Comparison of different frequencies of transcutaneous electrical diaphragmatic stimulation

Most transcutaneous electric diaphragmatic stimulation (TEDS) studies use a stimulation frequency (SF) of 30 Hz, although the reason for this SF value is not completely understood. Objective: The purpose of this study was to compare the acute effect of two TEDS frequencies on the respiratory muscle strength and endurance, muscle activation, muscle thickness, diaphragmatic mobility, cardiovascular variables and safety in healthy subjects. Methods: Randomized crossover clinical trial with 20 healthy subjects subjected to two interventions: SF=30 Hz group and SF=80 Hz group. TEDS was applied at the diaphragm motor points with a symmetric biphasic pulsed current (pulse duration= 500 μs) for 30 minutes. The evaluated outcomes were systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), respiratory muscle strength by maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP), inspiratory peak flux (PIF), diaphragm thickness during inspiration (DTI) and expiration (DTE), diaphragm mobility and activation, and endurance (S-Index). Results: SF-30 Hz showed a reduction with respect to baseline values for SBP (p= 0.04), HR (p<0.001), DTE (p= 0.02), IPF (p= 0.01), and S-Index (p= 0.03). SF-80 Hz showed a reduction with respect to baseline values for HR (p<0.001) and an increase in MEP (p<0.001). However, these changes were not clinically important and there were no between-groups differences for any of the evaluated outcomes. No complications were observed. Conclusion: TEDS with SF-80 Hz produces similar effects to SF-30 Hz in healthy subjects and both frequencies proved to be safe (NCT03844711).