This week, let’s discuss the rotational chair exam. Rotational chairs are not commonly found in many private offices performing vestibular tests, simply because they are so expensive. There is little discussion of the effectiveness and sensitivity of the rotational chair in helping diagnose patients with vestibular disorders. Many Veterans Administration and Military Hospitals use them routinely (at taxpayers expense), but private practitioners struggle to financially justify the expense/reimbursement ratio. Major university medical centers also typically use rotational chairs as part of a comprehensive vestibular assessment.
First, a description of the test apparatus from my most recent book,
“Rotational chair testing is considered “passive” rotation because the patient sits in a chair that is rotated by a servo-controlled torque motor. The speed and velocity of rotation are controlled by the examiner and measured by a tachometer attached to the chair. The patient’s head is restrained, so the assumption is made that chair speed and velocity equal head speed and velocity. The patient’s eye movement responses are recorded through EOG or infrared video. Calculations of gain, phase, and symmetry can then be completed.”
The rotational chair test is typically the first thing we do because it is the most sensitive test of whether the inner ear knows when, where and how fast it is moving, and whether the brain processes that information correctly and sends correct signals to the eyes to accommodate head movements. This test will almost always be abnormal if there has been a recent significant injury to the inner ear.
The concept behind rotational chair testing is that it isolates the ears from other parts of the body that sense movement. Whenever you move your head in day to day life, four things are happening. The first obviously is that you have made a conscious or reflexive decision to move your head. You also get feedback from the muscles, nerves and joints in the neck. The eyes give you feedback about where you are relative to your environment, and the ears sense head movement and head tilt. By having the patient’s head fixed to the chair, with the eyes in total darkness, and with the chair making the decisions about when, where and how fast to move, only the inner ear is stimulated. We record and analyze the eyes responses to see if there is any deficit in inner ear function.
I finish today with a second excerpt from my book that describes a study exploring sensitivity of rotational chair versus other, more tradional and available test methods: “<a href=”http://www.ncbi.nlm.nih.gov/pubmed/16143176
“>Arriaga, Chen and Cenci presented data (2005) exploring the sensitivity and specificity of Electrynystagmography (ENG) versus Rotational Char (RC) testing on a series of 478 patients. They calculate that RC has a sensitivity of 71% for detecting vestibular pathology, as opposed to a calculated 31% for ENG testing. Because ENG had a substantially higher specificity than RC, they recommend using RC as a primary vestibular test and ENG as a confirmatory test as it was found to have higher specificity. In their study, a normal rotational chair exam had a negative predictive value of 75%. In other words, if the rotational chair exam was considered normal, there was only a 25% chance of missing a vestibular pathology by foregoing caloric tests.”