Effect of exercise on deposition and subsequent retention of inhaled particles

To investigate the effect of exercise and its associated increase in ventilation on the deposition and subsequent retention of inhaled particles, we measured the fractional and regional lung deposition of a radioactively tagged ((99m)Tc) monodisperse aerosol (2.6 μm mass median aerodynamic diam) in normal human subjects at rest and while exercising on a bicycle ergometer. Breath-by-breath deposition fraction (DF) was measured throughout the aerosol exposures by Tyndallometry. Following each exposure gamma camera analysis was used to 1) determine the regional distribution of deposited particles and 2) monitor lung retention for 2.5 h and again at 24 h. We found that DF was unchanged between ventilation at rest (6-10 l/min) and exercise (32-46 l/min). Even though mouth deposition was enhanced with exercise, it was not large enough to produce a significant difference in the deposition fraction of the lung (DF(L)) between resting and exercise exposures. The central-to-peripheral distribution of deposited aerosol was larger for the exercise vs. resting exposure, reflecting a shift of particle deposition to more central bronchial airways. Apical-to-basal distribution was not different for the two exposures. Retention at 2.5 h and 24 h (R(24)) was reduced following the exercise vs. the resting exposure, consistent with greater bronchial deposition during exercise. The product of DF(L) and R(24) gave a measure of fractional burden at 24 h (B(24)), i.e., the fraction of inhaled aerosol residing in the lungs 24 h after exposure. B(24) was not significantly different between rest and exercise exposures. Therefore, total lung burden, i.e., B(24) times the amount of aerosol inhaled, for this particle size increases directly with the increased ventilation of exercise. Finally, for both rest and exercise exposures we found significant variability in B(24) between subjects. These findings may be important in understanding pulmonary toxicity associated with inhaled particles.