Efficient Suprahyoid Muscle Contraction by Combined Modulated Currents in Mice.

Abstract

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. 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. 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. 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. N/A.