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Anatomy and Physiology /Vestibular Foundations - Session 5: Calorics

Vestibular Foundations - Session 5: Calorics

Anatomy and Physiology41 CardsCreated 8 months ago

The caloric test assesses the symmetry of the peripheral vestibular system by evaluating responses from the horizontal semicircular canals. It detects imbalances in neural signals that can cause dizziness, offering insight into both peripheral and some central vestibular function.

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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.

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Key Terms

Term

Definition

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 oppo...

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 semicircu...

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 s...

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 an...

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 examin...

what are the patient instructions for caloric?

Introduction:

“I am going to put warm and cool air into each of your ears.”
Explain ...

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 e...

What are the steps to perform a caloric test?

1- Perform a thorough otoscopy to ensure the ear canal is clear and assess orientation.

what are some common conditions associated with unilateral weakness?

Labyrinthitis
Vestibular Neuritis
INSERT QUESTON
sometimes the UW calculations show that unilateral weakness isn’t present but the butterfly graph shows very low peak sl...

what kind of further testing can be done if bilateral weakness is suspected?

ice water calorics
video Head Impulse Testing

what kind of further testing can be done if bilateral weakness is suspected?

ice water calorics
video Head Impulse Testing
what is the Directional Preponderance (DP) formula?
DP%= (RW+LC) - (LW+RC) / RC+RW+LC+LW and then times this all by 100

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Vestibular Foundations - Session 5: Calorics

Term	Definition
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
what kind of further testing can be done if bilateral weakness is suspected?	ice water calorics video Head Impulse Testing Rotational Chair Testing
what is the Directional Preponderance (DP) formula?	DP%= (RW+LC) - (LW+RC) / RC+RW+LC+LW and then times this all by 100
how is the Directional Preponderance (DP) formula interpreted?	if the DP value is greater than 20% DP exists AND if the result is negative = left DP vice versa
What causes DP?	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).
How should DP be interpreted?	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.
Is spontaneous nystagmus normal?	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).
Why is the ability to fixate on an object important for the balance system?	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.
What is the fixation index?	The fixation index measures the ability to suppress nystagmus by focusing on an object during caloric testing.
What is considered a normal visual fixation index?	A normal fixation index shows a reduction in nystagmus intensity by at least 50% during fixation.
What does an abnormal fixation index indicate?	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.
How is fixation measured during caloric testing?	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.
what are hyperactive caloric responses?	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.
What does unilateral hyperactivity indicate?	*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.
Why should all four caloric measurements be taken when considering hyperactivity?	To ensure accuracy and confirm that the hyperactivity is not due to technical error or a unilateral issue.
Formulas and Normal limits for: Canal Paresis/ UW Directional Preponderance Visual Fixation Index	▪ 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%
What temperatures are used to irrigate the ear with water and air?	water: warm= 44 degrees cool= 24 degrees air: warm= 50 degrees cool= 24 degrees
for how long are the ears irrigated with water and air?	water= 30s air= 60s
what considerations are there for performing calorics?	back problems neck problems ear infections etc
How can caloric testing results differentiate between peripheral and central vestibular lesions?	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.