title: Effect of Posture on Regional Deposition of Coarse Particles in the Healthy Human Lung.
abstract: 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.
authors.affiliation: 1 Department of Medicine, University of California , San Diego, La Jolla, California.
authors.forename: Rui Carlos
authors.initials: RC
authors.lastname: Sá
authors.affiliation: 2 Department of Medicine, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina.
authors.forename: Kirby L
authors.initials: KL
authors.lastname: Zeman
authors.affiliation: 2 Department of Medicine, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina.
authors.forename: William D
authors.initials: WD
authors.lastname: Bennett
authors.affiliation: 1 Department of Medicine, University of California , San Diego, La Jolla, California.|3 Department of Radiology, University of California , San Diego, La Jolla, California.
authors.forename: G Kim
authors.initials: GK
authors.lastname: Prisk
authors.affiliation: 1 Department of Medicine, University of California , San Diego, La Jolla, California.
authors.forename: Chantal
authors.initials: C
authors.lastname: Darquenne
mesh_terms: 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 / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000378:metabolism*; D012123:Pulmonary Ventilation; D019275:Radiopharmaceuticals / Q000008:administration & dosage / Q000493:pharmacokinetics*; D065589:Respiratory Tract Absorption; D016683:Supine Position; D013671:Technetium Tc 99m Sulfur Colloid / Q000008:administration & dosage / Q000493:pharmacokinetics*
chemical_list: D000336:Aerosols; D019275:Radiopharmaceuticals; D013671:Technetium Tc 99m Sulfur Colloid
keywords: aerosol deposition; gamma scintigraphy; human lung; posture