Vestibular Foundations - Session 5: Calorics

• 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.

*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.

-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)

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.

-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.

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?”

Asking questions acts as a mental alerting task

• 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).

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.

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.

• 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

UW%= (RC+RW) - (LC+LW) / RC+ RW +LC + LW and then times it all by 100

-to allow the clinician to make a comparison between the total response of the left ear vs total response of RE

a difference of 20%+ suggests abnormal vestibular function f the weaker side

<20% = normal

*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.

-lateral SCC
-afferent neural pathway
-the root entry zone of the 8th nerve into the brainstem

• Labyrinthitis

• Vestibular Neuritis

• Meniere’s disease

• Anterior vestibular artery infarction

• Wallenberg Syndrome

• Vestibular Migraines

• Vestibular Schwannoma

• Demyelization of the vestibular nerve

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.

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.

History: chronic systemic disease, recent illness.
Symptoms: Chronic unsteadiness

-OTOTOXICITY (most common cause)
- cerebellar degeneration
- autoimmune disease
- head trauma
-bilateral Meniere’s
- systemic infection

• ice water calorics

• video Head Impulse Testing

• Rotational Chair Testing

• ice water calorics

• video Head Impulse Testing

• Rotational Chair Testing

DP%= (RW+LC) - (LW+RC) / RC+RW+LC+LW and then times this all by 100

if the DP value is greater than 20% DP exists
AND

if the result is negative = left DP vice versa

*Most Common Cause: Spontaneous Nystagmus

• Spontaneous nystagmus is involuntary eye movement that occurs without stimulation (not normal).

• Example: If someone has a natural right-beating nystagmus, it adds to the rightward caloric response and weakens the leftward response, causing rightward DP.

*Less Common Cause: Central Pathology

• If DP occurs without spontaneous nystagmus, it may indicate a central issue, such as:
  =Vestibular nerve damage.
  =Vestibular nuclei dysfunction in the brainstem.
  =Problems in the central nervous system (CNS).

1- Rule out technical errors (e.g., calibration issues with equipment).

2- Check for spontaneous nystagmus (likely a peripheral vestibular issue).

3- If DP exists without spontaneous nystagmus, suspect a central vestibular problem.

No, spontaneous nystagmus is not normal. It may indicate:

• Inner ear issues (e.g., vestibular neuritis or Ménière’s disease).

• Brainstem or CNS conditions (e.g., stroke, vestibular migraine).

Fixation allows us to track moving objects by keeping their image on the retina, which is essential for maintaining balance. Inability to fixate can cause a sense of imbalance.

The fixation index measures the ability to suppress nystagmus by focusing on an object during caloric testing.

A normal fixation index shows a reduction in nystagmus intensity by at least 50% during fixation.

• The patient was unable or unwilling to suppress nystagmus by fixating on the given object.

• It suggests central pathology, as the fixation index examines the interaction between the vestibular and visual neural pathways.

• the patient is presented with an object (usually a small light in goggles) to focus on after the slow phase peak velocity (SPV) of nystagmus is recorded.

• The fixation measurement requires active participation, so the patient must be properly instructed.

those in which the total of the warm and the cool responses in each individual ear is greater than 140 degrees/second.

• True hyperactivity is a central process and should be bilateral.

*Unilateral hyperactivity is not normal and is likely due to:

1) Physical abnormalities, such as:

• Perforated eardrums.

• Altered or open mastoids allowing greater heat transfer.

2) Technical errors, which are the most common cause.

To ensure accuracy and confirm that the hyperactivity is not due to technical error or a unilateral issue.

▪ Canal Paresis
▪ (RW+RC) – (LW+LC) / (RW+RC+LW+LC) x 100%
▪ Directional Preponderance
▪ (RW+LC) – (LW+RC) / (RW+RC+LW+LC) x 100%
▪ Visual Fixation Index
2 x Average SPV with fixation /
Average SPV before and after fixation*
x 100%

Normal Limits:
▪ Canal Paresis is abnormal when MORE THAN OR EQUAL TO
20%
▪ Directional preponderance is abnormal when MORE THAN OR
EQUAL 20%
▪ Visual Fixation index is abnormal when MORE THAN OR EQUAL
50%

*water:

• warm= 44 degrees

• cool= 24 degrees

*air:

• warm= 50 degrees

• cool= 24 degrees

• water= 30s

• air= 60s

• back problems

• neck problems

• ear infections etc

*Peripheral lesion: Nystagmus follows the COWS rule:

• Warm water → Nystagmus beats to the same side.

• Cold water → Nystagmus beats to the opposite side.

*Central lesion: Nystagmus does not follow the COWS rule, showing abnormal or inconsistent responses due to disrupted central vestibular processing.