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 cen tral nervous system injuries, for detection and follow-up of posttracheosto my tracheal stenosis. Design: Case series. Setting: A rehabilitation hospital, Brasilia, Distrito Federal, Brazil. Patients: Ten consecutive neurologically impaired patients, who had previou sly undergone tracheostomies, with tracheostenosis without current tracheos tomy or other tracheal lesion. Interventions and measurements: FOT evaluati ons were compared to tracheal diameter before and after bronchoscopic trach eostenosis 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 increa se in resonance frequency (Rf), Consistent reversal of this pattern with la rge 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 successfu l dilatation. Diameter of the stenosis was strongly correlated with Rf, Zre sp, and R 5 Hz, The change in diameter before and after dilatation was simi larly 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 non invasive detection and follow-up of airway stenosis. This may be especially useful for patients with concomitant neurologic disabilities who are at ri sk of airway stenosis.