Vestibular System Function Vestibular Examination Rehabilitation Carmen Casanova Abbott PT PhD PT 8690 Spring 2012 Provides information concerning gravity rotation and acceleration Serves as a reference for the somatosensory visual systems Contributes to integration of arousal conscious awareness of the body via connections with vestibular cortex thalamus and reticular formation Allows for gaze postural stability sense of orientation detection of linear angular acceleration 2 Ascending Pathways Vestibular Anatomy Peripheral sensory apparatus detects relays information about head angular linear velocity to central processing system orients the head with respect to gravity Central processing system processes information in conjunction with other sensory inputs for position and movement of head in space Motor output system generates compensatory eye movements and compensatory body movements during head postural adjustments Vestibular nerve Vestibular nuclei Cerebellum Oculomotor complex Cranial nerves 3 4 and 6 Along with vestibulospinal reflexes coordinate head and eye movements 3 Relay Centers Cerebellum Monitors vestibular performance Readjusts central vestibular processing of static dynamic postural activity Modulation of VOR Inhibitory drive of VOR Thalamus Connection with vestibular cortex and reticular formation arousal and conscious awareness of body discrimination between self movement vs that of the environment Vestibular Cortex Junction of parietal and insular lobe Target for afferents along with the cerebellum 5 Both process vestibular information with somatosensory and visual input Descending Pathways Provide motor output from the vestibular system to Extraocular muscles part of VOR Spinal cord skeletal muscles generate antigravity postural activity to cervical trunk lower extremity muscles Netter 1997 Response to changing head position with respect to gravity righting equilibrium responses 8 Principles of the Vestibular System Vestibulospinal Reflex VSR Generates compensatory body movement to maintain head and postural stability thereby preventing falls Tonic firing rate Vestibular Ocular Reflex PushPush Pull mechanism Inhibitory cutoff Velocity storage system 9 Compensatory Eye Movements Vestibular Ocular Reflex VOR Optokinetic reflex Smooth pursuit reflex saccades vergence Neck reflexes All combine to stabilize object on the same area of the retina visual stability VestibularVestibular Ocular Reflex VOR Causes eyes to move in the opposite direction to head movement Speed of the eye movement equals that of the head movement Allows objects to remain in focus during head movements 12 Vestibular Processing Gain Keeps eye still in space while head is moving Ratio of eye movement to head movement equals 1 VOR Target fixation 14 Vestibular Processing Velocity Storage Mechanism Vestibular Dysfunction Perseveration of neural firing in the vestibular nerve by the brainstem after stimulation of SCC to increase time constant SCC respond by producing an exponentially decaying change in neural firing to sustained head movement Otolith somatosensory input also drive mechanism Injury Location Inner ear Vestibular nerve Central structures and pathways 15 Vestibular Pathophysiology Disorders of tone or gain vertigo movementmovement induced vertigo Vestibular nerve nuclei give abnormal sensory information Tone automatically recovers in a few days does not need visual input Compensation for reduced gain depends on visual images takes month to years to complete high speeds accelerations may never be complete Nystagmus usually transient sign of vestibular lesion movementmovement induced symptoms can be chronic 18 VOR Dysfunction Vertigo Direction of gaze will shift with the head movement Cause degradation of the visual image In severe cases visual world will move with each head movement vertigo An asymmetrical firing of the two vestibular systems Gives an illusion of spinning movement Indicative of any one or combination of causes acute UVH BPPV brainstem lesion vascular hypotension hypotension Oscillopsia Visual illusion of oscillating movement of stationary objects Can arise with lesions of peripheral or central vestibular systems Indicative of diminished VOR gain motion of images on fovea diminished visual acuity Vestibular Dysfunction Demographics Demographics Vestibular disorders manifested by vertigo are a significant health problem secondary only to LBP NIH study estimates that 40 of the population over the age of 40 will experience a dizziness disorder during their lifetime 23 Falls most common cause of TBI TBI accounted for 46 of fatal falls in older adults CDC 2008 Dizziness most common symptom of TBI occurring initially in 98 Dizzy Patient Presentation Unexplained or new onset of symptoms Bilateral Vestibular Loss Medical referral Constant vertigo Lateralpulsion Facial asymmetry Speech or swallowing difficulties Oculomotor dysfunction Vertical nystagmus Severe headaches Recurrent falls Unilateral hearing loss tinnitis tinnitis fullness ear pain VOR cannot be recalibrated Compensatory mechanisms are used 25 26 Central Vestibular Disorders Compensatory Mechanisms Sensory substitution Motor substitution Predictive anticipatory strategies Vascular Wallenberg Wallenberg s Syndrome Head Injury Cerebellar Infarct Postconcussive Syndrome Demyelinating Disease Congenital 27 Traumatic Brain Injury 28 Central Vestibular Disorders 3030 65 suffer symptoms of vestibular pathology during recovery Clinical classification according to three major planes of action of the VOR Mechanisms of injury Determined by ocular motor postural perceptual signs concussion fractures intracranial pressure hemorrhagic lesions central vestibular lesions Herdman Herdman 2000 29 30 ROLL PLANE SIGNS YAW PLANE SIGNS ipsiversive at pontomedullary level contraversive at pontomesemcephalic level lateral medulla including root entry zone of VIII and or vestibular vestibular nuclei Horizontal nystagmus Past pointing Rotational lateral body falls Horizontal deviation of perceived straightstraightahead Torsional nystagmus Skew deviation Ocular torsion Tilts of head body perceived vertical 31 32 PARIETINSULAR VESTIBULAR CORTEX PITCH PLANE SIGNS bilateral lesions or bilateral dysfunctioin of the flocculus flocculus Upbeat downbeat nystagmus Forward backward tilts falls Vertical deviations of perceived straightstraightahead Main sensorimotor integration center Dysfunctions vestibular seizures signs tilt of perceived vertical