Percutaneous localization of conduction abnormalities in human entrapment neuropathies.
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Electrodiagnosis↗
Biomedical subjects
W F Brown
Publications and source records attributed to W F Brown.
Physiological observations in the median nerve during carpal tunnel surgery.
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Carpal Tunnel Syndrome↗
The origin of spontaneous electrical activity at the end-plate zone.
Two types of spontaneous electrical activity are present at the end-plate zone: low-voltage negative potentials that correspond to miniature end-plate potentials, and larger voltage negative-positive potentials. The electrogenic origin of the latter has been uncertain. The origin of these larger potentials was investigated in the rat phrenic nerve diaphragm preparation and in human gastrocnemius muscle just prior to intubation during administration of preoperative anesthesia. In the hemidiaphragm the larger voltage negative-positive potentials were rarely triggered by intracellular or tungsten microelectrodes. The negative-positive potentials, however, were clearly triggered by contact of the concentric needle electrode with muscle hemidiaphragm at the end-plate region. The potentials were abolished by curare. Likewise, the equivalent potentials observed at the human gastrocnemius end-plate zone were blocked by neuromuscular blocking agents. Therefore, these positive-negative discharges represent postsynaptic muscle fiber action potentials and not nerve fiber activity. They were probably presynaptically activated by mechanical irritation of the motor axon terminal and preterminal branches.
Animals↗
The pneumatic tourniquet: a biomechanical and electrophysiological study.
The pneumatic tourniquet is used routinely in extremity surgery, not only to prevent unnecessary blood loss, but also to increase the safety of the operative procedure. The mechanical part of this study shows that the system can fail in either of two major ways, each causing serious problems. The tourniquet may be inadequate if the pressure delivered to the cuff is not accurately displayed on the gauge or if the pre-set pressure is not maintained for the duration of the operative procedure. In our hospital, three of seven tourniquets (43%) in daily use showed significant errors in this regard. The electrophysiological part of this study indicates that nerve conduction does not necessarily return to preoperative levels immediately postoperatively, and that the conduction block is generally at the level of the cuff. Our observations confirm those of others and implicate both direct pressure as well as ischemia as the cause of the problem.
Arm↗
The pathogenesis of pneumatic tourniquet paralysis in man.
The relative importance of ischaemic and direct mechanical injury to nerves compressed by a tourniquet, in the pathogenesis of tourniquet paralysis in man has not been established. To investigate this question, conduction in ulnar or median nerve fibres has been measured in healthy subjects both at the level of the pneumatic tourniquet and distal to the tourniquet. Measurement was prior to, for the period of tourniquet inflation, and following release of the tourniquet. The earliest conduction delays and block were observed at the level of the tourniquet, particularly across the proximal tourniquet border zone. However, a proximal to distal progression in conduction abnormalities distal to the tourniquet suggested that the earlier conduction abnormalities at the level of the tourniquet were primarily ischaemic in origin. Mechanical compression, however, probably contributed to disproportionate conduction delays and blocks across the border zones of the tourniquet.
Arm↗
Relative preservation of lumbrical versus thenar motor fibres in neurogenic disorders.
At late stages of median nerve entrapment in the carpal tunnel there may be total denervation of the thenar muscles. Surface electrodes over the thenar endplate zone may record an initial and predominantly positive "M" response to supramaximal median nerve stimulation. By a combination of techniques, it has been established that this surface positive response originates from surviving lumbrical muscles innervated by the median nerve. Their relative preservation may be related to their location in the median nerve. Intraoperative investigations have shown that the thenar motor fibres are primarily located in the ventral-lateral part of the median nerve whereas lumbrical motor fibres are in a more dorsal location and hence are probably better protected against the flexor retinaculum. This relative preservation of lumbrical motor fibres has been observed in other peripheral neuropathies and motor neuron disease, but not in median nerve regeneration of the following nerve transection. The importance of the observation lies in the more precise localisation voltage source for "M" response in terminal or near-terminal carpal tunnel median nerve entrapments and avoidance thereby of possible misinterpretation of electrophysiological observations in this most common nerve entrapment syndrome.
Action Potentials↗
Light-stimulus-evoked blink reflex: methods, normal values, relation to other blink reflexes, and observations in multiple sclerosis.
The blink reflex may be evoked by auditory click or light stimulation, the latter being constantly present in all healthy subjects. The latency and amplitude of the light-stimulus-evoked blink response (L-BR) is influenced by the light intensity, distance between the light stimulus and the eye, attention, and background facilitation. The L-BR was abnormal in 75% of definite and 61% of probable multiple sclerosis (MS) patients. When abnormal, the L-BR was more commonly absent than delayed. Optic nerve lesions could be identified by the pattern of abnormalities in the L-BR in some patients. The L-BR has proved to be a sensitive detector of abnormalities in the visual connections and, in combination with the Vth nerve stimulation-evoked blink response, a valuable detector of brainstem lesions.
Adult↗
The human jaw jerk: electrophysiologic methods to measure the latency, normal values, and changes in multiple sclerosis.
The reflex contraction of the masseter muscles to the stretch imposed by a tap on the chin is a monosynaptic reflex. This reflex contraction of the master muscles was present in all control subjects but commonly absent in definite multiple sclerosis (MS) patients. In a few MS patients the latency was prolonged. Abnormalities in the jaw jerk, however, were less frequent than with the blink reflex responses to supraorbital nerve stimulation or light stimulation. Nonetheless, there were patients in whom the blink reflexes were normal but the jaw jerk responses was abnormal. The last observation suggests that the jaw jerk may be occasionally helpful in the detection of brainstem lesions in MS.
Adolescent↗
Cubital tunnel syndrome and ulnar neuropathy.
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Humans↗
Patterns of change in mature Angus cow weight and fatness during the year.
Postcalving cow weight and subcutaneous fatness change patterns were described for 80 mature spring-calving Angus cows. The cows grazed either high (regularly clipped fescue-legume) or low (fescue clipped once) quality pastures. Forage consumption was estimated continuously by an internal (acid detergent lignin)-external (Cr2O3) indicator technique. Milk production (calf-suckle technique) was estimated seven times during lactation. Wither height was measured during the fall after the period of intensive measurment. Angus cows grazing high quality pasture lost an average of 36 kg postcalving, whereas those grazing low quality pasture lost an average of 22 kilograms. Minimum weights were observed about April 1, prior to the season of large pasture quality differences in digestibility of consumed forage. Taller cows, when allowed increased nutrient density during midlactation (high versus low quality), responded by increasing (P < .05) fatness at a more rapid rate than less tall cows. For cows grazing high quality pasture, weight change was independent of level of milk production. Cows grazing low quality pasture and giving relatively large amounts of milk maintained less weight and fat during the middle and last part of lactation than did those giving smaller amounts of milk. Shapes of the curves depicting change in weight and fatness were closely related (P < .01) to digestible dry matter intake. Cows apparently consumed forage in such a manner that they became more alike in both weight and fatness as the grazing season progressed.
Adipose Tissue↗
Chronic progressive myelopathy: investigation with CSF electrophoresis, evoked potentials, and CT scan.
Chronic progressive myelopathy (CPM) is a difficult clinical problem. Many patients who present with CPM turn out to have a spinal form of multiple sclerosis (MS), but until there is clear lesion dissemination, a definite clinical diagnosis cannot be made. We have looked for MS-related abnormalities in 72 patients with CPM. The mean age of onset was 42 years, mean duration was ten years, and mean Kurtzke disability rating was 4.5. Studies performed were cerebrospinal fluid electrophoresis for oligoclonal banding, pattern-reversal visual evoked responses, blink reflex latencies, and computerized axial tomography. Oligoclonal banding was found in 32 patients (44%), patterned visual evoked responses were abnormal in 32 (44%), and blink latencies were abnormal in 40 (56%). A least one of these studies was abnormal in 61 patients (85%) and at least two in 48 (66%). The CT scan was abnormal in 38 )53%), 36 with atrophy and 3 with low-density or enhancing lesions. These results suggest that at least 44% of patients with CPM may have MS that could be diagnosed by oligoclonal bands. Other physiological tests suggesting diffuse or disseminated disease bring the total to 85%. Only autopsy follow-up will tell us the exact diagnostic accuracy of these studies in this complex syndrome.
Adult↗
Changes in motor unit populations in motor neurone disease.
In motor neurone disease changes in the functional properties of motor units, including the surface voltage, latency, conduction velocity, and response to repetitive stimulation, were investigated. Progression was marked by motor unit loss, increase in the proportion of larger motor unit potentials, and inclusion of motor unit potentials larger than normal in the remaining motor unit population. Even late in the disease, motor unit potentials with a low surface voltage persisted. The relationship between motor unit potentials, surface voltage, and latency, present in control subjects, broke down in motor neurone disease, large motor unit potentials having abnormally long latencies and small motor unit potentials unexpectedly short latencies. Amplitude decrements were more frequent and severe in motor unit potentials at later stages in the disease, particularly in those units with lower surface voltages. In one surviving motor unit potential there was evidence suggestive of functional recovery. The observations point to complex changes in the functional properties of motor units in motor neurone disease.
Cell Count↗
Characteristics of the F response: a single motor unit study.
Trains of 100 to 200 stimuli result in F discharges from less than one half of motor units of hand muscles. The maximum observed F discharge frequency was 10%. There was no relation between the surface voltage of motor unit potentials and the frequency of F discharge. The motor unit potentials of larger surface voltage were recruited at higher stimulus intensity levels, usually supramaximal for the antidromic sensory nerve action potential. No correlation was observed between F latency and the surface voltage of the motor unit potentials. In only one pathological example was a clear interaction observed between the frequency of F discharge in motor unit potentials and the recruitment of other single motor unit potentials by increments in the stimulus intensity. The observations suggested that caution should be exercised before the F discharge is accepted as a method for measuring proximal conduction times in human motor nerves.
Adult↗
Neuromuscular transmission in human single motor units.
A method, multiple point stimulation, has been reported to isolate 5-20 single hypothenar or thenar motor units for investigation. This method is attractive for testing neuromuscular transmission because the required stimulus intensities are much less than for supramaximal nerve stimulation, and movement artefact is less of a problem. In this investigation of controls, the changes in hypothenar and thenar motor unit surface voltage and latency of single muscle fibre action potentials belonging to the motor unit have been measured in response to trains of stimuli delivered to the motor nerve. In healthy motor units, increases in the surface peak-to-peak voltage and corresponding reductions in the peak-to-peak duration occurred, the changes being maximum at the shorter stimulus intervals and accompanied by increased synchronisation of motor unit muscle fibre action potential discharges. The investigations of the responses for healthy single motor units to repetitive stimulation provide the basis for investigations of neuromuscular transmission at the level of the motor unit in diseases of neuromuscular transmission.
Action Potentials↗
Neuromuscular transmission in myasthenic single motor units.
In patients with myasthenia gravis neuromuscular transmission has been tested in individual hypothenar and thenar motor units using trains of near threshold electrical stimuli delivered to the motor nerve. The most important observations included: (1) the proportion of motor units with pathological decrements varied from 0 to 90%, (2) the decrements in surface voltage were frequently much more normal in individual motor units than in the corresponding maximum compound potentials evoked by supramaximal nerve stimulation, and (3) the most abnormal decrements were observed in motor units at the low end of the surface voltage range. These observations can be interpreted to suggest important neurogenic factors in the pathogenesis of myasthenia gravis. An attractive alternative would be to suggest that the small motor units have the most abnormal neuromuscular transmission because they normally have a lower margin for safe neuromuscular transmission and, as a consequence, fail first in diseases of neuromuscular transmission.
Action Potentials↗
The muscular pain-fasciculation syndrome.
Five cases of a chronic neuromuscular syndrome consisted of muscular aching and sometimes burning pain, fasciculations, cramps, fatigue, and occasional paresthesia. The disorder affected the legs and, less commonly, the girdle, trunk, and arm muscles. The symptoms were enhanced by physical activity and were usually improved by rest. Neither muscular wasting nor weakness was found, although the condition was present for an average of 4.7 years and, in one patient, as long as 10 years. Electrophysiologic studies showed motor abnormalities indicative of axonal degeneration and muscle fiber denervation, most marked in the legs. Light microscopy of skeletal muscle and spinal cord in one case disclosed evidence of mild denervation atrophy in muscle, but no loss of anterior horn cells. The findings are compatible with a benign polyneuropathy.
Adult↗
Chronic progressive myelopathy: investigation with CSF electrophoresis, evoked potentials, and CAT scan.
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Adult↗
The location of conduction abnormalities in human entrapment neuropathies.
Direct stimulation of 23 median, 13 ulnar and 2 peroneal nerves at the time of surgical exploration has been used to locate, and characterize the conduction abnormalities in the nerves. The most frequent location of the major conduction abnormalities in the median nerve was in the first 1-2 cm distal to the origin of the carpal tunnel. In the ulnar nerve the important conduction abnormalities were located most frequently in the segments 1 cm proximal and distal to the medial epicondyle. In the peroneal nerve the major conduction abnormalities occurred proximal or distal to the entry point of the common peroneal nerve into the peroneus longus muscle.
Adolescent↗