Clinical Assessment of Nasal Airway Obstruction
For the evaluation of nasal airway obstruction physical examination, anterior rhinoscopy, laboratory workup, imaging studies, and rhinomanometric studies may be required. Laboratory workup may consist of counts of neutrophil investigating infectious diseases, eosinophil for allergy-related disorders, and mast cell in food allergy. Imaging workup contains computed tomography (CT) and magnetic resonance imaging. Physically based studies involve rhinomanometry and acoustic rhinometry techniques. Nasal resistance is responsible for more than 50% of the resistance of the total airway. Nasal resistance is made up of two layers: the deeper layer consists of underlying bone, cartilage, and muscle, while superficially the overlying mucosa forms the second layer. Environmental and intrinsic conditions both alter nasal resistance. Variables reducing resistance consist of sympathomimetics, atrophic rhinitis, exercise, rebreathing, along with erect posture. Exercise leads to sympathetic vasoconstriction and shrinkage of the ala nasi, dilating the nasal cavities. Infectious rhinitis, vasomotor rhinitis, allergic rhinitis, supine posture, hyperventilation, cold air, aspirin, and alcohol increase nasal resistance. To better understand the relations between form and resistance of the nasal air channel, one of the basic laws in fluid dynamics is very helpful. The law of Hagen–Poiseuille is valid for the resistance of round tubes, which means that in a tube, the resistance R increases linear with the viscosity of the fluid and the length of the tube but with the 4 power of the tube radius. Reducing the radius to the half leads to a 16-fold increase of resistance.
KeywordsNasal airway Obstruction Clinical assessment Nasal resistance The law of Hagen–Poiseuille
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