GH Mills, D Kyroussis, CH Hamnegard, MI Polkey, M Green and J Moxham
Department of Thoracic Medicine, Royal Brompton Hospital, London, United Kingdom.

We investigated whether bilateral magnetic stimulation of the phrenic nerves from an anterolateral approach (BAMPS) could combine the reproducibility and ease of use of cervical magnetic stimulation (CMS) with the specificity of bilateral electrical stimulation (BES) and whether it could be used in supine subjects. We placed two double 43-mm coils over the phrenic nerves in the neck. BAMPS produced supramaximal phrenic stimulation by electromyogram (EMG) assessment in six of seven subjects. There was no significant difference in the twitch gastric pressure/twitch esophageal pressure ratio (twitch Pgas/Pes) between BAMPS (1.2) and BES (1.3). Both differed from CMS (0.9, p < 0.001). The effect of a change in posture on twitch transdiaphragmatic pressure (TwPdi) and Pgas/Pes ratio was the same for BAMPS and BES. In normal subjects and patients BAMPS correlated significantly with BES (r = 0.97), maximal sniffs (r = 0.85), and CMS (r = 0.92). The mean difference between BAMPS and BES was 0.3 cm H2O (SD = 2.3). Two-minute maximal isocapnic ventilation produced a 19% fall in TwPdi elicited by BAMPS. BAMPS is easy, well tolerated and can be used in the supine subject. TwPdi and partitioning of Pes and Pgas were very close for BAMPS and BES, suggesting similar specificity for the diaphragm.

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