The study of maximal nasal inspiratory flow in humans

During inspiration through one nostril, airflow becomes limited to a maximal level (V̇l(max)) when the transmural pressure (Ptm) at a flow- limiting site (FLS) falls below a critical level (Ptm'). We compared two methods for measuring the Ptm' of the nasal FLS. Each of six subjects (four normal and two with allergic rhinitis out of season) performed multiple inspirations through one nostril as we varied the resistance at the nasal opening. Studies were performed after application of a topical decongestant without activation of the alae nasi. We determined Ptm' by regressing the resulting values of V̇l(max) on the corresponding transnasal pressure gradients (Regression Method). We also measured Ptm' directly using pressure catheters to measure the pressure surrounding the FLS and the lateral pressure near the FLS at V̇l(max) (Catheter Method). The mean value of Ptm' by the Regression Method was -3.8 ± 3.2 (SD) cmH₂O. The value by the Catheter Method with the catheter just downstream from the nasal FLS was - 3.5 ± 2.9 cmH₂O, which correlated closely with the Ptm by the Regression Method (r = 0.98). Our findings suggest that the Ptm' of the nasal airway can be determined by either method. The Catheter Method, however, requires only one inspiratory effort for each determination and simultaneously localizes the nasal FLS.