Deposition of Inhaled Particles in the Oral Airway During Oronasal Breathing

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Abstract
The deposition efficiency of inhaled particles in the oral airway was examined under experimental conditions that simulated natural oronasal breathing during moderate and heavy exercise in three human volunteers. Monodisperse, spherical, nonhygroscopic particles were generated by condensing di-2-ethylhexyl sebacate vapor onto nuclei of sodium fluorescein, a fluorescent tracer. The mass median aerodynamic diameter ranged between 3 and 16 μm. The aerosol was inhaled by mouth without a mouthpiece. After inhalation, the subject gargled to remove the deposited fluorescent tracer from the oral airway. On average, during simulated moderate exercise, 58% of the 10 μm diameter particles and 79% of the 15 μm particles deposited in the oral airway. During simulated heavy exercise, deposition efficiency in the oral airway was lower than during moderate work. The site of particle deposition as determined with a radioactive aerosol was influenced by how widely the mouth was opened, either naturally in heavy exercise, or artificially by using a mouthpiece.