Bilateral magnetic stimulation of the phrenic nerves from an anterolateral approach.

Abstract

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.

Effect of lung volume on the oesophageal diaphragm EMG assessed by magnetic phrenic nerve stimulation

“…However, with ES it can be difficult to sustain supramaximal phrenic nerve stimulation [10,12,13] especially when stimulation is performed bilaterally. Supramaximal stimulation is critical since the CMAP recorded from the oesophageal electrode is a summation from the left and right hemidiaphragms whose shape and polarity can be different.…”

“…Even with great care maximal stimulation may not be achieved constantly [13] since stimulating-electrode position is so critical. In contrast, with bilateral anterolateral magnetic stimulation the phrenic nerves can be reliably maximally stimulated [9,10]. The ability to easily achieve maximal phrenic nerve stimulation makes magnetic stimulation a useful investigative tool.…”

“…Bilateral magnetic stimulation of the phrenic nerves was performed using two 43 mm figure of eight coils (P/N 9784-00) powered by Magstim 200 stimulators (Magstim Co. Ltd., Whitland, Dyfed, UK). The coils were placed anterolaterally on each side of the neck over the phrenic nerves [9,10]. Five to seven supramaximal twitches were obtained at each lung volume.…”

Diabetic polyneuropathy is associated with respiratory muscle impairment in type 2 diabetes

“…BAMPS has been consistently demonstrated to achieve supramaximality in several previous studies and this was therefore not re-tested in the present study [25,28,29]. A fully automated and controlled inspiratory pressure trigger was applied at 0.5 kPa for TwPmo, as previously established [27,30].…”

“…During bilateral anterior magnetic phrenic nerve stimulation (BAMPS), twitch mouth (TwPmo), twitch oesophageal (TwPes) and twitch gastric (TwPga) pressures were recorded at functional residual capacity (Magstim 200 2 ; Magstim, Whitland, UK) [25][26][27]. BAMPS has been consistently demonstrated to achieve supramaximality in several previous studies and this was therefore not re-tested in the present study [25,28,29].…”