DEPOSITION OF 0.02–0.2 μm PARTICLES IN THE HUMAN RESPIRATORY TRACT: EFFECTS OF VARIATIONS IN RESPIRATORY PATTERN

Abstract

Experimental studies which quantify deposition of particles smaller than 0.5 μm diameter are few, and there is a paucity of experimental data clarifying deposition fraction (DF) for particles in the ultrafine (less than 0.1 μm) size range. We have measured the DF for 5 size fractions (0.024–0.24 μm) of a non-hygroscopic heterodisperse aerosol in the human respiratory tract. The aerosol was inhaled during steady state breathing from a chamber by normal male volunteers. Aerosol size distribution and concentration in inhaled and exhaled air were measured using an electrical aerosol analyzer. Initial studies were performed using a controlled respiratory pattern of 1 litre tidal volume (TV) at 12 breaths per minute, and a flow pattern modified from a recording of natural breathing. In subsequent studies, a fixed flow pattern was devised to facilitate study of the variations in TV and inspiratory pause (IP). Using the fixed flow pattern, a pause time of 0s, and TV of 1, the mean DF ranged from 0.49 for the 0.024 μm particle to 0.12 for the 0.24 μm particle, and from 0.68 to 0.32 when the IP was 2.5s. For the 2 litre TV, mean DF ranged from 0.63 for the 0.024 μm particle to 0.36 for the 0.24 μm particle. DF in the initial studies resembled DF measured with the fixed flow, 1 TV, 2.5s IP. This is because residence time for these two patterns was similar. The data demonstrate that deposition increases as particle size falls below 0.1 μm, and increases with increasing tidal volume and increasing inspiratory pause time. The observations agree with and validate predictions of earlier mathematical deposition models.