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Biomedical subjects

J F Cusick

Publications and source records attributed to J F Cusick.

At least 73 records · Page 4Linked to original sources
PubMed1978

Early somatosensory evoked potentials.

The early somatosensory evoked potential secondary to median nerve stimulation in the human had an onset latency of 9--12 msec when recorded from scalp electrodes at vertex-to-mastoid, vertex-to-inion or at the base of the skull. Similar latencies were observed from responses recorded over the cervical dorsal columns during neurologic surgery. A latency difference of 1.5 msec was observed between the early response and the responses recorded from the junction of medial lemniscus and nucleus ventralis posterior lateralis of the thalamus during human stereotaxic surgery. Cervical cord transections and transection at the midpontine levels of the monkey showed that the evoked potential was due to generators between these levels. Depth recording of the monkey indicate that the early evoked potential originates in the region of dorsal column nuclei, while the later components are secondary to generators in cerebral cortex.

Animals↗
PubMed1978

A myelographic technique for cysts in the spinal canal and spinal cord.

A collapsing cord in six patients with hydromyelia and a collapsing intraspinal arachnoid cyst in one patient are demonstrated. The authors describe the technique for two-position gas myelography and demonstrate that both intra- and extra-medullary intraspinal processes may collapse during myelography.

Adolescent↗
PubMed1978

Spinal evoked potentials in the primate: neural substrate.

Summated responses evoked by peripheral nerve stimulation were recorded from electrodes located in the epidural and subdural spaces anterior and posterior to the monkey spinal cord. Segmental microsurgical resection of the dorsal columns both at the thoracic and cervical levels resulted in total obliteration of the response recorded rostral to these lesions. Isolated segmental dorsal column preservation did not significantly alter response latency or wave form recorded at the rostral electrodes. Bilateral cervical dorsolateral column resection also resulted in no discernible alterations of these responses. These data indicate that spinal evoked potentials recorded from levels rostral to their root entry zones arise almost exclusively from the dorsal columns.

Animals↗
PubMed1977

Ventral root mapping of cardiac nerves in the canine using evoked potentials.

The sympathetic efferent contribution of left ventral roots T2, T3, and T4 to some cardiac nerves was studied using evoked potentials in mongrel dogs anesthetized with sodium pentobarbital. Electrical stimulation of the ventral roots while recording evoked potentials from the sympathetic chain, anterior ansa subclavia, posterior ansa, ventrolateral cervical cardiac nerve, ventromedial cervical cardiac nerve, and the vagosympathetic trunk demonstrated that A-, B-, and C-type fibers exist in these efferent neural pathways. The range of conduction velocities observed was 0.7-104 m/s. T2 contributed the largest number of A-type fibers, and T2 and T3 contributed C-type fibers equally, while T4 had the least number of fibers coursing through the cardiac nerves.

Animals↗
PubMed1977

Mechanical and physiological effects of dentatotomy.

The role of the dentate ligaments in the pathogenesis of myelopathy secondary to disease conditions that alter the normal biomechanics of the spinal canal was studied in 14 dogs. The effects of posterior cord elevation on somatosensory evoked potentials (SSEP's) and tension requirements were compared before and after dentate ligaments section in acute experiments. At levels of posterior elevation usually within the confines of the canine canal, the dentate ligaments were the most significant element increasing tension requirements and SSEP alternations. Human cadaver studies also showed an approximate 50% reduction of force after dentatotomy. These findings suggests that after dentate ligaments section the applied tension is distributed over a longer segments of the cord with a reduction in tension and disruption of axonal conduction at the level at which the force was applied.

Animals↗
PubMed1976

The effect of T-myelotomy on spasticity.

Dorsal myelotomy with lateral extension (T-myelotomy) provided excellent relief from spasticity in the lower limbs in 12 patients. Averaged evoked potential recordings helped delineate the limits of the myelotomy and were useful for evaluation of injury to the dorsal columns. While preservation of any residual motor function is unlikely following T-myelotomy, the risk of permanent loss of preserved sensory, bladder or sexual functions is not great.

Adult↗
PubMed1975

A comparison between anterior and posterior spinal implant systems.

In four patients with intractable pain from metastatic cancer, application of current through electrodes placed on the anterior surface of the cord produced analgesia and pain relief below the level of implant without the development of paresthesias. Application of current through electrodes placed on the dorsal columns in these patients also relieved pain, but to a lesser degree and with the development of associated paresthesias. In one patient, application of current from anterior electrodes to posterior electrodes produced a zone of dissociated sensory loss. While it is simpler to implant electrodes over the dorsal columns, the anterior location may be superior when currents are to be applied for the pain relief in the lower lumbar and sacral dermatomes.

Animals↗
PubMedDate not supplied

Evoked potentials in experimental myelopathy.

Evoked potentials recorded from the cerebral cortex and spinal cord secondary to peripheral stimulation are reversibly reduced in amplitude by both pathologic distraction and pathologic flexion of the vertebral column. While the cerebral responses are lost within two minutes after complete occlusion of the ascending aorta, the responses recorded from the spinal cord persist without change for approximately ten minutes and then gradually disappear. During the first few minutes after aortic occlusion, changes produced by spinal distraction and spinal flexion are indistinguishable from those produced when the same maneuvers are made with the aorta patent. The responses mediated by dorsal columns and corticospinal tracts are affected in the same way by flexion and distraction, suggesting that somatosensory evoked potential recordings should be a reliable means of detecting spinal cord dysfunction during surgical procedures affecting the spinal cord. It may also be possible to differentiate a mechanical from a vascular insult by the time required for the evoked potential to become abnormal following a particular surgical maneuver.

Animals↗
PubMedDate not supplied

Evaluation of electrode configurations in cerebellar implants.

Capacitively coupled currents of 100 Hz, 0.25 msec duration, were applied to multielectrode arrays implanted upon the superior and posterior surfaces of the chimpanzee cerebellum. The current required for 90% reduction in the amplitude of the evoked potential was inversely proportional to the number of electrodes upon the cerebellar surface. A study of various waveforms showed that z Hz, 0.25 msec pulse duration is near optimal for reduction of amplitude of the somatosensory evoked potential. The current densities per electrode were 5--11 mA/cm2 with a charge per pulse of 0.04--0.08 muC in humans with 15--20 electrodes on each superior surface and 10 electrodes on each posterior cerebellar surface.

Animals↗