Complaints of a "stuffy" nose may have as much to do with air temperature and humidity as with actual congestion of nasal passages, researchers said.
Combinations of air temperature and humidity that produced mucosal cooling were most likely to lead healthy volunteers to report clear nasal passages, whereas actual nasal patency was unrelated to reported sensations of nasal stuffiness, according to Kai Zhao, PhD, and colleagues at the Monell Chemical Senses Center in Philadelphia, a private nonprofit research institution.
Action Points
- Explain that a study in healthy volunteers found that breathing cold air and, to a lesser but still significant degree, lower humidity air led to a perception of greater nasal patency.
- Note that objective measures of patency did not correlate with perceived nasal congestion.
The 44 study participants indicated that they felt less nasal congestion when they breathed cold and dry air than when breathing normal room air, the researchers reported online in PLoS ONE.
Previous studies have suggested that physical obstruction of nasal passages is only one factor in patient-reported nasal and sinus congestion.
"A perception of a lack of nasal patency is the primary symptom that drives [some] patients to seek medical treatment," Zhao and colleagues explained, yet objective examination often reveals relatively clear airways.
A more important determinant appears to be the nature of stimuli delivered to nasal trigeminal nerves.
Past research has shown, for example, that topical or oral menthol "produces the illusion of decongestion and improved nasal airflow without actually altering nasal morphology," the researchers wrote.
Perceived coolness in the nasal passages, irrespective of how it is induced, appears to drive the perception of nasal patency, but the role of humidity has not been well examined, they noted.
Zhao and colleagues recruited 44 healthy individuals who, on successive occasions, breathed from boxes delivering normal room air, dry air, or cold air. Temperature and relative humidity parameters for the three air types were as follows:
- Normal room air: approximately 24° C (75° F), 55% humidity (range 40% to 67%)
- Dry air: approximately 24° C (75° F), 25% humidity (range 15% to 32%)
- Cold air: approximately 12° C (54° F), 55% humidity (range 50% to 67%)
Participants rated their perceptions of nasal stuffiness in each nostril on a visual analog scale of 0 to 3 before and after each sampling.
Actual nasal patency in each nostril was measured before and after the procedure with acoustic rhinometry and anterior rhinomanometry. Also assessed was participants' nasal trigeminal nerve reactivity by having them sniff from bottles containing mineral oil (the control) or butanol at various dilutions.
Participants were most likely to report stuffiness when breathing the regular room air. Unilateral patency was rated with a mean score of about 2.5 and bilaterally at 2.0.
In contrast, dry air led to mean patency ratings of about 1.7 both unilaterally (P=0.0063 versus room air) and bilaterally (not significant), with the lower scores indicating better patency.
Cold air produced the lowest scores: mean 1.0 unilaterally (P=0.0003 versus dry air) and 0.2 bilaterally (P=0.0037 versus dry air). Zhao and colleagues noted that absolute humidity in the cold air was the same as in the dry air -- "which may be the reason for the stronger effect," they wrote.
There was a significant correlation between air temperature and perceived patency with a Spearman r coefficient of 0.35 (P<0.05).
On other hand, there was no correlation between perceived patency and objective measures of airway obstruction or trigeminal reactivity.
The findings have implications for treatment of chronic nasal and sinus congestion, Zhao and colleagues indicated.
"By establishing that feelings of nasal congestion can be sensory-related, we open doors for more targeted treatment," Zhao said in a press release from Monell. "For example, effective treatments may need to include a focus on restoring optimal humidity and temperature in the patient's nasal airflow."
However, the researchers stressed that all the variables included in the study accounted for less than 20% of the variation in self-reported nasal patency.
They noted that other unmeasured factors such as activity of mechanosensors in the nasal mucosa may also help determine when patients feel congested.
The statement from Monell indicated that follow-up studies in patients reporting nasal congestion are planned.
Disclosures
The study was funded by the National Institutes of Health.
Study authors declared they had no relevant financial interests.
Primary Source
PLoS ONE
Zhao K, et al "Perceiving nasal patency through mucosal cooling rather than air temperature or nasal resistance" PLoS ONE 2011; DOI: 10.1371/journal.pone.0024618.