Search PubMed⌕ Search

Biomedical subjects

W F Brown

Publications and source records attributed to W F Brown.

At least 109 records · Page 6Linked to original sources
PubMed1976

Multiple point electrical stimulation of ulnar and median nerves.

A computer-assisted method of isolating single motor units (MUs) by multiple point stimulation (MPS) of peripheral nerves is described. MPS was used to isolate 10-30 single MUs from thenar and hypothenar muscles of normal subjects and patients with entrapment neuropathies, with the original purpose of obtaining a more representative mean motor unit potential for estimating the number of MUs in a muscle. The two important results that evolved from MPS however, were: (1) in the absence of 'alternation' MUs were recruited in an orderly pattern from small to large, and from longer to shorter latencies by graded electrical stimulation in both normal and pathological cases, (2) a comparison of the sizes of MUs recruited by stimulation proximal and distal to the elbow suggested that axonal branching can occur in the forearm 200 mm or more proximal to the motor point in intrinsic hand muscles.

Adult↗
PubMed1976

Some electrical properties of motor units and their effects on the methods of estimating motor unit numbers.

Long train (50) electrical pulses were applied to the ulnar, median, and deep peroneal nerves. The probability of firing, or firing index, of the first motor units (MU) recorded by surface and needle electrodes in the first dorsal interosseous, thenar, and extensor digitorum brevis muscles varied from 0-100% as the stimulus was increased from a minimum threshold voltage (V) to V + delta V (delta V = 2-4 volts). The voltage interval, delta V (firing level range), of even the first few MU recruited greatly overlapped in normal subjects, but may overlap less in some neuromuscular disorders such as amyotrophic lateral sclerosis. The mean size of the single MU isolated by (1) isometric voluntary contraction method, (2) F recurrent discharge method, and (3) stimulation at multiple locations along the nerve, were more than twice as large as the mean size of the incremental steps evoked by graded electrical stimulation. These results suggest that methods of estimating the number of MU in a muscle should incorporate a correction for the fluctuations in excitability and overlap in firing levels of MU, and in addition should include larger MU in the estimation of the mean MU potential.

Axons↗
PubMed1976

New methods of estimating the number of motor units in a muscle.

Two electrophysiological methods have been described for estimating the number of motor units (MU) in a muscle. The methods are based on the original methods of Mc Comas and others, which involve dividing the maximum compound potential (MCP) of muscle evoked by supramaximal electrical stimulation of nerve by a mean motor unit potential (MMUP). The important modifications in the methods are the incorporation of the fluctuations in the response of MU to electrical excitation and a possible correction for the overlap in the firing levels of motor axons. The methods have been used in the estimation of the number of motor units in the first dorsal interosseous, thenar, hypothenar, and extensor digitorum brevis muscles of normal subjects and patients with various neuromuscular disorders. The results indicate that previous motor unit estimates were in general erroneously high.

Axons↗
PubMed1975

The effects of motor cortical stimulation on the excitability of spinal motoneurons in man.

The pyramidal tract and particularly the direct cortico-motoneuronal components (DCM) have become increasingly important in the higher primates. Minimal single pulse precentral stimulation in man evokes EMG discharges from the contralateral hand muscles with a latency of 18-21 milliseconds. The excitability changes produced by such cortical stimulation on the upper limb H-reflex has been observed to include a short duration early facilitation probably corresponding to the DCM input and a later, longer lasting facilitation mediated by the same and probably other corticofugal projections. Potentiation of the H-reflex in the upper libs by means of postcentral excitation required much higher single pulse stimulus intensities and the changes in excitability produced on the spinal motoneurons could have been explained by physical extension of the stimulus current to the precentral region. Isometric contraction potentiated the H-reflex produced by combinations of precentral cortical and peripheral nerve stimulation but no direct evidence was found to support a possible transcortical basis for the V2 stretch reflex.

Electric Stimulation↗
PubMed1974

Variation of motor unit size in the human extensor digitorum brevis and thenar muscles.

One physiological method for estimating the motor unit number in a muscle depends on dividing into the maximum compound muscle action potential, the potential average of the first few motor unit potentials excited by a motor nerve stimulus above motor threshold. To be valid, such an average unit potential size must be representative of the whole motor unit population. This assumption may not be justified. The present study has shown that there are single motor units in healthy and abnormal, thenar, and EDB motor unit populations, many times larger than any motor unit excited close to the motor threshold. This finding suggests that previously reported motor unit estimates may not only be an overestimate of the true motor unit population number, but have excluded much larger motor units with higher thresholds. Low motor unit estimates in neuropathies may result from a change in the order of activation of motor units with the appearance of larger motor units, normally of higher threshold among the first few just above the motor threshold.

Action Potentials↗
PubMed1973

Thenar motor unit count estimates in the carpal tunnel syndrome.

Thenar motor unit counts were done in 19 subjects with symptoms characteristic of the carpal tunnel syndrome. Three-quarters of the patients had motor unit count estimates less than 2 SD lower limit of controls. Despite this, most did not have thenar wasting or weakness. Functional compensation by motor unit remodelling probably kept pace with motor axon loss and masked the true extent of axonal degeneration.

Action Potentials↗
PubMed1972

A method for estimating the number of motor units in thenar muscles and the changes in motor unit count with ageing.

A method for estimating the number of motor units in median innervated thenar muscles is described. In normal human subjects under 40 years of age, the mean and 1 SD was 253+34. The number of motor units falls with increasing age, especially after mid life, so that elderly subjects often have less than one-half the number in youth despite good strength. The cause is not known but probably includes peripheral nerve trauma and `primary neuronal cell death'.

Action Potentials↗