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Bilateral Anterolateral Magnetic Stimulation of the Phrenic Nerves Can Detect Diaphragmatic Fatigue^*

^* From the Division of Pulmonary, Critical Care and Sleep Medicine, State University of New York at Buffalo, Buffalo, NY.

Correspondence to: M. Jeffery Mador, MD, Associate Professor of Medicine, Division of Pulmonary, Critical Care & Sleep Medicine, Section 111S, State University of New York at Buffalo, Veterans Administration Medical Center, 3495 Bailey Ave, Buffalo, NY 14215; e-mail: Mador{at}acsu.buffalo.edu

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 techniques.

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.

Results: 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.

Key Words: diaphragm • muscle fatigue • phrenic nerve • respiratory muscles • transcutaneous nerve stimulation

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