THE USE OF INHALED RADIOISOTOPES FOR MEASURING THE EFFECT OF SPUTUM INDUCTION ON TRACHEOBRONCHIAL CLEARANCE RATES

Inhaled radioisotopes were employed to study the role of tracheobronch ial clearance in sputum induction, a technique used to diagnose Pneumo cystis carinii pneumonia in patients with acquired immune deficiency s yndrome (AIDS). Seven normal nonsmoking male subjects inhaled a nebuli zed aerosol of technetium-labelled human serum albumen, which was clea red from the lung solely by tracheobronchial clearance. The aerosol's particle size distribution ensured both alveolar and proximal airway d eposition, the site of P. carinii organisms and tracheobronchial clear ance mechanisms, respectively. Pulmonary emission counts were measured for 12 continuous 5-min periods before, and immediately after, sputum induction with nebulized 3% saline. A further 10-min scan was perform ed at 24 h to determine the alveolar fraction of deposited aerosol. Tr acheobronchial clearance rates (log10[activity]/time) were calculated after log linear regression, for the time periods before, during and a fter sputum induction, having corrected for isotope decay and alveolar deposition. Results were analysed by the Wilcoxon rank sum test. Trac heobronchial clearance rates increased significantly in all subjects d uring sputum induction, with a mean 65.5% reduction in pulmonary activ ity over this period. Mean clearance gradients for the three time peri ods before, during and after sputum induction were -1.2 X 10(-3) min-1 , -15.0 X 10(-3) min-1 and 0.4 X 10(-3) min-1, respectively (P < 0.025 ), which probably underlies the principal mechanism for success of the technique.