title: Non-invasive mechanical ventilation improves walking distance but not quadriceps strength in chronic respiratory failure.
abstract: BACKGROUND
  In patients with chronic respiratory failure (CRF) nocturnal mechanical ventilation (NMV) confers increased exercise tolerance. The hypothesis tested in the present study was that the increased exercise performance is associated with increased quadriceps strength.
  
  
  METHODS
  In 28 patients with CRF due to chronic obstructive pulmonary disease and restrictive thoracic disease (post-tuberculosis-sequelae, scoliosis and obesity-hypoventilation) NMV was started. Before and after 2-month NMV the exercise tests, namely shuttle and 6-min walking distance, were performed. Furthermore, quadriceps strength was measured as the twitch tension elicited by magnetic stimulation the femoral nerve (TwQ) and the maximum voluntary contraction force (MVC).
  
  
  RESULTS
  After 2 months therapy with NMV there was significant clinical and blood gas improvement. NMV significantly improved the walking distance by approximately 18% but there was no improvement in TwQ or MVC, the data could exclude a 15% improvement in TwQ with 82% confidence.
  
  
  CONCLUSIONS
  The strength of quadriceps does not change after 2 months of effective NMV in patients with CRF despite a marked increase in endurance time. Factors other than quadriceps strength account for the improved performance.
authors.affiliation: Krankenhaus Kloster Grafschaft, Zentrum für Pneumologie, Beatmungs- und Schlafmedizin, D-57392 Schmallenberg-Grafschaft, Germany. bernd.schoenhofer@t-online.de
authors.forename: Bernd
authors.initials: B
authors.lastname: Schönhofer
authors.forename: Christoph
authors.initials: C
authors.lastname: Zimmermann
authors.forename: Piotr
authors.initials: P
authors.lastname: Abramek
authors.forename: Stefan
authors.initials: S
authors.lastname: Suchi
authors.forename: Dieter
authors.initials: D
authors.lastname: Köhler
authors.forename: Michael I
authors.initials: MI
authors.lastname: Polkey
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D006801:Humans; D007866:Leg; D008168:Lung / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology / Q000628:therapy*; D012121:Respiration, Artificial / Q000379:methods*; D013718:Tensile Strength; D016138:Walking