Characteristics of nasal airflow and the effect of a nasal dilator in normal human subjects.

Nasal resistance contributes to negative airway pressure during breathing. We sought to define normal patterns of nasal flow and the effects of mechanical dilatation and splinting of the nares on flow during forced inspiration and expiration. Maximal inspiratory and expiratory flow volume loops (FVL) were determined in 17 normal subjects. Oral FVL were obtained with nares clamped and nasal FVL through a mask with and without dilatation of nares using a plastic splint (Nozovent®). Oral FVL were normal in all. Two patterns of nasal FVL were observed: one indicating ‘variable’ extrathoracic obstruction, the other indicating ‘fixed’ extrathoracic obstruction. Maximal inspiratory flow at 50% of vital capacity (FIF50) was improved by the Nozovent® only in those with a ‘variable’ pattern (FIF50 (L/sec): 1.54±0.3 to 2.86±0.5; P<0.05, versus 1.92±0.3 to 2.21±0.3; P=0.5). In subjects with a fixed pattern, failure of dilatation of the nares to increase flow suggests that the site of inspiratory flow limitation is within the bony nostril.