Nasal nitric oxide: A comparison of measurement techniques

Nasal nitric oxide measurement may be a surrogate marker of upper airway in flammation. There is, however, no standardized measurement technique; and t his led us to examine measurement techniques for acceptability and reproduc ibility In five subjects we examined the flow dependence of nasal NO. In 13 healthy volunteers, nasal NO was measured on-line by five methods: 1) Tida l nasal and oral breathing: NO sampling during exclusive nasal followed by exclusive oral tidal breathing; 2) Fixed flow exhalation: NO sampling durin g exclusive nasal followed by exclusive oral exhalation at 100 mL/second fr om total lung capacity, 3) Nasal-oral aspiration: air aspirated from the mo uth via both nares at 100 mL/second with glottis closure; 4) Aspiration fro m one nares: air aspirated from one nares at 3.3 mL/second using nitric oxi de analyzer sample line with velum closure; 5) Nasal Insufflation: NO sampl ed at one nares as air insufflated into the other nares at a flow of 100 mL /second with velum closure. Acceptability of all methods was assessed by su bjects and technicians. Nasal NO concentration showed a significant inverse correlation with transnasal flow rate. All methods showed excellent reprod ucibility as assessed by the intraclass correlation coefficient except tida l breathing, which showed highly variable breath-to-breath NO levels, altho ugh mean breath values were reproducible. Mean nasal NO concentrations with methods 1, 2, 3, 4, and 5 were 32.1, 50.2, 62.8 1381, and 60.0 ppb, respec tively. Velum closure was not always achieved in methods 4 and 5 whereas me thods I and 2 required separate nasal and oral procedures. Method 5 had red uced acceptability. NO concentrations were similar with methods that used t he same airflow (2, 3. and 5). Nasal NO can be sampled in different ways wi th excellent reproducibility. In view of the flow dependence of nasal NO, i t is vital to use a constant flow rate, and lower airway NO contribution mu st be excluded or subtracted The fixed flow exhalation appears to be the pr eferred method as it is highly reproducible and acceptable.