Increased carbon monoxide in exhaled air of patients with seasonal allergic rhinitis

Background Carbon monoxide (CO) can be detected in exhaled air and is incre ased in asthmatic patients. However, it is uncertain whether exhaled CO is increased in patients with allergic rhinitis. Objective and methods To study whether exhaled CO is increased in patients with allergic rhinitis, exhaled CO concentrations were measured on a CO mon itor by vital capacity manoeuvre in 86 patients with seasonal allergic rhin itis during and out of the cedar pollen season. Results During the season, exhaled CO concentrations were 3.6 +/- 0.3 p.p.m . and decreased to 1.2 +/- 0.1 p.p.m. out of the season. The values of exha led CO out of the season were similar to those in age-matched non-smoking h ealthy control subjects (1.2 +/- 0.1 p.p.m.). Exhaled CO concentrations wer e significantly higher in patients with symptoms than in those without symp toms (P < 0.01). Exhaled CO concentrations in patients did not differ signi ficantly among oral and nasal exhalation, and oral exhalation with an expir atory resistance (P > 0.20). Conclusion These findings suggest that allergic rhinitis increases the conc entration of CO in exhaled air and increases in exhaled CO may be derived f rom lower airways. Keywords: airway inflammation, alveolar macrophages, ast hma, carbon monoxide, haem oxygenase, nitric oxide.