Mj. Mador et al., TWITCH POTENTIATION FOLLOWING VOLUNTARY DIAPHRAGMATIC CONTRACTION, American journal of respiratory and critical care medicine, 149(3), 1994, pp. 739-743
Citations number
21
Categorie Soggetti
Emergency Medicine & Critical Care","Respiratory System
The purpose of this study was to determine whether twitch potentiation
(a transient augmentation of twitch tension following Vigorous muscul
ar contraction) occurs in the human diaphragm invivo. Six healthy subj
ects were studied. To determine whether twitch potentiation occurs, th
e subjects attempted to maximally activate their diaphragm by performi
ng the combined Mueller-expulsive maneuver with visual feedback (Pdi(m
ax) maneuver). Twitches were obtained before, at 10 s after the transd
iaphragmatic pressure (Pdi) maneuver, and at intervals over the ensuin
g 10 min. We also determined whether twitch potentiation would occur f
ollowing submaximal voluntary diaphragmatic contractions (33 and 66% o
f Pdi(max)). In addition, we examined whether repeated voluntary contr
actions would result in greater twitch potentiation compared with that
observed after a single voluntary contraction. Twitch potentiation wa
s observed in every subject. The number of maximal voluntary contracti
ons (MVC) (one, two, or four) had no significant effect on the degree
of twitch potentiation. The increase in twitch amplitude (expressed as
a percentage of the control value) averaged 63 +/- 35% (SD) (pooled d
ata from one, two, and four contraction trials). Twitch potentiation d
ecayed in a monoexponential fashion (r = 0.99) with a time constant of
125 s (95% Cl = 100 to 160 s). Twitch potentiation was also observed
after submaximal voluntary diaphragmatic contractions. Again, the numb
er of voluntary contractions (one or four) had no significant effect o
n the degree of twitch potentiation. After submaximal diaphragmatic co
ntractions of 66% of Pdi(max), the degree of twitch potentiation was n
ot significantly different, 61 +/- 36% (pooled data from one and four
contraction trials) from that observed following the maximal voluntary
contraction maneuvers. However, twitch potentiation was significantly
less, 19 +/- 17% (p < 0.0001) (pooled data from one and four contract
ion trials) after submaximal diaphragmatic contractions of 33% of Pdi(
max) compared with that observed at higher levels of contractions.