William F. Brown

McMaster University, Hamilton, Ontario, Canada

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Publications (21)34.67 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Frequency-dependent conduction block (FDB) across segments of demyelination in response to high-frequency nerve stimulation has been well demonstrated in animals and has been explored in humans. However, attempts to demonstrate this phenomenon in sensory fibers involved in entrapment neuropathies have been unsuccessful. Therefore, we investigated the effects of high-frequency nerve stimulation in the median motor nerve in patients with carpal tunnel syndrome (CTS) with moderate to severely increased distal motor terminal latencies (MTL). As a group, the mean decrease in negative peak amplitude (npAmp) during 20 stimuli at 30-HZ frequency was significantly greater in CTS subjects (-11.3%) than in controls (+7.9%). The degree of FDB was greater when MTL was more prolonged (i.e., -4.9% at 5.0 ms and -25.3% at 9.4 ms) and FDB was more pronounced at higher stimulation frequencies (20 and 30 HZ). Our results suggest that the safety margin for impulse transmission is impaired in the motor axons of patients with a focal demyelinating lesion. These findings may correlate with the observation of weakness in the absence of conduction block in patients with entrapment neuropathies.
    Muscle & Nerve 05/2006; 33(5):619-26. · 2.31 Impact Factor
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    ABSTRACT: Decomposition-based quantitative electromyography (DQEMG) allows for the collection of motor unit potentials (MUPs) over a broad range of force levels. Given the size principle of motor unit recruitment, it may be necessary to control for force when using DQEMG for the purpose of deriving a motor unit number estimate (MUNE). Therefore, this study was performed to examine the effect of force on the physiological characteristics of concentric needle- and surface-detected MUPs and the subsequent impact on MUNEs obtained from the first dorsal interosseous (FDI) muscle sampled using DQEMG. Maximum M waves were elicited in 10 subjects with supramaximal stimulation of the ulnar nerve at the wrist. Intramuscular and surface-detected EMG signals were collected simultaneously during 30-s voluntary isometric contractions performed at specific percentages of maximal voluntary contraction (MVC). Decomposition algorithms were used to identify needle-detected MUPs and their individual MU firing times. These MU firing times were used as triggers to extract their corresponding surface-detected MUPs (S-MUPs) using spike-triggered averaging. A mean S-MUP was then calculated, the size of which was divided into the maximum M-wave size to derive a MUNE. Increased levels of contraction had a significant effect on needle- and surface-detected MUP size, firing rate, and MUNE. These results suggest that force level is an important factor to consider when performing quantitative EMG, including MUNEs with this method.
    Muscle & Nerve 04/2005; 31(3):365-73. · 2.31 Impact Factor
  • K. Ming Chan, William F. Brown
    01/2003;
  • 01/2003;
  • William F. Brown, Bradley V. Watson
    Neuromuscular Function and Disease: Basic, Clinical, and Electrodiagnostic Aspects, Edited by Brown WF, Bolton CF, Aminoff Mj, 01/2002: chapter Volume Conduction: pages 96-101; W.B. Saunders Company., ISBN: 0-7216-8922-1
  • William F. Brown, Bradley V. Watson
    Neuromuscular Function and Disease: Basic, Clinical and Electrodiagnostic Aspects, Edited by Brown WF, Bolton CF, Aminoff MJ, 01/2002: chapter Recording of electrical activity in nerve trunks and conduction in human sensory and motor nerve fibers: pages 21-55; W.B. Saunders Company., ISBN: 0-7216-8922-1
  • William F. Brown, Bradley V. Watson
    Neuromuscular Function and Disease: Basic, Clinical, and Electrodiagnostic Aspects, Edited by Brown WF, Bolton CF, Aminoff MJ, 01/2002: chapter Pathophysiology of conduction in peripheral neuropathies: pages 56-95; W.B. Saunders Company., ISBN: 0-7216-8922-1
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    ABSTRACT: The relative impact of training on motor units (MUs) with differing physiological characteristics remains controversial. To examine this issue, we longitudinally tracked the contractile and electrical characteristics of six human thenar MUs in 2 young healthy subjects before, during, and following an intermittent, high-frequency electrical stimulation program. Responses of MUs with differing baseline physiological characteristics varied widely. While the twitch and maximal tetanic tensions of the slower and fatigue-resistant MUs increased, tensions of the faster and more fatigable MUs declined. The fatigue resistance of the faster and more fatigable MUs, on the other hand, increased while that of the slower MUs remained unchanged. Although electrical stimulation of individual MUs allowed their training to be precisely controlled, it will be of practical importance to determine whether similar divergent MU contractile changes also occur with voluntary training.
    Muscle & Nerve 03/1999; 22(2):186-95. · 2.31 Impact Factor
  • K. Ming Chan, Daniel W. Stashuk, William F. Brown
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    ABSTRACT: The sequence of pathophysiological changes in amyotrophic lateral sclerosis (ALS) at the single motor unit (MU) level is not well understood. Using a recently described technique, a comprehensive range of physiological properties in two thenar MUs in ALS were intensively studied. In the first MU, despite a marked decline in the ability of the subject to voluntarily recruit the MU, the physiological properties of this MU remained remarkably stable over a 2-year period. In contrast, the physiological properties of the other MU declined rapidly over 5 months despite the fact that this MU could be recruited with ease throughout the study period. These differences between the progressively dysfunctional changes in these two MUs illustrates the value of such longitudinal studies of specific MUs in improving our understanding of the evolution of changes in single motoneurons in ALS. The broader application of longitudinally tracking the pathophysiological changes of the surviving MUs may prove to be a sensitive measure of disease progression and in evaluating the effectiveness of treatments.
    Muscle & Nerve 01/1999; 21(12):1714-23. · 2.31 Impact Factor
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    ABSTRACT: The surface EMG area often exhibits progressive enlargement during a submaximal fatiguing contraction, but the underlying reasons still remain uncertain. Fatigue-induced changes in the surface-detected motor unit action potentials (S-MUAPs) of 10 human thenar motor units (MUs) with widely differing physiological properties were examined. After 2 min of repetitive 40-Hz stimulation, the size of the S-MUAPs of all MUs increased, the magnitude of which was negatively correlated with their tetanic tension changes. These findings suggest that during muscle fatigue, in addition to reflecting recruitment of new MUs and increases in firing rates of the active MUs, the surface EMG may also be markedly influenced by changes in the S-MUAPs, especially in fast fatigable muscles.
    Muscle & Nerve 01/1999; 21(12):1786-9. · 2.31 Impact Factor
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    ABSTRACT: Electromyographic signals detected from the quadriceps femoris during various constant force contractions were decomposed to identify individual motor unit discharges and mean firing rates (FRs). Subject and group mean FRs were calculated for each force level. Mean FR values and FR variability increased with force. Individual, subject, and group mean FRs showed slight increases until 30% of maximum voluntary contraction and larger increases thereafter. Findings are discussed in relation to motor unit recruitment, frequency modulation, and fatigue.
    Muscle & Nerve 11/1998; 21(10):1338-40. · 2.31 Impact Factor
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    ABSTRACT: Cervical spondylytic myelopathy (CSM) is common. Magnetic resonance imaging (MRI), although sensitive, often reveals extensive and sometimes clinically irrelevant findings. The purpose of this study was to investigate the usefulness of central motor conduction studies in localizing the rostral level of cord involvement in 6 patients with CSM. Central motor conduction was assessed using high-voltage stimulation for the spinal roots and magnetoelectrical stimulation for the motor cortex, recording from "marker muscles" innervated by successively higher cervical cord segments. Abnormal central motor conduction affected all subjects at C8-T1, 5 subjects at C7, but none at the C5-C6 levels. The MRI showed abnormalities at multiple levels as high as C4. Our results suggest that central motor conduction studies are helpful in localizing the clinically relevant levels of spinal cord compression in CSM and correlate well with motor abnormalities on clinical examination.
    Muscle & Nerve 10/1998; 21(9):1220-3. · 2.31 Impact Factor
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    ABSTRACT: Serial motor unit number estimates have shed important light on the extent and rates of motoneuron losses in aging and amyotrophic lateral sclerosis. However, the estimates alone provide few clues to the health and functional status of surviving motor units. A reliable means for assessing the functional status of the surviving motor units would therefore by a welcome addition to our present tools for studying motor units. Examining the physiological properties of samples of motor units drawn at intervals during the course of a motoneuronal disease suffers from the important limitation that the samples may not be representative of one another. The latter problem could be circumvented by serially studying the same motor units. This study describes a noninvasive technique capable of longitudinally tracking the contractile and electrical properties of specific single thenar motor units in healthy subjects, in some instances over several years. The technique proved to be reasonably reliable and provided information on a wide range of contractile and electrical properties of motor units. Such an approach could serve as a potentially powerful and sensitive means of studying the life histories of single motor units in aging, diseases of the motoneuron, and in the latter instances, the responses of the motoneurons to treatment.
    Muscle & Nerve 08/1998; 21(7):839-49. · 2.31 Impact Factor
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    ABSTRACT: Decomposition-enhanced spike-triggered averaging (DE-STA) was applied to the vastus medialis muscle to examine size distributions of surface-detected motor-unit action potentials (S-MUAPs) at various force levels. Using DE-STA, 15-20 S-MUAPs were identified during 5%, 10%, 20%, and 30% of maximum voluntary contraction. Average S-MUAPs showed increase in peak to peak (and negative peak) amplitude with force (In microV): 5% = 37.9 +/- 6.1 (16.6 +/- 2.5), 10% = 44.0 +/- 4.0 (20.4 +/- 1.8), 20% = 80.7 +/- 9.3 (41.3 +/- 4.5), and 30% = 102.5 +/- 10.3 (53.6 +/- 5.0). Test-retest variability of peak to peak (and negative peak amplitude) between repeated trials was 0.10 (0.14), 0.14 (0.14), 0.17 (0.15), and 0.21 (0.20) at 5%, 10%, 20%, and 30% respectively. A relationship was found between the S-MUAP amplitude and force (r2 = 0.78, df = 90, F = 160, P < 0.001). Increase in average S-MUAP amplitude with force suggests that STA performed only at low levels of contraction may result in a biased sampling and small average S-MUAP amplitudes.
    Muscle & Nerve 08/1997; 20(8):976-82. · 2.31 Impact Factor
  • William F. Brown, K. Ming Chan
    Muscle & Nerve 02/1997; 5:S70-3. · 2.31 Impact Factor
  • William F. Brown, A. Lee Dellon, William W. Campbell
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    ABSTRACT: The role of electrodiagnosis in managing patients with focal neuropathies is discussed from the differing perspectives of a peripheral nerve surgeon and a practitioner of electrodiagnostic medicine. Both clinical evaluation and electrodiagnosis are useful methodologies, each having limitations. Dr. Dellon labels the overreliance on electrodiagnosis and the "WOG" (Word of God) syndrome, and describes its signs, symptoms, and treatment. Dr. Brown contends Dr. Dellon's crusade is misdirected. The exchange is an eloquent polemic on the virtues and foibles of these different approaches to evaluating peripheral nerve function and the imperative to practice them in a complementary rather than a contentious manner.
    Muscle & Nerve 12/1994; 17(11):1336-42. · 2.31 Impact Factor
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    ABSTRACT: An automated technique for estimating the number of motor units based on single motor unit action potentials in the F-response is described. The average surface detected motor unit action potential (S-MUAP) was calculated from the datapoint-by-datapoint average of a sample of S-MUAPs automatically selected from a population of F-responses. The technique was applied to the thenar muscles of young (n = 18, aged 31 +/- 11 years) and older (n = 15, aged 68 +/- 3) subjects. Motor unit number estimates based on the automated selection of S-MUAPs from the F-responses compared well with those derived using a computer-assisted manual method for selecting S-MUAPs from the F-response (automated 245 +/- 105 vs. manual 241 +/- 100, r = 0.93) and were similar to estimates obtained using multiple point stimulation (219 +/- 77). The advantages of the automated technique for collecting S-MUAPs from the F-response include the ready tolerance of the technique by subjects, the minimal amount of operator interaction required, and the additional information relating to the conduction velocities and latencies of single motor axons.
    Muscle & Nerve 09/1994; 17(8):881-90. · 2.31 Impact Factor
  • William F. Brown, Bradley V. Watson
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    ABSTRACT: Acute radial neuropathies localized to the retrohumeral course of the radial nerve are common. Most individuals fully recover within a matter of days or, at the most, a few weeks. In a few, recovery may take longer and occasionally remains incomplete. In almost all instances the site of injury to the radial nerve can be accurately localized to the region of the spiral groove and the relative contributions of conduction block and axonal degeneration assessed using electrophysiologic techniques.
    Muscle & Nerve 08/1993; 16(7):706-11. · 2.31 Impact Factor
  • William F. Brown, Thomas E. Feasby, Angelika F. Hahn
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    ABSTRACT: The acute "axonal" form of Guillain-Barre syndrome is characterized by rapid progression to severe widespread paralysis and respiratory dependence within 2-5 days of the onset of weakness with very poor and delayed recovery. In 3 cases studied within the first 7 days, the maximum thenar, hypothenar, tibialis anterior, and extensor digitorum brevis "M" potentials were either very reduced in size or absent in response to stimulation at the usual most distal sites of stimulation at the wrist, fibular head, and/or ankle. In the latter instances, advancing the site of stimulation closer to the motor point often evoked an M response. Furthermore, continued distal advance of the site of stimulation evoked progressively larger sized M potentials. Over succeeding days even these very distally evoked M potentials disappeared. Maximum conduction velocities in motor nerve fibers just prior to total loss of excitability were often very reduced. The pattern in these cases is most consistent with progressive loss of excitability and conduction in nerve fibers undergoing axonal degeneration, although coexisting primary demyelination in the terminal segment could not be excluded as the basis for the sometimes very slowed conduction velocities.
    Muscle & Nerve 03/1993; 16(2):200-5. · 2.31 Impact Factor
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    ABSTRACT: Eleven acute radial nerve palsies were examined between 3 days and 14 weeks following the onset of the neuropathy. Our objective was to quantify the relative extent of axon loss and conduction block in radial motor fibers supplying the extensor and abductor pollicis longus (EPL/APL) muscles. In 10 of 11 cases, conduction block exceeded axon loss. Maximum motor and sensory conduction velocities were normal distal to the spiral groove, suggesting that the larger myelinated fibers were not selectively involved in this acute neuropathy. The localization of the conduction block and slowing was, in every case, across the spiral groove. This method provides a relatively simple way of assessing the approximate contributions of axon loss and conduction block, and fits well with the early and usually complete clinical recovery in these cases.
    Muscle & Nerve 06/1992; 15(7):768 - 773. · 2.31 Impact Factor

Publication Stats

250 Citations
34.67 Total Impact Points

Top Journals

Institutions

  • 2005–2006
    • McMaster University
      • Division of Neurology
      Hamilton, Ontario, Canada
  • 1993–1999
    • New England Baptist Hospital
      Boston, Massachusetts, United States
    • The University of Western Ontario
      • Division of Nephrology
      London, Ontario, Canada
  • 1994
    • University of Waterloo
      • Department of Systems Design Engineering
      Waterloo, Quebec, Canada