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

Determine if the middle ear transmucosal nitrous oxide (N₂O) exchange rate is affected by nasal inflammation caused by topical application of histamine.

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% O₂ for 20 minutes, and 100% O₂ for 10 minutes. Throughout, heart rate, blood pressure, and blood O₂ 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% O₂ 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 pressure-time slopes were evaluated using repeated measures ANOVAs.

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.

The transmucosal N₂O exchange rate for the middle ear is increased during inflammation caused by nasal histamine exposure.