title: Optimum interpulse interval for transcranial electrical train stimulation to elicit motor evoked potentials of maximal amplitude in both upper and lower extremity target muscles.
abstract: OBJECTIVE
  The aim of this study was to determine the optimum interpulse interval (OIPI) for transcranial electrical train stimulation to elicit muscle motor evoked potentials (TES-MEP) with maximal amplitude in upper and lower extremities during intra-operative spinal cord monitoring.
  
  
  METHODS
  Intraoperative spinal cord monitoring with TES-MEP was performed in 26 patients who had (corrective) spine surgery. Optimum interpulse interval (OIPI) were determined for the abductor pollicis brevis muscle (APB) representing the upper extremity and the anterior tibialis muscle (TA) representing the lower extremity. The IPI was varied between 0.5 and 4.0ms, where the OIPI was defined as the IPI with the highest muscle MEP amplitude for each muscle group. Differences between upper and lower extremity OIPIs were analyzed. Furthermore, the MEP amplitudes difference between the upper and lower extremity OIPIs and between the OIPI and IPI 2 ms was determined.
  
  
  RESULTS
  The mean OIPI(APB) representing the upper extremity was 1.78 ± 1.09 ms on the left side and 1.82 ± 0.93 ms on the right side. The lower extremity showed a mean OIPI(TA) of 2.26 ± 1.16 ms on the left and 2.73 ± 0.88 ms on the right side. The mean differences between the OIPI(APB) and OIPI(TA) were significant for p=0.019 (Student's T-test). No within patient differences in OIPIs between the left and the right side were found. The mean MEP amplitude reduction, the APB amplitude at OIPI(TA) compared to the APB at OIPI(APB), was 32.5 ± 27.9%. For the TA a mean amplitude reduction of 33.4 ± 27.4% was found. The mean amplitude reduction for the OIPI amplitudes compared to the amplitudes at IPI 2 ms was 53.6 ± 25.5% for the APB and 45.8 ± 28.3% for the TA.
  
  
  CONCLUSIONS
  Large intra- and interindividual differences were found between the mean OIPIs of the TA and APB muscles (range 1.78-2.73 ms) representing the upper and lower extremity.
  
  
  CONCLUSIONS
  Based on the results of this study, it is advisable to perform a set-up procedure for each individual patient undergoing TES-MEP to determine the optimal parameter settings when using supramaximal intensity of TES.
authors.affiliation: Department of Orthopedics, Sint Maartenskliniek, Postbus 9011, 6500 GM, Nijmegen, The Netherlands. chantalvanhal@hotmail.com
authors.forename: C
authors.initials: C
authors.lastname: van Hal
authors.forename: E
authors.initials: E
authors.lastname: Hoebink
authors.forename: H E
authors.initials: HE
authors.lastname: Polak
authors.forename: I
authors.initials: I
authors.lastname: Racz
authors.forename: M
authors.initials: M
authors.lastname: de Kleuver
authors.forename: H L
authors.initials: HL
authors.lastname: Journee
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001132:Arm / Q000502:physiology; D002648:Child; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D007206:Individuality; D007866:Leg / Q000502:physiology; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D018482:Muscle, Skeletal / Q000502:physiology*; D011930:Reaction Time; D013116:Spinal Cord / Q000502:physiology*; D013122:Spinal Diseases / Q000503:physiopathology* / Q000601:surgery*; D013123:Spinal Fusion; D034941:Upper Extremity; D055815:Young Adult
keywords: Optimum interpulse interval; Spinal cord monitoring; TES-MEP