Tracheobronchial deposition and clearance in small airways in asthmatic subjects

Abstract

Asthma tends to impair mucociliary clearance, as assessed from measurements 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 asthma and 10 healthy subjects after inhalation of 6 µm (aerodynamic diameter) monodisperse Teflon particles labelled with 111 In. The particles 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, in particular in the small ciliated airways (bronchioles). Lung retention 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 tracheobronchially-deposited particles were on average 41 and 47% for asthmatic and 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, either in asthmatics or in healthy subjects.Our results indicate that particles 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 tracheobronchial deposition both in healthy and asthmatic subjects, i.e. practically independent of airway dimensions, by inhaling rather large aerosol particles extremely slowly. This may be a useful therapeutic approach.

Bronchiolar aerosol deposition and clearance

“…Taken together, aerosol bolus and probe developments have added to the belief that we can now understand and predict particle aerodynamic behaviour within the lungs. They thus support the proposition that we can predictably target test particles onto the bronchiolar airways [9,10].…”

“…Transit times through each individual airway unit are then long enough, and yet internal diameters small enough, for many particles to deposit by sedimentation under the influence of gravity. Calculations [9,11] based on WEIBEL model geometry [12] demonstrate the magnitudes of the effects involved.…”

“…In this issue of the Journal, SVARTENGREN et al [9] describe their evaluation of small airways deposition and clearance. The findings and approach of this study offer a chance to reconsider the "mystery zone" status of the small airways and to look again at their defence role in the lungs.…”

“…Recently, major emphasis has been placed on retention at tracheobronchial sites [8,16]. The idea is not new but has gained impetus from inhalation studies using radioactive aerosol bolus techniques [17,18], with support from studies aiming at bronchiolar deposition by the slow inhalation technique [9,10]. Utilizing either technique, the proposition is that the aerosol particles are carried only a fairly short distance into the bronchial tree and there undergo efficient deposition.…”

Use of simulated epithelial lung fluid in assessing the human health risk of Pb in urban street dust

“…It can be seen (Table 3) that values for the tracheobronchial retention appear to be limited in terms of occurrence and range. An experimentally derived value, from human volunteers, identified that the TR was 47 ± 8% (Svartengren et al, 1996). Unfortunately, this was only done on b 6 μm particles.…”