Efficient Suprahyoid Muscle Contraction by Combined Modulated Currents in Mice

OBJECTIVE: This study aimed to optimize electrical stimulation modalities for the suprahyoid muscles to improve swallowing function. We hypothesized that novel stimulus patterns (amplitude-modulated, mid-frequency sinusoidal, exponentially amplified, and short-pulse waveforms) would enhance contraction efficiency. METHODS: We delivered 80-Hz rectangular pulse, 2-kHz alternating current (AC) with nth-power sinusoidal modulation (n = 1, 5, 7, 9, 11), and 4- and 8-kHz sine waves. We also tested 2-kHz AC with nth-power sinusoidal modulation combined with short-pulsed currents. These were applied via subcutaneously embedded Ag-AgCl ball electrodes targeting the suprahyoid muscles in anesthetized mice. Threshold intensities were determined using isometric contraction measurements. Discomfort levels for each stimulus were then assessed in awake conditions. RESULTS: Increasing the power of sinusoidal modulation in AC significantly reduced muscle contraction thresholds. Waveforms combining amplitude-modulated sinusoids and short pulse trains (20 μs duration) further lowered thresholds over non-pulsed stimuli. Discomfort thresholds did not differ significantly across AC and composite stimulation. CONCLUSION: Our findings reveal an exponential relationship between amplitude-modulated AC and suprahyoid muscle contraction efficiency, and show that integrating pulsed current with sinusoidal stimulation synergistically optimizes activation. These results provide a foundation for advanced neuromuscular electrical stimulation strategies for swallowing rehabilitation. LEVEL OF EVIDENCE: N/A.