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Mechanism of balance & vestibular function test Dr Utkal Mishra

This powerpoint elaborates the mechanism of balance & anatomy of vestibular apparutus. It also depicts the anatomy & physiology of haircells in detail. I also explained the vestibular function tests used for diagnosis of various vestibular disorders.

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Mechanism of balance & vestibular function test Dr Utkal Mishra

  1. 1. Mechanism Of Balance By Dr. Utkal Mishra
  2. 2. Introduction  The main function of the mammalian vestibular system is to  Provide general orientation of the body with respect to gravity  Enable balanced locomotion and body position  Readjust autonomic functions after body reorientation  Ensure gaze stabilization.
  3. 3. Introduction
  4. 4. Physiology of equilibrium Balance of body during static or dynamic positions is maintained by 4 organs: 1. Vestibular apparatus 2. Eye 3. Posterior column of spinal cord 4. Cerebellum
  5. 5. Vestibular apparatus  Semicircular canals - Angular acceleration & deceleration  Utricle - Horizontal linear acceleration & deceleration  Saccule - Vertical linear acceleration & deceleration
  6. 6. Relevant Anatomy
  7. 7. Orientation of semicircular canals RALP PlaneLARP Plane
  8. 8. Motion Decomposition  Every motion in space can be broken down into  3 Rotational degrees of freedom – 1. Yaw (SCC) 2. Pitch 3. Roll  3 Translational degrees of freedom – 1. Left–Right (U & S) 2. Up–Down 3. For–Aft
  10. 10. Cristae  Location – Ampullated ends of 3 SCC.  Elevated sensory area containing sensory hair cells  Tips of cilia are embedded in a gelatinous mass composed of polysaccharide called – CUPULA  Cupula functions as a water tight partition & displacement occurs in one direction at a time as a swing door.
  11. 11. Macula  Located in utricle – floor (horizontal) & saccule – posterior wall (vertical)  The hair cells are embedded in a gelatinous layer impregnated with crystals of CaCO3 called OTOLITH MEMBRANE.  A filamentous network connects the lower surface of otolithic membrane with sensory epithelium called SUBCUPULAR MESHWORK .  A virtual curved line called STRIOLA divides utricular hair cells into medial & lateral groups & sacuular hair cells into ventral & dorsal groups with opposite orientation
  12. 12. Vestibular Sensory Cells  Vestibular sensory epithelium consists of 2 types of hair cells – TYPE 1 – Flask shaped sorrounded by cup shaped thick myelinated single afferent nerve terminal TYPE 2 – Cylindrical with multiple thin afferent nerve terminals at its base  The apex of hair cells is bathed in endolymph and is sorrounded by nonsensory supporting cells & dark cells.
  13. 13. Hair Cells  Hair cell consists of a hair bundle at the apical end.  Each HAIR BUNDLE consists of 1 large knobed KINOCILLIUM & 20 - 300 STEREOCILLIA
  14. 14. Stereocillia  Have a cytoskeleton made up of actin filament crosslinked by fibrin  Arranged in a HEXAGONAL configuration  With shortest steriocillia at one end & tallest at other end like a staircase.  The ion channel involved in mechanoelectrical transduction are located in steriocillia.  Connected to each other by fibrillary strands called TIP LINKS  The upper end of each tip link is anchored to the stereocilium at a point called INSERTIONAL PLATE or PLAQUE.  Tension in the tip link controls the opening or closing of the ion channels.
  15. 15. Kinocillium  It is a true cillium consisting of an axoneme (9+2).  Only function of kinocillium is - transmission of stimulus forces to stereocillia.  Displacement of stereocillia towards kinocillium causes depolarization.
  16. 16. Hair Cell Physiology
  17. 17. Mechanotransduction Displacement of stereocillia towards kinocillium Stretches Tip links Influx of K+ & Ca+ Depolarization
  18. 18. Gating Compliance  An intrinsic property of direct mechano- electrical transduction that enhances hair cell sensitivity.  Hair bundle displacement in the positive direction opens transduction channels.  Channel opening decreases the stiffness of the hair bundle  This in turn promotes further movement in a positive direction resulting in a positive feedback mechanism
  19. 19. Adaptation  It prevents saturation of mechano-transductor response from large sustained stimuli > 25ms.  It also allows a cell to detect small stimuli in the presence of an enormous background input.  2 distinct models of adaptation –  Active Motor Model  Calcium Dependent Closure Model
  20. 20. Active Motor Model Myosin 1b Hair bundle deflection towards kinocilium increases tension in tip links with opening of transduction channels DEPOLARIZATION Motor cannot resist the increased tension & slips down the stereocillium Tip link tension reduced & channels closed HYPERPOLARIZATION Stereocillia returns to resting stage
  21. 21. Calcium Dependent Closure Model Opening of transduction channel Calcium enters & binds to channel protein Closure of channel
  22. 22. Vestibulo-Ocular Reflex • It is a reflex eye movement due to stimulation of cristae of SCC during head rotation • It helps in Gaze Stabilization by producing eye movements in the direction opposite to head movement, thus preserving the image on the fovea. • Movement of head to left  left horizontal canal stimulated & right horizontal canal inhibited • To keep eyes fixed on a stationary point, both eyes move to right side by stimulating right lateral rectus & left medial rectus muscles.
  24. 24. Vestibulospinal reflex  Effector organs - Extensor muscles of neck, trunk, arms and limbs.  The driving input here is mainly Gravity detected by the otolith system.  These reflexes are mediated through projections of the vestibular nuclei on to the Medial and Lateral Vestibulospinal tract.  Similar to the VOR, the same push–pull mechanisms are used for controlling the balance between extensor and flexor muscles.
  25. 25. Cervicoocular reflex  When the head is fixed but the body is rotated, nystagmus may be observed.  This reflex is based on the stimulation of neck receptors.  In humans, this reflex is very unreliable and unpredictable  Only in subjects with congenital peripheral vestibular loss, does this alternative strategy for gaze stabilization become helpful.
  26. 26. Central Projections Of Vestibular System  In the brain stem there are 4 vestibular nuclei  Superior  Lateral  Medial  Descending  From there several projections are found to  Occulomotor Nuclei  Lateral & Medial Vestibulospinal Tract  Parapontine Reticular Formation  Vestibulocerebellum- Floculus, Nodulus  Nucleus Tractus Solitarius  Cingulate Gyrus
  28. 28. Vestibular Function Tests  Assessment of vestibular function can be divided into 2 groups –  1. CLINICAL TESTS  2. LABORATORY TESTS
  29. 29. Clinical Tests Of Vestibular Function  1. Clinical examination of eye movements  2. Fistula Test  3. Romberg Test  4. Gait  5. Tests Of Cerebellar Dysfunction
  30. 30. Clinical Examination of Eye Movements The oculomotor examination should include:  Nystagmus  Convergence;  Smooth pursuit;  Saccades;  Vestibulo-ocular reflexes;  Positional manoeuvres.
  31. 31. Nystagmus  It is defined as involuntary rhythmic oscillatory movement of eyes.  Described under headings – 1. Plane – Horizontal, Vertical, Torsional 2. Waveform – Saw tooth / Jerk – Contains a fast & slow phase Pendular- Quasisinusoidal No fast or slow phase 3. Direction – Indicated by direction of fast component 4. Intensity – ALEXANDERS LAW 1st degree – Nystagmus present when looks in direction of fast component. 2nd degree - Nystagmus present when looks straight ahead. 3rd degree – Nystagmus present when looks in direction of slow component.
  32. 32. Types of Nystagmus DIFFERENCE Peripheral Central Latency 2-20 s No latency Duration < 1 min > 1 min Direction Direction fixed Direction changing Fatiguability Fatiguable Non fatiguable Symptoms Severe Vertigo None Suppressed by Visual fixation None Enhanced by Darkness or by using Frenzel’s glasses None  Vestibular nystagmus is of 2 types  Peripheral - Due to lesions of Labyrinth or VIIIth Nerve.  Central – Due to lesions of Vestibular Nuclei, Brain stem, Cerebellum.
  33. 33. Central Nystagmus Type of Nystagmus Cause Remarks Pendular Nystagmus Multiple Sclerosis Can be disconjugate – vertical in one eye & horizontal in other eye. Purely Torsional Syringomyelia Vertical Downbeat Arnold Chiari Malformation Vertical Upbeat Pontomedullary juncn. lesions Congenital Nystagmus Jerk Nystagmus with slow phase velocity exponentially increasing. Seasaw Nystagmus Mid-brain lesions One eye goes up other goes down Dissociated Nystagmus Internuclear Opthalmoplegia Only abducting eye shows nystagmus Periodic Alternating Nystagmus Lesions in Nodulus of Cerebellum Changes direction every 2 minutes Perverted Nystagmus Multiple Sclerosis Nystagmus occuring in a a plane other than that of vestibular stimulation.
  34. 34. Vestibulo-Occular Reflex  VOR stabilizes gaze in space during head movements  By generating slow phase eye movements of an equal velocity but in opposite direction to head movement.  Clinical Tests for VOR are – 1. Doll’s Head Manoeuvre 2. Dynamic Visual Acuity 3. Head Impulse Test
  35. 35. Doll’s Head Manoeuvre Examiner oscillates the patients head from side to side at a frequency of approx. 0.5-1Hz. Maintain fixation (Normal VOR) Interrupted Eye movements with catch up saccades towards fixation target (Abnormal VOR) Post Meningitis / Ototoxicity Patient sits in front of examiner & fixates a part of examiners face(nose)
  36. 36. Dynamic Visual Acuity Patient reads a visual acuity chart 6/6 Standing behind the patient Examiner oscillates the patient’s head at approx. 1Hz. While a new visual acuity is taken Gross reduction of VOR Deterioration of Two linesNo change in Visual Acuity NORMAL
  37. 37. Head Impulse Test Patient seats in front of Examiner & fixate a target across the room Head is turned briskly by 15 degree across midline by the examiner Fixation maintained NORMAL Acute Vestibular Neuronitis Eyes moves with head & refixate with catch up saccades.
  38. 38. Positional Manoeuvre (Hallpike) Patient sits on a couch & looks straight ahead at one point on the examiner’s face Examiner holds the patient head & turns it 450 to right Patient placed in supine position with head hangs 300 below horizontal Patient eyes are observed for nystagmus for minimum 20 sec Nystagmus appearing after a latent period of 2-20 s Last for < 1 min & is always in one direction On subsequent repetitions nystagmus disappears (Fatiguable) Nystagmus appearing immediately, changing direction & non fatiguable BPPV CENTRAL LESIONS
  39. 39. Fistula test  Intermittent pressure on tragus induces nystagmus by pressure changes in EAC which is transmitted to labyrinth.  Results - Negative  Normal Positive  Erosion of Horz. SCC  Fenestration Operation  Post-Stapedectomy Fistula  Rupture of round window False Negative  Cholesteatoma covering the fistula  Dead Labyrinth False Positive  Hypermobile stapes (Congenital Syphilis)  Stapes connected to Utricular macula by fibrous bands (Meniere’s disease)
  40. 40. Romberg’s Test Sways to the side of lesion (Peripheral Lesion) Shows instability (Central Lesion) No sway or instability Sharpened Romberg’s Test Pt. stands with one heel in front of toes & arms folded across the chest Patient stands with feet together & arms by the side with eyes open then closed
  41. 41. Unterberger’s Test Turns towards the Hypoactive side (Peripheral Lesion) Shows instability (Central Lesion) Patient asked to walk on the spot with eyes closed & keeping the arm & index fingers pointing towards examiners index fingers
  42. 42. Gait Sways to the side of lesion (Peripheral Lesion) Shows instability (Central Lesion) Paradoxical Improvement with fast walking Acute Vestibular Neuronitis Patient is asked to walk along a straight line to a fixed point, first with eyes open then closed
  43. 43. Tests of Cerebellar Dysfunction DISEASE OF SIGNS CEREBELLAR HEMISPHERE  Asynergia  Dysmetria  Adiadochokinesia  Rebound Phenomenon MIDLINE OF CEREBELLUM  Wide base Gait  Falling in any direction  Inability to make sudden turns while walking  Truncal ataxia
  44. 44. Laboratory Tests of Vestibular Function  Caloric Test  Modified Kobrak Test  Fitzgerald-Hallpike Test  Cold Air Caloric Test  Electronystagmography  Optokinetic Test  Rotation Test  Galvanic Test  Posturography
  45. 45. Caloric Test  Principle- Changes in temperature in Extn. Auditory canal induces convection currents in endolymph of Lateral SCC causing vertigo & nystagmus  Advantage – Only test available to test each labyrinth separately.  Disadvantage – Anatomic abnormality of Extn. Or Middle ear interfere with results  Types – 3 types  1. Modified Kobrak Test  2. Fitzgerald-Hallpike Test  3. Cold Air Caloric Test
  46. 46. Modified Kobrak Test Patient is seated with head tilted 600 backwards (Horz. Canal in vertical position) Ear irrigated with ice water for 60 sec Start with 5ml NO RESPONSE Nystagmus beating towards opposite ear 10 ml NORMAL 20 ml 40 ml DEAD LABYRINTH
  47. 47. Fitzgerald- Hallpike Test Patient lies supine with head tilted 300 forward (Horz. Canal in vertical position) Procedure follows order LEFT COLD>>RIGHT COLD>>LEFTWARM>>RIGHT WARM Gap of 5 minutes Cold water induces nystagmus to opposite side & warm water to same side of irrigation Time taken from the start of irrigation to end of nystagmus recorded in a chart called CALORIGRAM Irrigation for 4 min with water at 200C Ear is irrigated for 40 sec alternately with water at 300C & 440 C NO RESPONSE NO RESPONSE DEAD LABYRINTH
  48. 48. Cold Air Caloric Test  It is done when there is Tympanic membrane perforation.  Test is done with Dundas – Grant tube which is a coiled copper tube wrapped in cloth.  Air in the tube is cooled by pouring ethyl chloride & blown into ear  This is only a rough qualitative test.
  49. 49. Interpretations of Caloric Test  There are 3 main abnormalities of caloric response-  1. Bilateral Absence of Caloric Response  2. Unilateral Canal Paresis  3. Directional Preponderance
  50. 50. Bilateral Absence of Caloric Nystagmus  Occurs in –  Post- Meningitis  Ototoxic drugs  Meniere’s Disease  Head Trauma  Idiopathic
  51. 51. Unilateral Canal Paresis  It indicates a reduced or absent response from one ear.  Causes are –  Acoustic neuroma  Post labyrinthectomy  Vestibular nerve section  Can be expressed as percentage as Response from Left ear = L30 + L44 × 100 L30 + L44 + R30 + R44
  52. 52. Directional Preponderance  It indicates that the Duration of nystagmus to one side is 25-30% more than other side irrespective of whether it is elicited from right or left labyrinth.  DP occurs towards the side of central lesion & away from the side of peripheral lesion  Right beating nystagmus = L30 + R44 L30 + L44 + R30 + R44 × 100
  53. 53. Electro/Video nystagmography  It is a method of detecting & recording of nystagmus.  It depends on the presence of corneoretinal potentials recorded by surface electrodes placed around orbit.  Advantage –  1. Detect fine nystagmus not visible to naked eye  2. To keep a permanent record  3. To detect nystagmus in dark.  Disadvantage –  1. Cannot record torsional eye movement  2. Other biological potentials can be picked up as artifact (EEG)
  54. 54. Optokinetic test  Patient is asked to follow a series of vertical stripes on a rotating drum.  Normally it produces nystagmus with slow component in the direction of moving stripes & fast component in opposite direction.  Abnormality indicates central lesion.
  55. 55. Rotational Tests  Patient is seated in a Barany’s revolving chair with head tilted 300 forward rotated 10 turns in 20 s.  The chair is stopped abruptly & nystagmus is observed towards the side of rotation.  2 types of rotation-  Velocity Step/ Impulsive Rotation  Sinusoidal Rotation  Normally nystagmus lasts for 25-40s.  Advantage – Test can be performed in cases of congenital abnormalities where SCC failed to develop  Disadvantage- Both the labyrinths are simutaneously stimulated.
  56. 56. Galvanic Test  Only test which differentiates an end organ lesion from that of vestibular nerve.  Patient stands with his feet together eyes closed & arms outstretched & then a current of 1mA is passed to one ear.  Normally patient sways towards the side of anodal current. (Intact vestibular nerve)
  57. 57. Posturography  It is a method to evaluate vestibular function by measuring postural stability.  2 main types  Static Posturography- Fixed platform  Computerized Dynamic Posturography – Movable platform