Potentiation of diaphragmatic twitch after voluntary contraction in normal subjects.
BACKGROUND
Skeletal muscle twitch responses may be transiently increased by previous contractions, a phenomenon termed twitch potentiation. The aim of this study was to examine the extent and time course of diaphragmatic twitch potentiation and its relationship to both the magnitude and duration of the preceding voluntary diaphragmatic contraction.


METHODS
Twitch transdiaphragmatic pressure (PDI) was measured in six normal subjects, before and after voluntary diaphragm contractions of 100%, 75%, 50%, and 25% of maximum PDI (PDImax) sustained for five and 10 seconds.


RESULTS
Twitch PDI was significantly increased after 100%, 75%, and 50% contractions. Following maximal contractions sustained for 10 seconds the mean increase in twitch PDI was 52%. Following 50% contractions sustained for five seconds the mean increase in twitch height was 28%. In all runs twitch PDI returned to rested levels within 20 minutes.


CONCLUSIONS
Twitch potentiation can be substantial, even following submaximal contractions, and must be taken into account when twitch pressure is used to assess diaphragm contractility.
Wragg
S
S
Department of Thoracic Medicine, King's College Hospital, London, UK.
Hamnegard
C
C
Road
J
J
Kyroussis
D
D
Moran
J
J
Green
M
M
Moxham
J
J
D000328:Adult; D003964:Diaphragm / Q000502:physiology*; D004558:Electric Stimulation; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D010791:Phrenic Nerve; D012119:Respiration / Q000502:physiology