Trachea, diameter

Although the estimates of deposition in the respiratory tract are generally most sensitive to the input parameters of trachea diameter (<4), particle mass density (p), and... 

Breathing rate, trachea diameter and particle mass density have the greatest infiuence on particulate deposition for 1 pm AMAD particles. 

Generally, fractional deposition in the lung, as modeled in ICRP 66 (1994), is directly proportional to particle mass density and BR, and inversely proportional to trachea diameter. Other parameters play a relatively minor role in modefing regional deposition within the respiratory tract for adults, adolescents and 10-year-old children. The parameters of anatomical dead space and windspeed are more important to deposition in infants and children. Research into these more sensitive parameters and their distributions may lead to reduction in the uncertainty of... 

In the central airways (the trachea, bronchi, and bronchioles greater than 2 to 4 mm in internal diameter), inflammatory cells and mediators stimulate mucus-secreting gland hyperplasia... 

The deposition of ultrafine particles has been measured in replicate hollow casts of the human tracheobronchial tree. The deposition pattern and efficiency are critical determinants of the radiation dose from the short lived decay products of Rn-222. The experimental deposition efficiency for the six airway generations just beyond the trachea was about twice the value calculated if uniform deposition from laminar flow is assumed. The measured deposition was greater at bifurcations than along the airway lengths for 0.2 and 0.15 ym diameter particles ... 

Fig. 3.1 Schematic diagram of the human respiratory system. The gross anatomy of the lung, the covering membranes (pleura), airways and air sacs (alveoli) are shown. The average diameter of portions of the air flow system are indicated trachea, 20 mm bronchus, 8 mm terminal and respiratory bronchioles, 0.5 mnn alveolar duct, 0.2 mm alveolar sacs, 0.3 mm.

Inhaled particles of 20 [im diameter or more tend to be retained in upper parts of the respiratory tract (trachea, pulmonary bronchi and terminal bronchioles) and then removed by ciliary action. In contrast, smaller particles of around 6 pm diameter reach all parts of the respiratory system including the alveolar sacs. Smaller (2 pm) and very small particles (0.2 pm) may not reach the alveolar sacs, only the terminal bronchioles and alveolar ducts. Particles of diameter 1 pm or less may be absorbed if they reach the alveolar sacs. 

As a very crude model for air flow in the trachea, assume fully developed laminar pipe flow at a Reynolds number of KKK). The diameter is 2.0 cm. 

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