Late Breaking Abstract - Effect of body position on inspiratory and sensory responses to rapid bilateral anterolateral magnetic phrenic nerve stimulation

Mechanical ventilation can induce lung injury and diaphragmatic dysfunction, which may be attenuated by rapid bilateral magnetic phrenic nerve stimulation (rBAMPS), as recently explored in the ICU. Given that a change in body position during mechanical ventilation alters patient prognosis, knowing effectiveness, perception and tolerance of rBAMPS in different positions is essential. Thus, this study compared inspiratory responses, perception and tolerance to rBAMPS in healthy participants while semirecumbent, supine, and seated. 17 participants (8F) underwent 3 blocks of 1-s rBAMPS trains at 25Hz starting at 20% of maximal stimulator output with increases of 10% until participant cessation. Transdiaphragmatic pressure (p_di) was recorded via balloon catheters, flow (and thus tidal volume [V_T]) via a pneumatometer, and discomfort, pain, and paresthesia via a 0–10 point scale. Participants' tolerance was assessed as the highest stimulator output tolerated in each position. Levels of resting breathing (mean V_T semirecumbent=0.88±0.50L, supine=0.70±0.38L, sitting=0.78±0.40L) and pressure generation (mean p_di semirecumbent=10.8±5.7cmH₂O, supine=8.3±4.5cmH₂O, sitting=10.3±4.7 cmH₂O) could be achieved in all participants and positions. V_T and p_di were significantly higher when semirecumbent compared to supine (mean increase: 2.4mL•kg⁻¹ of body weight, p<0.001; 2.5cmH₂O, P=0.004). Tolerance was highest while semirecumbent and lowest while sitting, with no differences in sensory ratings. Thus, semirecumbent may be ideal to increase the diaphragm stimulus, while supine may limit V_T and lung overdistension when using rBAMPS as a therapeutic intervention in the ICU.