Calorics Flashcards
What is the goal of calorics?
Discover the degree where the vestibular system is responsive and how symmetric the responses are between L/R ears.
Which vestibular structures does calorics test?
- Lateral semicircular canals
- Superior nerve branch pathway alone
What does calorics not assess?
- The vertical canal
- Otolithic Function
What does caloric test provide?
Low frequency ear specific information due to the cupula deflecting
What kind of vestibular test is calorics? And what is the labyrinth sensitive to?
Peripheral vestibular test
Sensitive to temperature change
What does warm stimulation cause?
Excitation of the SCCs
What does cold stimulation cause?
Inhibition to SCCs
For caloric testing, why are patients placed in a dark room?
To eliminate fixation to accentuate peripheral vestibular nystagmus
For caloric testing, what does the change in temperature in the EAC cause?
Change in temperature in the EAC is sent to the horizontal canal since it’s closest to the TM of the EAC
For calorics, what is the flow of irrigation?
1st ear canal is irrigated —> Promontory —> Distal portion of H-SCC
For calorics, how should the pt be positioned?
- Reclined
- Head inclines at 30 d/s
For calorics, what are the temperatures for water?
It needs to be 7 d/s above or below 37 d/s (body temperature)
• Warm = 44 d/s
• Cold = 30 d/s
For calorics, what are the air temperatures?
It needs to be 13 d/s above or below 37 d/s (body temperature)
• Warm = 50 d/s
• Cold = 24 d/s
What does warm/cold air or water cause for calorics?
It causes a temperature gradient across the H-SCCs
Due to the flow of gravity, what happens to the endolymph in relation to temperature?
Gravity causes the endolymph to flow from the cooler area in the ear canal, to where the endolymph is more dense and then it’ll flow into the warmer area of the canal that is less dense.
Describe what is mechanically happening for warm caloric irrigation.
- The vestibular afferent nerve innervates the H-SCC to excite
- Thus causing horizontal nystagmus with fast phase components to the ear that is stimulated.
Describe what is mechanically happening for cold caloric irrigation.
Cold caloric causes an opposite response compared to warm caloric.
- Inhibition of the H-SCC afferents
- Nystagmus with fast phase are directed to the opposite ear to which the caloric is being applied to.
How long is the irrigation and recording time?
Irrigation: 50 secs
Recording: at least 1min once irrigation ends
When is the peak velocity post-irrigation?
~ 30-40secs
For calorics, when should the subject fixate on a target? What should occur? & what does it mean if it doesn’t occur?
- 40 secs
- Eye velocity should decrease by at least 50% with fixation
- If not, potential central finding and there should be commonality in OPK & Smooth Pursuit tests
For calorics, how long does nystagmus build for and when does it decay?
- 30-60secs
- Decays over 2mins
List the five normal data we use for caloric testing.
- Caloric Weakness/Canal Paresis/Unilateral Weakness
- Directional Preponderance
- Fixation Suppression
- Bilateral Weakness
- Hyperactivity
Based on temperature layout on the screen, what kind nystagmus would one suspect?
• RW + LW = RB
• LW + LC = LB
What is the formula and normative data for caloric weakness/unilateral weakness/ canal paresis?
CP = 100 c [(LW + LC) - (RW + RC)] / LW+LC+RW+RC
What’s the purpose of directional preponderance (DP)?
It looks for an increased intensity of nystagmus towards a certain direction compared to the other ear.
When is DP normally seen?
It’s controversial, but DP is commonly seen in pts with spontaneous nystagmus that occurs towards the same direction.
What is the formula and normative data for DP?
(LW+RW) - (RC+RW)/ LC+LW+RC+RW x 100%
~ 22-33%
What is fixation suppression (FI)?
A ratio of nystagmus intensity that’s recorded before and after and after the pt fixates on a target.
What is the formula and normative data for FI?
SPEV Post Fixation (what is nystagmus w/fixation) / SPEV Pre Fixation (peak eye velocity)
How is the formula for FI obtained?
It is calculated for at least one RB testing and one LB test
What does FI of 0% & 100% mean?
0% = Complete Fixation
100% = No fixation
What is the normative range for FI?
Based on published research: ~50-60%
For FI what does failure to fixate indicate?
Failure to suppress nystagmus with fixation is a sign of central vestibular pathology.
What is the normative data for bilateral weakness?
Only abnormal if total is <12%
What does bilateral weakness indicate & why should clinicians be cautious if results indicates this?
Both area are not responding and need to ensure pt understood the task and they aren’t on any drowsy medication.
What is the normative data for hyperactivity?
Abnormal if each ear total is >140 d/s per sec
What are contraindications for calorics?
- Skull fracture
- TM Perf
- Otitis Media & Externa