An indication on the biological variability of aerosol total deposition in humans.

A technique for the assessment of the total deposition efficiency, DE, in the human respiratory tract is described. It is based on the use of non-wettable solid spherical monodisperse particles in the 0.3 to 1.5 micron range and on the measurement of particle concentrations in the inhaled and exhaled air. The results of total deposition measurements as a function of particle size taken on 6 volunteers are presented. A wide variability has been found among the subjects; it is discussed and, in contrast with some literature data, there is no apparent correlation with normal expiratory reserve volumes, ERVN. Therefore at 0.6 micron the deposition has been measured at various ERV. The scatter of data is considerable, but it can be greatly reduced if the relative deposition (ratio of the effective DE to DEN, the deposition at "normal" volumes) is expressed as a function of the relative ERV, (the ratio of the effective ERV to the normal ERVN). Measurements have been performed with monodisperse and unipolarly charged particles on two subjects characterized by different DEN and ERVN. The contribution of electrostatic effects to deposition was not distinguishable in the two subjects.

On the deposition of unipolarly charged particles in the human respiratory tract.

The effect of unipolar electrostatic charges on the total deposition efficiency in the human respiratory tract has been investigated. Monodisperse carnauba wax particles of diameter between 0.3 and 1.1 micron were charged, in a corona discharge apparatus, with a number of elementary charges ranging from about 30 to 110 per particle, with a narrow distribution. The experiments were performed with volunteers breathing through the mouth at 12 resp/min at constant flow rate, without pauses. The increase in deposition was of the order of 15 to 30% relative to neutral but otherwise unchanged monodisperse aerosol. The increase depended on the charges carried by each particle, but was independent of the concentration. Therefore it may be concluded that the variation can be ascribed to the effect of electrostatic attraction between the particle charge and the image charge on the airway wall.