Evaluation of the Ability of the Nasal Cavity to Warm and Humidify Inspired Air —Based on Moisture Recovery Rate—

Abstract

There is no easy method to evaluate the ability of the nose to warm and humidify inspired air, although it is one of the most important functions of the nasal cavity. It is necessary to insert a sensor into the narrow nasal cavity in order to evaluate the ability to warm and humidify, but this procedure is difficult in outpatient care. It has been shown in several previous investigations that even if the cold, dry ambient air goes into the nostrils, air temperature and relative humidity in the nasopharynx will be about 30°C and nearly 90%, respectively. Generally, the ability to warm and humidify inhaled air in the oral cavity is lower than that in the nasal cavity.
We focused our attention on expiration instead of inspiration. We defined the moisture recovery rate as the ratio of the absolute humidity of expired air and alveolar air (43.93 g/m³).
Eighteen healthy volunteers were examined in this study. Statistically, the moisture recovery rates of the nose were significantly higher than oral rates (P<0.001). The moisture recovery rates of the nose after nasal decongestant administration were lower compared to the values before nasal decongestant administration (P<0.01).
In our study, the nasal cavity collected more moisture from expiration than the mouth. Therefore, a dry feeling in the mouth is caused by only mouth-breathing while this situation does not occur in the nose by only nose-breathing. If the nose is medicated with a blood vessel contraction agent, we feel a dry sensation in the nose because the recovery of moisture falls from expiration. We therefore conclude that the moisture recovery rate is an effective reference for evaluation of the humidification function of the nasal cavity during inspiration.