Day-to-day changes in ventilatory function in relation to the environment: Part II. Peak expiratory flow values

Abstract Measurements of peak expiratory flow have been made on four normal subjects on each working day for 5 years. Although there was no clear relationship between day-to-day changes in peak flow and evironmental factors, analysis of the results over the whole period showed small seasonal variations for each subject, with lower values on the colder, more polluted days in winter. A gradual increase rather than the decrease expected with age was found during the 5 years of the study. Multiple regression analyses on the combined results for the four subjects showed that after removing the trend with time the environmental factor explaining the largest proportion of the residual variance was the concentration of sulphur dioxide. The decrease in peak flow corresponding with a large increase in sulphur dioxide concentration, however, was small, and much of the day-to-day variation in peak flow was due to factors other than the concentrations of smoke or sulphur dioxide, temperature, or relative humidity. Reductions in peak flow were often associated with respiratory infections, and, as in the parallel study of spirometric measurements, the possibility that pollution had indirect effects on ventilatory function by affecting the course of respiratory infections was considered.