Rotatory chair testing electricity out


clinicians can use it, such as a hospital laboratory. At Chicago Dizziness and Hearing we use a Micromedical rotatory chair. Click here for a movie of our rotatory chair in motion. Most of the illustrations on this page are taken directly from our rotational chair. Role of rotatory chair testing in diagnosis of dizziness

someone with a unilateral vestibular loss. Note that at frequencies above roughly 0.1 hz, the unilateral loss and normal person are indistinguishable, because gain asymptotes at these frequencies. Phase differences are also greatest at low frequencies. Thus, rotatory chair testing is most sensitive to vestibular problems at low frequencies !

Theoretical gain and phase in patient with unilateral vestibular loss (Tc=7) compared to normal (Tc=14.5 and 21). Peak gain is set to 0.8 in all cases. On the top plot, the higher curve is 21. An identical plot, for the 14.5 Tc, can be found in Dimitri et al (1996) — this is to show we got our math right (:

Step responses should be completely predictable from sinusoidal testing. High gain on step responses should correlate with high gains on rotatory chair testing. Small time constants should be associated with increased low frequency phase lead. When there is a mismatch, this can be valuable in figuring out whether the patient is consistent as well as one’s equipment is functioning.

Ideally subjects undergoing rotational tests should have no sedating medications for the last 24 hours. Sometimes this is difficult, as for example, when persons are addicted to medications in the Valium family. In this situation, usually 12 hours is sufficient. More data about medication effects is found here. Optokinetic nystagmus (OKN) testing and OKAN (optokinetic after-nystagmus)

Contemporary rotatory chairs often implement optokinetic patterns that have no clinical utility. For example, a row of smiley faces. A "real" optokinetic stimulus should include at least 50% of the patient’s visual field, and be a pattern rather than a line. Visual-vestibular interaction (VVI)

Normal is defined by gain and phase points staying within the white area on the graph above. Generally speaking, gain points below the lower limit suggest vestibular damage. Gain points above the upper limit suggest a technical error (such as a light leak or uncalibrated chair speed).

According to Maes and associates (2014), children’s rotatory chair testing show no effect of age (between 4-12 years of age). In older persons, there is also surprisingly little effect on rotatory chair testing results, although one would expect a downward trend in gain/phase based on pathological studies showing loss of vestibular hair cells and neurons in the ganglia. Rotatory chair testing in bilateral vestibular loss

There are several commercial devices, not incorporating motorized chairs, that provide data that overlaps in part with the data provided by rotational chairs. These devices are called "active head" devices, and compare eye movements induced by active motion of the head (rather than the passive movement induced by a motorized chair). Both of these tests measure — the

As can easily be seen from the plot above, these devices assess the high frequency range, but do not assess the low frequency range. They are not equivalent to rotatory chairs because the low-frequencies are missing. See this page for more details and examples of output. Blunders in rotatory chair testing (see also this page)

The plot above shows the most common blunder — a lack of "tasking" — in other words, the technician did something else than keep the subject distracted during the test (? checked Facebook perhaps ?). Following is a brief list of chair blunders. See the " blunders" page if you are interested in more.