The airways (nose-trachea-lungs) and the digestive tract (mouth-esophagus-stomach) cross paths in the throat (larynx). By upper airways is meant the space above the larynx. Located here are the nasal cavity and pharynx. In addition, the oral cavity is connected (end-to-side) to the upper airways, but gas flow through the mouth is usually prevented by the soft palate. Many persons breath through the mouth when large tidal volumes with high rates are necessary (or if the nose is closed by swollen mucous layers). In such a situation, flow through the nasal cavity is usually blocked by the soft palate, which is pressed against the hard palate. The same applies during a pulmonary function investigation when a person is breathing via an oral mouthpiece. Producing a model of this area has proved to be a difficult venture (Proctor 1964). Recent investigations using ultrasonic measurements give a more detailed description (Fredberg 1980). Even under normal physiological conditions, slight deformations can occur as a result of movements of the tongue and lower jaw, rapid gas flow, and articulation.
KeywordsDead Space Total Delay Esophageal Pressure Pleural Pressure Occlusion Test
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