Toward the Optimal Waveform for Electrical Stimulation
Electrical stimulation (ES) is used to strengthen muscle, improve abnormal tone, and improve the healing rate of pressure sores. Four male and three female research subjects received four minute bouts of electrically stimulated isometric contractions equal to 10% of the maximal voluntary contraction (MVC) of their right quadriceps muscle to study subjective comfort and physiological responses to different waveforms, including Russian, interferential, sine, and square. Frequency remained constant at 30pps. The pulse width for the Russian waveform was 200ps, while the sine, square, and interferential waveforms used a lOOps pulse width. The amplitude of stimulation was adjusted to maintain the contraction elicited by ES at 10% of MVC. A visual analog scale (VAS) and verbal response scale (VRS) were used to monitor subjective comfort levels. Measures of physiological response including skin temperature change (local and systemic), surface blood flow, systolic and diastolic blood pressure (SBP and DBP), heart rate (HR), ventilation (VE), oxygen consumption (VO2), carbon dioxide production (VCO2), respiratory quotient (RQ), and galvanic skin resistance (GSR) were recorded for a one- to two-minute baseline, during each four-minute contraction, and for a five minute recovery period. A contraction equal to 10% of the MVC was unable to be stimulated using the interferential waveform. The stimulated contractions utilizing the sine waveform required significantly less mean stimulation current to maintain the desired force of contraction with lower VAS and VRS scores. Ve, VO2, and VCO2 increased during the electrically stimulated isometric contractions as a response to the isometric exercise and not as a sympathetic response to noxious stimuli. Galvanic skin resistance. which is used to measure the sympathetic nervous system’s response to painful stimuli. showed a consistently greater increase during Russian waveform stimulations. The sine waveform allows the desired muscle tension to be stimulated with the least tissue trauma while providing the most subjective comfort. Keywords: Electrical stimulation (ES), Isometric exercise, Waveform, Comfort, Physiological response
Physical Therapy, Electric Stimulation; Isometric Contraction; Decubitus Ulcer -- therapy.
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