Environmental allergies are the most common causes of inflammation of nasal membranes, followed by inhaled irritants (eg, cigarette smoke, perfumes, various chemicals, and other noxious odorants).
Nonallergic or vasomotor rhinitis results from dysfunction of the autonomic nervous system or blood flow changes from iatrogenic or drug-related causes. Increases in blood flow or parasympathetic tone or decreases in the sympathetic tone increase congestion and drainage of the nasal cavity. Conversely, reduction of blood flow, suppression of the parasympathetic system, and stimulation of the sympathetic system decrease nasal congestion and discharge. Supplemental female hormones or hormonal changes caused by pregnancy or menstruation may affect nasal systems. Any medications taken for hypertension or cardiac dysfunction may affect nasal physiology.
Nasal physiology also is affected by anatomic deformities that may have a varying effect on congestion, drainage, and olfaction. Septal deviation and enlarged turbinates can affect airflow into the nasal cavity, transforming it from a laminar pattern to a more turbulent pattern (see
Images 1-2). Turbulent airflow causes further irritation to nasal membranes, with a resultant increase in nasal drainage and congestion.
Nasal airway obstruction from turbinate hypertrophy, secondary to upper respiratory illness (URI) or allergic response, is the most common cause of temporary loss of smell. The sense of smell is important for quality of life, for taste, and for detecting smoke and other harmful odorants that could be life threatening.
In the upper airways, nasal cavities and paranasal sinuses are the main sources of nitric oxide (NO). Although the exact role of NO in nasal physiology remains poorly understood, the functions are thought to be host defense, ciliary motility, and an improved ventilation-perfusion ratio in the lungs by auto-inhalation. Low NO concentrations were reported in certain diseases, such as primary ciliary dyskinesia, cystic fibrosis, and acute and chronic maxillary sinusitis, whereas high concentrations were detected in upper airway infection, allergic rhinitis, and nasal polyposis.
Tests of nasal physiology include studies of airflow, ciliary function, and olfaction.
Rhinomanometry attempts to quantify nasal airflow and total nasal area during exclusive nasal breathing. Differential pressure measurements are obtained by placing a nasal catheter into the nasopharynx. Nasal resistance measurement assesses all resistive components of the nasal airway from the anterior nares to the nasopharynx and is sensitive to small changes in airway caliber. This technique has been validated and is most useful for documenting changes in nasal patency caused by pharmaceutic or surgical interventions. It is moderately invasive, slow to perform, and requires patient assistance to complete.
Acoustic rhinometry is a newer technique for evaluating the cross-sectional area of the nose and the volume of the nasal cavity by analysis of incident and reflected sound during a brief cessation of nasal breathing. This technique also has been validated and is also useful for documenting changes in nasal patency caused by pharmaceutic or surgical interventions. It is minimally invasive, quick to perform, and requires little patient cooperation.
