Estimating nasal nitric oxide from measured fractional exhaled nitric oxide and nasal fractional exhaled nitric oxide.

Background: Nasal nitric oxide (nNO) is an effective screening indicator for primary ciliary dyskinesia (PCD) and a potential biomarker for nasal diseases; however, Measurement of nNO using standard methods is not available everywhere. Therefore, we aimed to estimate nNO values from measured fractional exhaled NO (FeNO) and nasal FeNO (nFeNO) levels using a widely used FeNO analyzer. Methods: In this single-center cross-sectional study, the proportion of NO from the lower airway mixed with nFeNO was calculated by simultaneously measuring nFeNO and nNO in 15 healthy participants. Additionally, nNO values were estimated from the measured FeNO and nFeNO in healthy controls and patients with asthma or PCD. Results: The average rate of mixed NO from the lower airway tract was 0.86±0.04. Assuming NO to be 0.86, nNO estimated from the measured FeNO and nFeNO was 329.1±127.8 and 313.4±203.7 parts per billion (ppb) in healthy participants (n=53) and patients with asthma (n=19), respectively. Among patients with asthma, no significant difference was observed in the estimated nNO values between patients with and without peripheral blood eosinophilia; however, the nNO-FeNO ratio was significantly lower in those with eosinophilia. The estimated nNO value in four of eight patients with PCD was <77 nL/min and was used as a cutoff used to identify patients with PCD. Conclusions: The estimated nNO value, which is derived from the average rate of NO contamination from the lower respiratory tract, may be a possible substitute for nNO and can be measured with instruments that are widely used.