Evoked Potential ppt.pptx

this is presentation power point to discuss on the evoked potential. this presentation was done for the physiotherapy students in Father Mullers medical college mangalore.
this is uploaded for who ever need this and also for personal storage,

1. Evoked potential Presentar : Ashik Dhakal Moderator : Ms. Ziona

2. Content Introduction Types Anatomical and physiological response Variables influencing EP Clinical implication of EP

3. An electrical potential recorded from a human or animal following presentation of a stimulus

4. Classification

5. Sensory evoked potential Visual evoked potential (VEP) Auditory evoked potential (AEP) Somatosensory evoked potential (SSEP)

6. Electrode placement

7. Measurements for electrode placement Nasion - Anion pre auricular Circumference Parasaggital Horse shoe

8. Visual evoked potential

9. Anatomical and physiological basis of VEP

10. Basic VEP abnormalities Latency prolongation Amplitude reduction Combined abnormalities

11. Types of VEP 1. Pattern reversal VEP Primary visual system is arranged to emphasise the edges and movements. So, shifting patterns with multiple edges and contrasts are the most appropriate method to assess visual function.

12. 2. Flash VEP Stroboscopic flash units Primarily use when an individual cannot cooperate or for gross determination of visual pathways. eg, in infants/comatose patient .

13. Procedure Electrodes : active (Oz), reference (Cz), ground (Fpz)

14. Patient position : Each eyes separately Patient seated at the distance of 0.75 to 1.5 meters. Eyes glasses to be worn Eye not tested should be patched Gaze at the centre of the monitor.

15. Stimulation patterns Black and white checkerboard Size of the checks : 14*16 Contrast : 50-80 %

16. Video

17. VEP response The P100 latency of PSVEP(pattern shift) increases with decrease of luminance . Reduce contrast between black and white squares — increases latency and decreases amplitude of P100. Constricted pupil — increases average latency of P100.

18. Normal values

19. Variables influencing VEP Age- influencing latency of P100 at the rate of 2.5 ms/decade after 5th decade. Age related changes in retina and rostral part of visual system. Gender- P100 latency- longer in adult male compared to female. Less than 19 does not vary with gender. :. Larger head size and lower core body temperature in male. Amplitude- mean P100 amplitude > in female rather male

20. Eye dominance- P100 wave obtained by stimulating the dominant eye is shorter and amplitude is greater compared to non dominant eye. :. Attributed to neuroanatomic symmetries of human cortex. Eye movement- Eye movement- reduces the amplitude of P100 : latency not affected . nystagmus— normal visual pathway— normal P100 latency.

21. Visual acuity— Pronounced diminution of visual acuity— P100 latency remains normal Visual acuity as low as 20/120 - P100 latency normal. Further reduction of visual acuity— amplitude decreases. Drugs— Drugs producing pupillary constriction (Pilocarpine) can increase P100 latency :. Attributed to reduced area of retinal illumination. Unmotivated patient- may alter - P100 latency or amplitude by closing the eye, gazing of the screen, converging in front of target (nose).

22. Clinical utility Cataract and glaucoma : decrease in P100 amplitude . Optic neuritis Monitoring visual pathways integrity during surgeries.

23. Multiple sclerosis: Focal demyelination in visual pathway- delays in conduction. P100 latency is prolonged with or without attenuation of amplitude. Prolonged by 10-30ms — in definite MS, rarely 100ms.

24. 7 days post methyl prednisolone therapy In Multiple Sclerosis

25. Limitations of VEP Disturbances anywhere in the visual system can produce abnormal VEP, localising value of VEP is limited.

26. BAEP AEP/ BAEP are the potentials recorded from the ear and vertex — in response to — brief auditory stimulation, to assess — the conduction through the auditory pathway. Clinically helpful in Assessment of hearing in uncooperative patients and very young children. Severity of hearing deficits in infants. Function of the middle portion of the brainstem.

27. Anatomy and Physiological Basis

28. Procedure Subject lying supine with a pillow under his head. Room should be quit. Clean the scalp and apply electrodes. Check for impedence. Apply ear phone (red for the right ear and blue for the left ear) Select the ear in the stimulator and apply masking to the opposite ear.

29. Electrode placement

30. Identification of waves Identify wave V which is the most persitent wave. It comes as IV-V complex, and wave V comes to the baseline. Go in reverse order, wave IV, III, II, I. Observe their latency., eg, latency of wave I will be less than 2msec.

31. Waveform Waveform Generators I VIII nerve II Cochlear nucleus III Superior Olivary nucleus IV Lateral Lemniscus V Inferior colliculi

32. BAEP testing

33. Basic Abnormalities Absence of waveform Absence of inter peak latency Right to left symmetry

34. Interpretation Wave I : small amplitude, delayed or absent may indicate cochlear lesion. Wave V : small amplitude, delayed or absent may indicate upper brainstem lesion I-III IPL : Prolongation may indicate lower brainstem lesion . III-V IPL : prolongation may indicate upper brainstem lesion . I-V IPL : prolongation may indicate whole brainstem lesion . Shortening of wave the interval with normal latency of wave V indicate cochlear involvement.

35. Normal values

36. Patient Related Factors Age: Older adults have slightly longer I-V (IPL) by 0.1-0.15ms compared to younger individuals. Gender: Females have shorter latency and higher amplitude of BAEP. The I-V IPL is shorter by 0.1ms in females compared to males.

37. Temperature: On lowering body temperature IPL is prolonged. On 1 degree C reduction of body temperature, 0.17ms increase in wave V latency. At 32.5 degree C the BAEP values are distinctively abnormal. At 27 degree C waveform disappear. Drugs: Slight prolongation of wave V latency with barbiturates or alcohol, :. Attributed to lowering of body temperature.

38. Hearing Impairment: Can alter BAEP, therefore, before starting the study, external ear should be examined with an auto-scope for blockage by cerumen (earwax). Audiometry test or hearing should be tested.

39. Clinical neurophysiological correlation Cerebelopontine angle tumor Intrinsic brainstem tumor MS

40. Somatosensory evoked potential Somatosensory Evoked Potential (SSEP) is a noninvasive diagnostic test to assess the speed of electrical conduction across the spinal cord . The technique involves applying electrical stimulus at s pecific nerves in the arms and legs and measuring the impulses generated by the stimulus at various points in the body. If the spinal cord is pinched, the electrical signals will travel slower than usual. Can distinguish central vs peripheral nerve lesion. SSEP may also be used to monitor spinal cord function during surgical procedures, particularly for cervical or thoracic spine surgery.

41. Anatomical and physiological basis of SSEP

42. Procedure The information about sensory symptoms , signs and peripheral nerve injury should be obtained. SSEP can be recorded by stimulating any large nerve. eg. median and posterior tibial nerves. Positioning: Comfortable position, comfortable temperature Stimulus : electrical — square wave pulse by surface or needle electrode Duration, intensity : 100-200 msec, 15mA. In peripheral neuropathy higher current with higher duration is required. Unilateral stimulation for localization , Bilateral stimulation for intra-operative monitoring.

43. Upper extrimity SSEP Electrode placement : Recording el : ERB’s point, Cervical spine, (C2 or C5), contralateral scalp overlying the area of the primary sensory cortex (C3 or C4) Reference : forehead Fz Ground : proximal to stimulation site

44. Electrode placement for SSEP of median nerve

45. Median nerve SSEP Channel 1 Scalp (Cc-Fz): N20 -P23 - thalamocortical radiation and primary sensory cortex Channel 2 (Cc-EPc) - P14 Channel 3 (C5Sp- EPc) Cervical spine : N13 - dorsal column nuclei Channel 4 (Epi-EPc) Erb’s point : N9 - brachial plexus

46. Patient-Related Factors Age: In young children - N9 and N13 , potentials of Median SEP occurs early . In elderly- Normal limit for latencies are longer by 5-10% , occurs in >55years old . Gender: Females have a shorter central conduction time than males. (reason unknown) Sleep: may change median N20 latency by increasing the amplitude.

47. Drugs: Sedation- for better recording in uncooperative patients. 10mg Diazepam orally- reduces muscle artefacts of SEP recording, improvement in lumbar and neck recordings, increased reproducibility, increased ease of measurement and greater tolerance of the procedure. Temperature: Peripheral nerve conduction is slowed by lowering the limb temperature. With temperature changes, the peripheral conduction is affected more than the central.

48. Clinical application of SSEP SSEP have good correlation with impairment of joint position and vibration sensations but not with pinprick and touch. For SSEP abnormalities , significant degree of sensory impairment is necessary. A combination of both latency and amplitude abnormalities are found in compressive lesions .

49. Important conditions where SSEP are evaluated- Demyelinating disease Trauma Degenerative diseases like cervical and lumbar spondylosis Spinal cord tumor

50. Surgical Monitoring Intraoperative monitoring (IOM): provide a physiological look at : BRAIN BRAINSTEM SPINAL CORD CRANIAL NERVES And NERVE ROOTS During neuro-spinal procedures IOM prevents the possible iatrogenic injury to the nervous system

51. Electrode is placed in 10-20 placement system. SSEP and MEP both are used in neuro spinal surgeries, as there are two different pathways, and it is important to keep tract of both. SSEP are mainly used in scoliosis surgery , neurosurgical (tumors, vascular malformations, bony malformations, and trauma of spinal cord) and cardiovascular surgery (if the aortic cross-clamping time exceeds 18min and 14s it can result in ischemic myelopathy. Thus, spinal cord is vulnerable to ischemia especially during surgery for aneurysm and coarctation of aorta)

52. Motor evoked potentials Used to assess motor functions of deeper structures Stimulus may be electrical or magnetic Similar to SSEP but stimulus is given centrally, recorded peripherally in distant muscles.

53. Pathways

54. Electrode placement

55. Effect of activation in MEP

56. Clinical utility To diagnose disorders that affect central and peripheral motor pathways. examples: multiple sclerosis, Parkinson’s D, CVA, Myelopathy of cervical and lumbar plexus. Intra-operative monitoring.

57. Event related/cognitive evoked potentials Record cortical activity evoked by a stimulus with cognitive significance. Stimuli : presenting randomly occurring infrequent stimuli interspersed with more frequent occurring stimuli.

58. Electrode placement

59. Waveform is called ‘P 300’ with a positive peak.

60. Video

61. Variables affecting P300 Attention Task - task harder - latency increases. Age : latency increases with > age. 1-1.5 ms/year after age of 20. Amplitude decreases after the age of 80 years.

62. Drugs Technical parameters intraindividual variability

63. Clinical implication Prolongation of P 300: Aging Dementia Neurodegenerative disorders Schizophrenia Autism multiple sclerosis

64. Thank you