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Biomedical subjects

R R Smith

Publications and source records attributed to R R Smith.

At least 73 records · Page 4Linked to original sources
PubMed1992

Carbon dioxide reactivity in the evaluation of cerebral ischemia.

Carbon dioxide reactivity, as measured by transcranial Doppler, has been determined in a group of patients with carotid artery disease and compared to a control group. CO2 reactivity was readily evaluated using transcranial Doppler by having the patients breathe 5% CO2 via a rebreathing circuit. There were significant differences (P less than 0.01) between the symptomatic patients and asymptomatic controls, as well as between symptomatic and asymptomatic hemispheres (P less than 0.05) in the patients with carotid artery disease. Five patients had revascularization procedures with all showing improved CO2 reactivity in the symptomatic and asymptomatic hemispheres. The improvement occurred early in patients after carotid endarterectomy. Two patients demonstrated improved reactivity at 6 to 13 months after extracranial-to-intracranial bypass. Transcranial Doppler has proven to be an easily performed and repeatable method of evaluating CO2 reactivity and its response to treatment.

Administration, Inhalation↗
PubMed1992

Lateral cervical spine dislocation and vertebral artery injury.

Although anterior and posterior traumatic displacement of cervical vertebrae are commonly noted, and the devastating neurological deficits associated with these injuries have been amply defined, lateral displacement with fractures has been rarely recognized, and the clinical significance of this injury has been overlooked. This report describes five cases of cervical spine fractures with lateral dislocation. All patients had lateral and anteroposterior cervical spine radiographs as well as cervical angiography or postmortem study demonstrating either complete occlusion or significant impairment of flow of the vertebral arteries. Two cases had traumatic vertebral artery occlusion with secondary medullary and cerebellar infarction resulting in the patient's death. Vertebral artery injury apparently is not uncommon in this particular type of fracture. The diagnosis of these vascular injuries may require angiography or magnetic resonance angiography. A vertebral occlusion or dissection is a problem of considerable complexity, requiring individualized management depending on the patient's symptomatology, location and nature of the injury, and time lapsed since the injury.

Adult↗
PubMed1992

Leuko-araiosis: description and clinical correlates.

The term leuko-araiosis as predicted by Hachinski may now have outlived its usefulness. Careful delineation of the white matter changes seen in MR imaging by use of the MR characteristics and by the location of the lesions may reduce the apparent heterogeneity of the associate clinical and neuropathological findings. As currently defined, leuko-araiosis is seen in aggregate more commonly in subjects with cerebro-vascular disease or with cerebro-vascular risk factors but it is a common finding associated with aging in otherwise normal, healthy elderly subjects. Its clinical significance as an isolated finding in these populations should therefore be treated cautiously. Its appearance should alert the physician however to seek for and treat potential cerebro-vascular risk factors.

Alzheimer Disease↗
PubMed1991

Direct surgery of the cavernous sinus: patient selection.

The cavernous sinus is involved either in lesions arising primarily in the sinus or in lesions invading the sinus from surrounding structures. Experience with direct surgery of the cavernous sinus is encouraging, but no conclusive evidence exists concerning the roles of conservative, surgical, and radiological treatments in terms of effectiveness, morbidity, and long-term results. Consequently, management is individualized according to the patient and the lesions. We discuss these factors in patient selection for cavernous sinus surgery.

Brain Neoplasms↗
PubMed1991

The petrosal approach: indications, technique, and results.

Surgical access to the clivus and petrous apex remains a formidable challenge. Intradural tumours at the clivus and petroclival area are superbly exposed via the petrosal approach described here. To date, we have operated on 33 patients having benign tumours using this approach. Total removal was achieved in all patients except 3 with meningiomas. There was no mortality, morbidity included 1 patient with hemiparesis and several with cranial nerve deficits.

Brain Neoplasms↗
PubMed1991

Adventitial red blood cells produce intimal platelet accumulation in cerebral arteries of cats following subarachnoid hemorrhage.

After dividing 21 cats into three equal groups, we exposed their right middle cerebral arteries transorbitally and adventitially irrigated them with 2 ml washed red blood cells, blood plasma, or saline. To determine arterial intimal platelet accumulation in each cat, we injected [111In]oxine-labeled platelets intravenously immediately before injecting the various experimental solutions. Animals were sacrificed 2 or 4 hours following the injection of labeled platelets. Irrigation with washed red blood cells produced a significantly greater intraluminal accumulation of platelets than irrigation with saline (p less than 0.05). Plasma tended to have less of an effect on platelet accumulation than washed red blood cells, but this difference was not significant. These data suggest that the adventitial blood fraction responsible for intimal platelet accumulation in cerebral arteries following subarachnoid hemorrhage may be derived mainly from the red blood cell fraction.

Animals↗
PubMed1991

Effect of tissue plasminogen activator on intimal platelet accumulation in cerebral arteries after subarachnoid hemorrhage in cats.

Recombinant tissue plasminogen activator may be effective in preventing cerebral vasospasm after subarachnoid hemorrhage by resolving subarachnoid clots. We previously demonstrated that blood placed on the adventitial surface of cerebral arteries enhances intimal platelet accumulation, positively correlating with endothelial damage and other pathologic changes in vessel walls. In this study, we investigated the ability of a single bolus injection of tissue plasminogen activator to prevent platelet accumulation in cerebral vessels after subarachnoid hemorrhage. Subarachnoid hemorrhage was produced in cats by the transorbital intracisternal injection of 2.5 ml autologous arterial blood around the proximal part of the right middle cerebral artery. In 10 animals, 25 micrograms tissue plasminogen activator was injected at intervals of 10 (five cats) and 60 minutes (five cats) after subarachnoid hemorrhage. Intracisternal physiological saline (0.5 ml) was injected in six cats 10 minutes after subarachnoid hemorrhage. Platelets labeled with indium-111 were injected intravenously just before subarachnoid hemorrhage, and their radioactivity was measured in cerebral arteries at death. The results indicated that, after subarachnoid hemorrhage, early injection of tissue plasminogen activator inhibited intimal platelet accumulation, but later injection did not, although the extent of subarachnoid clot was reduced at both plasminogen injection times.

Animals↗
PubMed1990

Pediatric brainstem glioma. Post-radiation clinical and MR follow-up.

Thirty-four pediatric patients, twenty with presumed and fourteen with biopsy or autopsy proven brainstem gliomas were imaged by CT and MR before radiation therapy. Twenty-eight patients received radiotherapy. Of these, eighteen fit the protocol for combined clinical and MR post-treatment evaluation. No cases of radionecrosis were seen at autopsy. This study shows that MR can demonstrate tumor response to radiation therapy, tumor progression prior to clinical deterioration, post-treatment cyst formation and hemorrhage. Although MR clinical correlation was not optimal on six week post-treatment evaluation, 4-10 month post-treatment MR scanning correlated well with clinical evaluation. MR appears useful in post-therapeutic monitoring of tumor response.

Adolescent↗
PubMed1990

Brain stem tumors.

The most common brain stem tumor in both the adult and pediatric population is the brain stem glioma. MR has significant advantages over CT in detecting the presence of the tumor as well as evaluating its extent. Diagnosis must be as precise as possible, since therapy is generally administered without biopsy material available for pathologic examination. Defining the extent of the tumor is mandatory so that appropriate radiation therapy margins are available and geometric misses do not occur. Unenhanced CT may yield some prognostic information regarding patients who have brain stem gliomas. Further work must be done to determine if any MR correlates, such as calculated T1- or T2-relaxation times, can provide similar information. Also, work relating to any prognostic information provided by the appearance of gadolinium enhancement should be undertaken. With MR, the ability to differentiate brain stem glioma from other posterior fossa tumors and from benign lesions that often do not require therapy now exists.

Adult↗
PubMed1990

Cerebrospinal fluid factors following subarachnoid haemorrhage accelerate collagen lattice contraction by fibroblasts.

Proliferation in the intimal layer and medial necrosis are the most consistent findings in the cerebral artery following subarachnoid haemorrhage (SAH) in man. Recently, SEM studies from our laboratory have also shown marked endothelial injury as demonstrated by a profuse platelet carpet. Myofibroblasts proliferate in response to the platelet derived growth factor (PDGF), and abundant collagen is present in the vessel wall. We have employed experiments using fibroblast-populated collagen lattices to study cerebrospinal fluid (CSF) from patients with recent SAH. Isolated rat tail collagen and cultured human dermal fibroblasts are mixed together, placed in 35 mm Petri dishes, and allowed to gel. CSF samples are placed on the surface of the collagen lattice, using 0.2 ml saline for control. The collagen lattices are then incubated and daily measurements recorded. We found that CSF samples from patients with recently ruptured aneurysms significantly accelerate contraction of the collagen lattice. The factor in CSF is heat stable and has a molecular weight of less than 6000.

Cells, Cultured↗
PubMed1990

Efficacy of tissue plasminogen activator in the lysis of thrombosis of the cerebral venous sinus.

Therapy for thrombo-occlusive disease of the cerebral venous sinuses remains controversial. Although several thrombolytic agents, such as urokinase and anticoagulants, are recommended for treatment, major significant risks include cerebral hemorrhage, especially in patients with venous infarction. Tissue plasminogen activator (tPA) has shown a high affinity for fibrin-bound plasminogen, while exhibiting a low affinity for circulating plasminogen. The purpose of this study was to evaluate this drug for use in cerebral sinus thrombo-occlusive disease. Eleven adult male rabbits were chosen as experimental animals. All animals underwent microsurgical dissection of their major dural venous sinuses. Direct compression was used to form a thrombus within the sinus. The presence of significant venous thrombosis was confirmed radiographically by iohexol sinography. Subsequently, tPA was delivered systemically via the marginal ear vein at a dose of 3000 units/h; the result was total lysis of the clot documented by a sinogram 1 hour after the drug was administered. Postmortem pathological examination confirmed total lysis in seven of eight animals. One animal showed partial retained clot fragments. No significant coagulopathic state was observed. In three control animals, saline was infused without clot lysis. We conclude that tPA is a highly effective agent for the lysis of acute induced venous sinus thrombosis in an experimental model.

Animals↗
PubMed1990

Spinal cord thromboplastin-induced coagulopathy in a rabbit model.

Coagulopathy results from many diverse events, including several neurogenic causes. Using a rabbit model, we produced coagulopathy by injecting autologous spinal cord and extracted thromboplastin intravenously. Serial coagulation panels were performed to evaluate the activation of the thrombotic and fibrinolytic pathways. Group 1 animals (n = 4) received intravenous injections of homogenized spinal cord tissue. Coagulopathy was not produced with 36 mg of homogenized spinal cord tissue, but 50 mg or more resulted in death. Group 2 animals (n = 12) received intravenous injections of extracted rabbit cord thromboplastin, which contained approximately 60% activity of a commercially purified rabbit brain thromboplastin. Five animals receiving 2.5 to 5.5 mg of thromboplastin per kilogram of body weight survived with evidence of coagulopathy. Seven animals receiving 2.5 to 100 mg of thromboplastin per kilogram of body weight died. Group 3 (4 control animals) received normal saline injections without changes in clinical or laboratory status. The thrombotic pathway was activated in all animals as evidenced by decreased platelet counts and fibrinogen levels. Activation of the fibrinolytic system was demonstrated by increased concentrations of protamine sulfate and abnormal euglobulin clot lysis times. The most sensitive parameters were the platelet count, protamine sulfate concentration, and white cell count (margination), which became abnormal within 15 minutes after the injections and returned to normal within 1 hour.

Animals↗
PubMed1990

Shunt for bypass graft of the cavernous carotid artery: an anatomical and technical study.

During direct surgery of neoplastic and vascular lesions of the cavernous sinus, the intracavernous carotid artery may be injured beyond repair, or its total isolation may be necessary for surgical management of these lesions. The newly developed procedure of a saphenous vein graft bypass of the cavernous carotid artery allows re-establishment of carotid circulation. Patients with poor collateral circulation are at high risk for ischemic complications induced by the prolonged temporary occlusion required to perform the bypass graft. Optimal management of these patients is to perform the venous bypass graft for permanent vascularization while maintaining carotid cerebral circulation through an intraoperative shunt. We studied this procedure in cadavers, and three shunt types were evaluated: the external intrapetrous-supraclinoid shunt (Type A), the internal intrapetrous-supraclinoid shunt (Type B), and the neck internal carotid-supraclinoid shunt (Type C). Anatomical landmarks, techniques, distances, caliber, and materials used are presented. The rationale and candidates for such a procedure are discussed. The specifications of an optimal balloon shunt are presented, and the three procedures are compared.

Anastomosis, Surgical↗
PubMed1990

Accelerated non-muscle contraction after subarachnoid hemorrhage: cerebrospinal fluid testing in a culture model.

The cause of chronic cerebral vasospasm after subarachnoid hemorrhage has been studied intensively, but it is still controversial whether the observable luminal narrowing should be attributed to the contraction of vascular smooth muscle cells or whether it results from some organic change in the wall. A proliferation of myointimal cells, accompanied by increased deposition of collagen, as well as myonecrosis, have been frequently observed several days after aneurysm rupture. Studies from our laboratory showed that these myointimal cells had characteristics identical to myofibroblasts. In this study, we quantitatively and morphologically examined the effect of cerebrospinal fluid on the ability of myofibroblasts to alter collagen matrices using an in vitro model. Myofibroblasts contract the collagen matrix by rearranging or compacting the framework of collagen fibers. Cerebrospinal fluid obtained from patients with recently ruptured aneurysms significantly accelerated lattice contraction, especially when the patient developed symptomatic vasospasm. This study suggests that myofibroblasts in the spastic artery can produce a contractile force that contributes to chronic vasospasm, tightening the proliferated collagen. Some unknown agent present in bloody cerebrospinal fluid accelerates the rearrangement of the collagen lattice by myofibroblasts, both of which have, until now, been considered non-contractile components.

Adult↗
PubMed1990

Neuroimaging of disseminated germ cell neoplasms.

The purpose of this study was to determine the role of neuroimaging in the management of patients with metastatic germ cell tumors. Retrospective evaluation of 299 patients treated in 1986 and 1987 for initial presentation or recurrence of testicular, retroperitoneal, and mediastinal germ cell tumors was performed to determine indications for neuroimaging, frequency and site of CNS metastases, and occurrence of other CNS abnormalities. Sixty-six patients required CNS imaging with myelography, CT, or MR. Studies were normal in 24 patients. Twenty patients had CNS metastases including 11 with intracranial metastases, eight with spine lesions, and one with both brain and spine involvement. Sixteen had cerebral or cerebellar atrophy of unclear origin and functional significance. Two patients had ventriculomegaly without symptoms of hydrocephalus. Four patients had questionable lesions that were never confirmed. None of the 25 asymptomatic patients with elevated serum tumor markers had brain metastases. Fifteen of 17 patients with focal neurologic deficits and three of six patients with seizures had CNS metastases. CNS imaging to detect germ cell tumor metastases is most useful in the presence of neurologic deficits or seizures but is not useful in patients with unexplained elevation of serum tumor markers in the absence of neurologic deficits.

Adolescent↗