Deposition in Man of Particles Inhaled in Air or Helium-Oxygen at Different Flow Rates

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Abstract
Deposition in mouth and throat, and in tracheobronchial and alveolar regions of 3.6 μm (aerodynamic diameter) Teflon particles labelled with 99mTc was estimated in eight healthy subjects by external measurement of the radioactivity in the body. After test particle inhalation mucociliary clearance was stimulated with a cholinergic aerosol. The retention after 6 hours (Ret6) was taken to represent deposition in the alveolar (non-ciliated) region. The particles were inhaled in air or helium-oxygen mixture (He-O2) at 0.4,0.8, and 1.21/sec. Deposition in mouth and throat, was significantly lower with He-O2and Ret6 was significantily higher. The differences in deposition seemed to be larger at the higher flow rates than at the lowest one. The results show the importance of controlling the inhalation flow rates and that inhaled drugs can be deposited more peripherally when inhalation is done with He-O2 than with air. One mechanism behind the differences in deposition between the inhalations with air and He-O2 might be differences in the degree of turbulent flow.