Background and study objectives: Measurement of twitch
transdiaphragmatic pressure (TwPdi) during bilateral phrenic nerve
stimulation is presently the best method to detect diaphragmatic
fatigue in humans. The stimulation methods that are currently employed
(ie, transcutaneous electrical stimulation [TES] and
cervical magnetic stimulation [CMS]) have limitations. Bilateral
anterolateral magnetic stimulation of the phrenic nerves (BAMPS) was
recently described. The purpose of this study was to determine whether
BAMPS can reliably detect diaphragmatic fatigue, and to compare the
results with BAMPS with those obtained with the other stimulation
Subjects: Twelve healthy subjects
participated in the study.
Methods: TwPdi was measured
during TES, CMS, and BAMPS before and 10, 30, and 60 min after a
potentially fatiguing task. Voluntary hyperpnea to task failure was
used as the fatiguing task because this task has previously been shown
to reliably produce contractile fatigue of the diaphragm. To determine
the reproducibility of BAMPS, TwPdi was measured before and after a
nonfatiguing task in 10 of the subjects.
TwPdi fell significantly after the hyperpneic task with all three
stimulation techniques, and the amount by which TwPdi fell after
hyperpnea was not significantly different for the different stimulation
techniques. The percentage fall in TwPdi after hyperpnea was
significantly correlated between stimulation techniques (CMS vs BAMPS,
r = 0.72; TES vs BAMPS, r = 0.84; and
TES vs CMS, r = 0.67). The mean (± SE)
within-subject, between-trial coefficient of variation for TwPdi during
BAMPS was 5.1 ± 0.1%.
Conclusion: BAMPS is highly
reproducible and at least as good at detecting diaphragmatic fatigue as
the other stimulation techniques.