Chest
Volume 120, Issue 1, July 2001, Pages 69-73
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Clinical Investigations
Techniques
Forced Oscillation Technique to Evaluate Tracheostenosis in Patients With Neurologic Injury

https://doi.org/10.1378/chest.120.1.69Get rights and content

Study objectives

To determine the utility of forcedoscillation technique (FOT) for measuring pulmonary resistance andreactance in patients with central nervous system injuries, fordetection and follow-up of posttracheostomy tracheal stenosis.

Design

Case series.

Setting

Arehabilitation hospital, Brasilia, Distrito Federal, Brazil.

Patients

Ten consecutive neurologically impaired patients, who had previously undergone tracheostomies, with tracheostenosiswithout current tracheostomy or other tracheal lesion.

Interventions and measurements

FOT evaluations werecompared to tracheal diameter before and after bronchoscopictracheostenosis dilatation procedures. Forced spirometry examinationswere also obtained and compared.

Results

Trachealstenotic lesions were characterized by marked increase in resistanceand reduction in reactance at low frequency and a marked increase inresonance frequency (Rf). Consistent reversal of thispattern with large reductions in total impedance of the respiratorysystem (Zresp) Rf and resistance at 5 Hz (R 5 Hz) werenoted in all patients after each successful dilatation. Diameter of thestenosis was strongly correlated with Rf, Zresp, and R 5Hz. The change in diameter before and after dilatation was similarlycorrelated with the changes in FOT values of Rf and Zresp. Spirometry values did not correlate well with the diameter ofthe tracheal stenosis.

Conclusion

The strongcorrelation of Rf, Zresp, and R 5 Hz to diameter oftracheostenosis suggests a previously unappreciated role for FOT in thenoninvasive detection and follow-up of airway stenosis. This may beespecially useful for patients with concomitant neurologic disabilitieswho are at risk of airway stenosis.

Section snippets

Materials and Methods

During the period July 1,1998 to August 1, 2000, 43 patients were diagnosed by bronchoscopy with cicatricial tracheostenosis of ≥ 50% of the diameter of the trachea. All but one had undergone tracheostomy for airway management of the complications of neurologic disease or injury. Excluded from this analysis were patients in whom we encountered multiple lesions, such as chondromalacia, granulomas, open tracheostomy fistulas, and vocal cord paralysis concomitant with the tracheostenosis. The

Results

The 10 patients (Table 1), 7 men and 3 women, ranged in age from 13 to 55 years, with a mean of 26.3 years. The diameters of the tracheal stenosis ranged from a minimum of 2 mm before and a maximum of 13 mm after dilatation. Length of the stenosis varied from 3 mm to 3 cm. Principal admission diagnosis was tetraplegia in four patients and brain injury in five patients. One patient suffered combined cervical spine and brain injury.

Tracheal diameter was strongly correlated with resonance

Discussion

The FOT described by Dubois et al8 in 1956 has been used for pulmonary function studies in children,9veterinary medicine,10 and epidemiologic studies.11 Wassermann et al7 have presented another technique, using local pressure and flow measurements during bronchoscopy to discriminate between stenoses requiring surgery and those not requiring surgery. We are not aware of any prior studies demonstrating the use of FOT for the noninvasive diagnosis or follow-up of tracheal stenosis. This is likely

Conclusion

The demonstrated sensitivity of the FOT values of Rf, Zresp, and R/5 Hz may allow a role in predicting the presence of an upper airway stenosis in patients with prior airway intubation and tracheostomy. Once an airway lesion has been confirmed as a cicatricial stenosis, FOT values, especially Rf, may be used as a follow-up device. It may allow the timing of intervention to be based on deterioration in Rf. FOT may be especially useful in evaluating and following up tracheal stenosis for patients

References (16)

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    Our data did not show any significant correlation between resistance and the percentage of tracheal narrowing. Horan et al. evaluated the utility of FOT in patients with central nervous system injuries, for detection and follow-up of post tracheostomy tracheal stenosis.20 FOT evaluations were compared to tracheal diameter before and after bronchoscopic tracheostenosis dilatation procedures.

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This study was supported solely from the funds of the University SARAHin Rehabilitation Sciences and the Hospital SARAH, Brasília, DF, Brazil.

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