Experimental determination of the regional deposition of aerosol particles in the human respiratory tract

Abstract

The experimental techniques and the results of inhalation studies with radioaerosols on normal non-smokers for mouth-breathing are described and discussed. Monodisperse iron oxide particles tagged with 198Au are produced with a spinning top generator in the aerodynamic size range between 1 to 10 micrometers. An aerosol inhalation apparatus enables the subjects to breathe under standardized conditions with respect to tidal volume and breathing frequency. The calculation of total deposition is based upon measurements of the number of in- and exhaled particles per breath by means of photometric methods and pneumotachography. The retention of the radioactive particles present in the body after aerosol administration is measured with a body counter designed and constructed for these experiments. Retention measurements as functions of time after inhalation are carried out in extrathoracic-, chest- and stomach-position. The body counter consists of four shielded NaF(TI)-detectors. The geometrical arrangement, the collimation and the shielding of the four detectors have been optimized by computer calculations in such a way that the response of the counter is independent of the distribution of activity within the chest. Another characteristic feature of the body counter is its low sensitivity to neighboring organs and to neighboring regions within the respiratory tract. For the evaluation of extrathoracic deposition, the activity measured in the stomach immediately after inhalation is added to extrathoracic activity. The elimination of material from the chest (intrathoracic airways) is found to be much slower for the material deposited in the alveolar region (non-ciliated air spaces) than for the amount deposited in the tracheobronchial tree (ciliated airways). This allows the intrathoracic deposition to be divided into tracheobronchial and alveolar deposition by means of the different slopes of the normalized chest retention function. Different normalized chest retention functions are presented and analysed with respect to their different elimination rates belonging to the tracheobronchial and alveolar region. Total, tracheobronchial, alveolar and extrathoracic deposition data are reported in the aerodynamic diameter range between 1 and 10 micrometers.