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Biomedical subjects

W A Friedman

Publications and source records attributed to W A Friedman.

At least 109 records · Page 6Linked to original sources
PubMed1987

Thoracic aortic occlusion: somatosensory evoked potential monitoring and neurologic outcome in a canine model.

Somatosensory evoked potentials (SEPs) were monitored in 17 canines during spinal cord ischemia induced by balloon occlusion of the thoracic aorta. Graded distal aortic hypotension to 40 mmHg in seven animals had no significant effect upon the evoked potential. A significant alteration in the SEP did result in 21 +/- 9.8 minutes when distal aortic pressures were reduced in a graded fashion below 30 mmHg. Acute occlusion of the thoracic aorta (10 animals, distal pressure 15-25 mmHg) was associated with a change in the SEP in 8.4 +/- 4.3 minutes. Continuation of aortic occlusion for 30 minutes beyond an evoked potential change resulted in a moderate to severe motor deficit in all cases. Somatosensory evoked potentials obtained 72-96 hours after the ischemic injury were closely correlated with sensory deficits, but were not predictive of motor examination. Histologic examination of the spinal cords demonstrated central gray necrosis of the lumbar region in all animals with a severe deficit, and a variable degree of neuronal loss in the intermediate and dorsal gray matter zones in animals with moderate deficits. This balloon occlusion method is relevant as a model of spinal cord injury during aortic occlusion, such as may occur during aortic surgery.

Acute Disease↗
PubMed1987

Interstitial brachytherapy of malignant brain tumors using computed tomography-guided stereotaxis and available imaging software: technical report.

The implantation of radioactive sources into malignant intraaxial brain tumors, interstitial brachytherapy, is a theoretically attractive treatment for these nearly uniformly fatal lesions. Optimal application of this treatment modality requires careful preoperative planning, computer-assisted dosimetry, and computed tomography-guided stereotactic implantation of the isotope-bearing catheters. A method is presented by which available computed tomographic imaging software can be used with a standard radiotherapy treatment planning computer and the Brown-Roberts-Wells stereotactic system for preoperative imaging, dosimetry planning, and brachytherapy catheter insertion. Dedicated computer facilities are not required, making this method available to any neurosurgeon with access to a current generation computed tomographic scanner.

Brachytherapy↗
PubMed1987

Evoked potential monitoring during aneurysm operation: observations after fifty cases.

Somatosensory or brain stem auditory evoked potentials (EPs) were monitored during 50 aneurysm procedures. Base line EPs were obtained shortly after the induction of general anesthesia and were recorded continuously during operation. Absolute latency, interpeak latency, and cortical EP amplitude were subsequently determined. Statistical analysis confirmed that significant changes in these parameters are routine during aneurysm operation. Arbitrary definitions of abnormal latency and amplitude changes led to an excessive false-positive/false-negative rate. From the time of dural opening to the time of closure, prolongation of central conduction time, decrease in cortical amplitude, or disappearance of the EP was predictive of postoperative sensory or motor deficit in all patients monitored, except those undergoing operation on basilar artery aneurysms. In basilar aneurysm cases, outcome could not be reliably predicted with either EP technique.

Adult↗
PubMed1987

Effects of aortic occlusion on regional spinal cord blood flow and somatosensory evoked potentials in sheep.

Somatosensory evoked potentials (SEPs) were recorded continuously during aortic occlusion in sheep, with simultaneous measurement of spinal cord blood flow (SCBF) by radiolabeled microspheres. Aortic occlusion was associated with disappearance of the SEPs in seven of nine sheep in 7.8 +/- 4.1 (SD) minutes. SCBF at the time of initial cross clamping and 30 minutes after the onset of ischemia revealed a severe reduction in white and gray matter flow in the thoracolumbar cord. Release of the aortic clamp was associated with reactive hyperemia in these ischemic regions. In two animals, the SEP persisted during aortic cross clamping. The total SCBF in the thoracic and lumbar regions of these two animals exceeded 20 ml/100 g/min after 30 minutes of ischemia and was significantly greater than the flow recorded in sheep whose evoked response disappeared. The relation between spinal cord ischemia and evoked potential alterations is discussed in detail.

Afferent Pathways↗
PubMed1987

Somatosensory evoked potentials after sequential extremity stimulation: a new method for improved monitoring accuracy.

A new method for improving the accuracy of somatosensory evoked potential (SEP) monitoring is described. Two extremities are stimulated at 5 Hz, with an interextremity stimulus interval of 100 ms. Information from a "control" extremity, such as an arm during scoliosis operation, may allow more rapid and accurate interpretation of changes in SEPs during intraoperative monitoring.

Computers↗
PubMed1986

Regeneration in peripheral nerve grafts to the cat spinal cord.

Peripheral nervous system grafts have long been known to promote CNS axonal elongation in the rodent. To investigate whether these principles also apply to a higher order animal, more suitable for physiologic studies, we performed autogenous sciatic nerve grafts to the adult cat spinal cord. This report is a brief, initial study of these grafts. In an effort to study both descending and ascending fibers as separately as possible, laminectomies were performed at both thoracic (T2-T9) and lumbar (L2-L4) levels. Aspiration lesions were made in the left side of the cord and the sciatic grafts were introduced. Three cats were studied with standard histological techniques, confirming previous reports of glial scar formation, collagen deposition, and cyst formation at the graft-CNS junction. In 7 other animals, at 146-179 days after the initial operation, the axonal origins were traced retrogradely using horseradish peroxidase and the tetramethyl benzidine technique. Reinnervation of the graft was found by intrinsic spinal cord neurons and dorsal root ganglia neurons. The number of reinnervating neurons was found to be greater than previously reported in the rodent. There was, however, no evidence of regeneration from brainstem nuclei when the grafts were placed at spinal levels where this has been seen in the rat. This may support an absolute maximum for regenerative distances vs a relative one. Although the amount of data was limited, it did support previous reports that peripheral axotomy enhances the regenerative response seen in primary sensory neurons.

Animals↗
PubMed1986

Respiratory-related cortical potentials evoked by inspiratory occlusion in humans.

It has long been recognized that humans can perceive respiratory loads. There have been several studies on the detection and psychophysical quantification of mechanical load perception. This investigation was designed to record cortical sensory neurogenic activity related to inspiratory mechanical loading in humans. Inspiration was periodically occluded in human subjects while the electroencephalographic (EEG) activity in the somatosensory region of the cerebral cortex was recorded. The onset of inspiratory mouth pressure (Pm) was used to initiate signal averaging of the EEG signals. Cortical evoked potentials elicited by inspiratory occlusions were observed when C3 and C alpha were referenced to CZ. This evoked potential was not observed with the control (unoccluded) breaths. There was considerable subject variability in the peak latencies that was related to the differences in the inspiratory drive, as measured by occlusion pressure (P0.1). The results of this study demonstrate that neurogenic activity can be recorded in the somatosensory region of the cortex that is related to inspiratory occlusions. The peak latencies are longer than analogous somatosensory evoked potentials elicited by stimulation of the hand and foot. It is hypothesized that a portion of this latency difference is related to the time required for the subject to generate sufficient inspiratory force to activate the afferents mediating the cortical response.

Adult↗
PubMed1986

Effects of induced hypotension during experimental vasospasm: a neurological, electrophysiological, and pathological analysis.

Vasospasm of the vertebrobasilar system was induced in seven dogs by the intracisternal injection of autologous blood. Somatosensory and brain stem auditory evoked potentials were recorded before and after the induction of angiographically confirmed vasospasm. Additionally, somatosensory evoked potentials were monitored during graded hypotension to 40 mm Hg. There was no significant alteration in the evoked potentials by vasospasm or hypotension. Detailed clinical examination and postmortem histopathological studies did not demonstrate any focal neurological deficit or infarction attributable to vasospasm. Previous studies have noted close correlations between decreased cerebral blood flow and evoked potential alterations. Induced hypotension to a mean arterial pressure of 40 mm Hg in the presence of documented vasospasm was not sufficient to cause evoked potential changes, focal neurological deficit, or pathological evidence of infarction in the canine model.

Animals↗
PubMed1986

Somatosensory evoked potential monitoring of spinal cord ischemia during aortic operations.

Somatosensory evoked potentials were monitored in 22 consecutive patients undergoing surgical correction of an aortic coarctation. Induction of spinal cord ischemia by cross clamping of the aorta elicited a change in the evoked potential in 9 patients (41%). These alterations occurred within 5 minutes of aortic clamping in 3 cases and after 18 to 21 minutes in the remaining 6 cases. Loss of the somatosensory evoked potential for more than 14 minutes was associated with postoperative neurological deficit. Alteration of the evoked potential within 5 minutes of aortic cross clamping was significantly related to poor collateral circulation shown on the preoperative aortogram. The pathophysiology of evoked potential changes in spinal ischemia is discussed in detail.

Adolescent↗
PubMed1985

Somatosensory evoked potentials in hysterical paraplegia.

Somatosensory evoked potentials were determined in three patients with hysterical neurologic deficits after minor trauma. In each case the patient denied any sensation of the stimulus in the affected extremity; however, normal evoked potentials were recorded. Objective evidence of the hysterical nature of the neurologic deficit was, therefore, provided.

Adult↗
PubMed1985

Percutaneous discectomy: an anatomical study.

Percutaneous discectomy is a viable alternative in the treatment of herniated intervertebral discs of the lumbar spine. Anatomical analysis of the retroperitoneal surgical path utilizing computed tomography suggests that the risk of vascular injury is negligible at the L-4, L-5 level, but substantial at the L-5, S-1 level. In addition, one-third of patients otherwise suitable for percutaneous discectomy have segments of bowel obstructing the surgical path. Obtaining an abdominal computed tomographic scan with the patient in the surgical position seems to be a valuable screening technique in the evaluation of candidates for this procedure.

Humans↗
PubMed1985

Intraoperative brain-stem auditory evoked potentials during posterior fossa microvascular decompression.

Recent technological advances have led to increased interest in intraoperative evoked potential monitoring. Although theoretically valuable, its precise role remains to be defined, and useful criteria for predicting neurological deficit are not well established. The authors used brain-stem auditory evoked potential (BAEP) monitoring during 21 posterior fossa microvascular decompression procedures to assess the value of this technique in predicting postoperative deficit. The surgeon was notified only if there was complete disappearance of wave V. Although no patients had postoperative deafness, BAEP latencies changed significantly in all cases. In four patients, wave V totally disappeared during cerebellar retraction. The BAEP appears to be a very sensitive monitor of auditory function, such that "false positive" results will be frequent if latency criteria alone are used to trigger alterations in surgical technique.

Adult↗
PubMed1984

Pitfalls in the computed tomographic diagnosis of toruloma.

A case of multiple intracerebral mass lesions is presented in which significant "improvement" in the computed tomographic appearance was noted following steroid and radiation therapies. Nonetheless, the patient's clinical course was one of rapid deterioration, and an autopsy revealed multiple torulomas. It seems that the computed tomographic appearance of torulomas can mimic those of other intracranial mass lesions and can be greatly altered by steroid and radiation therapies, either singly or in combination.

Brain Diseases↗
PubMed1984

Automatic artifact rejection during intraoperative recording of somatosensory evoked potentials. Technical note.

A device is described that performs automatic artifact rejection for somatosensory evoked response analysis in intraoperative and other electrically noisy environments. Although based on amplitude discrimination, rejection is not triggered by the large stimulus-dependent voltage transients associated with somatosensory evoked potentials. The device readily interfaces with commercially available evoked potential equipment.

Electrophysiology↗