Feasibility of Bionic Reanimation of a Paralyzed Face: A Preliminary Study of Functional Electrical Stimulation of a Paralyzed Facial Muscle Controlled with the Electromyography of the Contralateral Healthy Hemiface

Abstract

Sir: Functional electrical stimulation, a modality for producing contractions in paralyzed muscles by electrical currents, has been developed to restore upper and lower extremity, bladder, bowel, and respiratory function in individuals suffering from spinal cord injury or stroke.1 The principles of safe and reliable activation of neural tissue and methods for generating stable and controllable muscle contractions have been established.1 However, for functionally efficient control of extremities in patients, complex configuration systems are required to recognize neuronal signals from the central nervous system, leaving some issues for its clinical use.2 In contrast, in cases of facial paralysis, the desired movements of the paralyzed mimetic muscles on the affected side are usually equivalent to those of the contralateral healthy mimetic muscles. Therefore, it might be possible for the motion of the corresponding contralateral mimetic muscles to be used as a source of information for contraction of the paralyzed muscles. In September of 2006, we began to develop an implantable device capable of detecting facial muscle motion on the healthy side, which then causes synchronous contraction of the corresponding paralyzed muscle by electrical stimulation.3 The basic circuit design of the device was the same as that of the integrated volitional electrical stimulator developed by Muraoka for rehabilitation of the limbs.4 The device delivers biphasic, 20-Hz electrical stimulation pulses of configurable amplitude. The duration of each square pulse (pulse width) was set so that it was in proportion to the maximal amplitude of volitional electromyography, which was obtained with two monitoring electrodes. The acquisition of electromyography and the oscillation of stimulation pulses were temporized separately (Fig. 1) and the circuit was specially designed to suppress the artifacts resulting from stimulation pulses.[5]Fig. 1.: Schema of the configuration (pulse width modulation) of the stimulation pulses. The acquisition of electromyography (EMG) and oscillation of the stimulation pulses were separately temporized. Each pulse width (duration) was in proportion to Amax. K was adjusted for each subject.To assess the clinical feasibility of our system for treating facial paralysis, a simulation study was performed on healthy volunteers under a protocol approved by the research ethics committee. In the study, local anesthetics were used to anesthetize the temporal branch of the facial nerve on one side to induce the transient paralysis of the frontal muscle. After confirming the stoppage of frontal muscle movement, a set of stimulation transcutaneous needle–type electrodes and a set of detection needles were inserted into paralyzed and nonparalyzed frontal muscle, respectively. With the injection of local anesthetics to the left side, transient paralysis of the left frontal muscle was induced, and the subjects were unable to elevate their left brow (Fig. 2) (seeVideo, Supplemental Digital Content 1, which demonstrates paralyzed forehead without the functional electrical stimulation device, https://links.lww.com/PRS/A193). After turning on the device, smooth movement of the paralyzed forehead and brow was achieved, although with a slight time lag. Symmetrical eyebrow elevation was obtained without erroneous contractions (Fig. 2) (seeVideo, Supplemental Digital Content 2, which demonstrates forehead movement when the device was operating, https://links.lww.com/PRS/A194).Fig. 2.: Paralyzed forehead movement with and without the functional electrical stimulation device. After the injection of local anesthetics, the left frontal muscle was transiently paralyzed. Two electrodes for monitoring muscle potential were inserted into the right frontal muscle, and two functional electrical stimulation electrodes were inserted into the left paralyzed frontal muscle. An earth (ground) wire was placed on the right side of the neck. (Above) When gazing upward without the functional electrical stimulation device, no elevation of the left brow with accompanying wrinkles was seen in the corresponding region. (Below) When gazing upward while the device was operating, elevation of the left brow was seen on both the intact and paralyzed sides. With functional electrical stimulation, smooth symmetrical movement of the face was regenerated.Videos.: Supplemental Digital Content 1 demonstrates paralyzed forehead without the functional electrical stimulation device, https://links.lww.com/PRS/A193. After the injection of local anesthetics, the left frontal muscle was transiently paralyzed. Two electrodes for monitoring muscle potential were inserted into the right frontal muscle, and two functional electrical stimulation electrodes were inserted into the left paralyzed frontal muscle. An earth (ground) wire was placed on the right side of the neck. When gazing straight ahead, no elevation of the left brow or blepharoptosis of the left upper eyelid was seen. When gazing upward, no elevation of the left brow with accompanying wrinkles was seen in the corresponding region. Supplemental Digital Content 2 demonstrates forehead movement when the device was operating, https://links.lww.com/PRS/A194. When gazing straight ahead, elevation of the brows was seen bilaterally. When gazing upward, elevation of the left brow was seen on both the intact and paralyzed sides. With functional electrical stimulation, smooth symmetrical movement of the forehead was regenerated without erroneous contractions.Our simulation experiment clearly showed successful functional and aesthetically acceptable motion of the paralyzed facial expression muscle controlled with electromyography of the contralateral corresponding facial muscle. The development of implantable devices for the face appears to be feasible in light of the positive clinical results obtained with functional electrical stimulation for other types of morbidities.1 DISCLOSURE The authors have no competing financial interests. Masakazu Kurita, M.D. Akihiko Takushima, M.D. Department of Plastic and Reconstructive Surgery Kyorin University School of Medicine Yoshihiro Muraoka, Ph.D. Clinical Research Center National Hospital Organization Murayama Medical Center Tomohiro Shiraishi, M.D. Kiyonori Harii, M.D. Department of Plastic and Reconstructive Surgery Kyorin University School of Medicine Tokyo, Japan