Documentation of the nasal nitric oxide response to humming: methods evaluation

Rationale Nitric oxide (NO) is present at higher concentrations in the nasal cavity than in the lower airway, and at even higher concentrations within the paranasal sinuses proper. When the paranasal sinus ostia are patent, acoustic activity produced by vocalization with closed lips (humming) promotes mixing of sinus with nasal gases, producing a further increase in nasal NO. We wished to evaluate procedures for the documentation of the nasal NO response to humming. Materials and methods We compared two ATS‐recommended sampling methods: 1) active exhalation of lower airway gas (parallel technique) and 2) passive aspiration of nasal gas with closed velopharynx (series technique). Variables controlled for included sampling rate, external resistance (parallel method), humming frequency, humming duration, and intertrial interval. Prior to upper airway sampling, exhaled lower airway NO was determined utilizing ATS‐standardized technique. Results Ten volunteers (seven males and three females, aged 21–58) with no history of respiratory allergies or sino‐nasal disease were studied in a single session each. The parallel technique documented an increase in nasal NO during the humming manoeuvre in all subjects (mean ratio of humming‐to‐quiet NO, 4·2), whereas the series technique did so in eight of 10 subjects (mean ratio 2·1). Correcting for admixture from the lower airway, the ratio of humming‐to‐quiet NO was greater with the parallel than series sampling technique (P