Oscillometric assessment of airway obstruction in a mechanical model of vocal cord dysfunction

Vocal cord dysfunction (VCD) is characterized by inappropriate adduction of the vocal cords, particularly during inspiration, resulting in obstruction and airflow limitation. Direct visualization of the vocal cords with laryngoscopy is the 'gold standard' for diagnosing VCD. However, it is an invasive technique that may induce airway irritation. The aim of this study was to determine whether the forced oscillation technique (FOT) is useful to estimate the degree of closure of a non-linear orifice under conditions mimicking those found in VCD. The FOT (5 Hz, +/-1 cm H(2)O) was applied to an airway model simultaneously with constant levels of flow in the normal breathing range (0-0.8l/s). Pressure-flow (P(0)-V'(0)) curves, quasi-static resistance (R(eff)) and oscillatory resistance (R(FOT)) were measured in orifices with different areas (0.15-1.12 cm2) and shapes and in an orifice with variable area. Their pressure-flow relationship followed a quadratic model. Changes in R(FOT) normalized by flow (DeltaR(FOT)/V'(0)) were related to changes in the area of the vocal cord model (1/A(VC2)(2)-1/A(VC1)(2)) from maximum aperture (A(VC1)) to different degrees of closure (A(VC2)): DeltaR(FOT)/V'(0)=1.93(1/A(VC2)(2)-1/A(VC1)(2))+2.08 cm H(2)Os(2)/l(2); r(2)=0.99. We conclude that FOT could be a useful tool for non-invasively assessing glottic closure in VCD diagnosis, obviating the need for other invasive techniques.