Histamine Applied Topically to the Nasal Mucosa Increases the Transmucosal Nitrous Oxide Exchange for the Middle Ear

Objective: Determine if the middle ear transmucosal nitrous oxide (N2O) exchange rate is affected by nasal inflammation caused by topical application of histamine. Methods: In a randomized, double-blind, crossover study, 20 adults were challenged intranasally with histamine (5 mg) and placebo on separate occasions. At each session, the subjects were fitted with a non-rebreathing mask and breathed room air for 20 minutes, 50% N2O: 50% O-2 for 20 minutes, and 100% O-2 for 10 minutes. Throughout, heart rate, blood pressure, and blood O-2 saturation were monitored, and bilateral middle ear pressure was recorded by tympanometry every minute. The primary outcome measure was the slope of the middle ear pressure-time function for the 50% N2O: 50% O-2 breathing period, which is a measure of the transmucosal N2O exchange-constant. The effects of challenge substance, session, and period on the measured vital signs and of treatment, session, ear disease history, and test ear on the pressuretime slopes were evaluated using repeated measures ANOVAs. Results: The post-challenge total symptom score and the slope of the middle ear pressure-time function were greater after histamine when compared to placebo challenge. Of the signs, only heart rate was affected, responding to challenge substance and study period. Conclusion: The transmucosal N2O exchange rate for the middle ear is increased during inflammation caused by nasal histamine exposure.