High frequency diaphragmatic fatigue detected with paired stimuli in humans.
OBJECTIVE
The purpose of this study was to determine whether high frequency fatigue was present in the diaphragm after intense whole body endurance exercise.


METHODS
We used bilateral phrenic nerve stimulation (BPNS) before and during recovery from whole body exercise to detect fatigue in the diaphragm. To detect high frequency fatigue we used paired stimuli at 10, 20, 50, 70, and 100 Hz frequency and determined the transdiaphragmatic pressure (Pdi) response to the second stimulation (T2).


RESULTS
The subjects (N = 10) exercised at 93.3 +/- 2.3% of their VO2max for 9.9 +/- 0.5 min. The Pdi response to "twitch" and 10 Hz "tetanic" stimulation was decreased immediately after exercise versus pre-exercise values (-23.4 +/- 3.3%). The T2 amplitude was substantially reduced at all frequencies immediately after exercise (-28.0%), but by 30 min into recovery the T2 amplitude at 70 and 100 Hz was not different from pre-exercise values. In contrast, at 10 and 20 Hz the T2 response was still significantly reduced.


CONCLUSIONS
We interpret these data to mean that high frequency fatigue as well as low frequency fatigue were present in the diaphragm after intense whole body endurance exercise.
Babcock
M A
MA
John Rankin Laboratory of Pulmonary Medicine, Department of Preventive Medicine, University of Wisconsin-Madison 53705-2368, USA.
Pegelow
D F
DF
Taha
B H
BH
Dempsey
J A
JA
D000328:Adult; D003964:Diaphragm / Q000502:physiology*; D004558:Electric Stimulation; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D010791:Phrenic Nerve / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*