Efficient Suprahyoid Muscle Contraction by Combined Modulated Currents in Mice

Area of Science:

• Biomedical Engineering
• Neuroscience
• Rehabilitation Science

Background:

• Swallowing dysfunction (dysphagia) affects millions, often linked to impaired suprahyoid muscle function.
• Current neuromuscular electrical stimulation (NMES) techniques for dysphagia have limitations in optimizing muscle activation.
• Developing advanced stimulation patterns is crucial for improving swallowing rehabilitation outcomes.

Purpose of the Study:

• To optimize electrical stimulation (ES) parameters for suprahyoid muscles to enhance swallowing function.
• To investigate novel stimulus waveforms, including amplitude-modulated alternating current (AC) and pulsed currents.
• To determine the most effective ES modalities for improving muscle contraction efficiency and reducing activation thresholds.

Main Methods:

• Tested various ES waveforms: 80-Hz rectangular pulse, 2-kHz AC with nth-power sinusoidal modulation (n=1, 5, 7, 9, 11), and 4/8-kHz sine waves.
• Evaluated combined 2-kHz AC with sinusoidal modulation and short-pulsed currents (20 μs duration).
• Applied stimuli via subcutaneous electrodes in anesthetized mice, measuring threshold intensities and discomfort in awake subjects.

Main Results:

• Increasing sinusoidal modulation power in AC significantly reduced muscle contraction thresholds.
• Composite waveforms (amplitude-modulated sinusoids + short pulse trains) lowered thresholds more than non-pulsed stimuli.
• No significant difference in discomfort thresholds was observed between AC and composite stimulation types.

Conclusions:

• An exponential relationship exists between amplitude-modulated AC and suprahyoid muscle contraction efficiency.
• Integrating pulsed current with sinusoidal stimulation synergistically optimizes muscle activation.
• Findings provide a basis for advanced NMES strategies in swallowing rehabilitation.