Dalrymple Ashley N, Hooper Charli Ann, Kuriakose Minna G, Capogrosso Marco, Weber Douglas J
Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, United States of America.
NeuroMechatronics Lab, Carnegie Mellon University, Pittsburgh, PA, United States of America.
J Neural Eng. 2023 Jan 18;20(1). doi: 10.1088/1741-2552/acabe8.
Spinal cord neuromodulation has gained much attention for demonstrating improved motor recovery in people with spinal cord injury, motivating the development of clinically applicable technologies. Among them, transcutaneous spinal cord stimulation (tSCS) is attractive because of its non-invasive profile. Many tSCS studies employ a high-frequency (10 kHz) carrier, which has been reported to reduce stimulation discomfort. However, these claims have come under scrutiny in recent years. The purpose of this study was to determine whether using a high-frequency carrier for tSCS is more comfortable at therapeutic amplitudes, which evoke posterior root-muscle (PRM) reflexes.In 16 neurologically intact participants, tSCS was delivered using a 1 ms long monophasic pulse with and without a high-frequency carrier. Stimulation amplitude and pulse duration were varied and PRM reflexes were recorded from the soleus, gastrocnemius, and tibialis anterior muscles. Participants rated their discomfort during stimulation from 0 to 10 at PRM reflex threshold.At PRM reflex threshold, the addition of a high-frequency carrier (0.87 ± 0.2) was equally comfortable as conventional stimulation (1.03 ± 0.18) but required approximately double the charge to evoke the PRM reflex (conventional: 32.4 ± 9.2C; high-frequency carrier: 62.5 ± 11.1C). Strength-duration curves for tSCS with a high-frequency carrier had a rheobase that was 4.8× greater and a chronaxie that was 5.7× narrower than the conventional monophasic pulse, indicating that the addition of a high-frequency carrier makes stimulation less efficient in recruiting neural activity in spinal roots.Using a high-frequency carrier for tSCS is equally as comfortable and less efficient as conventional stimulation at amplitudes required to stimulate spinal dorsal roots.
脊髓神经调节因在脊髓损伤患者中显示出改善运动恢复的效果而备受关注，这推动了临床适用技术的发展。其中，经皮脊髓刺激（tSCS）因其非侵入性而具有吸引力。许多tSCS研究采用高频（10kHz）载波，据报道该载波可减轻刺激不适。然而，近年来这些说法受到了质疑。本研究的目的是确定在引发后根 - 肌肉（PRM）反射的治疗幅度下，使用高频载波进行tSCS是否更舒适。
在16名神经功能正常的参与者中，使用1ms长的单相脉冲进行tSCS，分别有和没有高频载波。改变刺激幅度和脉冲持续时间，并记录比目鱼肌、腓肠肌和胫前肌的PRM反射。参与者在PRM反射阈值时将刺激期间的不适程度从0到10进行评分。
在PRM反射阈值时，添加高频载波（0.87±0.2）与传统刺激（1.03±0.18）同样舒适，但引发PRM反射所需的电荷量约为传统刺激的两倍（传统：32.4±9.2C；高频载波：62.5±11.1C）。带有高频载波的tSCS的强度 - 时间曲线的基强度比传统单相脉冲大4.8倍，时值窄5.7倍，这表明添加高频载波会使刺激在募集脊髓神经根神经活动方面的效率降低。
在刺激脊髓背根所需的幅度下，使用高频载波进行tSCS与传统刺激同样舒适，但效率较低。
