title: Predictive significance of the six-minute walk distance for long-term survival in chronic hypercapnic respiratory failure.
abstract: BACKGROUND
  The 6-min walk distance (6-MWD) is a global marker of functional capacity and prognosis in chronic obstructive pulmonary disease (COPD), but less explored in other chronic respiratory diseases.
  
  
  OBJECTIVE
  To study the role of 6-MWD in chronic hypercapnic respiratory failure (CHRF).
  
  
  METHODS
  In 424 stable patients with CHRF and non-invasive ventilation (NIV) comprising COPD (n = 197), restrictive diseases (RD; n = 112) and obesity-hypoventilation-syndrome (OHS; n = 115), the prognostic value of 6-MWD for long-term survival was assessed in relation to that of body mass index (BMI), lung function, respiratory muscle function and laboratory parameters.
  
  
  RESULTS
  6-MWD was reduced in patients with COPD (median 280 m; quartiles 204/350 m) and RD (290 m; 204/362 m) compared to OHS (360 m; 275/440 m; p < 0.001 each). Overall mortality during 24.9 (13.1/40.5) months was 22.9%. In the 424 patients with CHRF, 6-MWD independently predicted mortality in addition to BMI, leukocytes and forced expiratory volume in 1 s (p < 0.05 each). In COPD, 6-MWD was strongly associated with mortality using the median [p < 0.001, hazard ratio (HR) = 3.75, 95% confidence interval (CI): 2.24-6.38] or quartiles as cutoff levels. In contrast, 6-MWD was only significantly associated with impaired survival in RD patients when it was reduced to 204 m or less (1st quartile; p = 0.003, HR = 3.31, 95% CI: 1.73-14.10), while in OHS 6-MWD had not any prognostic value.
  
  
  CONCLUSIONS
  In patients with CHRF and NIV, 6-MWD was predictive for long-term survival particularly in COPD. In RD only severely reduced 6-MWD predicted mortality, while in OHS 6-MWD was relatively high and had no prognostic value. These results support a disease-specific use of 6-MWD in the routine assessment of patients with CHRF.
authors.affiliation: Center for Pneumology, Donaustauf Hospital, Donaustauf, Germany. stephan.budweiser@klinik.uni-regensburg.de
authors.forename: Stephan
authors.initials: S
authors.lastname: Budweiser
authors.forename: Felix
authors.initials: F
authors.lastname: Heidtkamp
authors.forename: Rudolf A
authors.initials: RA
authors.lastname: Jörres
authors.forename: Frank
authors.initials: F
authors.lastname: Heinemann
authors.forename: Michael
authors.initials: M
authors.lastname: Arzt
authors.forename: Stephan
authors.initials: S
authors.lastname: Schroll
authors.forename: Kathrin
authors.initials: K
authors.lastname: Schmidbauer
authors.forename: Andre P
authors.initials: AP
authors.lastname: Hitzl
authors.forename: Michael
authors.initials: M
authors.lastname: Pfeifer
mesh_terms: D000368:Aged; D015992:Body Mass Index; D005080:Exercise Test / Q000592:standards*; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000175:diagnosis* / Q000209:etiology / Q000401:mortality; D008297:Male; D008875:Middle Aged; D010845:Obesity Hypoventilation Syndrome / Q000150:complications; D011379:Prognosis; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications; D012121:Respiration, Artificial; D012131:Respiratory Insufficiency / Q000175:diagnosis* / Q000209:etiology / Q000401:mortality; D012307:Risk Factors; D016019:Survival Analysis