Problems in evaluating the effect of secretolytic agents on the mucociliary system by means of radioactive particles

In a double-blind cross-over study the effect of two secretolytic agents on the mucociliary clearance was tested in 8 patients with mild chronic obstructive bronchitis. Clearance was assessed from the removal rate of previously inhaled sulfur colloid particles, tagged with 99Tcm. For the interpreatation of the results, obtained by this method, it is essential to take into account the pattern of particle deposition. For example there was a faster clearance under placebo compared to the secretolytic drugs because of a more central deposition. To overcome this problem different approaches were therefore tested. The following constellations proved to be useful in assessing the effect of secretolytic drugs: (1) change in deposition patter; (2) clearance rate, if no change in deposition takes place; (3) clearance rate from a peripheral area of the lung. An attempt to apply a simple three compartment model proved to be unpracticable probably becuase of the complexity of the mechanism involved. One of these mechanisms could be a reversal in mucus transport, observed at least in one patient, a finding which might be of pathophysiological relevance.