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Biomedical subjects

S Borenstein

Publications and source records attributed to S Borenstein.

At least 55 records · Page 3Linked to original sources
PubMed1980

Range of variations in motor unit potentials during reinnervation after traumatic nerve lesions in humans.

Successive stages in the reinnervation of denervated muscle fibers following a complete or partial motor nerve lesion in humans were analyzed with the concentric needle electrode during voluntary contraction. Motor unit potential (MUP) patterns were displayed by coherent EMG, in which the potential triggers an oscilloscope sweep and a digital delay line enables the early part of the MUP to be displayed. After a complete nerve lesion, MUPs showing the response of as few as one to three muscle fibers can be observed. MUPs become highly polyphasic as more muscle fibers are incorporated. Marked latency jitter and intermittent blocking of components as well as the occurrence of linked potentials result in complex patterns that may be confused with a "myopathic" pattern of brief small spikes if conventional observation of free-running sweeps is used alone. After a partial nerve lesion, the healthy motor axons achieve extensive collateral reinnervation of the denervated muscle fibers whereby linked potentials of various latencies are added after the original MUP. Adequate understanding of these characteristic features can help clarify some current issues in electromyography. The mechanisms by which long-latency linked potentials and desynchronized components are produced during remodeling of motor units in the course of regeneration involve a number of factors such as slow conduction along regenerated axon branches, ectopic motor end-plates, insecure neuromuscular transmission, and muscle fiber atrophy.

Adolescent↗
PubMed1980

Analysis of lung volume restriction in patients with respiratory muscle weakness.

We investigated pulmonary mechanics in 25 patients, 9 to 55 years of age, with a variety of generalised neuromuscular diseases and variable degrees of respiratory muscle weakness. The average degree of inspiratory muscle force was 39.2% (range 8-83%) of predicted. The lung volume restriction far exceeded that expected for the degree of muscle weakness: the observed decrement in respiratory muscle force should, theoretically, decrease vital capacity to 78% of its control value, while the mean VC in our patients was only 50% of predicted. Analysis of lung pressure-volume curves indicated that the two principal causes of the disproportionate loss of lung volume were a reduction in lung distensibility probably caused by widespread microatelectasis, and a decrease in the outward pull of the chest wall. Because it reflects both direct (loss of distending pressure) and secondary (alterations in the elastic properties of the lungs and chest wall) effects of respiratory muscle weakness on lung function, we conclude that, in these patients, the vital capacity remains the most useful measurement to follow evolution of the disease process or response to treatment.

Adolescent↗
PubMed1977

Myotonic dystrophy with nerve hypertrophy. Report of a case with electrophysiological and ultrastructural study of the sural nerve.

A striking enlargement of peripheral nerves was observed in a patient with myotonic dystrophy (Steinert's disease). Clinical findings disclosed a polyneuropathy which was confirmed by electrophysiological and morphological investigations. Myopathic as well as neurogenic alterations were found on electromyography in wasted hand muscles. The prominent finding on ultrastructural study of sural nerve biopsy was an important collagen infiltration with rather few "onior bulb" formations. This extensive endoneural collagen formation appeared to be responsible for the nerve hypertrophy. Evidence of segmental demyelination and remyelination was also found. Glycogen deposits were present in some myelinated axons and is some Schwann cells. Peculiar crystalline inclusions were observed in fibroblasts processes. The relation between myotonic dystrophy and polyneuropathy remains a matter of discussion.

Electromyography↗
PubMed1976

Regeneration in Duchenne muscular dystrophy. Electromyographic evidence.

Eight patients with Duchenne muscular dystrophy (DMD) and seven normal children of similar age were studied with a new electromyographic method for coherent displays of potentials. Five hundred motor unit potentials (MUPs) were analyzed in 20 proximal and distal muscles representing a wide spectrum of dystrophy. The progressive MUP disintegration by dropping out of muscle fibers was documented, as well as a high incidence of spontaneous fibrillation. A total of 386 late component (LC) potentials followed the 500 MUPs at consistent latencies. No LC occurred in normal children. The LCs result from motor axon sprouts innervating muscle fibers that are newly formed either by segmentation of existing muscle fibers (focal neucrosis and membrane repair) or by muscle regeneration. Axons in DMD can thus collaterally innervate additional muscle fibers. These processes must delay the onset and progression of clinical weakness in DMD patients.

Adolescent↗
PubMed1975

Local cooling in myasthenia. Improvement of neuromuscular failure.

Weak myasthenic muscles were tested by nerve stimulation both at normal temperature and after local cooling that was accomplished by exposing the skin to ice bags or cold paraffin oil. Reduction of intramuscular temperature from 35 C to 28 C increased the voltage of the bellytendon electrical response, the force of the tetanus elicited by 10/sec or 20/sec nerve stimulation. The myasthenic decrement of successive muscle responses was less marked after cooling, as were "delayed rundown" and "postactivation exhaustion." All these effects were reversed on rewarming the muscle. The abnormal neuromuscular jitter in motor-unit components was also reduced by local cooling. These observations may explain why diagnostic application of repetitive stimulation may be false-negative; muscle temperature must be controlled.

Adolescent↗
PubMed1971

Velocity of chromosome replication in thymine-requiring and independent strains of Bacillus subtilis.

Chromosomes in spores of a thymineless mutant of Bacillus subtilis strain 168 were shown to have a replication fork, unlike chromosomes in spores of the thy(+) strain which are in a complete form. As a consequence the number of replication forks in germinating cultures is higher in the thy(-) strain than in the thy(+) one. Chromosome replication time (C) in the thy(+) strain was found to be about 53 min for growth rates from 20 to 60 min. In the thy(-) strain, C was about 75 min at high growth rates and increased with decreasing growth rate when the thymine concentration was not limiting. With limiting thymine concentrations in the medium replication velocity decreased independently of growth rate.

Adenine↗