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Biomedical subjects

M F Levin

Publications and source records attributed to M F Levin.

11 recordsLinked to original sources
PubMed1992

Reciprocal and coactivation commands for fast wrist movements.

According to the equilibrium-point hypothesis, movements are produced by means of displacement of the invariant torque/angle characteristic (IC) of the joint and change in its slope. Displacement is produced via the central reciprocal (R) command while the coactivation (C) command specifies the slope of the IC. Neurophysiologically, the R command is associated with reciprocal changes in the membrane potentials of agonist and antagonist motoneurons while the C command is associated with their simultaneous depolarisation. These commands were investigated in single joint wrist movements by perturbation methods. Subjects normally made free flexion movements to a target at 30 degrees but on random trials they were either opposed by a spring-like load or assisted by a load. The former was generated using negative linear position feedback; the latter using positive position feedback to a torque motor. Subjects were instructed not to correct errors arising from perturbations. Both peak velocity and EMG patterns were strongly affected by load conditions. Subjects undershot or overshot the target when opposing or assisting loads were presented, respectively. However, after removing the load (700 ms later), the target position was regained indicating that the IC was stable despite the perturbation. In two other experiments, subjects initially trained to reach the target with opposing or assisting loads, while on random trials, the load was not presented. Depending on training conditions, the subject shifted the IC by different amounts. The slope of the IC varied independently of the magnitude of its positional shift. We conclude that R and C commands can be specified independently.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Relief of hemiparetic spasticity by TENS is associated with improvement in reflex and voluntary motor functions.

Our previous studies showed that a single 45 min application of transcutaneous electrical nerve stimulation (TENS) prolonged soleus H and stretch reflex latencies in hemiparetic subjects. In addition, 9 daily 30 min TENS applications enhanced vibratory inhibition of the H reflex and tended to decrease hyperactive stretch reflexes. These findings suggested that longer-term TENS may be effective in reducing hemiparetic spasticity. Our present objectives were 2-fold: to determine whether longer-term repetitive TENS stimulation would lead to a reduction in clinical spasticity in hemiparetic subjects, and whether such a reduction could be associated with a decrease in stretch reflex excitability and an improvement in voluntary motor function. We compared the effects of 15 daily 60 min TENS treatments over a 3 week period, with those of placebo stimulation applied to the common peroneal nerve of the affected leg in similar groups of spastic hemiparetic subjects. Our test battery consisted of 5 measurements which assessed (1) clinical spasticity scores, (2) maximal H reflex to M response ratios, (3) vibratory inhibition of H reflex, (4) stretch reflexes, and (5) maximal voluntary isometric plantarflexion and dorsiflexion, in standing. In contrast to placebo stimulation which produced no significant effects, repeated applications of TENS over time decreased clinical spasticity (P less than 0.05), and increased vibratory inhibition of the soleus H reflex (P = 0.02) after 2 weeks. These changes occurred with a substantial improvement in voluntary dorsiflexing force up to 820%, but not plantarflexing force. They were followed by a reduction in the magnitude of stretch reflexes (P = 0.05) in the spastic ankle plantarflexor, concomitant with a decrease in the EMG co-contraction ratios after a further week of stimulation. Our results thus indicated that repeated applications of TENS can reduce clinical spasticity and improve control of reflex and motor functions in hemiparetic subjects. Furthermore, the underlying mechanisms may be due partly to an enhancement in presynaptic inhibition of the spastic plantarflexor, and partly to a possible "disinhibition" of descending voluntary commands to the paretic dorsiflexor motoneurons.

Aged↗
PubMed1992

CT findings in patients with small-bowel transplants.

Orthotopic small-bowel transplantation procedures are being performed increasingly often worldwide. CT plays an important role in both the preoperative assessment and the postoperative care of these patients. This pictorial essay serves to acquaint radiologists with the CT findings related to small-bowel transplantation.

Abscess↗
PubMed1992

Ultrasonographic findings in the anterior segment of the eye obtained with a nondedicated unit.

Many abnormalities of the anterior segment of the eye can be detected by ultrasonography (US), and associated anomalies of the posterior segment that are difficult to detect clinically may also be demonstrated by this modality. A total of 48 patients with ultrasonographically detectable abnormalities in the anterior segment were examined with real-time high-resolution US; 51 abnormalities were demonstrated. The most common problems were cataract (19 cases), intraocular lens implant (10), dislocated lens (9) and tumour (8). In addition, 23 abnormalities of the posterior segment of the eye were found. Six of the lesions in the posterior segment were obscured by those in the anterior segment and could be detected only by US.

Adult↗
PubMed1992

Tuberculosis of the odontoid bone: a rare but treatable cause of quadriplegia.

Radiologic investigation plays an important role in the diagnosis and management of tuberculosis of the odontoid bone. Immediate confirmation of the condition by examination of tissue and surgery may save lives and reduce the morbidity rate substantially. When the clinical history is appropriate, a diagnosis of tuberculosis is strongly suggested by plain films of the cervical spine showing precervical swelling of the soft tissues, narrowing of the disk spaces and focal erosion of the bones and by computed tomography scans demonstrating details of the soft-tissue abnormality, focal bony erosion and sclerosis.

Adult↗
PubMed1992

Colour-flow Doppler imaging of a carotid-cavernous fistula.

The authors describe a case of carotid-cavernous fistula evaluated with both conventional carotid angiography and colour-flow Doppler ultrasonography. The findings in the colour-flow Doppler images correlated well with those from angiography; in addition, Doppler imaging supplied extra information about the direction and the velocity of flow. After embolization, colour-flow Doppler imaging demonstrated a marked decrease in the flow. The authors conclude that colour-flow Doppler imaging may be useful for noninvasively detecting and evaluating a carotid-cavernous fistula, as well as for monitoring the patient's progress after therapy.

Aged↗
PubMed1992

Peripancreatic fluid collections: vascular structures masquerading as pseudocysts.

Five patients with splanchnic arterial aneurysms and one patient with a tortuous splenic vessel presented with peripancreatic masses that exhibited an anechoic portion in real-time ultrasonography (US) images; the masses were incorrectly diagnosed as pseudocysts. In two patients a vascular abnormality was suspected, and colour-flow Doppler and pulsed Doppler US were performed; these techniques showed the presence of pseudoaneurysms. In the other four patients the possibility of a pseudoaneurysm was not entertained until further studies had been performed. These results emphasize the need for colour-duplex US evaluation of all peripancreatic fluid collections during the initial US examination to avoid the misinterpretation of an aneurysm or a pseudoaneurysm as a simple or complex fluid collection and to prevent the potential disaster of performing biopsy, surgery or other interventions.

Adult↗
PubMed1992

Current status of magnetic resonance imaging of the ankle and the hindfoot.

With the increasing use of magnetic resonance imaging (MRI) for examining the musculoskeletal system, numerous applications have been found in the evaluation of ankle and hindfoot problems. For example, MRI is ideal for assessing tendon disorders, which are common in this region. In addition, the technique allows accurate staging of osteochondral fractures, as well as both soft-tissue and bony neoplasms. Tarsal coalition can be readily evaluated and the type determined. Increasingly, arthritis and synovial abnormalities are coming under scrutiny with MRI; this is currently an area of avid interest. In this article the authors review the current status of MRI of the ankle and the hindfoot and illustrate a variety of these disorders.

Ankle Joint↗
PubMed1992

Current status of magnetic resonance imaging of the wrist.

Conventional imaging of the wrist has relied heavily on plain radiography, tomography, fluoroscopy and arthrography. More recently, computed tomography and magnetic resonance imaging (MRI) have been added to this armamentarium. In this article the authors review the normal anatomy of the wrist and demonstrate a variety of pathologic conditions that can be assessed with MRI, including avascular necrosis and tears of the intrinsic and the extrinsic ligaments and the triangular fibrocartilage. MRI of the wrist is still evolving rapidly, and its place in the work-up of wrist disorders is only now being defined.

Bone Diseases↗