Does symptom-limited cycle exercise cause low frequency diaphragm fatigue in patients with heart failure?
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.
Dayer
Mark J
MJ
Respiratory Muscle Laboratory, Royal Brompton and Harefield N.H.S Trust, Royal Brompton Hospital, London, UK. markdayer@gmail.com
Hopkinson
Nicholas S
NS
Ross
Ewen T
ET
Jonville
Sophie
S
Sharshar
Tarek
T
Kearney
Mark
M
Moxham
John
J
Polkey
Michael I
MI
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