K. Svartengren et al., TRACHEOBRONCHIAL DEPOSITION AND CLEARANCE IN SMALL AIRWAYS IN ASTHMATIC SUBJECTS, The European respiratory journal, 9(6), 1996, pp. 1123-1129
Asthma tends to impair mucociliary clearance, as assessed from measure
ments in large airways, However, very Little is known about clearance
in the smallest airways of the tracheobronchial region. Deposition and
clearance was estimated in 11 subjects with stable asymptomatic asthm
a and 10 healthy subjects after inhalation of 6 mu m (aerodynamic diam
eter) monodisperse Teflon particles labelled with In-111. The particle
s were inhaled at an extremely slow flow, 0.05 L . s(-1). Theoretical
calculations and experimental data in healthy subjects using this slow
flow support an enhanced deposition in the tracheobronchial region, i
n particular in the small ciliated airways (bronchioles). Lung retenti
on was measured at 0, 24, 48 and 72 h. Clearance was significant every
24 h both for asthmatic and healthy subjects, with similar fractions
of retained particles at all time-points. The fractions of tracheobron
chially-deposited particles were on average 41 and 47% for asthmatic a
nd healthy subjects, respectively, as compared to a maximal deposition
of 30% using a normal inhalation flow (0.5 L . s(-1)). No significant
correlation was found between lung retention and lung function, eithe
r in asthmatics or in healthy subjects. Our results indicate that part
icles clear equally well from small ciliated airways in asthmatic and
healthy subjects, maybe as a consequence of an optimal asthma therapy,
Furthermore, our results show that it is possible to enhance tracheob
ronchial deposition both in healthy and asthmatic subjects, i.e. pract
ically independent of airway dimensions, by inhaling rather large aero
sol particles extremely slowly. This may be a useful therapeutic appro
ach.