Vestibular Laboratory Testing: VNG, vHIT, VEMP, and Rotary Chair
Videonystagmography
VNG includes oculomotor subtests, positional and positioning tests, and caloric irrigation. Caloric testing uses warm and cool water or air to create convection currents in the horizontal canal; it assesses low-frequency function and can show canal paresis. Unilateral weakness is calculated from the sum of responses; directional preponderance reflects asymmetry. Fixation suppression should reduce peripheral nystagmus but may not reduce central nystagmus.
vHIT and VEMP
Video head impulse testing measures the VOR gain at high frequency and detects covert and overt saccades across all six canals. It is useful in acute vertigo and in bilateral hypofunction. Cervical VEMP tests saccular function via the vestibulocollic reflex; ocular VEMP tests utricular function via the vestibulo-ocular pathway. Reduced cVEMP suggests inferior vestibular nerve or saccular involvement; reduced oVEMP suggests superior vestibular nerve or utricular involvement.
Rotary chair
Rotary chair provides physiologic, low-frequency testing with sinusoidal or step velocity protocols. It helps confirm bilateral vestibulopathy and can show reduced gain with normal caloric testing. It is less useful for unilateral lesions.
Common traps
Assuming normal caloric testing excludes vestibular disease; caloric testing is low-frequency and can be normal in high-frequency deficits. Interpreting VEMP asymmetry without correcting for age and hearing. Confusing cervical and ocular VEMP anatomy. Artifact from poor electrode placement or muscle tension.
Rule of thumb
Match the test to the frequency and pathway: calories and rotary chair for low-frequency horizontal function, vHIT for high-frequency canal function, VEMP for otolith pathways. Abnormal VEMP with normal vHIT suggests a selective otolith or nerve branch lesion.