Changes in aerodynamics during vocal cord dysfunction Dennis O. Frank-Ito n , Kristine Schulz, Gina Vess, David L. Witsell Division of Otolaryngology- Head and Neck Surgery, Duke University Medical Center, Durham, NC, USA article info Article history: Received 22 September 2014 Accepted 5 December 2014 Keywords: Vocal cord dysfunction Airflow Computational fluid dynamics Resistance Extrathoracic airway obstruction 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 (0.04 Pa.s/mL versus 0.02 Pa.s/mL) than in VCD; while resistance at the glottis and trachea remained roughly the same (0.04 Pa.s/mL) during normal inhalation, it escalated during VCD (0.11 Pa.s/mL and 0.13 Pa.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. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction Vocal cord dysfunction (VCD) is a respiratory condition where the larynx exhibits intermittent paradoxical closure of the vocal cords during respiration; this condition is also known in the literature as “paradoxical vocal fold motion”, “paradoxical vocal cord motion disorder”, “episodic laryngeal dyskinesis”, “paradoxical vocal cord dysfunction”, etc [1–5]. Typical episodes of VCD last from seconds to a few minutes; occur primarily during inspiration and are felt around the upper respiratory tract (neck), resulting in symptoms identical to extrathoracic airway obstruction such as cough, choking, and shortness of breath [6–8]. VCD is often misdiagnosed as asthma which leads to inappropriate choice of treatment options for subjects with this condition [4–11]. Management of this disorder includes speech therapy; education and anxiolytics in severe cases; and inhalation of heliox mixture, particularly for acute episodes [4,7–9,11,12]. Though the prevalence of VCD in adults and kids is not clear, it is estimated that the rate of incidence is between 2.5% and 26.9% [4,7–9,13]. In addition, young females and athletes have been reported to have a higher rate of being diagnosed with this disorder [3–8,11–15]. When symptoms of VCD are suspected, it is important to complete a diagnostic work up to rule out pulmonary, cardiac, or other serious conditions that require medical treatment. VCD is not usually seen on exam after the episode, largely because it is intermittent. However, a continuous laryngoscopy during exercise test is the gold standard for medical diagnosis of this disorder since it allows direct visualization of the vocal cords to determine paradoxical motions with a high degree of accuracy [4,6,8–10,13,16]. As VCD is intermittent, it can be difficult to conduct laryngoscopic examination in the middle of an acute attack due to patient distress. For this reason, provocation techniques such as performing an exercise on a treadmill or bicycle, and noxious stimuli such as methacholine, odor irritant and erg- ometer stress are sometimes used to trigger VCD during continuous laryngoscopic examination [1,4–7,13,16]. Spirometric measurement of inspiratory and expiratory airflow volume is an additional diagnostic tool for VCD; spirometry is less invasive and easier to obtain than Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/cbm Computers in Biology and Medicine http://dx.doi.org/10.1016/j.compbiomed.2014.12.004 0010-4825/& 2014 Elsevier Ltd. All rights reserved. n Correspondence to: Division of Otolaryngology - Head and Neck Surgery Duke University Medical Center Box 3805 Durham, NC 27710. Tel.: þ1 919 681 7247; fax: þ1 919 613 6524. E-mail address: dennis.frank@duke.edu (D.O. Frank-Ito). Computers in Biology and Medicine 57 (2015) 116–122