Yue Wang, Qi Guo

1Department of Rehabilitation Medicine, Tianjin Medical University, Tianjin China; 2Department of Rehabilitation Medicine, TEDA International Cardiovascular Hospital, Tianjin China

Review

Progress inResearch on Vestibular Rehabilitation Therapy

Yue Wang1, Qi Guo2

1Department of Rehabilitation Medicine, Tianjin Medical University, Tianjin China;2Department of Rehabilitation Medicine, TEDA International Cardiovascular Hospital, Tianjin China

vestibule, infection, rehabilitation, progress

The deterioration of vestibular function is a side effect of numerous diseases of the inner ear. Vertigo is the most common symptom of vestibular dysfunction. Vestibule-suppressing drugs can control symptoms but impede the rehabilitation of vestibular function. Surgical treatment can effectively resolve vestibular dysfunction associated with some progressive diseases, including tumors. However, unilateral vestibular function remains permanently damaged after surgery, causing problems like vertigo and imbalance. To enhance the understanding of Vestibular rehabilitation therapy, this paper presents a summary of the progress in research on Vestibular rehabilitation therapy for patients with vestibular dysfunction.

The deterioration of vestibular function is a side effect of numerous diseases of the inner ear. These diseases include blood disorders, such as hypertension, hyperviscosity syndrome, and atherosclerosis, as well as various infections,such as vestibular neuritis, labyrinthitis, and Meniere's disease.Vertigo is the most common symptom of vestibular dysfunction. If a patient with vestibular dysfunctiondoesnot receive timely treatment, psychological problems,such asdepression and anxiety, will occur andgreatly af f ect the patient's quality of life[1]. Vestibule-suppressing drugs can control symptoms but impede the rehabilitation of vestibular function.Surgical treatment can effectively resolvevestibular dysfunction associated with some progressive diseases,including tumors. However,unilateral vestibular function remains permanently damaged after surgery, causing problems like vertigo and imbalance. Vestibular rehabilitation therapy(VRT), which isbased on compensatory mechanisms,has gradually become the main treatment methodfor vestibular dysfunction givenits effectiveness and reliability[2,3].

Concept and development history of VRT

Byas early as the 1940s, Cawthorne and Cooksey had proposed the possibility ofimprovingvestibular functions through systematic rehabilitation training. Their proposed treatment method is called Cawthorne–Cooksey Exercises.In 1972, based on the theories of Cawthorne and Cooksey,McCabe suggested that rehabilitation training could alleviate symptoms of vertigo. In 1974, Heeker etal.reported that 89 patients who were trained for 2 months in accordance with the above methodsexperienceda significant therapeutic effect: vertigo disappeared in 17% of the patients, symptoms improved in 67% of the patients, and symptoms were aggravated in 4% of the patients[4]. Vestibular rehabilitation therapy (VRT) is a training-based therapy methodfor patients with vestibular dysfunction. This method is implemented with the aimof improving thepatient's sense for vestibular position, vision, and proprioception in coordinated control over the balance and transfer of the compensatory function of the central nervous system. VRT is not strictly defined and can be understood as a series of professionally prepared sports training. VRTis repeatedly conducted for the head, neck, and body to: 1) strengthen balance; 2)increase postural stability; 3) improve vertigo symptoms; and 4) improve daily life. VRT can boost the balancing functions of patients and increase the ability to resist dizziness. As its effectiveness and reliability have been demonstrated by increasing numbers of clinical studies,VRThas graduallybecome another important treatment methodfor vestibular dysfunction in addition to medicine and surgery[5,6].

Mechanism of action

VRT is realized through the plasticity and functional compensation of the central nervous and vestibular systems. Vestibular compensation is a central process with an extremely complicatedmechanism of occurrence.All structures related to the vestibular systemmight participate in this process[7].VRT possibly induces vestibular compensation via the following mechanisms.

Vestibular adaptation

Through the adaptability of the central nervous system to vestibular damages,the vestibular system adapts to the longterm input of asymmetric information from the peripheral vestibule.The vestibular system exertsadaptive control over the vestibular reflexby changingthe gain, time phase,and direction of the vestibular reflex[8].The main vestibular reflexes are: 1) Vestibulo-spinal reflex (VSR), which mainly maintains balance through the dominance of the lateral vestibulospinal tract over the trunk and limbs after combined input from peripheral senses like vision, proprioceptive sense,and vestibular sense. Romberg's test is the first to evaluate VSR.In recent years, VSR has been commonly evaluated using posturography (PG) technology. 2)Vestibulo-ocular reflex (VOR), in whichthe signal is transferred to the center through the nuclei of cranial nerves III, IV, and VI on the adjacentand opposite sides of the cerebrum.The vestibular sense can immediately create reflexive ocular movement and allow the eyeball to turn to the opposite side when the head rotates to one side, thus maintainingstable vision[9]. In patients with reduced unilateral vestibular functions, the gain in their VOR decreases and the visual image appears to repeatedly slide in the retina. This sliding signal repeatedly irritates the vestibular nervous system and enables the vestibular center to increase the gain in VOR, causing vestibular adaptation.

Vestibular habituation

The reactivity of thevestibular system gradually decreases after suffering from a series of repeatedirritations.Themechanism of vestibular habituation includes two components: the neural storage section, which is used to store spatial sensory information; and the comparative unit, whichenables the comparison ofpreviously stored sensory information with currently interceptedinformation[10]. Its specific mechanism remains unknown. Vestibular habituation is directional and metastatic. Once formed, it can be maintained for a certain period and can be sustained for even longer durations if continuously irritated. The exercise methods for habituation are similar to those for astronauts to overcome space sickness and include swinging and turning in a rotating chair.

Vestibular compensation

Symptoms like vertigo, nausea,and physical imbalance occurwhen the peripheral vestibule is damaged on one side. After some time, however,these symptoms retreat or disappear. Possible mechanismsfor vestibular compensation includechanges in the contralateral vestibular nucleus,particularly inthe expression of nitricoxide synthase and in the secretion of neurotransmitters, such as choline acetyltransterase; these changesadjust the excitability of the vestibular center[11].

Substitution

To sustain body balance, the lost functions of the vestibule are replaced by vision and proprioception orneck-eye reflexes.

Substitution of vision and proprioception

Although vision and proprioception can aid the recovery of postural stability when unilateral or bilateral vestibular functions are lost, they do not always work in any situation,e.g. they fail in a dark environment.Therefore, this substitution method has some limitations.

Neck-eye reflex

Neck-eye reflexes are slow-phase eye movements that result from sensory input after the irritation ofcervical tendons, muscles, and articular surface. These responses can compensate for the insufficiency of VOR in slow and instantaneous head movement. The dif f erent mechanisms for VRT are crucialfor the design of a specific rehabilitation scheme. Not all patients with vestibular dysfunction can benefit from rehabilitation training. Vestibular compensation can achieve optimal effects only if some physiological mechanisms in the body remainintact[12]. Given the dif f erent degrees of damage to vestibular function and the compensation ability of dif f erent patients,the vestibular functions of patientsshould be first checked and evaluated prior to the preparation of suitable rehabilitation training programs[13].

Training method for VRT

General training

Cawthorne–Cooksey Training is the most common VRT training method. Theprinciple of this training method is thatpatients should desensitize themselves by performing activities with gradually increased speed and scope. Patients complete the following actions under the direction of aphysician:1) In a recumbent position, the patient first moves their eyeballs quicklyand then slowly;moves their head slowly and then quickly; andfinally closes their eyes.2)In asitting position, in addition to eye and head movement,the patient shrugs,turnstheir shoulder, and bendsforward to pick an object from the ground. 3)In anerect position, in addition to completing the related actions done in the sitting position with their eyes open orclosed.The patient then changes from the sitting position to the erect position. With bothhands below the eye plane, the patient throwsasmall ball back and forth. The patient repeats the same action with both handsbelow the knee plane. The patient then moves from the sitting position to erect position and turns around simultaneously. The patient then walks around one person and throws or passesa largeball to or from the person in the center of the circle, walksaround with their eyes first open and then closed, walks uphill and downhill with eyes first open and then closed, climbsupstairs and downstairs with eyes first open and then closed. Cawthorne–Cooksey Training is mainly suitable for patients with poorfunctions of the vestibule.Early and regular training provides good clinical effects. The main advantages of this method are economy and convenience. Moreover, this methodwill be more effective if built on the basis of accurate diagnosis.

Individualized physical therapy

The VRTmethod advocated by Horak etal. in the 1980s complementsthe pertinent training program based on the functional defects and diagnosis of patients, as well as onthe timely adjustment of the rehabilitation plan based on the patient's conditions during treatment. Its main training measures include: fixation stability, vision reliability training, proprioception reliability training, and posture reliability training[15]. Fixation stability training improves the gain of the vestibule-eye reflex andimproves symptoms like clouded vision and dizziness during head movement and walking. This training method is suitable for patients whose unilateral vestibular functions are pooror lost and whose bilateral vestibular functions have been completely lost.By closing their eyes during vision reliability training,the patientdecreasesvisual irritations and visual reliance, and can better use the input of proprioception or vestibular sense.This training method should be combined with exercises that increase postural stability.

In proprioception reliability training, patients stand or work on a cushion, a surface mimicking a sandy beach, a plastic foam mat, or a cross bar.Standing or working on these surfaces intervenes with the proprioception of the patient,thusdecreasing reliance on proprioception and extending vestibule and vision input.This training is suitable for patients with low or lostunilateral vestibular functions, but should be combined with exercisesthat increase fixation and posturalstability.

In posture reliability training, patients stand on foam plates of dif f erent densities. Patients thenstand on their tiptoes and spread orclose theirlegs with their eyes open orclosed. These exercises aim to improveposturalstability by training proprioception. Individualized physical therapy is more expensive than general trainingbut providessignificant therapeutic effects.

New VRT methods

With the rapid development of science and technology,some training devices have beengradually integratedin VRT; virtual reality training is an example VRT integrated with technology[16]. In this training method, a computer is utilized to generate a vivid three-dimensional audiovisual stereoscopic projection, allowing the patient to interact with the virtual world and realize the effect of VRT by irritating retina sliding and through vestibular habituation in specific environments[17].The virtual reality training method is promising and provides challenging environments undersafe and easily controlled conditions to strengthen training effects. Virre etal.[16]suggested thatthis method increases vestibule–eye reflex grain and reducesthe degree of dizziness.Thus, this method is suitable for vertigo patients with low grain in vestibule–eye reflex or psychological disorders like acrophobia and agoraphobia. Nevertheless, the virtual reality training method remains at the testing stage without largesize clinical trials.

Application of VRT in various patients with dizziness

Benign paroxysmalpositional vertigo

Benign paroxysmalpositional vertigo (BPPV) is a paroxysmal transient vertigo induced by the changes in specific head position ora common lesion of the peripheral vestibular organ. BPPV is mainly treated with manual reduction,including the Epley and Barbeque roll maneuvers. Wu Ziming etal.[18]found that BPPV can appear in patients with inner ear lesions and manifests as sudden deafness, vestibular neuritis, and Meniere's disease. The effects of manual reduction on secondary and primary BPPV are similar. Liu Xingjian, etal.[19]used the Epley Maneuver to treat 402 BPPV patients with ear disease symptoms. Of these patients,376 patients were cured after repositioningonce, 17 patients werecured after repositioningtwice, and 9 patients did not show any improvement.Kong Weijia etal.[20]used the Epley maneuver to treat 55 patients with posterior semicircular canalBPPV. They also usedthe Barbeque roll maneuver to treat eightpatients with lateral semicircular canal BPPV. They reported that symptoms were completely alleviated after one or multiple treatments. Banfield, etal.[21], however, argued that although Epley maneuver and VRT present the same long-term therapy effect, the long-term therapy effect of VRT is superior to that of Epley maneuver;the researchers also emphasized the application value of VRT in the treatment of BPPV. In addition, manual reduction is unsuitable for some elderly patients and BPPV patients with cervical spondylosis.VRT should be selected to relieve the symptoms of these patients.

Unilateral vestibular hypofunction

Patients with poor spontaneous compensation induced by non-progressive vestibule lesions[22], such as unilateral vestibular hypofunction (UVH) caused by postlabyrinthectomy, post-acoustic neuroma surgery, and vestibular neuritis, can use VRT as the preferred therapy method. The results ofprevious studies suggested thatVRT is unsuitable for patients with Meniere’s disease given thelarge fl uctuation in the state of illness. Whitney etal.[23], however,found that VRT during the symptomatic remission of patientsimprovestheability of patients to conduct their daily activities.Bittar etal.[24]stated that VRT can promote the effect of the vestibule–spinal cord reflex and compensation of patients who underwent unilateral vestibular surgery or postacoustic neuroma surgery, thus significantly improvingthe symptoms of vertigo. This conclusion and the findings of Tokumasu etal. are identical.

Bilateral vestibular hypofunction

Symptoms of bilateral vestibular hypofunction (BVH)generally include oscillopia, dizziness, and tinnitus with less true vertigo. The main origin of BVHis drug-induced ototoxicity. Ward etal.[26]recently conducted a large-scale study in the United States. Their reportshowedthat among 100,000 adult Americans, 28% have BVH. The symptoms of44% of these patients are linked to their driving habit and those of 56% are due to a decrease in their social activities. VRT is used to substitute vision function and proprioception for missing or attenuatedvestibular signals,thus improvingbalance. However,most of the patients had difficulty recovering to their normal functional level because of habituation.

Abnormality of vestibular function in the elderly

Although symptoms like dizziness usually appear in the elderly due to their age and organ function failure, no abnormalities of vestibular function are generally found uponexamination with electronystagmogtam. At this point,VRT will helpmaintainposture balance among the elderly[27].

Central vestibular dysfunction

Central vestibular dysfunction (CVD) mainly results from traumas andtumors.Given its primary focus, VRT does not have a significant effect on CVD but greatly influencesposturalstability[28]. The balance and dizziness of patients with vertigo from the relapsing–remitting form of MS significantly improve afterundergoing rehabilitation training.

Conclusion

The deterioration of vestibular function caused by various diseases has drawn increasing attention from clinicians given that it causes extreme discomfortand greatly influencesthe quality of life of patients. Regardless of the origin, duration,and intensity of the disease and the ages of the patients,VRT is suitable for patients with stable vestibular lesionsand whose vestibular function is decompensated. Although there have been numerouspieces of evidence for the validity of VRT, its safety remains problematic and there are currently no reliable means for evaluatingits effect. VRT is another important means to treat the deterioration of vestibular function in addition to surgery and drugs. Patients who have been treated with this method experience no adverse reactions.Given its simplicity, economy, and easy acceptance,VRT is worth popularizing.

Declarations

Acknowledgements

No.

Competing interests

The authors declare that they have no competing interest.

Authors’ contributions

Y Wang made the literature analysis and wrote, discussed and revised the manuscript of this review. Q Guo critically analyzed and corrected the manuscript. All authors read and approved the final manuscript.

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CorrespondenceQi Guo,

E-mail: guoqijp@gmail.com

10.1515/ii-2017-0142