POTENTIATION OF DIAPHRAGMATIC TWITCH AFTER VOLUNTARY CONTRACTION IN NORMAL SUBJECTS

Background - Skeletal muscle twitch responses may be transiently incre ased by previous contractions, a phenomenon termed twitch potentiation . The aim of this study was to examine the extent and time course of d iaphragmatic twitch potentiation and its relationship to both the magn itude and duration of the preceding voluntary diaphragmatic contractio n. 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 afte r 100%, 75%, and 50% contractions. Following maximal contractions sust ained for 10 seconds the mean increase in twitch PDI was 52%. Followin g 50% contractions sustained for five seconds the mean increase in twi tch height was 28%. In all runs twitch PDI returned to rested levels w ithin 20 minutes. Conclusions - Twitch potentiation can be substantial , even following submaximal contractions, and must be taken into accou nt when twitch pressure is used to assess diaphragm contractility.