Air-conditioning characteristics in nasal cavity models exhibiting nasal cycle states.

The air-conditioning characteristics in nasal cavity models obtained from two subjects exhibiting different degrees of the nasal cycle states in terms of the airflow partition were investigated using computational fluid dynamics. A constant inspiratory flow rate of approximately 250 mL/s was considered, and the air temperature and relative humidity at the inlet were assumed to be 25 °C and 35%, respectively. The air-conditioning capacities of the congested and decongested sides were assessed by the amounts of epithelial heat and water vapor transferred to the inhaled air through the airway from the nostrils to the end of the septum. The results revealed that the air temperature and relative humidity near the end of the septum, respectively, reached approximately 31.4-32.5 °C and 81.4-88.0% in the decongested sides and 34.0-35.9 °C and 95.3-100% in the congested sides. The differences seen in the air temperatures and relative humidity between the congested and decongested sides were found to be larger in the cavity model that showed a larger degree of reciprocal change in the airflow rate. From a fluid mechanics perspective, while the congested side is in a rest period during the nasal cycle such that a lower amount of airflow is transported through it, this side, in effect, works to provide assistive air-conditioning capacity to the nasal cavity and aids when insufficiently conditioned airflow passes through the decongested side so that the inhaled air merging after the septum can approach the alveolar condition favorably through the nasopharynx.