Chest
Volume 121, Issue 2, February 2002, Pages 452-458
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Clinical Investigations
Neuromuscular Disease
Bilateral Anterolateral Magnetic Stimulation of the Phrenic Nerves Can Detect Diaphragmatic Fatigue

https://doi.org/10.1378/chest.121.2.452Get rights and content

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.

Section snippets

Subjects

Twelve healthy subjects (eight men and four women) with a mean (± SE) age of 27.7 ± 2.0 years participated in the study. The mean height and weight of the subjects were 1.76 ± 0.03 m and 83.4 ± 5.3 kg, respectively. The study was approved by the appropriate institutional review boards, and informed consent was obtained from all subjects.

Phrenic Nerve Stimulation

The phrenic nerves were stimulated by the following three different techniques: TES, CMS, and BAMPS. Gastric pressure (Pga), esophageal pressure (Pes), and

Effect of Hyperpnea on Twitch Pressures

TwPdi values from before and after hyperpnea to task failure are shown in Figure 1 . TwPdi fell significantly after hyperpnea with all three stimulation techniques. In three subjects, maximal stimulation could not be achieved with transcutaneous stimulation. These subjects were not included in the analysis of the transcutaneous TwPdi data. Expressing the TwPdi after hyperpnea as a percentage of the baseline value (to normalize for differences in baseline TwPdi between stimulation techniques),

Discussion

The major findings of this study are the following: (1) TwPdi during BAMPS is as good at detecting diaphragmatic fatigue as the other stimulation techniques; (2) TwPdi during BAMPS is reproducible; 3) the results of measuring TwPdi during BAMPS in the fresh state were similar to those observed during CMS but were larger than those observed during TES; and (4) twitch pressure during BAMPS plateaued at power outputs well below the maximum.

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