An investigation of upper extremity impedance modeling and sensory thresholds in envelope wave electrical stimulation

Objectives: To investigate how impedance values and sensory thresholds at various human upper limb sites affect the parameter settings of electrical stimulation equipment in low and medium frequency envelope electrical stimulation therapy. Methods: The study involved testing different upper limb sites on 22 healthy subjects (ages 21-25, 11 males and 11 females) by adjusting the modulation wave frequency, carrier frequency, and current intensity of the output. Five types of electrodes of various sizes were used in the tests. Results: The impedance test results for the human upper limb showed a wide range of impedance values across electrodes of different sizes. A new impedance model of the human upper limb was proposed, which accurately fits the relationship between frequency and impedance values. In electrical stimulus sensory experiments, the voltage perception threshold (VPT) introduced in this study was identified as a novel metric for electrical stimulus sensation. Unlike the current perception threshold, VPT does not consider the effects of current magnitude and output frequency. The range of sensory thresholds was 6-8 V, while the suprathreshold was 9-11 V. Neither experiment showed gender differences. Conclusions: Determining the value of the power supply and the output intensity of device power amplification circuitry based on the VPT can provide a more precise therapeutic dose for electrical stimulation therapy.