Inspiratory and expiratory aerosol deposition in the upper airway.

Aerosol deposition efficiency (DE) in the extrathoracic airways during mouth breathing is currently documented only for the inspiratory phase of respiration, and there is a need for quantification of expiratory DE. Our aim was to study both inspiratory and expiratory DE in a realistic upper airway geometry. This was done experimentally on a physical upper airway cast by scintigraphy, and numerically by computational fluid dynamic simulations using a Reynolds Averaged Navier?Stokes (RANS) method with a k-? SST turbulence model coupled with a stochastic Lagrangian approach. Experiments and simulations were carried out for particle sizes (3 and 6 µm) and flow rates (30 and 60 L/min) spanning the ranges of Stokes (Stk) and Reynolds (Re) number pertinent to therapeutic and environmental aerosols. We showed that inspiratory total deposition data obtained by scintigraphy fell onto a previously published deposition curve representative of a range of upper airway geometries. We also found that expiratory and inspiratory DE curves were almost identical. Finally, DE in different compartments of the upper airway model showed a very different distribution pattern of aerosol deposition during inspiration and expiration, with preferential deposition in oral and pharyngeal compartments, respectively. These compartmental deposition patterns were very consistent and only slightly dependent on particle size or flow rate. Total deposition for inspiration and expiration was reasonably well-mimicked by the RANS simulation method we employed, and more convincingly so in the upper range of the Stk and Re number. However, compartmental deposition patterns showed discrepancies between experiments and RANS simulations, particularly during expiration.

Lung deposition patterns of directly labelled salbutamol in normal subjects and in patients with reversible airflow obstruction.

BACKGROUND--Earlier studies of aerosol deposition in the lungs have relied on indirect labelling of Teflon spheres of a similar size distribution to the drug in question and have assumed similar aerodynamic properties. Using a modification of a new technique for directly labelling salbutamol, the deposition of salbutamol within the lungs of normal subjects and patients with asthma has been studied with the use of a metered dose inhaler (MDI) alone, an MDI with a spacer device, and a dry powder inhaler (DPI). METHOD--Salbutamol was directly labelled with technetium-99m and placed in an MDI or DPI. Ten normal subjects and 19 patients with asthma inhaled 200 micrograms of salbutamol by means of the MDI alone, the MDI with a spacer device attached, and by DPI on separate days. Deposition was assessed by a dual headed gamma camera after inhalation of the drug. RESULTS--The total mean (SD) percentage deposition of the drug in the normal subjects was 21.6% (8.9%) with the MDI alone, 20.9% (7.8%) with the MDI with spacer, and 12.4% (3.5%) with the DPI. For the patients, the mean percentage deposition was 18.2% (7.8%) with the MDI alone, 19.0% (8.9%) with the MDI and spacer, and 11.4% (5.0%) with the DPI. Bronchodilatation achieved by the patients was similar with all three techniques. Mean peripheral lung deposition was significantly greater with a spacer device than when the MDI was used alone in both normal subjects (49.4% (6.1%) v 44.1% (9.9%)) and patients (38.6% (11.1%) v 30.4% (9.4%)). CONCLUSIONS--The deposition of directly labelled salbutamol from an MDI is greater than previously estimated by indirect labelling techniques. The deposition of labelled salbutamol from a DPI, however, is little different from that measured by indirect techniques.