Estimation of alveolar deposition ratio of inhaled radioaerosol.

The lung retention ratio (LRR) and the alveolar deposition ratio (ALDR) are mandatory to calculate the other three indices for quantitatively evaluating mucociliary clearance function of the ciliated airways; the airway deposition ratio (ADR), the airway retention ratio (ARR) and the airway clearance efficiency (ACE). According to our original method, the LRR required 2-hr continuous measurement of radioactivity in the thorax and the ALDR a repeat measurement at 24-hr after radioaerosol inhalation. The 2-hr continuous measurement is, however, too long for a clinical examination and the 24-hr repeat measurement cumbersome. The purpose of the study was to find a way to get the ALDR by calculation without repeating the 24-hr measurement and by counting radioactivity for the shortest possible period and yet without sacrificing the visual evaluation by compiling radioaerosol inhalation lung cine-scintigraphy. By using the derived formulae listed in Table 1, the ALDR was calculable. Forced expiratory volume (FEV) in one sec divided by FEV in per cent (FEV1.0%), the initial 60 min measurement of radioactivity without repeating 24-hr measurement, and smoking history were the minimum requirements to calculate the ALDR. The calculated ALDR appeared reliable enough to estimate the other indices.