Increased plasma viscosity during an air pollution episode: A link to mortality?

Background Air pollution episodes have been consistently associated with increased mortality, and most strikingly with mortality due to cardiovascular disease. One hypothesis to explain this association is that inflammation of the peripheral airways caused by pollution might increase blood coagulability. We have tested this hypothesis in a cross-sectional study by comparing measurements of plasma viscosity during a severe episode of air pollution during 1985 with those made on less polluted days. Methods Plasma viscosity was measured as part of the MONICA Augsburg survey during the winter of 1984-85 in 3256 randomly selected men and women aged 25-64 years. Daily mean concentrations of air pollutants and meteorological variables were measured in Augsburg as part of the automated Bavarian air-quality network. We compared measurements of plasma viscosity made in 324 people who attended for screening during the pollution episode and in 2932 people screened during the remainder of the survey period. Findings In January, 1985, high concentrations of sulphur dioxide (mean 200 mu g/m(3)) and total suspended particles (mean 98 mu g/m(3)) were recorded during a 13-day period in Augsburg. In men, the odds ratio for plasma viscosity above the 95th percentile of the distribution (1.38 mPa s) was 3.6 (95% CI 1.6-8.1) comparing measurements during the air pollution episode with non-episode measurements after adjustment for cardiovascular risk factors and meteorological variables. The corresponding odds ratio for women (95th percentile of plasma viscosity 1.37 mPa s) was 2.3 (1.0-5.3). High concentrations of carbon monoxide were also associated with increased plasma viscosity in women. Interpretation During the 1985 air pollution episode, an increased risk of extreme values of plasma viscosity was observed in both men and women. Altered blood rheology due to inflammatory processes in the lung that induce an acute-phase reaction might therefore be part of the pathological mechanisms linking air pollution to mortality.