Diagnostic Vestibular Pocket Guide: Evaluation of Dizziness, Vertigo, and Imbalance by Julie A. Honaker;

Author:Julie A. Honaker; [Неизв.]
Language: eng
Format: epub
Publisher: Plural Publishing Inc.
Published: 2020-05-17T21:00:00+00:00

 (C) example of prolonged time constant from central pathology, (D) gain of the initial peak SPV response.

• Shortened TC values (<10 seconds) suggest possible peripheral involvement provided there are no central indications (Shepard et al., 2016). Reduced TC values in one direct suggest unilateral involvement and reduced TCs in both directions suggest bilateral involvement (Figure 6–6B).

• Prolonged TC values (>30 seconds) suggest central nervous system involvement requiring further clinical correlation. Patients with migraine may also present with prolonged TC values (Zalewski, 2018). See Figure 6–6C.

The second outcome of interest is VOR gain (peak SPV/peak head-chair velocity; see Figure 6–6D). Step velocity testing at 60 or 100°/second is considered a low frequency response of the VOR: Gain values may not completely represent compensatory eye movements to head-chair movements. According to Shepard et al., (2016), normal VOR gain values are 0.40 or higher although normative range should be based on equipment and laboratory protocols. Asymmetrical (>30%) gain values are sometimes observed in cases of acute uncompensated unilateral peripheral vestibular dysfunction. Step velocity gain values are also impacted by other factors (e.g., fatigue, mental tasking, and visual fixation).

Some rotational chairs are equipped for high peak velocity (e.g., 240°/second) step velocity testing, and the outcome of interest is gain alone (cannot properly estimate canal-ocular time constants due to speed of the chair). Similar to head impulse testing (Chapters 3 and 7), the high-peak velocity testing is designed to tease out asymmetrical peripheral vestibular function that may not be evident during low peak velocity (e.g., 60°/second) step testing.

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