ONLINE LASER-PHOTOMETRIC MONITORING OF AEROSOL DEPOSITION IN VENTILATED RABBIT LUNGS

A photometric technique was developed for on-line measurement of aeros ol deposition in isolated, ventilated, and perfused rabbit lungs. A je t nebulizer was used for aerosolization of saline (hygroscopic particl es) and di(2-ethylhexyl) sebacate (nonhygroscopic particles). Aerosol concentration (laser photometer, constructed for measurements in rabbi t lungs) and flow rate (commercial pneumotachograph) were continuously monitored at the inlet of the tracheal cannula. Computer-assisted dat a processing allowed the breath-by-breath calculation of inhaled and e xhaled aerosol mass, thus providing the deposition fraction. With the use of hygroscopic particles, however, this approach was hampered by t he humidity-induced particle growth in the airways, leading to an over estimation of the aerosol concentration in exhaled air. This effect wa s corrected by an algorithm using a ''particle growth factor'' derived breath by breath from the photometer signal. To test the reliability of this approach, saline particles carrying technetium-99m label were aerosolized into rabbit lungs with the use of various ventilator setti ngs, and the aerosol deposition was assessed in parallel by photometry and by radioactivity detection over the lung and over a trap in the e xhaled-air circuit. Superimposable curves of cumulative aerosol deposi tion, with changes in kinetics dependent on the ventilator mode, were obtained. For a given ventilator setting, absolute values of the depos ition fraction were 0.32 +/- 0.04 (radiotracer quantification) and 0.3 6 +/- 0.04 (photometry; means +/- SD; n = 4). We conclude that the pre sented laser-photometric technique allows reliable on-line monitoring of the deposition of both nonhygroscopic and hygroscopic aerosol parti cles in ventilated lungs.