Effect of Posture on Regional Deposition of Coarse Particles in the Healthy Human Lung.
BACKGROUND
Understanding the regional partition of deposition of inhaled particles within the lung is important for improving targeted delivery of inhaled aerosolized drugs. One factor affecting regional deposition is gravity. As the lung deforms under its own weight, changes in lung volume, in airway geometries, and in spatial patterns of ventilation distribution between postures have the potential to alter the regional distribution of deposited particles.


METHODS
Using gamma-scintigraphy, we measured regional deposition and clearance of (99m)Tc labeled particles (5 μm) in 6 healthy subjects, with aerosol inhalation occurring both in the supine and seated postures at constant flow (0.5 L/sec) and breathing rate (15 breaths/min). After aerosol deposition, mucociliary clearance data were collected in the seated posture, immediately post-particle administration, 1 h 30 min, 4 h, and 22 h post-inhalation. Relative regional deposition was computed using retention (R) at the different time points, with (1-R(1h30min)), (R(1h30min)- R(4h)), and (R(4h)- R(22h)) corresponding to deposition in the large, intermediate, and small airways, respectively. Alveolar deposition was estimated as the relative retention at 22 h (R(22h)).


RESULTS
Relative deposition of coarse particles in the alveolar region decreased from 60±8% seated to 34±16% supine (p=0.04). This change was accompanied by an increase in relative deposition in the intermediate (7±3% seated to 16±17% supine, P=0.09) and small airways (19±6% seated to 34±13% supine, p=0.06) when inhalation occurred in the supine posture. No change was observed in central to peripheral deposition (C/P ratio), the skew of the deposition distribution, or the apex-to-base ratio of deposition between seated and supine postures.


CONCLUSIONS
Inhalation of coarse particles in the supine posture shifts relative deposition from the alveolar to the bronchial airways, when compared to the seated posture, likely driven by changes in functional residual capacity, and airway size, as well as changes in the regional distribution of ventilation between postures.
['Sá|Rui Carlos|RC|', 'Zeman|Kirby L|KL|', 'Bennett|William D|WD|', 'Prisk|G Kim|GK|', 'Darquenne|Chantal|C|']
D000280:Administration, Inhalation D000328:Adult D000336:Aerosols D005260:Female D006112:Gravitation D064368:Healthy Volunteers D006801:Humans D008297:Male D008875:Middle Aged D009079:Mucociliary Clearance D010316:Particle Size D011187:Posture D011650:Pulmonary Alveoli D012123:Pulmonary Ventilation D019275:Radiopharmaceuticals D065589:Respiratory Tract Absorption D016683:Supine Position D013671:Technetium Tc 99m Sulfur Colloid
posture human lung aerosol deposition gamma scintigraphy