Pulmonary deposition of inhaled particles with diameters in the range 2.5 to 7.5 micron

Monodisperse polystyrene particles of 2.5,5 and 7.5 micron diameter, labelled with technetium-99m, were administered to mouth-breathing subjects respiring at a rate of 10 breaths min-1. Measurements of radioactivity, made with collimated coaxial detectors above and below the chest, were continued for 24 h, when it was considered that all particles remaining represented those deposited in the pulmonary region. Measurements, made following the ingestion of labelled particles, showed that material in the gut contributed to the counting rate in the chest region even after 24 h. The results showed that in healthy non-smokers, of the material deposited below the level of the larynx, 84% of 2.5 micron, 65% of 5 micron and 30% of 7.5 micron particles were deposited in the pulmonary region. Lateral scans of the chest were also made. These enabled the position of the maximum activity on either side of the midline to be determined. The significance of these measurements is discussed.