Physiological study reveals that most exhaled nitric oxide originates within the nasopharynx in humans, indicating substantial gas uptake by the respiratory tract.
Key Points
To determine the contribution of the nasal passages and nasopharynx to exhaled nitric oxide concentrations at rest and during breathholding in humans.
Measured exhaled nitric oxide (NO) in human subjects (n=8) during nose breathing, mouth breathing, and voluntary closure of the soft palate (VCSP).
Mapped regional NO concentrations via bronchoscopy across the nasopharynx, epiglottis, and trachea in five subjects.
Quantified peak exhaled NO following a breathhold with and without balloon occlusion of the nasopharynx.
Exhaled NO was significantly higher during nose breathing (141 ± 17 nl/min/m²) than mouth breathing (68 ± 6 nl/min/m², p < 0.001), decreasing further to 30 ± 4 nl/min/m² during soft palate closure (p < 0.001).
Isolated nasal NO release during soft palate closure (217 ± 19 nl/min/m²) significantly exceeded exhaled NO during normal nose breathing (141 ± 17 nl/min/m², p < 0.001).
Peak exhaled NO after breathholding fell from 33 ± 7 ppb to 10 ± 4 ppb after balloon occlusion of the nasopharynx (p < 0.001), reflecting greater NO accumulation in the nasopharynx than in the trachea.