MEASUREMENTS OF AIRWAY DIMENSIONS AND CALCULATION OF MASS-TRANSFER CHARACTERISTICS OF THE HUMAN ORAL PASSAGE

This paper presents measurements of the geometric shape, perimeter, an d cross-sectional area of the human oral passage (from oral entrance t o midtrachea) and relates them through dimensionless parameters to the depositional mass transfer of ultrafine particles. Studies were perfo rmed in two identical replicate oral passage models, one of which was cut orthogonal to the airflow direction into 3 mm elements far measure ment, the other used intact for experimental measurements of ultrafine aerosol deposition, Dimensional data were combined with deposition me asurements in two sections of the oral passage (the horizontal oral ca vity and the vertical laryngeal-tracheal airway) to calculate the dime nsionless mass transfer Sherwood number (Sh). Mass transfer theory sug gests that Sh should be expressible as a function of the Reynolds numb er (Re) and the Schmidt number (Sc). For inhalation and exhalation thr ough the oral cavity (O-C), an empirical relationship was obtained for flow rates from 7.5-30.0 1 min(-1): Sh = 15.3 (ReSc-0.986)-Sc-0.812 A n empirical relationship was likewise obtained for the laryngeal-trach eal (L-T) region over the same range of flow rates: Sh = 25.9 (ReSc-13 7)-Sc-0.861 These relationships were compared to heat transfer in the human upper airways through the well-known analogy between heat and ma ss transfer. The Reynolds number dependence for both the O-C and L-T r elationships was in good agreement with that for heat transfer. The ma ss transfer coefficients were compared to extrathoracic uptake of gase s and vapors and showed similar flow rate dependence. For gases and va pors that conform to the zero concentration boundary condition, the em pirical relationships are applicable when diffusion coefficients are t aken into consideration.