Forced oscillation technique to evaluate tracheostenosis in patients with neurologic injury.

STUDY OBJECTIVES To determine the utility of forced oscillation technique (FOT) for measuring pulmonary resistance and reactance in patients with central nervous system injuries, for detection and follow-up of posttracheostomy tracheal stenosis. DESIGN Case series. SETTING A rehabilitation hospital, Brasilia, Distrito Federal, Brazil. PATIENTS Ten consecutive neurologically impaired patients, who had previously undergone tracheostomies, with tracheostenosis without current tracheostomy or other tracheal lesion. INTERVENTIONS AND MEASUREMENTS FOT evaluations were compared to tracheal diameter before and after bronchoscopic tracheostenosis dilatation procedures. Forced spirometry examinations were also obtained and compared. RESULTS Tracheal stenotic lesions were characterized by marked increase in resistance and reduction in reactance at low frequency and a marked increase in resonance frequency (Rf). Consistent reversal of this pattern with large reductions in total impedance of the respiratory system (Zresp) Rf and resistance at 5 Hz (R 5 Hz) were noted in all patients after each successful dilatation. Diameter of the stenosis was strongly correlated with Rf, Zresp, and R 5 Hz. The change in diameter before and after dilatation was similarly correlated with the changes in FOT values of Rf and Zresp. Spirometry values did not correlate well with the diameter of the tracheal stenosis. CONCLUSION The strong correlation of Rf, Zresp, and R 5 Hz to diameter of tracheostenosis suggests a previously unappreciated role for FOT in the noninvasive detection and follow-up of airway stenosis. This may be especially useful for patients with concomitant neurologic disabilities who are at risk of airway stenosis.