Biomedical subjects

S Aravabhumi

Publications and source records attributed to S Aravabhumi.

5 recordsLinked to original sources

PubMed1990

Clinical electromyography. Principles and practice.

In this article the principles and practice of clinical EMG are described. The basic components of EMG instrumentation include specialized intramuscular recording electrodes, a preamplifier, amplifier, and displays. Displays are usually both visual and auditory, using the CRO and a loudspeaker, respectively. The motor unit is the functional unit of muscles and is the anatomic basis for clinical EMG. There are distinct sites along the motor unit pathway where pathologic changes may produce EMG abnormalities. These sites include (1) anterior horn cell; (2) spinal nerve root; (3) plexus; (4) peripheral nerve; (5) myoneural junction; and (6) muscle fiber. Normal EMG potentials in resting muscle (which is predominantly silent) include end-plate potentials and miniature end-plate potentials, which are present only in the region of the motor end plate. Individual motor unit potentials can be observed when a muscle contracts minimally. The morphology of motor unit potentials varies within a normal range, which is somewhat specific for each muscle, depending on its nerve-muscle fiber innervation ratio. Stronger contraction of a muscle produces an orderly recruitment of motor units, referred to as an interference pattern. In resting muscle the most commonly encountered abnormal potentials include (1) positive sharp waves, (2) fibrillation potentials, (3) fasciculation potentials, and (4) high frequency discharges. Abnormalities in motor unit morphology can be detected best in minimally contracting muscles. Polyphasic motor units contain more than four phases and constitute less than 15 per cent of all motor units in a given muscle. In myopathy the motor unit potentials are often polyphasic. They are of low amplitude and short duration. In neuropathy motor unit potentials may also be polyphasic; however, the size of the motor unit is either normal or of increased amplitude and duration depending on chronicity. Such findings in myopathy and neuropathy correlate with known pathoanatomic changes in these conditions. In myopathy the motor unit interference pattern will often be normal or enhanced despite clinical weakness in the muscle. In neuropathy the interference pattern will be reduced, and when neuropathy is severe a single large motor unit may produce a single motor unit pattern. Besides its application as a valuable aid in diagnosis of neuromuscular disorders, electromyography is also utilized for prognosis, determining the need for surgery, planning programs of rehabilitation, and providing evidence for medical legal purposes. Electromyographic findings most often serve as an adjunct to a thorough clinical evaluation of the patient. The electrophysiological data obtained may help support or rule out a specific clinical diagnosis.

Electrodes↗

PubMed1989

Sensory and motor deficits of central nervous system origin.

The sensory and motor deficits of the CNS are varied, depending on the etiologic factors and the structures involved. Nevertheless, the clinical picture is predictable, provided one has an adequate knowledge of the neuroanatomy and the functions of the different fiber tracts, nuclei, and other specific regions of the brain and spinal cord. The purpose of this section is to provide an overall view of the sensory and motor deficits of the CNS, which will enable the clinician to treat these patients in a more objective and effective manner. Etiologically, the diseases affecting the CNS can be grouped under the following categories: congenital, traumatic, inflammatory, neoplastic, and degenerative. Congenital conditions usually manifest in infancy and childhood. Examples are hydrocephalus, spina bifida, and Arnold-Chiari malformation. There are a host of other conditions, but the discussion in this article is confined to the more common entities. Traumatic conditions such as cerebral concussion, contusion, laceration, hematomas--extradural, subdural, or intracerebral--and spinal cord injuries can occur in any age group, though their incidence is higher during the more active period of life (20 to 35 years). Automobile accidents are by far the most common etiologic factor for the traumatic lesions. Others, such as falls, gunshot and stab wounds, and so forth account for the remainder. Among the inflammatory conditions, three conditions are important: brain abscess, meningitis, and transverse myelitis. Though brain abscess develops by direct extension from an adjacent focus of infection, often it forms as a result of metastatic infection, chiefly from lung abscess or bronchoectasis. It behaves more like an intracranial space occupying lesion. Of the various types of meningitis, meningococcal meningitis is the commonest. Transverse myelitis may be caused by viruses or bacteria. The clinical picture resembles that of spinal cord injury. Neoplasms of the brain and spinal cord present a wide and varied spectrum. They may be benign or malignant. Meningioma and neurofibroma are essentially benign lesions. Malignant tumors can be primary or secondary. Gliomas and specifically astrocytomas are the commonest primary malignant tumors. The commonest sites of metastatic tumors are lung, breast, kidney, and gastrointestinal tract. The clinical picture will depend on the location of the tumor and the structures pressed upon or infiltrated. Any age group can be affected. Many of the malignant tumors are slowly and relentlessly progressive. Complete surgical extirpation where possible, followed by radiation therapy, is the treatment of choice. Chemotherapy has not been of much benefit.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1989

Cerebrovascular accidents.

CVA comprises a large number of clinical entities, depending on the site of infarction in the brain. Accurate evaluation of deficits in the patient's sensory and/or motor systems and the patient's intellectual status are paramount in establishing realistic rehabilitation goals. With respect to the motor system, two types of voluntary movement may occur. These include synergistic or pattern movement and selective movement. Spasticity in the affected lower extremity may result in a variety of lower-extremity deformities and contractures. Those most commonly encountered include hip flexion and adduction contracture, inadequate knee flexion and knee flexion contracture, and ankle equinus, varus, and equinovarus. Correct evaluation of deformities may be aided by the use of poly-EMG analysis and evaluation after nerve block or motor point blocks. In hemiplegic gait dysfunction, the basic requirements for functional ambulation include (1) ability to maintain standing balance; (2) voluntary hip flexion; (3) leg stability; and (4) ability to follow instructions and adequate motivation. Often a hemiplegic patient can be trained to ambulate if an adequate extensor synergy pattern develops, since mass extension can provide stability of the leg for weight bearing. Medical rehabilitative management of the CVA patient includes early mobilization, restorative exercises (including neuromuscular facilitation techniques), measures to prevent or correct contractures, the use of AFOs, and occasionally functional electrical stimulation. Orthopedic management of deformities in CVA is indicated where conservative measures fail. Surgical procedures seek to alter the forces causing shortening of the muscles and tendons. Hence, the most commonly performed surgical procedures include (1) tendon lengthening or release; (2) soft-tissue release; and (3) tendon transfer. Surgery for hip contractures is not common; however, occasional release of hip flexors is indicated when hip flexion contracture impedes ambulation or prone lying. Inadequate knee flexion, caused by dysphasic quadriceps contraction, can be corrected by release of the vastus medialis and rectus femoris muscles. Distal hamstring tendon release with or without knee joint capsule release is the surgical procedure of choice for severe knee flexion contractures. Surgical correction of an equinus deformity is by TAL, with or without neurectomy of tibial nerve branches to the gastrocsoleus muscles. Severe ankle varus may require a SPLATT procedure. Surgery for equinovarus includes the combined surgery for both equinus and varus (that is, TAL and SPLATT procedures). Toe curling is corrected by toe flexor releases.(ABSTRACT TRUNCATED AT 400 WORDS)

Cerebrovascular Disorders↗

PubMed1987

Brainstem auditory evoked potentials: intraoperative monitoring technique in surgery of posterior fossa tumors.

Brainstem auditory evoked potentials (BAEPs) were used to monitor eight neurosurgical procedures involving posterior fossa tumors to assist the neurosurgeon in preservation of hearing postoperatively. The technique included placement of recording electrodes over the Cz (vertex) and both earlobes. Stimulation was accomplished intraoperatively with a specifically designed intraauricular click stimulator that did not interfere with surgical access to the suboccipital region. Continuous BAEP recording was performed with particular attention to the sequence of preincision, opening of the dura, tumor mobilization, tumor excision, and closure. Absolute latencies and interpeak latencies of all five waves were recorded when possible. In three patients BAEPs were not significantly altered intraoperatively, and hearing was preserved postoperatively. In another three patients the acoustic nerve was severed during surgery and intraoperative monitoring was discontinued. In the remaining two patients medical complications arose intraoperatively, and significant irreversible changes in BAEP were observed despite no gross anatomical damage to the acoustic nerve. Both of these patients experienced postoperative hearing loss. These two cases illustrated some of the BAEP abnormalities that occurred during surgery. Difficulties during the procedures included electrical noise and interference, use of a bipolar cautery device, and unclear wave forms. Solutions for these difficulties were braiding the electrodes and using extra ground electrodes and a spike suppressor; switching off the evoked potential equipment when the bipolar cautery device was in use; and increasing repetitions and changing click intensity and polarity, respectively. Monitoring BAEPs in posterior fossa surgery can be accomplished with presently available equipment and may aid the neurosurgeon in preserving or minimizing injury to auditory pathways and adjacent structures.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1985

Medial and lateral antebrachial cutaneous nerves: standardization of technique, reliability and age effect on healthy subjects.

Techniques for performing antidromic conduction velocity studies on forearm sensory nerves were evaluated in 157 healthy subjects from 17 to 80 years of age. The lateral antebrachial cutaneous nerve (LABCN) and the medial antebrachial cutaneous nerve (MABCN) were studied in the same upper extremity at a distance of 14 cm. The mean values for LABCN were amplitude 18.9 microV, latency to peak 2.8 ms and conduction velocity (CV) 61.5 m/s; for MABCN, amplitude 11.4 microV, latency to peak 2.7 ms and CV 62.7 m/s; and for median nerve, CV 62.3 m/s. SNAPs were obtained in 98% of subjects for each forearm sensory nerve. Age-related changes in the MABCN and LABCN were small, but included a decreased number of high value SNAP amplitudes and CVs with advancing age, whereas values for the median nerve showed a slight overall decrease with age. Sex effects were negligible. It is concluded that: LABCN and MABCN conduction studies can be performed with equal and high reliability using standard techniques and the same constant distance; The amplitude of the LABCN tends to be larger than that of the MABCN (76% of subjects); In some subjects MABCN studies are technically more difficult to perform than LABCN studies; Forearm sensory nerve studies may be used in addition to median nerve sensory studies in the evaluation of peripheral neuropathy, brachial plexopathy and local neuropathic conditions.

Action Potentials↗