Using Portable Ultrasound to Monitor the Neuromuscular Reactivity to Low-Frequency Electrical Stimulation

• Main Authors: Alin Petraş, Răzvan Gabriel Drăgoi, Vasile Pupazan, Mihai Drăgoi, Daniel Popa, Adrian Neagu
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Diagnostics
• Subjects: M-mode scan; muscle activation; Teager–Kaiser energy operator (TKEO); electrotherapy; sensory threshold; motor threshold
• Online Access: https://www.mdpi.com/2075-4418/11/1/65

Neuromuscular electrical stimulation (NMES) is useful for muscle strengthening and for motor restoration of stroke patients. Using a portable ultrasound instrument, we developed an M-mode imaging protocol to visualize contractions elicited by NMES in the quadriceps muscle group. To quantify muscle activation, we performed digital image processing based on the Teager–Kaiser energy operator. The proposed method was applied for 35 voluntary patients (18 women and 17 men), of 63.8 ± 14.1 years and body mass index (BMI) 30.2 ± 6.70 kg/m² (mean ± standard deviation). Biphasic, rectangular electric pulses of 350 µs duration were applied at two frequencies (60 Hz and 120 Hz), and ultrasound was used to assess the sensory threshold (ST) and motor threshold (MT) amplitude of the NMES signal. The MT was 23.4 ± 4.94 mA, whereas the MT to ST ratio was 2.69 ± 0.57. Linear regression analysis revealed that MT correlates poorly with body mass index (R² = 0.004) or with the thickness of the subcutaneous adipose tissue layer that covers the treated muscle (R² = 0.013). Our work suggests that ultrasound is suitable to visualize neuromuscular reactivity during electrotherapy. The proposed method can be used in the clinic, enabling the physiotherapist to establish personalized treatment parameters.