Perceiving nasal patency through mucosal cooling rather than air temperature or nasal resistance

Abstract

Adequate perception of nasal airflow (i.e., nasal patency) is an important consideration for patients with nasal sinus diseases. The perception of a lack of nasal patency becomes the primary symptom that drives these patients to seek medical treatment. However, clinical assessment of nasal patency remains a challenge because we lack objective measurements that correlate well with what patients perceive. The current study examined factors that may influence perceived patency, including air temperature, humidity, mucosal cooling, nasal resistance, and trigeminal sensitivity. Forty-four healthy subjects rated nasal patency while sampling air from three facial exposure boxes that were ventilated with untreated room air, cold air, and dry air, respectively. In all conditions, air temperature and relative humidity inside each box were recorded with sensors connected to a computer. Nasal resistance and minimum airway cross-sectional area (MCA) were measured using rhinomanometry and acoustic rhinometry, respectively. General trigeminal sensitivity was assessed through lateralization thresholds to butanol. No significant correlation was found between perceived patency and nasal resistance or MCA. In contrast, air temperature, humidity, and butanol threshold combined significantly contributed to the ratings of patency, with mucosal cooling (heat loss) being the most heavily weighted predictor. Air humidity significantly influences perceived patency, suggesting that mucosal cooling rather than air temperature alone provides the trigeminal sensation that results in perception of patency. The dynamic cooling between the airstream and the mucosal wall may be quantified experimentally or computationally and could potentially lead to a new clinical evaluation tool.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. Temperature (left) and relative humidity (right) measurement during each subject exposure session.

The temperature in the cold air exposure box was significantly lower than in the other exposure boxes, and the RH in the dry air exposure box was significantly lower than in the others (both p

Figure 2. Air exposure boxes and the visual analog scale used in the study.

The visual analogue scale includes a negative range to account for subjects that may rate their nasal patency as completely clear and then experience even less congestion in later exposures.

Figure 3. Flow chart of the test sequence for each participant: box exposure and patency rating (top), followed by rhinometry, rhinomanometry, and trigeminal assessment by butanol lateralization threshold (bottom).

Figure 4. Bilateral and unilateral subjective patency ratings and standard errors in room air, dry air, and cold air exposure boxes.

Subjects perceived significantly less nasal congestion (greater patency), both unilaterally and bilaterally, in the cold air box and unilaterally in the dry air box, compared to the room air box (p

Figure 5. Averaged total nasal heat loss versus patency visual analog scale (VAS) ratings for the three exposure box conditions.

Nasal heat loss is calculated assuming that, at the end of the breath, inspired air is always warmed and humidified to 35°C and 90% RH , . Data are averaged over subjects for the three exposure conditions.

Figure 6. Within subject, there was a significant difference in perceived patency between the high and low resistance nostrils.

Figure 7. Contour plot of nasal mucosal heat flux (J/m2) for a subject that received a nasal/sinus CT scan immediately before testing.

A CFD model was created for this subject using the method described by Zhao et al. in which nasal airflow and mucosal heat exchange are then simulated. The wall boundary condition at the mucosal surface is set similar to that described by Naftali et al. : fully saturated with water vapor and at body temperature, with an unlimited supply of heat and water vapor.