Radioaerosol assessment of mucociliary clearance: towards definition of a normal range

Radioaerosol measurements of mucociliary clearance have been assessed in relationship to depth of particle penetration into the lung. The tests analysed were performed with 5 microns diameter 99Tcm particles inhaled under standardised conditions but at varying inhalation flow rates. Aerosol lung penetration was assessed by (i) penetration index (PI), a ratio of outer to inner zone radioactivity determined from a gamma camera image; and (ii) alveolar deposition (AD), a measure of activity retained at 24 hours and taken to represent deposition distal to the ciliated airways. Clearance rates in 30 tests on 19 normal non-smokers under the age of 50 varied significantly with aerosol inhalation flow rate, PI and AD. A normal range varying with PI is proposed although normal inter-subject variability remains high even after allowance for PI. Nevertheless 8 out of 12 patients with stable asthma and 21 out of 24 patients with chronic bronchitis demonstrated slow clearance lying outside the PI-based normal range.