| Peripheral facial paralysis is caused by partially or completely lost of facial nerve function, which seriously affect the patient’s physical and mental health. Blink dysfunction maybe the most serious of all the symptoms caused by peripheral facial paralysis. That because it not only affect the appearance, but also brings some serious complications, such as dry eye, corneal infection or mechanical damage, or even it can cause blindness. There are currently several methods used to treat blink dysfunction caused by facial nerve paralysis; however all of them have significant drawbacks. The use of lubricating gels helps protect the cornea from permanent damage, but may obscure vision and offer little protection during sleep. Physical covering such as goggles, patches, or tape provide protection, but prevent use of the eye and are aesthetically displeasing. Surgical implantation of weights offer little protection during sleep and may result in surgical complications, such as infection or extrusion. Tarsorrhaphy, or partially sewing the eyelids together, provides incomplete closure, may block vision, and is also aesthetically displeasing. None of these methods provides a satisfactory solution to restore the contractive function of the paralysis orbicularis oculi. Functional electrical stimulation (FES) has significant advantages in restore paralysis muscle to contract, and it had being applied in clinical for more than half a century. Animal studies in rabbits and dogs have shown that FES with implanted or percutaneous electrodes can successfully produce a functional blink in animals with surgically denervated orbicularis oculi. But this method has not been applied to clinical to treat peripheral facial paralysis patients, and there are still some problems to be solved.ObjectiveTake the New Zealand white rabbits as a model of peripheral facial paralysis. To explore the effects of different waveforms and parameters of electrical stimulation in induce a blink.To explore the feasibility of FES system in restore synchronous blinking in the rabbit model of unilateral peripheral facial paralysis.To evaluate the effect of chronic electrical stimulation in preventing the atrophy and degeneration of the denervated orbicularis oculi muscle MethodsTwenty-four New Zealand white rabbits underwent unilateral facial nerve neurotmesis by cut the right facial nerve trunk. And then these rabbits were divided into three groups: group â… , group â…¡ and group â…¢. Pulse electrical current with different frequencies (25Hz,50Hz,100Hz) and widths (lms-9ms) were used to stimulate bilateral orbicularis oculi respectively to induce a blink. The pulse waveforms for the three groups were different, group I was square wave, group â…¡ was sine wave and group â…¢ was triangle wave. The threshold voltage and electric charge needed by different waveforms and parameters to induce a complete blink were compared.A FES system was constructed to treat six surgically induced unilateral facial nerve palsy rabbits. It consisted by an electromyogram (EMG) amplifier module which recorded the EMG of the healthy muscle, and a stimulator which could deliver a pulse train stimulation to the paralysis muscle. The EMG amplifier module was connected to the stimulator, so the EMG signal recorded by it will be transmitted into the stimulator. When EMG signal excess the trigger threshold, a pulse train stimulation will be delivered to the paralysis orbicularis oculi muscle. When the system was open, the cornea on the side of the healthy eyelid was lightly touched with a cotton swab in order to stimulate eyelid closure and generate EMG, at the same time, observe the movement of the paralysis eyelid.In the third part, bilateral facial nerve trunks of six rabbits were cut. On postoperative day7, electrical stimulation to the left orbicularis oculi muscle was began, the parameters was chosen according to the first part, and the stimulation protocol was:three times a day,20minutes per time, continuously75days. The right muscles as contrast control did not received stimulation. When the stimulation finished, the excitation of the bilateral eyelids were measured, and then the histologic evaluations of the denervated orbicularis oculi muscles were made.ResultsFor healthy or paralysis orbicularis oculi muscles, the pulse electrical current delivered in25Hz cannot induce a smooth blink. However, pulse stimulation delivered in50Hz or100Hz can induce a natural looking blink. To elicit a complete blink, the threshold voltage required by100Hz was lower than50Hz, but it cost more electric charge than50Hz, and will accelerate muscle fatigue. To elicit a complete blink, the threshold voltage that square waveform required was far lower than sine waveform and triangle waveform, but the total amount of electric charge it costs was similar to the other waveforms.When the FES system was open, an EMG signal could be recorded in the passive blink reflex of the left eye. At the same time, the stimulator was triggered to generate a pulse train stimulation, and a blink of the right eyelid was elicit. According to the macroscopic observation, there was no difference in blink rates between the two sides. While other facial muscles moving, the EMG signal recorded did not reach or exceed the triggering threshold of the digital stimulator.After75days continuous stimulation or82days from denervation, in contrast to the experimental group, the orbicularis oculi muscle of the control group had a reduced excitability. The diameter and cross-sectional area of the control group were decreased obviously, while the experimental group was remarkably larger than the control group in the two parameters. The expressions of myosin and actin in control group were significantly reduced in contrast to the experimental group, as showed in immunohistochemical staining. According to the results of transmission electron microscope examination, the orbicularis oculi muscles in control group showed muscle fiber atrophy, degeneration of mitochondria and sarcoplasmic reticulum, hyperplasia of collagen fiber. While the experimental group had a better ultrastructure morphological changes compared to the control group.ConclusionTo elicit a blink in New Zealand white rabbits, square pulse train delivered in50Hz is a preferable chooses.The method that uses the motion of the healthy eyelids as a source of information for stimulation of the paralyzed sides can restore the synchronous blink in unilateral facial nerve paralysis rabbits; it demonstrated the feasibility of FES treatment in unilateral facial nerve paralysis patients.Chronic electrical stimulation can effectively prevent the atrophy of orbicularis oculi muscles due to denervation, and maintain the expression of myosin and actin, therefore eventually maintain the excitation of the denervated orbicularis oculi muscles. |
