Gc. Smaldone, Physiological and pathological considerations for aerosol deposition: Expiration and models of deposition, J AEROSOL M, 13(4), 2000, pp. 387-391
Citations number
12
Categorie Soggetti
Envirnomentale Medicine & Public Health
Journal title
JOURNAL OF AEROSOL MEDICINE-DEPOSITION CLEARANCE AND EFFECTS IN THE LUNG
Theoretical models are often used to predict fractional and regional deposi
tion of inhaled particles in the respiratory tract. The distribution of par
ticle diameters in the aerosol, airway geometry, breathing pattern, and loc
al flow profiles are major determinants of deposition in the lung. However,
most models predicting deposition consider airway geometry to be fixed and
concentrate on inspiratory events in their calculations. When particle los
ses during expiration are estimated, inspiratory and expiratory flow patter
ns and airspace geometry are usually considered to be similar with similar
effects on deposition. The theme of this presentation will be the analysis
of events during expiration that influence particle deposition. In the norm
al lung, during quiet breathing, experiments performed on excised lungs hav
e suggested that convective forces may be different between inspiration and
expiration that significantly affect deposition. Bennett and Smaldone, in
excised dog lungs, by regulating the duty cycle of tidal breathing found th
at more particles deposited during inspiration than expiration and that the
effects were density dependent. In human subjects with obstructive lung di
sease, the situation is reversed. Major differences in large airway geometr
y between inspiration and expiration can occur with each tidal breath. Once
the FEV1 decreases to about 60% of the FVC, flow-limiting segments (FLS) a
re known to form in central airways. Large pressure drops can occur over sh
ort lengths of airway indicating disturbed regions of convective streamline
s that are not present during inspiration. Using radiolabeled monodisperse
particles, Smaldone and Messina have determined that FLS can be a major det
erminant of deposition in central airways. Theoretical predictive models of
particle deposition and clearance should consider inspiratory and expirato
ry differences in airway physiology in health and disease.