Transdiapragmatic pressure and contractile properties of the diaphragm following magnetic stimulation.

Insufficient normal values exist regarding twitch transdiaphragmatic pressure (twPdi) derived from standardized cervical and cortical magnetic stimulation (MS) of the diaphragm. Therefore, 63 subjects (24 men, 39 women; 34 ± 13 years) underwent transcortical and posterior cervical MS of the diaphragm with simultaneous recording of twitch oesophageal and gastric pressures (twPes, twPgas). Following cortical MS at functional residual capacity, twPdi amplitudes showed high intra-individual variability which was markedly reduced when an inspiratory pressure trigger was applied. Lower limit of the 95% confidence interval computed around the mean value (LLN) was 12 cmH2O, independent of gender or age. Following cervical MS of the phrenic nerves, twPdi amplitudes were well reproducible and unaffected by gender, but age-dependent (age 18-30: LLN 23 cmH2O; age ≥ 30: LLN 16 cmH2O; p < 0.05). The inspiratory pathway can be assessed using cervical MS of the phrenic nerves. If transcranial motor cortex stimulation of the diaphragm is also applied, a standardized inspiratory pressure trigger is recommended. Dynamics of diaphragm contraction appear to be age-dependent.