title: Central airway mechanics and flow limitation in acquired tracheobronchomalacia.
abstract: BACKGROUND
  Acquired tracheobronchomalacia (TBM) can cause central airway collapse in patients with COPD and may worsen airflow obstruction and symptoms. It is usually not known whether central airway malacia contributes to airflow obstruction. This study was undertaken to quantify central airway collapsibility and relate it to expiratory flow limitation in patients with TBM.
  
  
  METHODS
  Eighty patients evaluated for acquired TBM and 4 healthy control subjects were studied with measurements of central airway narrowing derived from bronchoscopic videotapes and simultaneous pressure measurements in the trachea and esophagus. Tracheal narrowing was assessed by a shape index and plotted against the transtracheal pressure to measure collapsibility. Subsequently, airflow and transpulmonary pressure (PL) were measured to identify expiratory flow limitation during quiet breathing and to determine the critical PL required for maximum expiratory flow.
  
  
  RESULTS
  Tracheal collapsibility varied widely among patients. Some had profound tracheal narrowing during quiet breathing, and others showed substantial collapse only during forced exhalation. Of the patients, 15% were not flow limited during quiet breathing, 53% were flow limited throughout exhalation, and 30% were flow limited only during the latter part of the exhalation. Patients with flow limitation at rest showed greater tracheal narrowing than those without (p = 0.009), but the severity of expiratory flow limitation was not closely related to tracheal collapsibility. Twenty-three patients were flow limited during quiet exhalation at PLs that did not cause central airway collapse.
  
  
  CONCLUSIONS
  In TBM, central airway collapse is not closely related to airflow obstruction, and expiratory flow limitation at rest often occurs in peripheral airways without central airway collapse.
authors.affiliation: Beth Israel Deaconess Medical Center, 330 Brookline Ave, DA 717, Boston, MA 02215, USA. sloring@bidmc.harvard.edu
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Loring
authors.forename: Carl R
authors.initials: CR
authors.lastname: O'donnell
authors.forename: David J
authors.initials: DJ
authors.lastname: Feller-Kopman
authors.forename: Armin
authors.initials: A
authors.lastname: Ernst
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000402:Airway Obstruction / Q000209:etiology / Q000503:physiopathology; D001982:Bronchial Diseases / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D001999:Bronchoscopy; D002357:Cartilage Diseases / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D005260:Female; D005500:Follow-Up Studies; D005540:Forced Expiratory Flow Rates / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D015656:Respiratory Mechanics / Q000502:physiology*; D012720:Severity of Illness Index; D014133:Tracheal Diseases / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D014741:Video Recording