Peak nasal inspiratory flow--the plateau effect.

To study the efficacy of peak nasal inspiration flow (PNIF) as a means of recording change in nasal patency 20 subjects were given increasing doses of intranasal xylometazoline. Nasal resistance (NR) and peak nasal inspiratory flow (PNIF) were measured in the resting state and after each xylometazoline administration. Successive increases in dose caused a progressive decrease in nasal resistance and an increase in PNIF but the change in peak nasal inspiratory flow (PNIF) was much less. Peak nasal inspiratory flow shows a plateau effect as nasal resistance decreases. The reasons for this plateau are discussed in terms of respiratory flow mechanics.