what is the purpose of the caloric test?
- Assesses if the peripheral vestibular system is symmetrical on both sides.
- Evaluates balance, which relies on equal and opposite input from the semicircular canals.
- In a healthy system, one side sends excitatory signals while the other sends inhibitory signals.
- A weak or impaired side leads to signal mismatch, causing dizziness.
- Specifically tests the horizontal canal and provides both peripheral and some central vestibular information.
how are caloric measures performed?
*Warm and cool stimuli are introduced into the ear canals, changing the temperature of the temporal bone and the endolymph in the lateral semicircular canal (SCC).
- Warm stimuli: Endolymph moves towards the ampulla → excitatory response.
- Cool stimuli: Endolymph moves away from the utricle, causing an inhibitory response.
- These temperature changes create endolymph motion, causing pressure differences across the cupula, which bends and stimulates the embedded hair cells. Neural signals are generated and sent to the brain, tricking it into perceiving motion. This results in visual nystagmus, recorded by video goggles.
what are common patient pre test instructions?
-No consumption of food or drink (particularly caffeine) 3 hours before the appointment. - Dress comfortably and do not wear eye make up. - Bring someone along to the appointment with you (to drive u home)
what happens when the patient arrives to the appointment?
1- a thorough otoscopic examination of the ear canals to: - determine the angle of the ear canal. -identify any middle ear pathology. -Check for any debris/ blockages that might keep the irrigation from reaching the full depth of the ear canal.
What is the room set up for VNG? for calorics
-Examination table: Patient lies comfortably with their head at a 30° angle in the vertical plane.
- Monitor: Positioned for the examiner to easily view eye movements and tracings.
- Space: Ensure sufficient space around the table for examiner manoeuvrability.
- Goggles: Place snugly but comfortably on the patient with their assistance.
- Calibration: Perform a brief calibration of equipment to ensure validity and reliability.
what are the patient instructions for caloric?
Introduction:
“I am going to put warm and cool air into each of your ears.”
Explain the Process:
“I will start by putting warm air into your right ear. The air will sound loud and feel warm/cool but should not be uncomfortable.”
“If you feel discomfort, let me know immediately.”
Duration:
“The air will be in your ear for approximately 60 seconds.”
“For water, the stimulus time will be 30 seconds.”
Post-Stimulus:
“After 60 seconds, I will stop and ask you some questions.”
Patient Instructions:
“I need you to do two things:
Keep your eyes open at all times, even if you feel like you’re spinning.
Focus on the questions I will ask during the test.”
Check Understanding:
“Do you have any questions before we begin?”
Why do you think it is important to ask the patient questions immediately after the caloric irrigation?
Asking questions acts as a mental alerting task
what to expect after caloric from a fully functional peripheral vestibular end organ?
- Response starts 15–30 seconds into irrigation and peaks at 60–90 seconds.
- Cool stimuli: Nystagmus beats away from the test ear.
- Warm stimuli: Nystagmus beats towards the test ear.
- Remember: COWS (Cold Opposite, Warm Same).
What are the steps to perform a caloric test?
1- Perform a thorough otoscopy to ensure the ear canal is clear and assess orientation.
2- Select the caloric test mode on the equipment.
3- Choose the desired condition (e.g., warm first, as it provides the strongest response).
4- Insert the irrigator deeply into the ear canal and press start.
5- Ensure the patient’s eyes are clearly visible on the monitor, and adjust goggles so pupils are easily tracked by the camera.
*Note: If crosshairs are not visible during the recording, tracings cannot be generated.
Successful test = visible tracings.
What happens during and after caloric testing?
1- Healthy Response: Nystagmus begins 15–30 seconds into irrigation.
2- Tracing and Analysis: Each nystagmus beat is marked and instantly analyzed.
3- Intensity Peak: Nystagmus intensity peaks between 60–90 seconds, with larger eye movements indicating stronger beats.
4- Fixation Light: At 90 seconds, a green fixation light appears inside the goggles for 10 seconds (marked by a green bar on tracings).
- During fixation, nystagmus should decrease.
- Instruct the patient to focus on the light.
5- Post-Fixation: After the light disappears, nystagmus should increase in frequency and intensity.
6- End of Recording: Stop the recording 10–15 seconds after the fixation period.
7- Repeat: Perform the same procedure for the other ear using the same temperature stimulus.
how do we calculate whether there is weakness to asymmetry in someones VS from caloric testing?
- peak slow phase velocity responses (where the nystagmus is at its greatest) that we are most interested in identifying. The average max slow phase velocity is key for interpretation
what is the formula used to calculate Unilateral Weakness (UW) which is aka Canal Paresis?
UW%= (RC+RW) - (LC+LW) / RC+ RW +LC + LW and then times it all by 100
What is the purpose of the UW/ Canal Parasis formula?
-to allow the clinician to make a comparison between the total response of the left ear vs total response of RE
what UW%/ Canal paresis is considered clinically significant and what is normal?
a difference of 20%+ suggests abnormal vestibular function f the weaker side
<20% = normal
how do i know which side the canal paresis is on and what does that mean?
*If the result is negative (-):
Left Side > Right Side
This means the right vestibular system is weaker because the total response (RW + RC) from the right is less than the total response (LW + LC) from the left.
Right Canal Paresis is diagnosed.
*If the result is positive (+):
Right Side > Left Side
This means the left vestibular system is weaker because the total response (LW + LC) from the left is less than the total response (RW + RC) from the right.
Left Canal Paresis is diagnosed.
where in the vestibular structure can a UW/ Canal Paresis stem from?
-lateral SCC
-afferent neural pathway
-the root entry zone of the 8th nerve into the brainstem
-
what are some common conditions associated with unilateral weakness?
- Labyrinthitis
- Vestibular Neuritis
- Meniere’s disease
- Anterior vestibular artery infarction
- Wallenberg Syndrome
- Vestibular Migraines
- Vestibular Schwannoma
- Demyelization of the vestibular nerve
INSERT QUESTON
sometimes the UW calculations show that unilateral weakness isn’t present but the butterfly graph shows very low peak slow phase velocity values. When this occurs, ignore caloric calculations and suspect bilateral weakness. Bilateral weakness is characterised by a loss or weakening of both left vestibular function.
How is bilateral vestibular weakness identified?
For each ear, add the maximum SPV from the warm and cool tests:
Left ear: (Warm SPV) + (Cool SPV)
Right ear: (Warm SPV) + (Cool SPV)
If the total for each ear individually is less than 12°/sec, it indicates bilateral vestibular weakness.
what kind of history would a patient with true bilateral weakness report?
History: chronic systemic disease, recent illness.
Symptoms: Chronic unsteadiness
what are some conditions associated with Bilateral weakness?
-OTOTOXICITY (most common cause)
- cerebellar degeneration
- autoimmune disease
- head trauma
-bilateral Meniere’s
- systemic infection
what kind of further testing can be done if bilateral weakness is suspected?
- ice water calorics
- video Head Impulse Testing
- Rotational Chair Testing
when does directional Preponderance occur?
when the nystagmus in one direction is stronger than the nystagmus in the other direction.
e.g. left beating nystagmus being stronger than a nystagmus beating to the right results in a left directional preponderance
what is the Directional Preponderance (DP) formula?
DP%= (RW+LC) - (LW+RC) / RC+RW+LC+LW and then times this all by 100
