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VRT Editorial by Dr. Alain Semont

Posted by Cynthia Ryan

Dr. Alain Semont is a French physiotherapist known for introducing the Semont manuever for treatment of BPPV and coining the term, "vestibular rehabilitation."

Introduction

Balance rehabilitation is commonly linked to disorders of the neuro-motor outputs of the equilibrium function. Disorders of stance, gait and posture are indications for balance rehabilitation or physiotherapy treatment, which include impairments for disorders of the cerebellum, Parkinson, proprioception, or functional impairments like astasia-abasia.

Some other disorders are involved in the production of symptoms such as: spinning vertigo, dizziness, unsteadiness, or poor postural control with respect to verticality. These symptoms find their origin in disorders of the neuro-sensory inputs, which is the vestibular system associated to vision and hearing. It is highly integrated with other systems to produce essential reflexes for orientation, body stabilization, and gaze stabilization, which is vision during movement. The cortical areas associated to the peripheral system are responsible of self motion perception that leads to the knowledge of position in space, relationship of “me” with the “others,” and then of human affect, as well as the negative side, that is, anxiety and distress. The fabulous interactions of the vestibular system with the other sensory inputs produce reflexes such as the vestibulo-ocular reflex, vestibulo-spinal reflex, vestibulo-collic reflex,  motion perception with optokinetic reflex and so forth. What differentiates rehabilitation of vestibular disorders from other balance impairments is that we address ourselves to reflexes that cannot be triggered by the own will of the patient. Therefore, we must say that vestibular rehab has never been balance rehab.

Another important thing is that we, as vestibular rehab professionals, move around in a particular field, which is neurosensory disorders. The vestibular system is necessary to the execution of eye movements and head movements. When you walk in the street and if there is a noise you rotate your head to the perceived direction of the source of the noise, your eyes then will tell you what it is and then you will decide if you keep going or if you stop and change direction. The vestibular system is called the sixth sense. This means that we need special tools to evaluate vestibular reflexes. They  have been specifically created for this particular entity. We must know as well that the functioning of this sensory system includes processes of perception that help create the cognition dedicated to this sense. But if we rehabilitate patients by teaching them to adapt volitionally, ignoring the simple reflexes, their rehab will be poor and non-adapted and may trigger symptoms such as unsteadiness, visual instability, and intellectual disorders associated with memory loss. Patients then report that there is something wrong with them, they feel dizzy and uncomfortable in some places when things move around them, nausea when there is too much movement around them, and so on. 

In order to be conscious of what we are talking about and working on necessitates we know a few numbers:

  • The labyrinth could fit in a thimble.

  • It has its definite size at birth. 

  • The diameter of the ring of a canal is 6mm

  • The diameter of a membranous canal is 1mm

  • The diameter of the ampula is 3mm

  • The size of the cupula height is 400µ 

  • The thickness of the cupula is 200µ

  • The amplitude of the cupula's displacement is between 0.009° to 1°. (1° is the value for a head movement whose velocity is 800°/s. The maximum velocity of a usual everyday life head movement is 450°/s, so the maximum displacement in our life is: 0,56°.) 

  • The surface of a macula is 1mm²

  • The size of an otoconia is between 0,5µ and 30µ,

  • The latency of the VOR is between 12 ms and 14ms

  • The latency of the VSR (vestibulo-spinal reflex) is 45ms

  • The latency of the myotatic reflex is 100ms

  • The latency of a voluntary act is 250ms.

The physiological processes that decrease symptoms are:

 

Habituation:

This is what ice skaters use in order to spin without being uncomfortable. It is the decrease of the gain (VOR) in the perception of an uncomfortable feeling following a stimulation. It requires training; but the benefits are not lasting. Once the training is stopped, things go back to normal. There is no restraint of the habituation effects. 

 

Compensation:

This is the physiologic process to decrease and inhibit the symptoms that occur following the accidental asymmetry between two normal symmetric structures, such as the right and left peripheral vestibular apparatus. Once established, compensation remain, but compensation is supposed to take place naturally. It does not take place like that because there are thresholds. Vestibular rehab helps compensation to take place and have a value, which helps the system to work normally.

 

Adaptation:

Physiological process used everywhere in the cortical functions to help functionning of tasks with precision and in relation with psysiological thresholds. The dynamic is activation-inhibition.

 

Substitution:

An example of sensory substitution is the individual who is born blind. The occipital cortical structures are invaded by auditory structures. It is triggered in our field only on bilateral loss of vestibular function.

Historical approaches of rehab treatments in vestibular related complaints come from Cooksey and Cawthorne in post-World War II. McCabe in the US presented similar head exercises in order to stimulate the vestibular system and then, through habituation, decrease the level of complaints. At the end of the sixties, advances in the microsurgical approaches in oto-neurotology, through middle and posterior fossa, decreased the negative effects observed with macrosurgery. The remaining disorders after microsurgery for acoustic neuroma removal or VIIIth nerve section for uncontrolled Meniere’s are low, with facial palsy and balance disorders most common. The effect of Cooksey and Cawthorne exercises appeared to have no statistically significant benefit over the one obtained with an active life. This is the reason why JM Sterkers and A. Semont created vestibular rehabilitation (VR) in 1970. The name of VR is commonly used now all over the world, but it does not necessarily represent what had been proposed then.

The following represents the methods of evaluation and therapy for vestibular rehabilitation patients which I believe are optimal.  It is important to know before any other knowledge that any treatment of more than three months has no scientific value.

 

Examination:

The examination starts with a long and precise clinical questionnaire concerning the patient’s symptoms. The goal is to try to fit signs and symptoms together and put aside what has nothing to do with the vestibulopathy. A careful medical history is taken in order to avoid confusion with iatrogenic effects from other treatments. 

The questionnaire is followed by a videonystagmoscopic observation of:

  • Spontaneous nystagmus, if there is one, in different gaze positions.

  • Lateral head tilt to observe the counter-rolling eye movements.

  • A constant velocity rotatory impulse test to objectivate and measure the vestibular dysfunction through the asymmetry of the responses.

  • A head shaking test to observe the asymmetry of vestibular tonus at high frequency.

  • A basic clinical test of oculometry (smooth pursuit and saccades) is performed, followed by the vestibulospinal tests such as: Babinski-Weill blind walk, Unterberger (Fakuda) stepping test, and Romberg.

  • The balance complaint is quantified with a computerized dynamic posturography (CDP).

  • The testing is ended by a high velocity rotatory Barany test in two conditions: 

  •  The subject is rotated eyes closed at a velocity of three rotations in three seconds, with a brisk stop. He then opens his eyes and stabilizes his eyes on a fixed target in front of him (distance: seven feet) and is asked to say "stop" when the target does not appear to move any more. We measure the duration of the motion of the visual surround with a stop-watch. The test is performed in both directions: clockwise and counterclockwise. The test gives an idea of the response of the vestibular system at high frequency without the bias of the directionnal preponderance.

  •  Eyes closed: the subject is rotated in the same conditions: velocity, amplitude, two directions. He is asked to keep his eyes closed when the rotation is stopped and to say "stop" when his self-perception of rotation in opposite direction ends. We measure the duration of the perception with a stop-watch. This test gives precise information on the central compensation to the vestibular asymetry. It also gives the information about the central component in case of a hyper-nystagmic response. 

 

Therapy:

The sessions are based on the examination results.

If the patient’s complaints are related to the vestibulo-ocular reflex and if there is a strong asymetry of response on the rotatory chair, the rotary chair will be used for treatment. The goal is to use the repetition of the rotations to decrease the value of the higher response in order to decrease or even suppress the spontaneous nystagmus. For instance, if the session begins with a left-beating spontaneous nystagmus the session will end with a right-beating spontaneous nystagmus and a strong decrease in the duration of the nystagmic response. Physiologically, this means that we decreased the time constant of the canal-ocular reflex of the good side.

At the end, when the values are symmetric and strongly decreased at any amplitude of rotation, there are two possibilities: the patient is asymptomatic or not. If he is asymptomatic, the treatment is over. The result is achieved with computerized dynamic posturography (see below). If he is symptomatic, we proceed to the next step.

Decreased but symmetric rotary chair responses: The next step in the treatment is the use of a three-axis optokinetic generator. The goal is to stimulate the opto-kinetic reflex which is, from a physiological point of view, the only system that communicates with the vestibular system when information about movement is needed during any of these situations: we are moving at constant velocity, not moving, or our vestibular system is not used by the brain or is defective.

The three-axis optokinetic generator: The individual is standing in the middle of a dark room. Walls, floor, and ceiling are used as screens, on which are projected luminous dots moving sideways or up and down. The velocity of the stimulus is adjusted in order to induce a perception of self-motion, as well as a postural sway. The direction of the stimulus is changed as soon as the induced postural sway drives the projection of the center of gravity nearly out of the foot surface, then changed again, and so on. The duration of the session is no longer than ten to twelve minutes and is repeated until there is no more postural sway following all directions and velocities of visual stimulation.

When the rotation-test values are symmetric and strongly decreased at any amplitude of rotation, the previous question arises: asymptomatic or not? If the subject is symptom free we use CDP for the follow-up. If the individual has some residiual complaint, the Smart-Equitest is used to work on the somatosensory input. In this case, the subject is standing in the machine with his eyes closed. The moving footplate is fed with a random signal in order to avoid any pre-programming reaction to control the sway.

 

Results: 

  • For acute unilateral vestibular loss, the rotatory chair is enough and eight to ten sessions are needed with a frequency of once a day. If the patient comes to us at day two, everything is finished in a week or maximum ten days.

  • For chronic unilateral loss (several month old), we theoretically need a chair and optokinetic stimulations two sessions a week for three months.

  • For bilateral loss, optokinetic and computerized posturography training system (e.g. Smart system) two sessions a week for six to eight months, especially for an individual who cannot walk. The result is an individual who can live quite normally and can drive a car, but cannot stay alone in complete darkness. 

  • Central disorders need opto-kinetic stimulations and very slow stimulations on the chair (<40°/s). Twenty sessions are needed; the frequency being adapted with the post-session after effects.

  • BPPV does not necessitate comprehensive vestibular rehab but a "liberatory maneuver." The patient is mostly seen twice: one for the maneuver, one for control a week later. The treatment is over. And successful.

  • Motion-sickness, visual dependence, and neuro-sensory disorganization necessitate ten sessions of opto-kinetic stimulation, twice a week.
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