CONCLUSIONS: There are short-term effects of metal particulates on AC and DC.