title: Does symptom-limited cycle exercise cause low frequency diaphragm fatigue in patients with heart failure?
abstract: BACKGROUND
  Reduced diaphragm contractility occurs in some healthy subjects when they exercise to exhaustion. This indicates low frequency fatigue, which may contribute to task failure. We hypothesised that patients with congestive heart failure (CHF) might be especially vulnerable to the development of low frequency diaphragm fatigue after exhaustive exercise.
  
  
  OBJECTIVE
  To study the effect of exhaustive incremental cycle exercise on diaphragm contractility in patients with CHF.
  
  
  METHODS
  12 patients with CHF with an ejection fraction of 36.5 +/- 7.3% and 12 healthy age-matched control subjects performed an incremental cycle test to exhaustion. The unpotentiated twitch transdiaphragmatic pressure (twitch Pdi) in response to bilateral anterolateral magnetic phrenic nerve stimulation (BAMPS) was measured before and after exercise.
  
  
  RESULTS
  Twitch Pdi at baseline was 20.2 +/- 6.7 cm H2O in the CHF group and 20.3 +/- .3 cm H2O in the controls (p = 0.957). 25 and 35 min post exercise the values were 19.9+/-5.4 and 20.0+/-5.1 cm H2O in the CHF group and 20.6 +/- 4.3 and 21.2 +/- 3.4 cm H2O in the control group; neither change was significant (F(2,27) = 0.007, p = 0.993; F(2,33) = 0.144, p = 0.866, respectively).
  
  
  CONCLUSIONS
  When patients with CHF cycle to exhaustion, low frequency fatigue of the diaphragm does not occur, and this is unlikely to be an important factor limiting exercise capacity of such patients.
authors.affiliation: Respiratory Muscle Laboratory, Royal Brompton and Harefield N.H.S Trust, Royal Brompton Hospital, London, UK. markdayer@gmail.com
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Dayer
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Hopkinson
authors.forename: Ewen T
authors.initials: ET
authors.lastname: Ross
authors.forename: Sophie
authors.initials: S
authors.lastname: Jonville
authors.forename: Tarek
authors.initials: T
authors.lastname: Sharshar
authors.forename: Mark
authors.initials: M
authors.lastname: Kearney
authors.forename: John
authors.initials: J
authors.lastname: Moxham
authors.forename: Michael I
authors.initials: MI
authors.lastname: Polkey
mesh_terms: D003964:Diaphragm / Q000503:physiopathology*; D005080:Exercise Test / Q000009:adverse effects*; D005541:Forced Expiratory Volume / Q000502:physiology; D006333:Heart Failure / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018763:Muscle Fatigue / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D011379:Prognosis; D012189:Retrospective Studies; D012720:Severity of Illness Index