Scintigraphic measurement of tracheal mucus velocity in vivo

Mucociliary clearance (MCC) is an important mechanism for removing inhaled particles, secretions and cellular debris from the respiratory tract. Here, a direct measurement of tracheal mucus velocity (TMV) for assessment of MCC, suitable for clinical and research use, is reported, and a comparison is made of TMV in normal subjects and patients with chronic obstructive pulmonary disease (COPD). A 0.1-mL bolus of radiolabelled (2-5 MBq), technetium-labelled macroaggregated human albumin (^99mTc MAA) was injected through the cricothyroid membrane into the trachea of 20 young (<50 yrs) and 12 older (>50 yrs) normal subjects and 34 patients with COPD. Repeat studies were carried out in 13 normal subjects and 16 COPD patients. Movement of the bolus in the trachea was recorded (15 min) using a gamma camera interfaced to a computer. Data were analysed using specifically designed software. The test was well tolerated by subjects and patients, and no significant adverse events were reported. No significant differences were observed between data recorded from different regions of the bolus (leading edge, peak, trailing edge) by analysis of variance (ANOVA). Bland-Altman plots of the repeat studies indicated that data were more variable in normal subjects (coefficient of repeatability (COR) 10.3 mm·min^-1) than in COPD patients (COR 5.5 mm· min^-1). TMV (mean±SD) in young normal subjects (n=20) was 10.7±3.5 mm·min^-1. TMV was reduced in older normal subjects (n=12; 6.5±2.6 mm·min^-1) and further reduced in COPD (n=34; 2.1±2.7 mm·min^-1 . In conclusion, this technique can be used to measure tracheal mucus velocity rapidly and safely in healthy subjects and patients with respiratory tract disease. This study has confirmed that tracheal mucus velocity declines with age and is further impaired in patients with chronic obstructive pulmonary disease.