vestib
what fluid is in bony labyrinth?
perilymph
what fluid is in membraneous labyrinth?
endolymph
role of the cupula
cupula is inside the ampulla of the SCC and has hair cells embedded in, the cupula moves when movement occurs and this causes the hair cells to bend to cause excitation or inhibition along the neural fibres
role of semi circular canls
provide info about angular changes in head velocity
role of the otolith organs
detect changes in linear acceleration and gravitational tilts
direction and role of utricle
horizonal and detects movement in horizontal plane
role and direction of saccule
vertical and detects movement in vertical plane
what is the macula
both otolith organs contain a macula which detects linear accelereation.
It contains hair cells and nerve fibres and has a gelatinous layer on top with otoconia (calcium carbonate crystals).
The otoconia weigh down on the gelinous layer so when head accelerates/tilts, the stereocilia ben
describe the vestibular ocular reflex
responsible for maintaining stable vision, produces eye movements that are equal and opposite in velocity and direction to any head movements, we can use the VOR to test the vestib system
what is nystagmus
unusual movement of the eye where the eye slowly drifts and then quickly comes back
desribe electronystagmography (and advantages and disadvantages)
electrical recording of N, measures eye movements through changes in the cornearetinal potential using electrodes (eye is more positive at front than at back)
electrodes are placed in the corners of each eye so potential difference of left and right sides of each eye is measured
ad: reliable, objective, non-invasive, good if patient can't wear goggles
diad: traces can be affected by external interference/electrical noise from facial muscles/changes in lighting ect
describe videonystagmography (and ad/disad
video recording of nystagmus, patient wears goggles containing cameras, computer monitors movement of the pupil
ad: isn't affected by electrical interference, complex eye movements can be analused, blackout can be achieved
disad: affected by faulty calibration, goggles can be heavy and move easily, difficult if eye is watery or patient has long eyelashes or droopy eyelids
what are gaze stability tests
records eye movements (for presence of nystagmus) as patient fixates on target at diff locations), mental alerting needed too, tests for central or peripheral lesions
what are saccade tests
measures ability of eyes to move in rapid single movements to fixate on target, randomised amplitude and direction of saccades
only tests central system not peripheral
what are smooth persuit tests?
measures ability to track target with continous movements (not rapid), tests central system, age-sensitive
desribe alexander's law
the slow-phase velocity of the nystagmus caused by unilateral vestib lesion increases with gaze in the beat direction
If the patient has left-beat nystagmus, this will get worse when they look in the left direction
describe the head impulse test
tests patient's ability to keep gaze fixated on target during rapid passive head turns (high freq head turns), measures all 3 SCC, normal response: patient can fixate on target, abnormal response: patient makes saccades
describe head shake test
patient's head is shaken and nystagmus is recorded, ENG/VNG used to record results,
abnormal response: at least 3 beats of N in same plane of movement as head shake
unilateral vestib pathology: as head is shaken, there is increased input on healthy side but reduced/no input from affected side so once head stops shaking, N occurs
normal response: no N
desribe dynamic visual acuity tests
uses a visual acuity chart to measure patient's ability to stabilise their gaze, measures oscillopsia, or identifies bilateral vestib loss
first visual acuity is measured when head is still, then when head is moving rapidly from side to side and up and down
normal reponse: VA stays same or worsens by one line on chart
abnormal: VA worsens by two or more lines on chart
what does BPPV stand for
Benign, paroxysmal, positional, vertigo
why does BPPV occur
otoconia from utricle become detached from gel membrane and move through the endolymph fluid and settle in SCC (usually posterior), this detatched otoconoia shifts when head moves which stimulates cupula to send false signals to the brain which creates a sensation of vertigo
causes and symptoms of BPPV
causes: head injury, degeneration of vestib sys, secondary vestib labyrinthitis
symptoms: rotatory vertigo, disoriented, sensation of falling/sinking, veering off to one side
desribe Dix-hallpike test
used to diagnose BPPV
patient sits on bed, head is turned 45 degrees, tester holds patient's head in position and rapidly moves patient to lying position so head is hanging off bed at an angle, tester observes N (patient remains in this position until nystagmus stops)
then tester returns patient to upright position, observes for N again
repeated on other side
normal results: no N or dizziness
abnormal: affected side has immediate or delayed onset N and fatigue after test
what are vestibular neuritis and labyrinthitis and the symptoms, cause and treatment?
neuritis: imflammation of vestib nerve
labyrinthitis: inflammation of vestib organ
symptoms:
-sudden serve vertigo lasting from days to weeks
-balance difficulties
-nausea/vomiting
with labyrinthitis you also get:
-hearing loss and tinnitus
causes: viral infection
treatment: vestibular suppressants, meds to treat virus
Meniere's disease (symptoms, cause, treatment)
disorder of inner ear causing vertigo, tinnitus and fluctuating hearing loss
symptoms: vertigo, hearing loss, tinnitus, sensation of fullness in ear, fluctuating symptoms
causes: unknown
treatment: vestibular suppressants, diuretics, diet control, hearing aids, labyrinthectomy
perilymph fistula (symptoms, cause, treatment)
tear/defect in the bony capsule of the labyrinth or in round or oval window
symptoms: ear fullness, fluctuating or sensitive hearing, vertigo (without spinning), motion intolerance, hearing loss, worsening symptoms with altitude
causes: head trauma, changes in atmospheric or intracranial pressure
treatment: surgery
superior semi circular canal dehiscence
opening in the bone that covers one of the SCC of the inner ear
cause is unknown, could be due or ear infections or head trauma
symptoms: vertigo, oscillopsia, autophony, sensitvity to loud sounds, fullness/pressure in ear
treatment: surgery, plugging the dehiscence
romberg/sharpened test (and ad/disad)
objective measure of postural stability, P stands still (tests eyes open and closed), normal: little/no swaying; abnormal: excessive swaying
ad: simply and non-intrusive, cheap
disad: resulst are subject to variations in interpretation, limited evidence for diagnosing a vestibular pathology
clinical test of sensory integration in balance
patient stands on a cushion/foam with their feet apart (eyes open, then eyes closed)
pass or fail crtiera (patient fails if they make corrective movement with their feet to stay upright)
gives info about which sensory input the patient relies on for good balance
good for distinguishing between patients with and without vestib disorders
unterberg's/fukuda stepping test
reflects somatosensory function more than vestibular
patient marches on the spot with eyes closed, specific amount of rotation is taken to suggest a vestib lesion on that side
what is the reason for the caloric test
stimulates the balance organs and tests difference in function between the two horizontal SCC (comparison not direct measure)
describe the caloric test
patient lies down and head is tilted so SCC is in horizontal plane
water heats the SCC, the fluid in the SCC rises and moves, this fluid movement pushes the cupula and bends the stereocilia
this changes the signal going through the vestib nerve
normal response: warm water creates an excitatory movement of cupula (firing rate increases) - VOR causes eye drift AWAY from side of irrigation (N beats towards side you're irrigating)
cool water: irrigation causes fluid to sink and leads to an inhibitory movement of cupula and decrease in firing rate of vestib nerve - VOR causes eye drift TOWARDS side of irrigation (N beats away from side you're irrigating)
what is COWS
for caloric test: cool opposite, warm same
-describing direction of N to side of irrigation
-direction: fast phase of N
if results don't follow cows, it could be a central issue
temp, volume and duration of flow of water and air for calorics
AIR: warm - 50 degrees; cool 24 degrees; 8 litres, 60 secs
WATER: warm - 44 degrees; cool 30 degrees; 250ml, 30 secs
what is canal paresis (and normal answer)?
calculation in calorics tests, tells you whether one horizontal SCC is working less efficiently than another
abnormal is more than 20%
+ve = left canal paresis
-ve = right canal paresis
what is directional preponderance (and normal answer)?
calculation in calorics test, measure of difference between intensity of right and left beating nystagmus
abnormal response is more than 20%
positive = right DP
negative = left DP
this doesn't give diagnostic info
what is visual fixation index (and normal answer)?
calculation from caloric tests, measure of effectiveness of visual fixation in suppressing caloric N (indicates whether lesion is central or peripheral)
-N should be better during fixation otherwise its central
N should be suppressed by at least 50% or its central
limitations of caloric testing
-only tests horizonal SCC
-only compares difference between two vestib organs not measuring function
-the equivalent angular acceleration of the head to the caloric stimulation is very low (tiny proportion of the freq range of the vestib sys)
describe the vHIT
video head impulse test, has high sensitivity and specificity, patient wears goggles, passive head turns and eye movements are recorded. normal: both eyes move to compensate.
what do VEMPS test and what can they identify?
tests otolith organs, can identify vestib patholgoies like vestib neuritis, menieires, central pathology, interaural differences are measured, can be used to diagnose semi circular canal dehiscense
cVEMPS (and contra-indications)
tests saccules, electrodes placed on neck muscle, neck muscle is contracted, loud sound is presented to patients ipsilateral ear, travelling wave is generated, muscle response/electrical acivity in reponse to nerve's stimulation of muscle is recorded
contraindications: cervical spine problems, conductive loss, hyperacusis, tinnitus
oVEMPS
tests utricle, electrodes placed over extraocular muscles, contralaterally tested
rotatory chair test
tests horizontal scc, patient is sat in rotating chair and goggles are worn to measure eye movementsm vor is activated in opposite direction to chair rotation to maintain stable visison, patient's head is slightly tilted so lateral scc are in horizontal plane, mental altering tasks performed, speed of eye movement is compared to speed of chair rotation
electrocochleography (ECochG) test
for patients with suspected Menieres or auditory neuropathy, loosk at electrical potentials of cochlea and distal portion of auditory nerve, can be used to test hearing threshold
habituation exercises
repeat movements that bring on symptoms so that the brain becomes accustomed to the dizziness, therefore dizziness reduces when those movements are performed
adaptation exercises
repeat movements that send an error signal to the brain so that it learns that there has been a change in the input and learns to inerpret the signal correctly
gaze stabilisation exercises
movements designed to improve the patient's ability to maintain gaze and resolve differences in info from the vestib system and their eyes
postural stability exercises
movements that are designed to reduced sway and stabilise the patient
gait excerises
movements designed to address problems with the patients gait
what are some treatments of BPPV and the ad/disad of both?
epley manoeuvre: returns otoconia to the utricle, ad: quick and immediately effective, diad: can't if they have neck/back probs, may have lightheadness for a few days after
exercises to habituate the brain to the error signal, ad: can be done at home, effective, can be done if have neck/back probs, disad: takes longer to treat condition and there's less patient compliance