The significance of an across-shift decrease in vital capacity--a re-analysis of a study on subjects exposed to...

Occupational exposure to diesel exhaust may develop acute as well as chronic lung function impairment. In this study, data from an earlier study on a group of subjects working at tunnel construction site were analyzed. The aim of the analysis was to examine the significance of an across-shift decrease in vital capacity with concern to other lung physiological measurements. There were no statistically significant differences, either in the average age, time of employment, vital capacity before a working shift after two days of no exposure, or the distributions of smoking habits and respiratory symptoms, between the eight workers who had an across-shift decrease in vital capacity and the five workers who had not. Subjects with an across-shift decrease in vital capacity had a significantly greater across-shift decrease in residual volume and total lung capacity than subjects without an across-shift decrease in vital capacity. The pathophysiological mechanisms for this across-shift decrease in residual volume is not fully understood. However, an altered defence mechanism in the lung may play a role for a prolonged retention time for the particles in the inhaled diesel exhaust, resulting in the across-shift decrease in residual volume. The results thus suggest that measurements of across-shift vital capacity is of importance in identifying susceptible subjects with occupational exposure to diesel exhaust.