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 tracheobronchial clearance in sputum induction, a technique used to diagnose Pneumocystis carinii pneumonia in patients with acquired immune deficiency syndrome (AIDS). Seven normal nonsmoking male subjects inhaled a nebulized aerosol of technetium-labelled human serum albumen, which was cleared from the lung solely by tracheobronchial clearance. The aerosol's particle size distribution ensured both alveolar and proximal airway deposition, the site of P. carinii organisms and tracheobronchial clearance 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 performed at 24 h to determine the alveolar fraction of deposited aerosol. Tracheobronchial clearance rates (log10[activity]/time) were calculated after log linear regression, for the time periods before, during and after sputum induction, having corrected for isotope decay and alveolar deposition. Results were analysed by the Wilcoxon rank sum test. Tracheobronchial clearance rates increased significantly in all subjects during sputum induction, with a mean 65.5% reduction in pulmonary activity over this period. Mean clearance gradients for the three time periods 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.