Acute respiratory effects of particles: mass or number?

Objectives-To determine whether associations might be found, in patients wi th chronic airflow obstruction, between symptoms, peak flow rate (PEF), and particle mass and numbers, and to assess which measure was most closely as sociated with changes in health. Epidemiological studies have shown associa tions between particulate air pollution and cardiovascular and respiratory disease, and if has been proposed that these may be mediated by particles o f nm size (ultrafine). Methods-Relations were investigated between symptom scores, PEF, and bronch odilator use in 44 patients aged greater than or equal to 50 years with chr onic obstructive pulmonary disease, and daily measurements of both mass of ambient particles of aerodynamic diameter less than 10 mum (PM10) and numbe rs of ultrafine particles (<100 nm), allowing for meteorological variables. Symptom scores, bronchodilator use, and PEF were recorded daily for 3 mont hs. 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). Results-Ultrafine particle counts indoors and outdoors were significantly c orrelated, those indoors being about half of those outdoors. No association s were found between actual PEF and PM10 or ultrafine particles. However, t here was a 19% increase in the rate of 10% decrements in daytime PEF with i ncreases in PM10 from 10 to 20 <mu>g/m(3) which was of borderline significa nce (p=0.05). A change in PM10 from 10 to 20 mug/m(3) was significantly ass ociated with a 14% increase in the rate of high scores of shortness of brea th (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 t emperatures (p=0.02). Higher use of medicines was also associated with high er PM10, but the increases were very small in clinical terms. Conclusions-Evidence was not found to support the hypothesis that the compo nent of particulate pollution responsible for effects on respiratory sympto ms or function resides in the fraction below 100 nm diameter. The consisten t associations between symptoms. and PM10 suggest that a contribution of th e coarser fraction should not be dismissed. Further studies will be needed before the conclusions of this specific project may be generalised.