Increased carbon monoxide levels in the nasal airways of subjects with a history of seasonal allergic rhinitis and in patients with upper respiratory tract infection

Background Carbon monoxide (CO) has emerged as an endogenously produced gaseous mediator known to be involved in bronchial smooth muscle regulation. Increased amounts of CO have been found in exhaled air during asthma and lower airway inflammation. Recently CO has been shown to be produced in the nasal airways, but there are no reports of altered CO levels in nasal airways during inflammation. Objective This study was designed to investigate if CO levels increase in the human nasal airways during inflammatory conditions, such as allergy and upper airway respiratory tract infection (URTI). Methods CO was sampled separately from the upper and lower airways of 13 healthy control subjects, six patients with a history of allergic rhinitis and six patients with URTI. Results Nasal CO levels were increased in subjects with allergic rhinitis, compared to healthy controls (2.07 +/- 0.15 ppm, n = 6 and 1.62 +/- 0.08 ppm, n = 13, respectively, P < 0.01). CO levels were also increased in patients with URTI, compared to the same controls (1.92 +/- 0.09 ppm, n = 6, P < 0.05). Normal levels of CO were found in air from the lower airways among subjects with allergic rhinitis, whereas corresponding levels in the URTI patients were increased. Conclusion The present data demonstrates that upper airway CO levels increase in parallel with different inflammatory stimuli, such as allergy and infection, suggesting a role for CO as marker or mediator of nasal inflammation.