Respiratory Physiology & Neurobiology 188 (2013) 133–142 Contents lists available at SciVerse ScienceDirect Respiratory Physiology & Neurobiology j ourna l ho me pa ge: www.elsevier.com/loca te/resphysiol Frictional resistance sheds light on the multicomponent nature of nasal obstruction: A combined in vivo and computational fluid dynamics study Bruno Louis a,b,c , Jean-Franc ¸ ois Papon a,b,c,d , Céline Croce a,b,c , Georges Caillibotte e , Gabriela Sbirlea-Apiou a,b,c,1 , André Coste a,b,c,d , Redouane Fodil a,b,c , Daniel Isabey a,b,c,∗ a Inserm, U955, Equipe 13, Cell and Respiratory Mechanics Department, 8, rue du Général Sarrail, F-94010 Créteil Cedex, France b Université Paris Est, UMR S955, UPEC, 8, rue du Général Sarrail, F-94010 Créteil Cedex, France c CNRS, ERL 7240, 8, rue du Général Sarrail, F-94010 Créteil Cedex, France d AP–HP, Groupe Hospitalier H. Mondor – A. Chenevier, CHI Créteil, Service d’ORL et de Chirurgie Cervico-Faciale, 51, Avenue du Maréchal de Lattre de Tassigny, F-94010 Créteil Cedex, France e Centre de Recherche Claude-Delorme, Air Liquide, CRCD, 1, chemin de la Porte des Loges, Les Loges-en-Josas, BP 126, F-78354 Jouy-en-Josas, France a r t i c l e i n f o Article history: Accepted 22 May 2013 Keywords: Nasal airway model Nasal compliance Nasal resistance Rhinomanometry a b s t r a c t Exploring nasal flow contributes to better understanding of pathophysiological functions of nasal cavities. We combined the rhinomanometry measurements of 11 patients and computational fluid dynamics (CFD) simulations in 3 nasal airway models to dissect the complex mechanisms that determine nasal flow obstruction: spatial complexity and pressure-dependent deformability of nasal airways. We quantified spatial complexity by calculating longitudinal variations of hydraulic diameter, perimeter and area of nasal cavities, and their impact on flow characteristics by examining the longitudinal variations of the kinetic energy coefficient and the kinetic to potential energy ratio. Airway distensibility variably affected in vivo pressure–flow relationships through the appearance of flow-limitation patterns characterized by maximum flow and/or flow plateau. We quantified deformability and spatial complexity effects on nasal airway resistance by normalizing all data with averaged reference parameters. The results show that discrepancies in nasal flow resistances reflect airway deformability and geometrical complexity, and thereby constitute a framework to better characterize nasal obstruction. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The nasal cavities are complex structures, whose inner geometry tightly controls airflow, enabling key physiological functions, e.g., breathing, sensation of inspired air, air-conditioning (i.e., warm- ing, humidification and filtering) (Dahl and Mygind, 1998; Jones and Rog, 1998; Proctor and Swift, 1970; Proetz, 1956; Schwab and Zenkel, 1998; Wolf et al., 2004). Moreover, nasal airways provide a paradigm of how geometric form controls flow and physiological functions (Gambaruto et al., 2011). Based on recent studies, it has ∗ Corresponding author at: INSERM, UMR 955 (équipe 13), Faculté de Médecine, 8, rue du Général Sarrail, 94010 Créteil Cedex, France. Tel.: +33 1 49 81 37 00; fax: +33 1 48 98 17 77. E-mail addresses: bruno.louis@inserm.fr (B. Louis), jean-francois.papon@hmn.aphp.fr (J.-F. Papon), croceceline@hotmail.com (C. Croce), Georges.Caillibotte@AirLiquide.com (G. Caillibotte), GAPIOU@PARTNERS.ORG (G. Sbirlea-Apiou), andre.coste@chicreteil.fr (A. Coste), redouane.fodil@inserm.fr (R. Fodil), daniel.isabey@inserm.fr (D. Isabey). 1 Present addresses: (1) Wellman Center for Photomedicine, Massachusetts Gen- eral Hospital, Boston, MA, United States. (2) Department of Dermatology, Harvard Medical School, Boston, MA, United States. become more-and-more evident that inter- and intra-individual differences in nasal geometry (Gambaruto et al., 2011; Segal et al., 2008; Wen et al., 2008), pressure/time-dependent deformabilities of nasal cavities (Churchill et al., 2004; Fodil et al., 2005; Liu et al., 2009) and flow heterogeneities in left–right passages (Eccles, 1996; Hanif et al., 2000), all contribute to an unknown extent to the con- trol of nasal flow and functions. Thus, exploring the complexity of nasal flow, as done by many recent studies, definitely contributes to a better understanding of medical and physiological functions of nasal cavities, including nasal drug delivery, nasal toxicology and disease diagnosis (Liu et al., 2009). One challenging question concerning upper airway flow is how to explain nasal flow resistances in various subjects, different geometries and conditions, while variability predomi- nates. Notably, upper airway-flow studies are rarely performed in more than one geometry (Hörschler et al., 2006; Kelly et al., 2000; Keyhani et al., 1997; Schreck et al., 1993) because in vivo upper airway-flow measurements are difficult to obtain (Sullivan and Chang, 1991) for multiple reasons, e.g., probe access, geometric variability. Moreover, the most frequent routine exploration of nasal cavities, namely rhinomanometry (Clement, 1984), provides 1569-9048/$ – see front matter © 2013 Elsevier B.V. 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