39 - The Nose and Control of Nasal Airflow

Abstract

The nose acts as an air conditioner to filter, warm, and humidify the inspired air. Nasal airflow is subject to changes in direction and velocity within the nasal cavity that cause the deposition of particulate matter on to the nasal turbinates. Nasal resistance to airflow is regulated by the sympathetic nerve supply to venous erectile tissue within the nasal turbinates and the wall of the nasal septum. The narrowest part of the nose and the whole airway is the nasal valve region that lies anterior to the tip of the inferior turbinate at the entrance to the bony nasal cavum. The resistance to airflow is controlled by the congestion and decongestion of the erectile tissue of the inferior turbinate and nasal septum. The nose should be considered as two separate airways, each with its own nerve and blood supply. Asymmetry of nasal airflow between the nasal passages is normal, and the spontaneous alternation of this airflow from one side of the nose to the other over a period of hours is termed a nasal cycle. Nasal sensation of airflow is mediated by trigeminal nerve endings that are sensitive to the cooling action of inspired air, and this sensation may be enhanced by cooling agents such as menthol. Any medicine or hormone that acts on blood vessels will also influence nasal airflow by its effects on nasal blood vessels. Adrenaline and sympathomimetic medicines cause a constriction of nasal blood vessels and a decongestion of the nasal airway. Exercise causes an increase in sympathetic activity and is an effective nasal decongestant. Histamine causes dilation of nasal blood vessels and nasal congestion.