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Board Review Series - Fix J.D.

Fix J.D. Board Review Series - London, 1995. - 430 p.
Download (direct link): boardreviewseries1995.djvu
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B. Vestibular nystagmus
-consists of involuntary to and fro, up and down, or rotary movements of
one or both eyes, -consists of a slow component, opposite the direction
of rotation, and a
fast compensatory component, in the direction of rotation, -is named after
the fast component, Śresults from the stimulation of hair cells within
the semicircular ducts
upon rotation or after caloric irrigation of the external auditory meatus
with hot or cold water.
C. Postrotational nystagmus
1. Test method
a. The subject sits in a Barany chair with head erect and inclined 30░
forward (to place horizontal canals in the plane of rotation).



--------------------------------------- 104

192 / Neuroanatomy
b. The subject is rotated to the right 10 turns within 20 seconds, after
which he is suddenly stopped.
2. Test results in normal subjects
a. The subject with normal labyrinths will have a horizontal nystag
mus to the left (fast phase).
b. The subject will past-point (show dysmetria), tend to fall to the
right, and experience a sensation of turning (vertigo) to the lef t.
c. The induced nystagmus usually lasts 15-40 seconds.
D. Caloric nystagmus (see Figure 12-3)
-may be induced with cold- or hot-water irrigation of the external audi-
tory meatus.
-may be used to stimulate each labyrinth separately, Śmay
be used to evaluate unconscious patients, -may be used to
stimulate individual semicircular canals.
1. Test method used to stimulate the horizontal semicircular
canal
a. While sitting erect, the subject tilts his head back 60░, or the recum
bent subject elevates his head 30░ from a horizontal positio n.
b. Cold or hot water is syringed into the external ear canal.
2. Test results in normal subjects
a. Cold-water irrigation results in nystagmus to the opposite side and
past-pointing and falling to the same side.
b. Hot water irrigation results in the reverse reactions.
c. Remember the mnemonic COWS = Cold, Opposite; Warm, Same.
3. Test results in comatose subjects
a. No nystagmus is seen.
b. With the brainstem intact, there is a deviation of the eyes to the
side of cold irrigation.

Cold H2O Cold H 2O Cold HO Cold HO Cold H2O Cold H 2O
2 2
Brainstem intact MLF (bilateral) lesion Low brainstem lesion
Figure 12-3. Ocular reflexes in comatose patients. The upper head shows the doll's head eye movements. The
external auditory meatus of the lower head is irrigated with cold water. If the brainstem is intact, the eyes devi-
ate toward the irrigated side. If the MLFs are transected, the eyes deviate toward the side of the abducted eye
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