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by low speech discrimination, abnormal tone decay time, and abnormal brainstem-evoked response
audiometry (BRA). More advanced methods of investigation, such as computed tomography (CT) or better
magnetic resonance imaging (MRI) are now routine in most hospitals.
The presence of a vestibular pathology (central or peripheral cause) may be indicated by a few essential
clinical tests. Romberg test13 , Bárány’s rotatory chair test14, Dix-Hallpike test15, test for spontaneous
nystagmus, the ability to walk a straight line, heel-to-toe with eyes blindfolded (or Unterberger’s stepping
test16) are sensitive indicators and easy for the examiner to perform. Also placing the finger to the nose and
then to the examiner's finger rapidly back and forth with the eyes blindfolded will demonstrate a drift (past
pointing) in acute labyrinthine disturbances and make apparent any latent ataxia. In case of irregular vestibular
test results the pilot should be referred for further evaluation using more sophisticated test methods such as
electro-nystagmography (ENG), video-nystagmography (VNG), caloric testing, vestibular autorotation test
(VAT), vestibular evoked myogenic potential (VEMP), equilibrium platform testing (EPT), etc.
CALORIC TESTING
Applicants with a history or evidence of vertigo should have caloric studies or other equivalent testing done.
In the caloric test, the lateral semi-circular canal is stimulated by introducing fluid into the external auditory
canal. If the fluid temperature differs from body temperature, the temperature difference will be conducted to
a sector of the lateral semi-circular canal. Endolymph in this sector will differ in density from the remainder
of the endolymph. If the plane of the semi-circular canal is aligned with gravity, this density difference will
cause the endolymph to fall if the fluid is colder, or to rise if the fluid is warmer than body temperature. Since
the caloric stimulus can produce a convection current which will rotate the endolymph in either direction, each
ear can be tested independently.
Many articles have been written on technique, modification and interpretation of tests with hot and cold water
stimulation of the semi-circular canals. A simple formula for the examiner to remember is ←COWS→. When
13 Romberg’s test: station test or Romberg’s sign. The test is postivie when a patient, standing with feet approximated,
becomes unsteady, or much more unsteady with eyes closed. After Moritz Romberg, German physician (1795-1873).
14 Bárány’s rotatory chair test: A test to measure vestibular function by rotating the patient in a swivel-chair and
observing the duration of the nystagmus produced under Frenzel's glasses.
15 Dix-Hallpike test: A test to determine whether vertigo is triggered by certain head movements. After Margaret R.
Dix , English physician, and Charles Skinner Hallpike, English neuro-otologist (both 20th century).
16 Unterberger’s stepping test: A test for vestibular pathology; the test is positive if the patient turns while walking on
the spot with eyes closed. Rotation to one side indicates labyrinthine disease on that side. After A. Unterberger,
German otologist (20th century).
ICAO Preliminary Unedited Version — October 2008 III-12-27
cold (C) water is used, the resultant nystagmus is to the opposite (O) side; when warm (W) water is used, the
nystagmus is to the same (S) side. One refers to nystagmus to the right or left according to the direction of the
fast component. The speed of the slow component of the nystagmus and its direction are the parameters. A
unilateral weakness of less than 20 per cent is considered normal. A directional preponderance of less than 25
per cent is within accepted normal limits. The test procedure uses water at 30°C and 44°C i.e. 7°C below and
above body temperature. This procedure is somewhat complicated and time-consuming for the non-specialist
medical examiner.
A more attractive way of inducing vestibular responses is by means of natural head movements and the
vestibular-ocular reflex (VOR). The vestibular autorotation test, or VAT, is a computerized test that has been
developed to measure the VOR during high-frequency head rotations (2-6Hz), using active head movement
that is cued by an auditory stimulus, instead of passive rotation in a chair. The test is an aviation relevant
replacement of caloric testing and is the preferred test in several aviation medical centres in Contracting States.
ELECTRONYSTAGMOGRAPHY/VIDEONYSTAGMOGRAPHY
The major drawback in the use of the caloric test in examination of vestibular function lies in the fact that the
induced nystagmus must be judged by direct observation and is, therefore, subject to the personal judgement
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Manual of Civil Aviation Medicine 2(88)
