Extrathoracic airways

Note chat turbulent flow (Reynolds number > 3000 is predicted only m the extrathoracic airways at flow races < 30 IVmin. 

Extrathoracic airways The portion of the human conducting airways prox-... 

The ICRP deposition model estimates the fraction of inhaled material initially retained in each compartment (see Figure 3-2). The model was developed with five compartments (1) the anterior nasal passages (ET,) (2) all other extrathoracic airways (ET2) (posterior nasal passages, the naso- and oropharynx, and the larynx) (3) the bronchi (BB) (4) the bronchioles (bb) and (5) the alveolar interstitium (AI). Particles deposited in each of the regions may be removed and redistributed either upward into the respiratory tree or to the lymphatic system and blood by different particle removal mechanisms. 

The advantage of measuring airway resistanee is that it is a simple, rapid, and extremely sensitive test of airway caliber, but the major disadvantage is that it cannot distinguish between resistance changes due to obstruetion of the extrathoracic airway (pharynx, larynx, glottis, and trachea) or the intrathoracic airway (bronchi, bronchioles, and alveoli). 

Targeting of extrathoracic airway snrfaces can be achieved by inspiring at high flow rate particles much larger than 1 pm in aerodynamic size and suspended in tidal air of small volume. 

KimbeU, J.S. (2001). Computational Fluid Dynamics of the Extrathoracic Airways, Medical AppUcations of Computer ModeUing The Respiratory System, WIT Press, United Kingdom. Krushkal, E.M. and GaUUy, I. (1984). On the Orientation Distribution Function of Non-Spherical Aerosol Particles in a General Shear How. I. The Laminar Case. J. CoUoid Interface Sci., Vol. 99, pp. 141-152. 

Class SR-2 Highly soluble or reactive complete deposition in the extrathoracic airways (ET2). For the purpose of calculation they are treated as though they were injected directly into the blood. in organic compounds and tritiated water... 

Experimental data, from several investigators who measured intrathoracic particle deposition during mouth breathing, were summarized by Stahlhofen et al. (184). Figure 12 shows these data as a function of the aerodynamic particle diameter. Because large particles are effectively collected by the extrathoracic airways, intrathoracic deposition does not increase or decrease monotonically with particle diameter, but exhibits maximal values for particles with diameters between 4 and 8 pm. It appears to be lowest for particles smaller than 1 pm. 

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