title: Mechanisms of improvement of respiratory failure in patients with COPD treated with NIV.
abstract: BACKGROUND
  Noninvasive ventilation (NIV) improves gas-exchange and symptoms in selected chronic obstructive pulmonary disease (COPD) patients with hypercapnic respiratory failure. We hypothesized NIV reverses respiratory failure by one or all of increased ventilatory response to carbon-dioxide, reduced respiratory muscle fatigue, or improved pulmonary mechanics.
  
  
  METHODS
  Nineteen stable COPD patients (forced expiratory volume in one second 35% predicted) were studied at baseline (DO), 5-8 days (D5) and 3 months (3M) after starting NIV.
  
  
  RESULTS
  Ventilator use was 6.2 (3.7) hours per night at D5 and 3.4 (1.6) at 3M (p = 0.12). Mean (SD) daytime arterial carbon-dioxide tension (PaCO2) was reduced from 7.4 (1.2) kPa to 7.0 (1.1) kPa at D5 and 6.5 (1.1) kPa at 3M (p = 0.001). Total lung capacity decreased from 107 (28) % predicted to 103 (28) at D5 and 103 (27) % predicted at 3M (p = 0.035). At D5 there was an increase in the hypercapnic ventilatory response and some volitional measures of inspiratory and expiratory muscle strength, but not isolated diaphragmatic strength whether assessed by volitional or nonvolitional methods.
  
  
  CONCLUSIONS
  These findings suggest decreased gas trapping and increased ventilatory sensitivity to CO2 are the principal mechanism underlying improvements in gas-exchange in patients with COPD following NIV. Changes in some volitional but not nonvolitional muscle strength measures may reflect improved patient effort.
authors.affiliation: Respiratory Muscle Laboratory, Royal Brompton Hospital, London, UK. annabel@medex.org.uk
authors.forename: Annabel H
authors.initials: AH
authors.lastname: Nickol
authors.forename: Nicholas
authors.initials: N
authors.lastname: Hart
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Hopkinson
authors.forename: Carl-Hugo
authors.initials: CH
authors.lastname: Hamnegård
authors.forename: John
authors.initials: J
authors.lastname: Moxham
authors.forename: Anita
authors.initials: A
authors.lastname: Simonds
authors.forename: Michael I
authors.initials: MI
authors.lastname: Polkey
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology* / Q000628:therapy*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012121:Respiration, Artificial; D015656:Respiratory Mechanics; D012132:Respiratory Muscles / Q000503:physiopathology