Olfactory and trigeminal thresholds and nasal resistance to airflow

Nasal congestion associated with the common cold or allergy is associated with a decreased sensitivity of the sense of smell. This study was designed to detect any relationship between nasal resistance to airflow and the ability to detect odors presented to the nose. In particular we were interested to determine if the asymmetrical nasal resistance to airflow associated with the nasal cycle influenced nasal thresholds to menthol which is detected by trigeminal nerves and vanillin which is detected by olfactory nerves. Nasal resistance to airflow and the thresholds for L-menthol and vanillin were measured for each nasal passage in 17 normal volunteer subjects. Nasal resistance to airflow was asymmetrical due to the nasal cycle with a resistance on the high side of 0.94 +/- 0.15 Pa/cm3 s (mean +/- S.E. n = 17). and 0.48 +/- 0.04 Pa/cm3 s on the low side. The range of unilateral nasal resistances varied from 0.31-2.55 Pa/cm3 s. Despite these variations in nasal resistance to airflow no relationship was found between nasal resistance to airflow and thresholds for menthol or vanillin. Since threshold and nasal resistance are not related in normal subjects this may indicate that it is not the level of nasal congestion that affects the sense of smell in nasal infection and allergy, but some other factor related to the inflammatory response of the nasal mucosa.