Objective: To assess its validity and to define the cut-off point of determining the nasal obstruction

Material and Method: The nasal patency of 141 ambulatory subjects with or without sino-nasal diseases was measured by the PNIF and active anterior rhinomanometry. Inclusion criteria was all subjects aged 18 to 75-years-old, sinonasal diseases/symptoms(nasal congestion, nasal discharge, nasal polyp, deviated nasal septum, nasal tumor, inferior turbinate hypertrophy, sinusitis, and allergic rhinitis), instant sensation of nasal obstruction, and nasal endoscopy finding were recorded. All subjects signed written consent. Compared with the active anterior rhinomanometry as the gold standard, the sensitivity, specificity, likelihood ratio, positive predictive value, and negative predictive value of the PNIF was analyzed. The cut-off point of nasal obstruction was defined from the Receiver Operating Characteristic curve analysis. The agreement between the PNIF and the stuffiness and between the PNIF and the presence of sino-nasal diseases were assessed by using Kappa.

Results: With the cut-off point of 90 L/min, the sensitivity of the peak nasal inspiratory flow was 0.87 (0.753-0.989). The specificity was 0.52 (0.429-0.617). The negative predictive value was 0.93 (0.872-0.997). The positive predictive value was 0.34 (0.237-0.446). The likelihood ratio was 1.81 (1.438-2.318). The mean of the PNIF in normal subjects was 97.11 ± 31.15. The agreement between the PNIF and the instant sensation of nasal blockage was 0.14 (-0.024-0.321) and the agreement between the PNIF and the sino-nasal diseases was 0.09 (-0.083-0.265).

Conclusion: The PNIF, regarding the cut-off point of 90 L/min, revealed good sensitivity and high negative predictive value but it had low specificity and low positive predictive value. The nasal peak flow did not agree well with the subjects’ symptoms of blockage and sino-nasal diseases.

Keywords: Peak nasal inspiratory flow, Active anterior rhinomanometry (AAR), Cut point, Sensitivity, Specificity, Receiver operating characteristic curve analysis