Measurement of nitric oxide in human nasal airway

The nasal output of nitric oxide (NO) is known to be high, but there have been varying reports of the exact level. We attempted to establish a quantitative measurement of nasal NO, and looked for a possible relationship with nasal resistance, at rest and during exercise. Nasal airway ventilation was performed by using an air pump at a constant flow rate, whilst the soft palate was elevated voluntarily. In a preliminary study, the flow rate for sampling was changed and concentrations of NO were measured. After determination of flow rate, rhinomanometry for nasal resistance and measurement of nasal NO by chemiluminescence were carried out before and after moderate exercise. The concentration of NO ([NO]) exhibited a hyperbolic relationship with flow rate of ventilation (V'E), indicating [NO] x V'E = net nitric oxide output (V'NO) = constant. Hence, nasal NO was expressed quantitatively as V'NO (nL.min-1). For 1 L.min-1 of ventilation, [NO] varied between 2 and 500 parts per billion (ppb) (mean = 323 ppb). The average nasal V'NO in 12 healthy male subjects was 323 +/- 91 nL.min-1 (mean +/- SD). After exercise on a treadmill (10 degrees, 5 km.h-1) for 4 min, nasal V'NO decreased to 229 +/- 63 nL.min-1. At rest, expiratory and inspiratory nasal resistance was 0.27 +/- 0.04 and 0.27 +/- 0.06 Pa.s.cm-3, respectively. After exercise, expiratory and inspiratory nasal resistance decreased to 0.17 +/- 0.04 and 0.16 +/- 0.04 Pa.s.cm-3, respectively. These data indicate that nasal NO can be measured quantitatively as V'NO and might be involved in the control of nasal resistance.