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Blaine A Chronik - One of the best experts on this subject based on the ideXlab platform.

  • sensory and motor stimulation thresholds of the ulnar nerve from electric and magnetic field stimuli implications to gradient coil operation
    Magnetic Resonance in Medicine, 2010
    Co-Authors: Bryan J Recoskie, Timothy J Scholl, M Zinkeallmang, Blaine A Chronik
    Abstract:

    Rapidly changing magnetic fields from gradient coils induce electric fields in the individual being imaged, which can potentially result in peripheral nerve stimulation (PNS). This is a safety concern in MRI. Nerves exposed to either electric fields or time-varying magnetic fields are presumed to display equivalent stimulation threshold characteristics. This assumption has motivated the use of electric stimulation literature to be applied to gradient field safety standards. The consistency of peripheral nerve stimulation thresholds were compared by measuring Chronaxie times for electric and magnetic stimulation for both motor and sensory fibers in the ulnar nerve for a group of healthy volunteers. Thresholds were determined with both electromyography and also by having the subjects report stimulation onset. Chronaxie times measured between motor and sensory fibers were statistically different. However, this difference does not account for the substantial discrepancy reported between measured electric and magnetic stimulation Chronaxie times. We further establish that sensation threshold as defined perceptually by the subject volunteer is adequate as a simple and reliable measurement tool. Based on these observations, significant adjustments may need to be made to nerve parameters taken from the electric field stimulation literature prior to applying them directly to gradient induced stimulation in MRI.

  • the discrepancy between human peripheral nerve Chronaxie times as measured using magnetic and electric field stimuli the relevance to mri gradient coil safety
    Physics in Medicine and Biology, 2010
    Co-Authors: Bryan J Recoskie, Timothy J Scholl, Blaine A Chronik
    Abstract:

    A recent electrostimulation study with human subjects (Recoskie et al 2009 Phys. Med. Biol. 54 5965-79) reported a large difference between Chronaxie times when stimuli were delivered to the same body locus (the wrist) either through contact electrodes (electric stimulation) or through a pulsed magnetic field (magnetic stimulation). This paper reviews the procedures and analytic methods used in that study that might account for the reported discrepancies. Factors possibly accounting for reported discrepancies include the maximum and minimum pulse widths of the experimental stimuli; variations in experimental waveforms vis-a-vis mathematically ideal functions; differences in the spatial distribution of the in situ electric field for the two methods of delivery and differences in derived Chronaxie relative to strength-duration time constants.

  • the discrepancy between human peripheral nerve Chronaxie times as measured using magnetic and electric field stimuli the relevance to mri gradient coil safety
    Physics in Medicine and Biology, 2009
    Co-Authors: Bryan J Recoskie, Timothy J Scholl, Blaine A Chronik
    Abstract:

    Peripheral nerve stimulation (PNS) resulting from electric fields induced from the rapidly changing magnetic fields of gradient coils is a concern in MRI. Nerves exposed to either electric fields or changing magnetic fields would be expected to display consistent threshold characteristics, motivating the direct application of electric field exposure criteria from the literature to guide the development of gradient magnetic field exposure criteria for MRI. The consistency of electric and magnetic field exposures was tested by comparing Chronaxie times for electric and magnetic PNS curves for 22 healthy human subjects. Electric and magnetic stimulation thresholds were measured for exposure of the forearm using both surface electrodes and a figure-eight magnetic coil, respectively. The average Chronaxie times for the electric and magnetic field conditions were 109 ± 11 μs and 651 ± 53 μ s( ±SE), respectively. We do not propose that these results call into question the basic mechanism, namely that rapidly switched gradient magnetic fields induce electric fields in human tissues, resulting in PNS. However, this result does motivate us to suggest that special care must be taken when using electric field exposure data from the literature to set gradient coil PNS safety standards in MRI.

Bryan J Recoskie - One of the best experts on this subject based on the ideXlab platform.

  • sensory and motor stimulation thresholds of the ulnar nerve from electric and magnetic field stimuli implications to gradient coil operation
    Magnetic Resonance in Medicine, 2010
    Co-Authors: Bryan J Recoskie, Timothy J Scholl, M Zinkeallmang, Blaine A Chronik
    Abstract:

    Rapidly changing magnetic fields from gradient coils induce electric fields in the individual being imaged, which can potentially result in peripheral nerve stimulation (PNS). This is a safety concern in MRI. Nerves exposed to either electric fields or time-varying magnetic fields are presumed to display equivalent stimulation threshold characteristics. This assumption has motivated the use of electric stimulation literature to be applied to gradient field safety standards. The consistency of peripheral nerve stimulation thresholds were compared by measuring Chronaxie times for electric and magnetic stimulation for both motor and sensory fibers in the ulnar nerve for a group of healthy volunteers. Thresholds were determined with both electromyography and also by having the subjects report stimulation onset. Chronaxie times measured between motor and sensory fibers were statistically different. However, this difference does not account for the substantial discrepancy reported between measured electric and magnetic stimulation Chronaxie times. We further establish that sensation threshold as defined perceptually by the subject volunteer is adequate as a simple and reliable measurement tool. Based on these observations, significant adjustments may need to be made to nerve parameters taken from the electric field stimulation literature prior to applying them directly to gradient induced stimulation in MRI.

  • the discrepancy between human peripheral nerve Chronaxie times as measured using magnetic and electric field stimuli the relevance to mri gradient coil safety
    Physics in Medicine and Biology, 2010
    Co-Authors: Bryan J Recoskie, Timothy J Scholl, Blaine A Chronik
    Abstract:

    A recent electrostimulation study with human subjects (Recoskie et al 2009 Phys. Med. Biol. 54 5965-79) reported a large difference between Chronaxie times when stimuli were delivered to the same body locus (the wrist) either through contact electrodes (electric stimulation) or through a pulsed magnetic field (magnetic stimulation). This paper reviews the procedures and analytic methods used in that study that might account for the reported discrepancies. Factors possibly accounting for reported discrepancies include the maximum and minimum pulse widths of the experimental stimuli; variations in experimental waveforms vis-a-vis mathematically ideal functions; differences in the spatial distribution of the in situ electric field for the two methods of delivery and differences in derived Chronaxie relative to strength-duration time constants.

  • the discrepancy between human peripheral nerve Chronaxie times as measured using magnetic and electric field stimuli the relevance to mri gradient coil safety
    Physics in Medicine and Biology, 2009
    Co-Authors: Bryan J Recoskie, Timothy J Scholl, Blaine A Chronik
    Abstract:

    Peripheral nerve stimulation (PNS) resulting from electric fields induced from the rapidly changing magnetic fields of gradient coils is a concern in MRI. Nerves exposed to either electric fields or changing magnetic fields would be expected to display consistent threshold characteristics, motivating the direct application of electric field exposure criteria from the literature to guide the development of gradient magnetic field exposure criteria for MRI. The consistency of electric and magnetic field exposures was tested by comparing Chronaxie times for electric and magnetic PNS curves for 22 healthy human subjects. Electric and magnetic stimulation thresholds were measured for exposure of the forearm using both surface electrodes and a figure-eight magnetic coil, respectively. The average Chronaxie times for the electric and magnetic field conditions were 109 ± 11 μs and 651 ± 53 μ s( ±SE), respectively. We do not propose that these results call into question the basic mechanism, namely that rapidly switched gradient magnetic fields induce electric fields in human tissues, resulting in PNS. However, this result does motivate us to suggest that special care must be taken when using electric field exposure data from the literature to set gradient coil PNS safety standards in MRI.

Timothy J Scholl - One of the best experts on this subject based on the ideXlab platform.

  • sensory and motor stimulation thresholds of the ulnar nerve from electric and magnetic field stimuli implications to gradient coil operation
    Magnetic Resonance in Medicine, 2010
    Co-Authors: Bryan J Recoskie, Timothy J Scholl, M Zinkeallmang, Blaine A Chronik
    Abstract:

    Rapidly changing magnetic fields from gradient coils induce electric fields in the individual being imaged, which can potentially result in peripheral nerve stimulation (PNS). This is a safety concern in MRI. Nerves exposed to either electric fields or time-varying magnetic fields are presumed to display equivalent stimulation threshold characteristics. This assumption has motivated the use of electric stimulation literature to be applied to gradient field safety standards. The consistency of peripheral nerve stimulation thresholds were compared by measuring Chronaxie times for electric and magnetic stimulation for both motor and sensory fibers in the ulnar nerve for a group of healthy volunteers. Thresholds were determined with both electromyography and also by having the subjects report stimulation onset. Chronaxie times measured between motor and sensory fibers were statistically different. However, this difference does not account for the substantial discrepancy reported between measured electric and magnetic stimulation Chronaxie times. We further establish that sensation threshold as defined perceptually by the subject volunteer is adequate as a simple and reliable measurement tool. Based on these observations, significant adjustments may need to be made to nerve parameters taken from the electric field stimulation literature prior to applying them directly to gradient induced stimulation in MRI.

  • the discrepancy between human peripheral nerve Chronaxie times as measured using magnetic and electric field stimuli the relevance to mri gradient coil safety
    Physics in Medicine and Biology, 2010
    Co-Authors: Bryan J Recoskie, Timothy J Scholl, Blaine A Chronik
    Abstract:

    A recent electrostimulation study with human subjects (Recoskie et al 2009 Phys. Med. Biol. 54 5965-79) reported a large difference between Chronaxie times when stimuli were delivered to the same body locus (the wrist) either through contact electrodes (electric stimulation) or through a pulsed magnetic field (magnetic stimulation). This paper reviews the procedures and analytic methods used in that study that might account for the reported discrepancies. Factors possibly accounting for reported discrepancies include the maximum and minimum pulse widths of the experimental stimuli; variations in experimental waveforms vis-a-vis mathematically ideal functions; differences in the spatial distribution of the in situ electric field for the two methods of delivery and differences in derived Chronaxie relative to strength-duration time constants.

  • the discrepancy between human peripheral nerve Chronaxie times as measured using magnetic and electric field stimuli the relevance to mri gradient coil safety
    Physics in Medicine and Biology, 2009
    Co-Authors: Bryan J Recoskie, Timothy J Scholl, Blaine A Chronik
    Abstract:

    Peripheral nerve stimulation (PNS) resulting from electric fields induced from the rapidly changing magnetic fields of gradient coils is a concern in MRI. Nerves exposed to either electric fields or changing magnetic fields would be expected to display consistent threshold characteristics, motivating the direct application of electric field exposure criteria from the literature to guide the development of gradient magnetic field exposure criteria for MRI. The consistency of electric and magnetic field exposures was tested by comparing Chronaxie times for electric and magnetic PNS curves for 22 healthy human subjects. Electric and magnetic stimulation thresholds were measured for exposure of the forearm using both surface electrodes and a figure-eight magnetic coil, respectively. The average Chronaxie times for the electric and magnetic field conditions were 109 ± 11 μs and 651 ± 53 μ s( ±SE), respectively. We do not propose that these results call into question the basic mechanism, namely that rapidly switched gradient magnetic fields induce electric fields in human tissues, resulting in PNS. However, this result does motivate us to suggest that special care must be taken when using electric field exposure data from the literature to set gradient coil PNS safety standards in MRI.

Durigan, Joao Luiz Quagliotti - One of the best experts on this subject based on the ideXlab platform.

  • Neuromuscular electrophysiological disorders and muscle atrophy in mechanically-ventilated traumatic brain injury patients: New insights from a prospective observational study.
    'Elsevier BV', 2019
    Co-Authors: Silva, Paulo Eugênio, Babault Nicolas, Maldaner Vinicius, Vieira Luciana, De Carvalho, Karina Livino, Gomes Hedian, Melo Priscilla, Cipriano Gerson, Durigan, Joao Luiz Quagliotti
    Abstract:

    International audienceErratum inCorrigendum to "Neuromuscular electrophysiological disorders and muscle atrophy in mechanically-ventilated traumatic brain injury patients: New insights from a prospective observational study" [J Crit Care 44 (2018) 87-94]. [J Crit Care. 2019]AbstractPURPOSE:It is unclear whether the muscular changes in mechanically-ventilated traumatic brain injury patients (TBI) are only associated with disuse or additionally to neuromuscular electrophysiological disorders (NED). The correlation between muscle atrophy and NED may affect functional outcomes and rehabilitation programs significantly.MATERIAL AND METHODS:An observational study was performed to investigate the presence of NED and muscle atrophy in TBI patients undergoing mechanical ventilation. NED was diagnosed by the stimulus electrodiagnosis test when Chronaxie was ≥1000μs. The muscle structure (thickness and echogenicity) was assessed by B-mode ultrasound. Tibialis anterior (TA), rectus femoris (RF), and biceps brachialis (BB) muscles were analyzed. Patients were followed from the first day of admission in the intensive care unit (ICU) to the fourteenth day.RESULTS:Twenty-two patients were analyzed. An increase of 48% in NED from day 1 to day 14 was detected in TA (p=0.004). All muscles presented a significant decrease in thickness (~18%, p

  • Intra- and inter-raters reliability and agreement of stimulus electrodiagnostic tests with two different electrodes in sedated critically ill patients
    'Informa UK Limited', 2019
    Co-Authors: De Araujo, Amaro Eduardo Tavares, Silva, Paulo Eugênio, Babault Nicolas, Karina Livinode De ,carvalho, Fachin-martins Emerson, Durigan, Joao Luiz Quagliotti
    Abstract:

    International audienceObjective: The aim of the present study was to verify the intra- and inter-rater reliability and agreement of the stimulus electrodiagnostic test (SET) measurements obtained by pen and square electrodes in the vastus lateralis and tibialis anterior muscles.Design: An intra- and inter-rater reliability and agreement study was performed for the SET by two independent raters. Two different sizes of cathode electrodes (1 cm2 and 25 cm2) and two muscles were assessed (tibialis anterior and vastus lateralis).Results: Chronaxie did not change according to the different electrodes. A high intra-rater reliability (0.72 ≤ r ≤ 0.88) was detected independently of the electrode and muscle assessed. Moreover, moderate and almost perfect agreements (0.51 ≤ Kappa ≤ 1.00) were detected on intra-rater assessment. Similar correlations (0.74 ≤ r ≤ 0.79) were found for intra-rater reliability. However, dissimilar inter-rater agreement was detected: Kappa ≤ 0.40 for tibialis anterior and Kappa = 1.00 for vastus lateralis.Conclusion: The SET presented high reliability and moderate agreement in intra-rater evaluations. A fair agreement was found in the inter-rater assessment of the tibialis anterior. Evaluations performed with different electrode sizes did not influence the results. Therefore, the SET should be performed by a unique rater in test retest situations

  • Neuromuscular electrophysiological disorders and muscle atrophy in mechanically-ventilated traumatic brain injury patients: New insights from a prospective observational study
    'Elsevier BV', 2018
    Co-Authors: Silva, Paulo Eugênio, Babault Nicolas, Maldaner Vinicius, Vieira Luciana, De Carvalho, Karina Livino, Gomes Hedian, Melo Priscilla, Cipriano Gerson, Durigan, Joao Luiz Quagliotti
    Abstract:

    International audiencePURPOSE: It is unclear whether the muscular changes in mechanically-ventilated traumatic brain injury patients (TBI) are only associated with disuse or additionally to neuromuscular electrophysiological disorders (NED). The correlation between muscle atrophy and NED may affect functional outcomes and rehabilitation programs significantly.MATERIAL AND METHODS: An observational study was performed to investigate the presence of NED and muscle atrophy in TBI patients undergoing mechanical ventilation. NED was diagnosed by the stimulus electrodiagnosis test when Chronaxie was ≥1000mus. The muscle structure (thickness and echogenicity) was assessed by B-mode ultrasound. Tibialis anterior (TA), rectus femoris (RF), and biceps brachialis (BB) muscles were analyzed. Patients were followed from the first day of admission in the intensive care unit (ICU) to the fourteenth day.RESULTS: Twenty-two patients were analyzed. An increase of 48% in NED from day 1 to day 14 was detected in TA (p=0.004). All muscles presented a significant decrease in thickness (~18%, p

  • Safety and feasibility of a neuromuscular electrical stimulation Chronaxie-based protocol in critical ill patients: A prospective observational study
    'Elsevier BV', 2017
    Co-Authors: Silva, Paulo Eugênio, Babault Nicolas, Mazullo, João Batista, De Oliveira, Tamires Pereira, Lemos, Bárbara Letícia, Carvalho, Vitor Oliveira, Durigan, Joao Luiz Quagliotti
    Abstract:

    International audiencePurpose: The aim of this study was to evaluate the safety and feasibility of a neuromuscular electrical stimulation (NMES) protocol based on neuromuscular excitability and applied in numerous muscle groups of critical ill patients.Materials and methods: We performed a prospective observational study using an NMES applied daily and bilaterally into 5 muscle groups in lower limbs for 3 consecutive days. The characteristics of NMES were 90 contractions per muscle, pulse width equal to Chronaxie, and a pulse frequency of 100 Hz. We assessed safety with central venous oxygen saturation, serum lactate, and creatine phosphokinase measurements. To evaluate feasibility, we recorded the time spent for the entire NMES protocol and the number of NMES sessions completed.Results: Eleven male patients finished the study. There were no significant changes observed in creatine phosphokinase from baseline up to 96 hours: 470 (+/- 270) IU/L and 455 (+/- 240) IU/L (P > .99). Central venous oxygen saturation and serum lactate had the same pattern with no significant variations (P =.23 and P =.8, respectively). The time spent during the whole procedure and the number of complete NMES sessions performed were 107 +/- 24 minutes and 84 sessions (85%), respectively.Conclusions: We demonstrated that NMES Chronaxie-based protocol is safe and feasible

Bart Nuttin - One of the best experts on this subject based on the ideXlab platform.

  • Chronaxie calculated from current duration and voltage duration data
    Journal of Neuroscience Methods, 2000
    Co-Authors: Jan Holsheimer, Emiel A Dijkstra, Hilde Demeulemeester, Bart Nuttin
    Abstract:

    To determine the rheobase and the Chronaxie of excitable cells from strength–duration curves both constant-current pulses and constant-voltage pulses are applied. Since the complex impedance of the electrode-tissue interface varies with both the pulsewidth and the stimulation voltage, Chronaxie values estimated from voltage–duration measurements will differ from the proper values as determined from current–duration measurements. To allow a comparison of Chronaxie values obtained by the two stimulation methods, voltage–duration curves were measured in human subjects with a deep brain stimulation electrode implanted, while the current and the load impedance of the stimulation circuit were determined in vitro as a function of both stimulation voltage and pulsewidth. Chronaxie values calculated from voltage–duration data were shown to be 30–40% below those estimated from current–duration data. It was also shown that in the normal range of stimulation amplitudes (up to 7 V) the load impedance increases almost linearly with the pulsewidth. This result led us to present a simple method to convert voltage–duration data into current–duration data, thereby reducing the error in the calculated Chronaxie values to ≈6%. For this purpose voltage–duration data have to be measured for pulses up to 10–20 times the expected Chronaxie.