title: Evidence of reduced respiratory muscle endurance in patients with heart failure.
abstract: OBJECTIVE
  We sought to investigate whether reduced respiratory muscle endurance contributes to increased dyspnea and decreased exercise capacity in patients with chronic heart failure.
  
  
  BACKGROUND
  In patients with heart failure, the sensation of dyspnea may be related to abnormalities of respiratory muscle function, such as diminished strength or endurance, or both.
  
  
  METHODS
  Respiratory muscle endurance was assessed by measuring maximal sustainable ventilatory capacity in 15 patients with congestive heart failure and 8 normal subjects using progressive isocapnic hyperpnea. Near-infrared spectroscopy of an accessory respiratory muscle, Borg scale recordings of perceived dyspnea, time in inspiration, time per breath and minute ventilation were measured. Exercise testing with measurement of oxygen consumption was also performed.
  
  
  RESULTS
  Maximal voluntary ventilation (normal subjects 167 +/- 40, heart failure group 89 +/- 31 liters/min) and maximal sustainable ventilatory capacity (normal subjects 90 +/- 23, heart failure group 53 +/- 22 liters/min) were significantly reduced in patients with heart failure (both p < 0.05). No significant accessory respiratory muscle deoxygenation was observed in either group. Borg scale recordings at maximal sustainable ventilatory capacity were comparable in both groups. At rest, the inspiratory duty cycle (i.e., time in inspiration divided by the time per breath) was comparable in the two groups (normal subjects 0.34 +/- 0.09, heart failure group 0.37 +/- 0.12, p = NS). However at maximal sustainable ventilatory capacity, only normal subjects had a significant increase in the inspiratory duty cycle (normal subjects 0.49 +/- 0.04, heart failure group 0.36 +/- 0.10, p < 0.05). This finding suggests obstruction to airflow in patients with congestive heart failure. Values for peak exercise minute ventilation did not differ significantly from values in maximal sustainable ventilatory capacity in either group and were significantly correlated (r = 0.84, p < 0.0001).
  
  
  CONCLUSIONS
  Respiratory muscle endurance as assessed by maximal sustainable ventilatory capacity is reduced in patients with heart failure.
authors.affiliation: Cardiovascular Section, Veterans Administration Medical Center, Philadelphia, Pennsylvania.
authors.forename: D M
authors.initials: DM
authors.lastname: Mancini
authors.forename: D
authors.initials: D
authors.lastname: Henson
authors.forename: J
authors.initials: J
authors.lastname: LaManca
authors.forename: S
authors.initials: S
authors.lastname: Levine
mesh_terms: D000328:Adult; D000368:Aged; D002908:Chronic Disease; D004417:Dyspnea / Q000209:etiology; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D006333:Heart Failure / Q000150:complications / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008451:Maximal Voluntary Ventilation; D008875:Middle Aged; D010101:Oxygen Consumption; D010807:Physical Endurance; D012044:Regression Analysis; D012119:Respiration; D012132:Respiratory Muscles / Q000503:physiopathology*