Mj. Mador et al., COMPARISON OF CERVICAL MAGNETIC AND TRANSCUTANEOUS PHRENIC-NERVE STIMULATION BEFORE AND AFTER THRESHOLD LOADING, American journal of respiratory and critical care medicine, 154(2), 1996, pp. 448-453
Citations number
19
Categorie Soggetti
Emergency Medicine & Critical Care","Respiratory System
Brief supramaximal stimulation of the phrenic nerves (twitch) is consi
dered a promising technique to detect diaphragmatic fatigue in humans.
However, the most commonly employed methodology (transcutaneous stimu
lation) is technically difficult. Cervical magnetic stimulation is a r
ecently described technique that is potentially simpler and may obviat
e some of the problems inherent with transcutaneous stimulation. The p
urpose of this study was to determine the ability of cervical magnetic
stimulation to evaluate diaphragmatic function. Accordingly, we measu
red transdiaphragmatic pressure (Pdi) during transcutaneous and cervic
al magnetic stimulation of the phrenic nerves before and after a poten
tially fatiguing task; inspiratory threshold loading to task failure.
During threshold loading, subjects generated approximately 60% of thei
r maximal esophageal pressure with each breath until they could no lon
ger reach the target pressure. At least 10 twitches were obtained duri
ng both transcutaneous and magnetic stimulation before and 10, 30, 60,
and 120 min after threshold loading. Control twitch Pdi was significa
ntly larger during magnetic stimulation compared with transcutaneous s
timulation: 39.3 +/- 3.0 (mean +/- SE) versus 27.4 +/- 2.3 cm H2O, p <
0.0005. This increase in twitch Pdi was solely due to the esophageal
component. Following threshold loading, a significant reduction in tra
nscutaneous twitch Pdi was seen in only three of the 10 subjects. Mean
transcutaneous twitch Pdi fell only slightly from 27.4 +/- 2.3 during
control to 25.1 +/- 2.2 cm H2O at 10 min after loading (p < 0.004). I
n contrast, magnetic twitch Pdi was significantly reduced in nine of t
he 10 subjects following threshold loading. Mean magnetic twitch Pdi f
ell from 39.3 +/- 3.0 during control to 31.1 +/- 3.0 cm H2O at 10 min
after loading (p < 0.0001). The average fall in twitch Pdi post-loadin
g (expressed as a percentage of the control value) was significantly g
reater for magnetic stimulation compared with transcutaneous stimulati
on: 21.0 +/- 3.1 versus 7.8 +/- 2.9%, p < 0.0001. In summary: (1) in t
he fresh state, twitch Pdi is larger with magnetic stimulation compare
d with transcutaneous stimulation, and (2) transcutaneous and cervical
magnetic twitch Pdi are affected differently by threshold loading to
task failure.