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San Carlos, CA, United States

Nandedkar S.D.,Natus Medical
PM and R | Year: 2013

Electrodiagnostic techniques have been used for many decades to study neuromuscular diseases. In recent years, we have seen the extension of these methods to study disease progression, complemented by other technologies, for example, ultrasonography. There also is a growing interest in using surface electromyography, which is generally better accepted by patients than needle insertions. This article will discuss these trends and give examples of a few new and emerging methods that have the potential for use in an electrodiagnostic laboratory. © 2013 by the American Academy of Physical Medicine and Rehabilitation. Source

Zhou P.,Hefei University of Technology | Zhou P.,University of Texas Health Science Center at Houston | Nandedkar S.D.,Natus Medical | Barkhaus P.E.,Medical College of Wisconsin
IEEE Transactions on Neural Systems and Rehabilitation Engineering | Year: 2014

We investigated the voluntary contraction direction dependence of motor unit number index (MUNIX) for multifunctional muscles in patients with amyotrophic lateral sclerosis (ALS). The MUNIX technique was applied in nine first dorsal interosseous muscles of eight ALS subjects, using surface electromyography (EMG) signals from index finger abduction and flexion, respectively. In seven examined muscles, the MUNIX derived from the index finger abduction mode was smaller than that from the flexion mode. For the remaining two muscles, one had the same MUNIX; the other showed an abduction mode MUNIX much higher than the flexion mode MNUIX. Across all muscles, the median MUNIX was 96 for the index finger abduction mode and 161 for the flexion mode. The findings reveal the dependence of multifunctional muscle MUNIX on voluntary contraction directions in ALS patients. Based on this analysis, we further explored the concept of "multidimensional MUNIX" for an appropriate performance or interpretation of MUNIX in multifunctional muscles of ALS patients. An effort towards such a development was presented using both abduction and flexion mode surface EMG for MUNIX calculation. © 2014 IEEE. Source

Nandedkar S.D.,Natus Medical | Barkhaus P.E.,Medical College of Wisconsin
Muscle and Nerve | Year: 2015

Introduction: Tibial F-wave recordings are remarkable for their complexity and persistence. We postulate that the signal recorded by the E2 (reference) electrode causes this pattern. Methods: Tibial F-wave recordings were made from the abductor hallucis (AH) muscle using the standard montage in 10 subjects. Additional far-field simultaneous F-wave recordings were made from the AH, the base of the large toe, and the base of the small toe with the E2 placed on the contralateral foot. Results: F-wave recordings made in the standard manner and from the base of the large or small toes showed complex waveforms and similar latencies. Recordings made from the AH-contralateral foot had simple waveforms in most subjects; in 2 subjects the latencies were longer, and 1 showed reduced persistence. Conclusions: The tibial F-waves are composed primarily of volume conducted recordings of the tibial-innervated foot muscles from the E2 electrode. © 2015 Wiley Periodicals, Inc. Source

Neuwirth C.,Neuromuscular Diseases Unit | Barkhaus P.E.,Medical College of Wisconsin | Burkhardt C.,Neuromuscular Diseases Unit | Castro J.,University of Lisbon | And 6 more authors.
Journal of Neurology, Neurosurgery and Psychiatry | Year: 2015

Background: Motor Unit Number Index (MUNIX) is a novel neurophysiological measure that provides an index of the number of functional lower motor neurons in a given muscle. So far its performance across centres in patients with amyotrophic lateral sclerosis (ALS) has not been investigated. Objective: To perform longitudinal MUNIX recordings in a set of muscles in a multicentre setting in order to evaluate its value as a marker of disease progression. Methods: Three centres applied MUNIX in 51 ALS patients over 15 months. Six different muscles (abductor pollicis brevis, abductor digiti minimi, biceps brachii, tibialis anterior, extensor dig. brevis, abductor hallucis) were measured every 3 months on the less affected side. The decline between MUNIX and ALSFRS-R was compared. Results: 31 participants reached month 12. For all participants, ALSFRS-R declined at a rate of 2.3%/month. Using the total score of all muscles, MUNIX declined significantly faster by 3.2%/month (p≤0.02). MUNIX in individual muscles declined between 2.4% and 4.2%, which differed from ASLFRS-R decline starting from month 3(p≤0.05 to 0.002). Subgroups with bulbar, lower and upper limb onset showed different decline rates of ALSFRS-R between 1.9% and 2.8%/month, while MUNIX total scores showed similar decline rates over all subgroups. Mean intraclass correlation coefficient for MUNIX intrarater reliability was 0.89 and for inter-rater reliability 0.80. Conclusion: MUNIX is a reliable electrophysiological biomarker to track lower motor neuron loss in ALS. © 2015, BMJ Publishing Group. All rights reserved. Source

Natus Medical | Date: 2014-10-22

A method and apparatus for determining the impedance of the plurality of channels comprising a plurality of channels having a plurality of first channels and a plurality of second channels, at least one reference channel, a signal generator electrically connected to the plurality of channels, a reference signal generator connected to the reference channel, at least one amplifier connected to each of the plurality of channels and the reference channel and at least one filter connected to an output of the at least one amplifier to filter the output signal from the at least one amplifier. The signal generator is configured to provide a plurality of input signals to the plurality of channels. The reference signal generator provides an input signal to the reference channel.

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