Regional Ventilation Is the Main Determinant of Alveolar Deposition of Coarse Particles in the Supine Healthy Human Lung During Tidal Breathing.
BACKGROUND
To quantify the relationship between regional lung ventilation and coarse aerosol deposition in the supine healthy human lung, we used oxygen-enhanced magnetic resonance imaging and planar gamma scintigraphy in seven subjects.


METHODS
Regional ventilation was measured in the supine posture in a 15 mm sagittal slice of the right lung. Deposition was measured by using planar gamma scintigraphy (coronal scans, 40 cm FOV) immediately postdeposition, 1 hour 30 minutes and 22 hours after deposition of 99mTc-labeled particles (4.9 μm MMAD, GSD 2.5), inhaled in the supine posture (flow 0.5 L/s, 15 breaths/min). The distribution of retained particles at different times was used to infer deposition in different airway regions, with 22 hours representing alveolar deposition. The fraction of total slice ventilation per quartile of lung height from the lung apex to the dome of the diaphragm at functional residual capacity was computed, and co-registered with deposition data-apices aligned-using a transmission scan as reference. The ratio of fractional alveolar deposition to fractional ventilation of each quartile (r) was used to evaluate ventilation and deposition matching (r > 1, regional aerosol deposition fraction larger than regional ventilation fraction).


RESULTS
r was not significantly different from 1 for all regions (1.04 ± 0.25, 1.08 ± 0.22, 1.03 ± 0.17, 0.92 ± 0.13, apex to diaphragm, p > 0.40) at the alveolar level (r22h). For retention times r0h and r1h30, only the diaphragmatic region at r1h30 differed significantly from 1.


CONCLUSIONS
These results support the hypothesis that alveolar deposition is directly proportional to ventilation for ∼5 μm particles that are inhaled in the supine posture and are consistent with previous simulation predictions that show that convective flow is the main determinant of aerosol transport to the lung periphery.
['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 D006801:Humans D008279:Magnetic Resonance Imaging D008297:Male D008875:Middle Aged D011650:Pulmonary Alveoli D012123:Pulmonary Ventilation D011877:Radionuclide Imaging D012119:Respiration D016683:Supine Position D013671:Technetium Tc 99m Sulfur Colloid D013990:Tidal Volume D013997:Time Factors
ventilation human lung coarse aerosol deposition multimodal imaging