Clinical experience with the low-frequency rotary chair test

The primary strength of the CRC test appears to be its sensitivity to monitor change within the vestibular system, particularly in the early detection of a bilateral, peripheral weakness. Although disagreement continues about the low-frequency rotary chair's ability to monitor physiological compensation following a sudden, unilateral vestibular insult, some points are worth reviewing. For example, in an acute, unilateral vestibular weakness, an asymmetry will usually be present in the direction of the spontaneous nystagmus. In addition, gain may be depressed (primarily in the low frequencies) and a large phase lead should be seen.As central compensation occurs, the degree of asymmetry will reportedly decrease or resolve completely (probably secondary to a decrease in the spontaneous nystagmus), and gain may improve as well. In contrast, the low-frequency phase lead appears to persist in most patients. Recall that the symmetry measure is likely a representation of a spontaneous nystagmus or directional preponderance, whereas gain can be affected by patient alertness and other extravestibular factors during low-frequency acceleration. For these reasons, the clinical significance of gain and symmetry change following low-frequency rotation remains somewhat obscure. Because the rotary chair is extremely sensitive to bilateral, peripheral vestibular lesions, it seems ideal for monitoring the effects of vestibulotoxic medications. If patient alertness is maintained, both low-frequency phase and gain can be used to monitor vestibular change, as is illustrated in case study 1. Another effective application of the CRC test is its use with special populations, especially infants and young children in whom caloric testing cannot be done. The test is easy to administer, takes a minimal amount of time, and is not adversive to most patients, unless claustrophobia is present. Even though the low-frequency rotary chair test has specific limitations (such as inability to identify consistently site of lesion or side of involvement in unilateral, peripheral vestibular disease), it has demonstrated a significant clinical usefulness, as described previously. It must be stressed, however, that the CRC results should be treated with a degree of caution. Our knowledge of the visual and vestibular systems is limited, and the low-frequency CRC test monitors only a fraction of the VOR. We must take into account other fctors, such as the otolith organs, the other semicircular canals, the brainstem integration of the response, and the cognitive processes, such as prediction, that may also affect the rest results. As is appropriate with all clinical assessments, the rotary chair results should always be interpreted in light of the history, symptoms, and other test findings. Future advances in stimulus presentation and response measurement however, should solidify the role of the CRC test in the evaluation of the patient with dizziness.