Advanced Arab Academy of Audio-Vestibulogy Journal

ORIGINAL ARTICLE
Year
: 2014  |  Volume : 1  |  Issue : 2  |  Page : 80--86

Standardization of rotatory chair velocity step and sinusoidal harmonic acceleration tests in an adult population


Mohamed FM Ahmed 
 Department of Otolaryngology, Faculty of Medicine, Mansoura University, Mansoura, United Arab Emirates

Correspondence Address:
Mohamed FM Ahmed
AuD, Hearing and Balance Clinic, ENT Department, Dubai Hospital, PO Box 7272, Al-Baraha Area, Dubai
United Arab Emirates

Abstract

Objective To standardize the rotatory chair sinusoidal harmonic acceleration and velocity step tests in an adult population. Study design Prospective study. Setting Clinical tertiary care vestibular function test center. Patients One hundred normal participants (66 men and 34 women without suspected vestibular disorder) were evaluated using bithermal binaural caloric and sinusoidal and step-velocity rotary chair tests. Intervention Hearing, videonystagmography, and rotary chair tests. Materials and methods All participants were selected according to the following criteria: (a) no history of dizziness; (b) normal otological examination; (c) normal hearing evaluation; (d) normal videonystagmography testing; and (e) rotational chair testing. The patient was positioned and secured to the rotational chair with the patient«SQ»s head restrained and adjusted so that both lateral semicircular canals were close to the plane of stimulus (30΀ forward tilt), the rotational chair testing paradigms used in this study were: (a): the rotational sinusoidal harmonic acceleration (SHA) test and (b): the rotational velocity step test. Results The demographic criteria for the study group were as follows: the age range was 18-56 years, mean age 36.47 years, and 66% of the participants were men and 34% were women. The mean, SD, range, and 95% confidence limits of the SHA and rotational velocity step test were calculated and compared with the manufacturer«SQ»s normal values. No statistically significant differences were found between our lab test results and the manufacturer-measured values of the rotational SHA test and the rotational step velocity test (SVT); this could be attributed to the strict selection criteria of the study group. Conclusion In summary, the information obtained from rotational chair testing may provide valuable information in the diagnosis and subsequent management of patients with vestibular disorders. It completes the spectrum of tests necessary for the diagnosis of vestibular abnormalities and aids the identification of peripheral vestibular deficits not detectable with existing procedures. The major clinical advantage of computerized rotational testing is the ability to produce angular accelerations that can be precisely controlled and repeated. Multiple stimuli of varying intensities can be applied to the vestibular system within a relatively short time.



How to cite this article:
Ahmed MF. Standardization of rotatory chair velocity step and sinusoidal harmonic acceleration tests in an adult population.Adv Arab Acad Audio-Vestibul J 2014;1:80-86


How to cite this URL:
Ahmed MF. Standardization of rotatory chair velocity step and sinusoidal harmonic acceleration tests in an adult population. Adv Arab Acad Audio-Vestibul J [serial online] 2014 [cited 2018 May 20 ];1:80-86
Available from: http://www.aaj.eg.net/text.asp?2014/1/2/80/149016


Full Text

 Introduction



The peripheral vestibular system consists of three semicircular canals (SCC) that are sensitive to angular accelerations, two otolith organs (utricle and saccule) that are sensitive to linear accelerations, and the vestibular nerve up to the root entry zone in the brain stem. The peripheral vestibular system acts through a range of intensities (acceleration) and frequencies [1] . The ability to evaluate the range of physiological function using an electronystagmography (ENG) evaluation is limited, given that the use of caloric irrigation stimulates the system in a manner equivalent to a frequency between 0.002 and 0.004 Hz and accelerations of less than 10 degrees/s. These values are below the level within which the vestibulo-ocular reflex (VOR) generally functions in daily activities [2] .

Therefore, rotatory chair testing has been used to expand the evaluation of the peripheral vestibular system as it can stimulate frequencies in the 0.01-1.28 Hz range, which are considered more physiologic frequencies [3] . The rotational chair testing is a test in which sequences of sinusoidal angular velocity signals at several test frequencies are applied for evaluation of the VOR function [1] . In 1907, Barany described a clinical test of vestibular function on the basis of rotational response. He placed patients in a swivel chair and rotated them to the left or right for several complete cycles and then suddenly stopped the rotation while observing the patients' eyes. The presence of postrotatory nystagmus evoked by this test is influenced by the level of vestibular function and by the status of velocity storage mechanisms [4] .

In 1948, Van Egmond described an elaboration of rotational chair testing as the patient was slowly accelerated to a series of different rotational velocities before being stopped suddenly. The duration of the nystagmus responses was measured and a 'cupulogram' was then generated by plotting nystagmus response duration versus the log of stimulus magnitude [4] . In 1960, the modern era of rotational testing began when methods became available for generating precise, repeatable rotational stimuli and for performing quantitative measurements of eye movements. Today, a computer controls all aspects of rotational testing including stimulus generation, response measurement, and data analysis [4] .

Hamid and colleagues reported that when the head is rotated on the vertical axis, the horizontal SCC on each side of the head is stimulated simultaneously. The activity of the horizontal canals is complementary. Head movement to the right increases neural discharge from the right horizontal SCC and decreases the neural discharge rate for the left horizontal SCC and vice versa. These changes in the discharge rate induce nystagmus. By measuring the VOR response, information can be obtained on the activity and interaction of the right and left vestibular systems [5] .

Studies of rotatory chair sinusoidal harmonic acceleration and velocity step tests are limited in the literature and the normal ranges for the test parameters are variable from lab to lab. Accordingly, this study was designed to standardize the rotational chair testing in our lab especially that our lab is serving very huge number of dizzy patients referred from primary, secondary, private…etc. health care centers. So, the rationale behind this study is to standardize the rotational chair testing as an objective tool for evaluation of dizzy patient.

 Materials and methods



This study was carried out in the hearing and balance clinic, ENT Department, Dubai Hospital, United Arab Emirates.

This study group included 100 normal healthy volunteers, 66 men and 34 women. Their ages ranged from 18 to 56 years, mean age 36.47 years. They were selected from among nurses, residents, medical students, relatives accompanying patients, etc. They were selected according to the following criteria:

No history of vertigo, ear disease, or intake of ototoxic drugs.Normal hearing sensitivity, and normal videonystagmography testing (VNG).No history of medical disease that might contribute toward disequilibrium such as diabetes mellitus, hypertension, severe visual loss, and neurological disorders.

All participants were subjected to the following:

Full assessment of history was performed for all participants, with a focus on the presence or absence of vertigo, ear diseases, ototoxic drugs, systemic diseases;Otological examination;Basic audiological evaluation: pure tone and speech audiometry, tympanometry and acoustic reflex study;VNG: VNG test battery including: oculomotor test, positional and positioning test, and caloric test; andRotational chair testing was performed using a Micromedical Technologies with the standard commercially available software (Micromedical Technologies, Inc. 10 Kemp Drive Chatham, Illinois, 62629, USA) for test analysis.

The patient was asked to refrain from using certain medications such as antihistamines, sedatives/hypnotics, and anxiolytics for 48 h before rotational chair testing. Eating for 2 h before the exam was discouraged as this may exacerbate nausea and emesis.

The patient was positioned and secured to the rotational chair with the patient's head restrained and adjusted so that both lateral SCC were close to the plane of stimulus (30° forward tilt) [6] [Figure 1]. During rotation, the patient was instructed to keep his/her eyes open and was provided with appropriate mental alerting tasks. The rotational chair testing paradigms used in this study were as follows.{Figure 1}

The rotational sinusoidal harmonic acceleration test

The rotational sinusoidal harmonic acceleration (SHA) test was performed at frequencies of 0.01, 0.02, 0.04, 0.08, 0.16, 0.32, and 0.64 Hz. The chair was rotated with a maximum velocity of 60 degrees/s at each test frequency. The program calculates the Gain (the ratio of the amplitude of eye movement to the amplitude of head movement), Phase (describes the timing relationship between head movement and reflexive eye response), and Symmetry (comparison of the slow component of the nystagmus when rotated to the right vs. left for each frequency).

The rotational velocity step test

The rotational velocity step (RVS) test was composed of two sections. In the first section, the chair was accelerated in one direction until it attained a preset constant velocity (100 degrees/s). This velocity was maintained for a designated length of time (45 s). During this section, a sudden burst of nystagmus occurred as the chair was accelerated. However, the nystagmus response decays exponentially as the chair maintains rotation at a constant velocity.

At the onset of the second section the chair was decelerated to a complete stop (0 degree/s 2 ) while eye movements continued to be recorded. Sudden stoppage causes nystagmus in the opposite direction as the patient perceived this stoppage as motion in the opposite direction; nystagmus will again decay exponentially until eye movements stop. The entire procedure was repeated with the initial rotation in the opposite direction.

For both sections, the computer automatically carries out data analysis; the GAIN (average eye velocity/stimulus velocity) and Time constant (time in seconds for the response to decay to 37% of its peak value) were calculated.

Statistical analysis

The SPSS version 13.0 for Windows (SPSS Inc., Chicago, Illinois, USA) was used. Results are presented as percentage, mean, and SD. A paired t-test was used to compare the results between the study group and the manufacturer's normal values. The level of significance was set at a P value of up to 0.05.

 Results



[Table 1] demonstrates the demographic characteristics of the study group (100 participants), the age range was 18 - 56 years, and the gender distribution was 66 males and 34 females. [Table 2] is showing the mean, standard deviation , range and 95% confidence limits of the Rotatory Sinusoidal Harmonic Acceleration (SHA) test gain, phase and symmetry in the study group. In terms of standardization of the rotatory velocity step (RVS) test, [Table 3] demonstrates the mean, standard deviation, range and 95% confidence limits of the RVS gain and time constant of the study group.{Table 1}{Table 2}{Table 3}

[Table 4] demonstrates the mean, standard deviation, t- and P- values of RVS (Gain, Time constant) for the study group in comparison to the manufacturer measured parameters (The manufacture is the Micromedical Technologies, Inc. located at 10 Kemp Drive, Chatham, Illinois 62629, USA). In terms of the rotational chair testing set up, [Figure 1] demonstrates that the patient was positioned and secured to the rotational chair with the patient's head restrained and flexed 30° forward. [Figure 2] demonstrates the mean of the gain, phase and symmetry at the tested frequencies (0.01, 0.02, 0.04, 0.08, 0.16, 0.32, 0.64 Hz) in the study group as compared to the manufacturervalues.{Figure 1}{Figure 2}

 Discussion



The present study was carried out on 100 normal participants fulfilling the following criteria: no previous history of dizziness or vertigo, normal hearing evaluation, normal VNG findings, and no systemic, neurological, or visual disorders. [Table 1] shows the demographic characteristics of the study group; the age range for the study group was 18-56 years, mean age 36.47 years, and 66% of the participant were men and 34% were women. Tokumau et al. [7] reported that peripheral vestibular disorders are more common in women than men. However, Kamal and colleagues found a slight increase in peripheral vestibular disorders among men [8],[9] .{Table 4}

Selection of the study group on the basis of the previously mentioned criteria indicated that more than 90% of the initially selected participants had normal hearing (patients with abnormal hearing were excluded from this study); this indicates that there is a strong correlation between hearing loss and vertigo/dizziness. Similarly, Asai et al. [10] reported such an association of hearing loss with vertigo. They reported that vertigo because of labyrinthine causes is more common than vertigo because of nonlabyrinthine causes.

[Table 2] shows the mean, SD, range, and 95% confidence limits of the SHA test. Amin defined the SHA testing as a type of angular acceleration stimulus applied to the rotational chair testing in which the patient is rotated in alternating directions (sinusoidal) at a given frequency. The parameters measured in SHA testing are Gain, Phase, and Symmetry. Gain is the ratio of the amplitude of eye movement to the amplitude of head movement (stimulus) [6] . It is calculated by dividing the slow component velocity of the eye by the velocity of the head (measured by chair velocities). It provides an indication of the overall responsiveness of the system [2] .{Table 2}

Abnormally low gain is observed in patients with bilateral vestibular weakness and they show markedly reduced gain at lower frequencies of rotation. Low gain is usually a consequence of bilateral chronic vestibular weakness, but may occur in response to acute labyrinthine lesions when the cerebellum deliberately suppresses output from all vestibular nuclei to minimize symptoms of rotation, nausea, and vomiting. Unilateral peripheral weakness can cause a mild reduction in gain. However, when gain is low, the vestibular system might not be stimulated sufficiently to provide meaningful data, Phase, and Symmetry calculations, and therefore cannot be interpreted [11] . Abnormally high gain can be observed in cerebellar lesions because of the absence of descending inhibition [12] .

Phase describes the timing relationship between the initiation of head movement and reflexive eye response when the head and eyes are moving at exactly the same velocity in opposite directions. They are considered to be exactly out of phase or 180°. If the reflex eye movement leads the head movement, a phase lead is present, and if the compensatory eye movement trails the head movement, a phase lag is present. An abnormal increase in phase lead (from low frequency, <0.04 Hz, sinusoidal rotations) implies an abnormally low system time constant suggestive of peripheral system involvement (labyrinthine, VIIIth nerve), although possible involvement at the level of the vestibular nuclei must be considered [12] . An abnormal decrease in phase lead (from a low frequency <0.04 Hz, sinusoidal rotations) implies that possible central system influences either at the level of the brain stem or in the posterior cerebellar area (nodulus) need to be considered if the result is to be considered reliable [12] .

Symmetry is a comparison of the slow component of the nystagmus when rotated to the right compared with rotation to the left [6] . Asymmetry is a measure of compensation and is calculated as the difference between the slow peak velocities of left-beating and right-beating nystagmus [13] . The peripheral vestibular pattern has a high level of asymmetry, especially acute lesions, which gradually decreases as symptoms improve. The central vestibular pattern has a low and variable asymmetry in conjunction with variable symptomatology [5] .

[Table 3] shows the mean, SD, range, and 95% confidence limits of the RVS test. Tusa and colleagues defined the RVS as a method of assessing the horizontal VOR evoked by head rotation through step changes in head velocity instead of sinusoidal rotation. The parameters measured in RVS testing are Gain and Time constant. Gain is the ratio of peak eye velocity to head velocity; Time constant is the time in seconds for the response to decay to 37% of its peak value [14] .{Table 3}

Shepard reported that although both ears are involved in responses to rotary stimuli, the right periphery (horizontal SCC and superior vestibular nerve) is primarily responsible for responding to accelerations to the right or decelerations from fixed velocity rotation leftward. The reverse is true for the left labyrinth.

Therefore, per-rotary and postrotary step tests also allow comparison of the time constant for dominant stimulation to one peripheral system. Averaging the data from multiple measures of per-rotary or postrotary slow component velocity would improve test reliability by reducing the impact from anxiety or drowsiness during a single trial [3] . Patients with unilateral peripheral vestibular lesion show directional asymmetries in response to velocity step stimuli.

[Figure 2] shows that the mean of the Gain, Phase, and Symmetry at the tested frequencies of 0.01, 0.02, 0.04, 0.08, 0.16, 0.32, and 0.64 Hz in the study group are within the normal range of the manufacturer's normal values; this may be attributed to the strict selection criteria of the study group. However, [Table 4] shows no statistically significant differences between our lab test results and the manufacturer-measured values of the rotational SVT (Gain, Time constant); this may also be attributed to the strict selection criteria of the study group.{Figure 2}

Finally, rotational chair testing is usually well tolerated by patients. It is a physiological stimulus whose frequency and amplitude can be varied precisely. Rotatory stimulation is unrelated to physical features of the external ear or the temporal bone [15] . It is useful in children who may not tolerate caloric testing and very useful in assessing patients with bilateral vestibular hypofunction, in patients receiving vestibulotoxic drugs, and in assessment of compensation [16] . Shepard established criteria for when chair testing may be of valuable clinical use over the ENG/VNG testing:

When the ENG/VNG is normal, chair testing is used to expand investigations of peripheral system involvement and compensation [3] .When the ENG suggest compensated status in terms of absence of spontaneous or positional nystagmus, despite the presence of a significant unilateral caloric weakness; Chair testing is used to expand the investigation of compensation in a patient with a known lesion site and complaints suggesting poor compensation [3] .When the caloric irrigations are below 10 degrees/s, when the caloric irrigations cannot be performed, or when results in the two ears may not be compared reliably because of anatomic variability. Chair testing is used to verify and define the extent of a bilateral weakness or when caloric studies are unreliable or unavailable [3] .When a baseline is needed to follow the natural history of a patient's disorders (such as possible early Meniere's) or to assess the effectiveness of a particular treatment such as chemical ablation of one or both peripheral vestibular systems [3] .The limitations of the rotational testing are that it is expensive and necessary to maintain a high level of mental alertness; it can test only horizontal SCC and cannot localize the side of vestibular dysfunction [15] .

 Conclusion



In summary, the information obtained from rotational chair testing may provide valuable information in the diagnosis and subsequent management of patients with vestibular disorders. It completes the spectrum of tests necessary for diagnosing vestibular abnormalities, and aids identification of peripheral vestibular deficits not detectable with existing procedures [16] . The major clinical advantage of computerized rotational testing is the ability to produce angular accelerations that can be precisely controlled and repeated. Multiple stimuli of varying intensities can be applied to the vestibular system within a relatively short time [17] .

Rotational chair testing is ideal in the assessment of patients with peripheral vestibular disorders because, unlike caloric testing, higher frequencies are also tested and both labyrinths are stimulated simultaneously. This allows for accurate determination of remaining vestibular function. Thus, it can differentiate central from peripheral and compensated from uncompensated vestibular disorders through abnormalities detected in Gain, Phase, Symmetry, and Time Constant [6] .

Recommendations

On the basis of the current study, we recommend the rotational chair test in patients with unilateral versus bilateral peripheral vestibular disorders and patients with central vestibular disorders and using the rotational chair testing as an objective test to measure the outcome of the vestibular rehabilitation therapy for these groups of patients.

 Acknowledgements



Conflicts of interest

None declared.

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