Comparing phrenic nerve stimulation using three rapid coils: implications for mechanical ventilation

Rationale Rapid magnetic stimulation (RMS) of the phrenic nerves may serve to attenuate diaphragm atrophy during mechanical ventilation. With different coil shapes and stimulation location, inspiratory responses and side-effects may differ. Objective To compare the inspiratory and sensory responses of three different RMS-coils either used bilaterally on the neck or on the chest, and to determine if ventilation over 10min can be achieved without muscle fatigue and coils overheating. Methods Healthy participants underwent bilateral anterior 1-s RMS on the neck (RMS BAMPS ) (n=14) with three different pairs of magnetic coils (parabolic, D-shape, butterfly) at 15, 20, 25 and 30Hz stimulator-frequency and 20% stimulator-output with +10% increments. The D-shape coil with individual optimal stimulation settings was then used to ventilate participants (n=11) for up to 10min. Anterior RMS on the chest (RMS aMS ) (n=8) was conducted on an optional visit. Airflow was assessed via pneumotach and transdiaphragmatic pressure via esophageal and gastric balloon catheters. Perception of air hunger, pain, discomfort and paresthesia were measured with a numerical scale. Main results Inspiration was induced via RMS BAMPS in 86% of participants with all coils and via RMS aMS in only one participant with the parabolic coil. All coils produced similar inspiratory and sensory responses during RMS BAMPS with the butterfly coil needing higher stimulator-output, which resulted in significantly larger discomfort ratings at maximal inspiratory responses. Ten of 11 participants achieved 10min of ventilation without decreases in minute ventilation (15.7±4.6L/min). Conclusions RMS BAMPS was more effective than RMS aMS, and could temporarily ventilate humans seemingly without development of muscular fatigue.