Part 15 Flashcards
what vestibular systems are tested by calorics
horizontal SCC and superior vestibular nerve
the temperature gradient in calorics generates what
cupullar deflections which mimic head movement thus activating VOR and generating nystagmus
cool irrigation
ampulofugal (opposite)
inhibition
- nystagmus in opposite ear of water
warm irrigation
ampulopetal (same)
excitation
- nystagmus in same ear as water
what % of this process is gravity independent and what does that mean
10% means that in space we would still have excitation if nerve heated
caloric irrigators
open loop water system
close looped water system *old, no longer made
air system
caloric procedure
head at 30 degrees from horizontal (vertical position)
vision denied goggles
initial calibration performed
alerting task
precaloric search for spontaneous nystagmus (30 seconds to record without stimulation)
Bithermal irrigation (warm and cold)
irigation ends (40s water, 60s air) alerting task continues
Fixation with goggles removed (10-15 seconds)
Bithermal irrigation temperatures and time
water +/- 7 for 40s
air +/- 13 for 60 sec
when does response hit peak velocity (caloric)
60-90 seconds after irrigation and declines 10-15 seconds after peak
what is the order of irigation
Rw-Lw_RC-LC
waiting period between irrigation
5 mins (body temperature to return)
unilateral caloric weakness is abnormal when
greater than 25%
unilateral caloric weakness is positive when
in left ear
unilateral caloric weakness is negative when
right ear
what does unilateral caloric weakness usually tell us
peripheral lesion (can be neural)
what side does the unilateral caloric weakness localize to
the side with lesion R ear if negative weakness, L ear if positive
bilateral caloric weakness
no response or weak in bithermal test stop calculations
- all 4 less than 8 degrees/sec and total RE and LE are each less than 12 deg/sec
hyperactive response criteria
check no artifacts perforation etc.
- when one or both ears are greater than 110 degrees (RC+RW or LC+LW)
what does hyperactive response indicate
cerebellum lesion
- inhibition not functioning
directional perponderance
should be less than 30% if greater its abnormal
directional preponderance is positive
right beating stronger
DP is negative
left beating stronger
if DP is +/- 100% what does that tell us
lack of total caloric response in one direction
what does DP tell us about side of lesion
nothing its non localizing
2 types of DP
pre-existing nystagmus (baseline shift) 99% of cases
2. Gain asymmetry (1%)- where nystagmus is truly beating in 1 direction stronger than other
fixation supression
ratio of nystagmus intensity before and after fixation
fixation suppression greater than what % is abnormal
60%
Fixation suppression of 0 means
fully supressed
Fixation suppression greater than 100 means
enhanced and is a characteristic of central pathology
lack of fixation supression indicates
possible central lesion
bilateral: cerebellar degeneration
unilateral: focal lesions of CPA
