Using Unidirectional Rotations to Improve Vestibular System Asymmetry in Patients with Vestibular Dysfunction

Stimulating the weaker side and inhibiting the stronger side, an idea originally proposed by Doctor Nayer Rassaian, has been demonstrated to decrease assymetry in individuals with vestibular imbalance. This technique provides a unique method for effectively stimulating the vestibular system in the dark and does not require complicated equipment. Unidirectional rotation could be used as a rehabilitation option for patients with an imbalance between vestibular inputs from the two sides as quantified by the vestibulo-ocular reflex.

This methods requires a rotating chair and professional supervision. The critical aspect is the slow deceleration to avoid stimulation of the opposite side at the end of the unidirectional rotation. To measure the vestibulo-ocular reflex, have the participant in a rotary chair and secure the participant with the harness.

Give the participant a pair of infrared goggles and fix the head in the headrest in the nose-down position at a 30-degree angle. After the participant has acclimated to the dark, have the participant look at laser targets projected on the wall at plus or minus 10-degree angles to calibrate the eye tracker. When the eye tracker has been calibrated accurately and the participant is ready, initiate a unidirectional rotation that consists of an asymmetric triangular velocity profile with an acceleration of 80 degrees per second squared over four seconds to reach a maximum velocity of 320 degrees per seconds.

To keep the participant alert and distracted during the testing, ask questions or have the participant perform mental arithmetic. Can you tell me all of the cities in Australia? Sydney, Canberra, Melbourne.

When the maximum velocity has been reached, slowly decelerate the rotation at 10 degrees per second squared to come to a full stop in about 30 seconds. It is critical to slow down the chair gradually to ensure that only the weaker side is simulated and that the stronger side is inhibited during the unilateral rotation. After the unidirectional rotation, have the participant remain in the chair to allow testing of the symmetry with the bidirectional sinusoidal harmonic acceleration rotation test at 0.05, 0.2, and 0.8-hertz frequencies with a peak velocity of 60 degrees per second at 40 and 70 minutes post unidirectional rotation.

Here, the peak eye velocity is measure during a sinusoidal rotation test in response to the rotations in the two directions and the change in the directional preponderance 70 minutes after rehabilitation are shown. Following the unidirectional rotation, the response to the rotations and the direction of the side with the lower response was increased and the response to the rotations in the direction with the stronger response decreased resulting in a change in the directional preponderance value due to the decrease in the vestibulo-ocular reflex assymetry. Exposing subjects the unidirectional rotation during multiple sessions further decreases the directional preponderance value, an effect that is retained between sessions and that results in most of the subjects exhibiting a directional preponderance in the normal range after only two sessions.

Although it is important to reach the effective peak velocity, slow declaration is critical part of rotation to ensure that the stimulation remains predominantly unidirectional. This method is safe and was well tolerated by subjects. Future studies that required to investigate how changes in the stimulation parameters, such as the peak acceleration and number of rotations, affect the efficacy and time course of the results.

Some questions that we plan to investigate include, how long does this effect last and are the eye movement changes paralleled by changes in subjective symptoms, such as imbalance and disease?