Acute respiratory effects of particles: mass or number?

To determine whether associations might be found, in patients with chronic airflow obstruction, between symptoms, peak flow rate (PEF), and particle mass and numbers, and to assess which measure was most closely associated with changes in health. Epidemiological studies have shown associations between particulate air pollution and cardiovascular and respiratory disease, and it has been proposed that these may be mediated by particles of nm size (ultrafine).

Relations were investigated between symptom scores, PEF, and bronchodilator use in 44 patients aged > or =50 years with chronic obstructive pulmonary disease, and daily measurements of both mass of ambient particles of aerodynamic diameter less than 10 microm (PM10) and numbers of ultrafine particles (<100 nm), allowing for meteorological variables. Symptom scores, bronchodilator use, and PEF were recorded daily for 3 months. Counts of ultrafine particles were made by the TSI model 3934 scanning mobility particle sizer (SMPS) and PM10 measurements by the tapered element oscillating microbalance (TEOM).

Ultrafine particle counts indoors and outdoors were significantly correlated, those indoors being about half of those outdoors. No associations were found between actual PEF and PM10 or ultrafine particles. However, there was a 19% increase in the rate of 10% decrements in daytime PEF with increases in PM10 from 10 to 20 microg/m(3) which was of borderline significance (p=0.05). A change in PM10 from 10 to 20 microg/m(3) was significantly associated with a 14% increase in the rate of high scores of shortness of breath (p=0.003). A similar change in PM10 as a moving average of the same day and 2 previous days was associated with a 31% increase in the rate of high scores for cough (p=0.02). Cough symptoms were also associated with lower temperatures (p=0.02). Higher use of medicines was also associated with higher PM10, but the increases were very small in clinical terms.

Evidence was not found to support the hypothesis that the component of particulate pollution responsible for effects on respiratory symptoms or function resides in the fraction below 100 nm diameter. The consistent associations between symptoms and PM10 suggest that a contribution of the coarser fraction should not be dismissed. Further studies will be needed before the conclusions of this specific project may be generalised.