HYSTERESIS OF THE NASAL PRESSURE-FLOW RELATIONSHIP DURING HYPERPNEA IN NORMAL SUBJECTS

Hysteresis of the nasal airway pressure-flow relationship (PFR) is see n during hyperpnea, with lower nasal resistance during increasing insp iratory flow than during decreasing flow. We hypothesized that the nas al PFR hysteresis arose in the nasal vestibule airway because of progr essive collapse during the inspiration. We measured the inspiratory tr ansnasal and transvestibular PFR for one nasal passage in five normal subjects breathing via a nasal mask during voluntary hyperventilation, both with voluntary nostril flaring and without flaring. The inspirat ory hysteresis (IH) was quantified as the ratio of the areas under the descending and ascending pressure-flow curves. Flaring reduced the ve stibular IH from 1.96 +/- 0.06 to 1.15 +/- 0.06 and the nasal IH from 2.05 +/- 0.13 to 1.28 +/- 0.06 (both P < 0.01). Our results demonstrat e that hysteresis arises in the compliant vestibule segment of the nas al airway, likely because of progressive collapse of the nasal vestibu le during inspiration. The findings suggest that hysteresis is prevent ed by voluntary nostril flaring maintained throughout inspiration.