title: Changes in aerodynamics during vocal cord dysfunction.
abstract: BACKGROUND
  Changes in laryngeal airflow dynamics during episodes of vocal cord dysfunction (VCD) have not been well described. Very little is known about how inspiratory airflow is impacted when the vocal cords transition from normal inhalation state to a paradoxical adducted state; and how much change in laryngeal airflow and resistance occur before symptoms of stridor and air hunger emerge. This study provides new insight on the effects of VCD on respiratory airflow using computational fluid dynamics (CFD) techniques.
  
  
  METHODS
  Computed tomography images of a subject with normal vocal cords opening at the time of scanning were digitally modified to mimic an episode of VCD. To quantify and compare changes in inspiratory flow during VCD attack and normal inhalation, steady-state, laminar simulations were performed for three different breathing rates.
  
  
  RESULTS
  Pressure-flow analysis during VCD revealed that increasing inspiratory effort is not as efficient as in normal inhalation. Airflow resistance at the epiglottis was higher in the normal state (0.04Pa.s/mL versus 0.02Pa.s/mL) than in VCD; while resistance at the glottis and trachea remained roughly the same (0.04Pa.s/mL) during normal inhalation, it escalated during VCD (0.11Pa.s/mL and 0.13Pa.s/mL at the glottis and trachea, respectively). Peak airflow velocity and vorticity occurred around the glottis during VCD, and at the epiglottis during normal inhalation.
  
  
  CONCLUSIONS
  This pilot study demonstrates that attempting to force more inspired air will yield greater glottal resistance during VCD. Furthermore, there were evidence of abrupt laryngeal pressure gradient, chaotic airflow and high concentration of shear stresses in the glottal region.
authors.affiliation: Division of Otolaryngology- Head and Neck Surgery, Duke University Medical Center, Durham, NC, USA. Electronic address: dennis.frank@duke.edu.
authors.forename: Dennis O
authors.initials: DO
authors.lastname: Frank-Ito
authors.affiliation: Division of Otolaryngology- Head and Neck Surgery, Duke University Medical Center, Durham, NC, USA.
authors.forename: Kristine
authors.initials: K
authors.lastname: Schulz
authors.affiliation: Division of Otolaryngology- Head and Neck Surgery, Duke University Medical Center, Durham, NC, USA.
authors.forename: Gina
authors.initials: G
authors.lastname: Vess
authors.affiliation: Division of Otolaryngology- Head and Neck Surgery, Duke University Medical Center, Durham, NC, USA.
authors.forename: David L
authors.initials: DL
authors.lastname: Witsell
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D006801:Humans; D057446:Hydrodynamics; D021621:Imaging, Three-Dimensional; D008297:Male; D012123:Pulmonary Ventilation / Q000502:physiology*; D014057:Tomography, X-Ray Computed; D064706:Vocal Cord Dysfunction / Q000000981:diagnostic imaging / Q000503:physiopathology*; D014827:Vocal Cords / Q000000981:diagnostic imaging / Q000503:physiopathology*
keywords: Airflow; Computational fluid dynamics; Extrathoracic airway obstruction; Resistance; Vocal cord dysfunction