Search PubMed⌕ Search

Biomedical subjects

H Yonas

Publications and source records attributed to H Yonas.

At least 73 records · Page 4Linked to original sources
PubMed1996

Suppression of cerebral metabolic rate for oxygen (CMRO2) by mild hypothermia compared with thiopental.

If the efficacy of hypothermia and barbiturates in ameliorating ischemic brain injury lies in reducing the cerebral metabolic rate of oxygen (CMRO2), the greater efficacy of mild hypothermia (34 degrees C) compared with barbiturates is inconsistent with the 15-20% reduction of CMRO2 caused by mild hypothermia compared with 50% caused by barbiturates. This paradox, we hypothesized, derives from the fact that whereas barbiturates lower CMRO2 associated with EEG activity or thiopental (TP)-suppressible CMRO2, not essential for cellular viability, hypothermia lowers CMRO2 associated with providing energy, i.e., adenosine triphosphate, to maintain transmembrane ion gradients or TP-nonsuppressible CMRO2, essential for neuronal viability. To test this hypothesis, we measured whole brain cerebral blood flow (CBF) and CMRO2 in two groups of rats mechanically ventilated with 70% N2O/30% O2 before and after TP-induced isoelectric EEG. In the normothermic group (n = 7), measurements were made at a brain temperature (Tb) of 38 degrees C, while in the hypothermic group (n = 7), they were made at 34 degrees C. In the normothermic group, TP-induced isoelectric EEG reduced CMRO2 by 50%, from 7.92 +/- 1.05 to 3.95 +/- 0.70 ml 100 g-1 min-1 (mean +/- = SD). Thus, at 38 degrees C, TP-suppressible and TP-nonsuppressible CMRO2 were both 50 +/- 4% of total CMRO2. In the hypothermic group, decreasing Tb from 38 to 34 degrees C caused a 17% decline in CMRO2, from 7.62 +/- 1.92 to 6.28 +/- 1.22 ml 100 g-1 min-1 (p > 0.05). AT 34 degrees C, TP infusion lowered CMRO2 to 2.15 = 0.46 ml 100 g-1 min-1. At 34 degrees C, TP-suppressible and TP-nonsuppressible CMRO2 values were 64 +/- 7% and 36 +/- 8% of total CMRO2, respectively. TP lowered CBF by 50% at both 38 and 34 degrees C. In conclusion, mild hypothermia selectively lowers TP-nonsuppressible CMRO2 associated with the maintenance of viability rather than EEG-associated or TP-suppressible CMRO2.

Anesthetics, Intravenous↗
PubMed1996

Paradoxical aggravation of vasospasm with papaverine infusion following aneurysmal subarachnoid hemorrhage. Case report.

Reports of intraarterial papaverine infusion as treatment for cerebral vasospasm are few and documented complications are uncommon. The authors report the case of a patient with paradoxical aggravation of cerebral arterial narrowing during selective intraarterial papaverine infusion intended to treat vasospasm following aneurysmal subarachnoid hemorrhage (SAH). A 48-year-old man presented to the authors' service with symptomatic vasospasm 10 days after experiencing an SAH. The ruptured anterior communicating artery aneurysm was surgically obliterated the following day, and thereafter maximum hypervolemic and hypertensive therapies were used. However, the patient remained lethargic, and a stable xenon-computerized tomography (CT) cerebral blood flow (CBF) study revealed CBF to be 15 cc/100 g/minute in the left anterior cerebral artery (ACA) and 25 cc/100 g/minute in the right ACA territories. Cerebral arteriography demonstrated diffuse severe left ACA and mild left middle cerebral artery (MCA) vasospasm. In response intraarterial papaverine was infused into the internal carotid artery just proximal to the ophthalmic artery. During the infusion the patient became aphasic and exhibited right hemiplegia. Arteriography performed immediately after the intraarterial papaverine infusion revealed diffuse exacerbation of vasospasm in the distal ACA and MCA territories. A repeat xenon-CT CBF study showed that CBF in the left ACA and the MCA had drastically decreased (2 cc/100 g/minute and 10 cc/100 g/minute, respectively). Despite aggressive management, infarction ultimately developed. This is the first clinical case to illustrate a paradoxical effect of intraarterial papaverine treatment for vasospasm following aneurysmal SAH. The possible mechanisms of this paradoxical response and potential therapeutic reactions are reviewed.

Cerebral Angiography↗
PubMed1996

The Q10 ratio for basal cerebral metabolic rate for oxygen in rats.

Previously the authors showed that hypothermia exerts a greater effect on the cerebral metabolic rate for oxygen (CMRO2) that is associated with the maintenance of cellular viability, or "basal" CMRO2, than on electroencephalogram (EEG)-associated CMRO2 or "functional" CMRO2. On the basis of their findings, the authors hypothesized that the ratio of CMRO2 over a 10 degrees C temperature range (Q10) for basal CMRO2 was greater than that for functional and total CMRO2. They tested their hypothesis by determining the Q10 for basal CMRO2 from 38 degrees C to 28 degrees C. They measured whole-brain cerebral blood flow (CBF) and CMRO2 in six rats during progressive hypothermia at a brain temperature of 38 degrees C and, after induction of an isoelectric EEG signal (50 microV/cm) with thiopental sodium, they repeated the measurements at 38 degrees C, 34 degrees C, 30 degrees C, and 28 degrees C. In a control group (five rats), six sequential measurements of CBF and CMRO2 were made while the animals were anesthetized by 0.5% isoflurane/70% N2O/30% O2 at a brain temperature of 38 degrees C over a time span equivalent to the hypothermic group, that is, approximately 3 hours. The Q10 for basal CMRO2 calculated over 38 degrees C to 28 degrees C was 5.2 +/- 0.92. However, the decrease in basal CMRO2 between 38 degrees C and 28 degrees C was nonlinear on a log plot, revealing a two-component response: a high temperature sensitivity component between 38 degrees C and 30 degrees C with a Q10 of 12.1, and a lower temperature sensitivity component between 30 degrees C and 28 degrees C with a Q10 of 2.8. The combined overall Q10 for basal CMRO2 between 38 degrees and 28 degrees C was 5.2. The energy-requiring processes associated with these high and low temperature sensitivity components of basal CMRO2 have yet to be identified.

Animals↗
PubMed1996

Xenon/computed tomography cerebral blood flow and its use in clinical management.

The main advantages of stable Xe/CT is that it noninvasively provides rapid access to high-resolution, quantitative, local CBF information coupled to CT anatomy. The information obtained is valid even in disease states because a partition coefficient is directly calculated for each voxel as small as 1 x 1 x 5 mm3. CBF studies can be repeated within 20 minutes, allowing the assessment of hemodynamic states. The technology can be incorporated into all existing CT technology at relatively little expense. The disadvantages are the radiation dose from the CT scanner, the pharmacologic effects of xenon gas, and the limitations of survey. The radiation dose is significant but it is focused to the least radiation-sensitive region of the body (scalp, skull, and brain) so that the effective cancer causation risk is lower than any other CBF study that delivers isotope indescriminatly to the body. The pharmacologic properties of xenon are associated with several potential problems. Xenon alters the sensorium of many individuals and may cause patient motion. This can be minimized with careful prestudy positioning and reassurance of the patient during the study. Most patients find the sensation enjoyable; however, occasionally, a patient cannot tolerate the perception of "losing control" and the study has to be stopped. One of the concerns regarding Xe/CT is that at the 80% level, xenon has anesthetic properties. At less than 33% xenon (with the difference being oxygen), the side effects have, in fact, been few and transient, with a mild hyperesthetic and disassociated feeling being the rule. Although xenon-induced apnea was reported as a consequence of xenon inhalation, the report involved the inhalation of 100% xenon, and at the levels recommended for imaging, holding one's breath for more than 20 seconds is rare. The other concern is the degree of flow activation that occurs with xenon inhalation and its effect on the accuracy of the measurements. In part, because of the "robust" nature of the Kety-Schmidt equations and because a significant xenon-induced flow activation is delayed for about 2 minutes, the effect of the flow activation is, in fact, minimal (less than 5% elevation of calculated flow values from true values). Although an earlier study by Obrist36 suggested that the error induced by flow activation was significant, a recent computer simulation study by the same author identified a maximal theoretical error of less than 5%. Previously, Xe/CT studies were limited to three brain levels, but with the new helical CT scanners, nine levels can now be studied. Most of the concerns over the technology have been resolved (Table 1). As a result, more clinicians around the world are beginning to use this technology when they need rapid access to quantitative CBF information about their patients.

Acetazolamide↗
PubMed1995

Comparison of functional magnetic resonance imaging with positron emission tomography and magnetoencephalography to identify the motor cortex in a patient with an arteriovenous malformation.

Alterations in gyral contour made it difficult to identify the motor cortex thought to be near an arteriovenous malformation (AVM) in a 24-year-old man considered for stereotactic radiosurgery. Functional imaging in three modalities was performed preoperatively to compare the reliability of localization using functional magnetic resonance imaging (fMRI) on a conventional scanner with positron emission tomography (PET) and magnetoencephalography (MEG). Similar tasks were used for each imaging modality in an attempt to activate and identify the sensory and motor cortex. Data from all three modalities converged for the sensory task, and fMRI and PET data converged for the motor task. The right hemisphere motor strip was localized adjacent and anterior to the AVM. These data were used in planning the radiosurgery isodose configuration to the AVM in order to reduce the irradiation of motor cortex parenchyma. A postoperative fMRI study was also performed using newer techniques to reduce head motion artifact and to improve signal-to-noise ratio. The data confirmed the conclusions derived from the preoperative evaluations. This study demonstrates how conventional MRI scanners can be used for functional studies of use in surgical planning.

Adult↗
PubMed1995

Evaluation of cerebral blood flow and hemodynamic reserve in symptomatic moyamoya disease using stable Xenon-CT blood flow.

Moyamoya disease is a vascular abnormality seen in children and adults characterized by progressive narrowing of the internal carotid, middle, anterior, and posterior cerebral arteries and the development of leptomeningeal and proximal internal carotid artery collaterals, which appear diaphanous on angiogram. Although adults tend to present with subarachnoid hemorrhage and children with ischemic events, the clinical sequelae in these two populations overlap. Expanding upon work done at this institution using stable xenon computer tomographic blood flow determinations with acetazolamide and carbon dioxide challenge to predict which population of patients with severe carotid disease and hemodynamic compromise would benefit from surgical intervention, we used similar rationale to determine which patients with moyamoya disease would likely benefit from revascularization. Data and outcome concerning four such patients make up the body of this report.

Adult↗
PubMed1995

Compromised cerebral blood flow reactivity is a predictor of stroke in patients with symptomatic carotid artery occlusive disease.

PURPOSE: The purpose of this study was to determine whether the hemodynamic consequences of extracranial carotid disease correlate with the risk of subsequent cerebral infarction. METHODS: In 95 patients with symptoms who had greater than or equal to 70% stenosis (31 patients) or who had occlusion (64 patients) of the ipsilateral carotid artery, cerebral blood flow was measured by the stable xenon/computed tomography technique both at baseline and after vasodilatory challenge with intravenous acetazolamide. Patients were stratified into group 1, 43 patients with no more than a 5% decrease in flow in any vascular territory, and group 2, 52 patients with greater than a 5% decrease in one or more vascular territories after an acetazolamide challenge. RESULTS: In group 2, 15 (28.9%) of 52 patients had a new stroke, but only one (2.3%) of 43 patients in group 1 did (p = 0.0005). Of patients with total carotid occlusion 10 (26%) of 38 in group 2 and none (0%) of 26 in group 1 had a new stroke (p = 0.003). Of patients with greater than or equal to 70% stenosis, five (36%) of 14 in group 2 and only one (6%) of 17 in group 1 had a stroke (p = 0.067). CONCLUSION: The loss of cerebral reactivity in patients with symptoms who had greater than or equal to 70% carotid stenosis or occlusion is an important predictor of impending cerebral infarction.

Acetazolamide↗
PubMed1995

Regional cerebral blood flow and CO2 reactivity in fulminant hepatic failure.

Alterations in cerebral hemodynamics are postulated to contribute to brain herniation, a major cause of death in patients with severe hepatic encephalopathy due to fulminant hepatic failure (FHF). In an effort to identify these changes in cerebral hemodynamics, regional and global cerebral blood flow (CBF) and CO2 reactivity were measured using stable xenon-enhanced computed tomography (Xe/CT) in 24 patients within 72 h of onset of severe hepatic encephalopathy. Regional variations in CBF, most notably, a relative decrease in CBF in the anterior circulation and an increase in CBF in the posterior circulation were found. CBF was significantly lower in FHF patients compared with controls, however, these values are well out of the established ischemic range. FHF patients also showed significant impairment in CBF response to hypoventilation, while the CBF response to hyperventilation remained intact. This study suggests that FHF patients demonstrate early changes in both CBF patterns and CO2 reactivity. The relatively "normal" CBF values obtained in FHF patients in severe hepatic encephalopathy coupled with the lack of vasodilatation to hypoventilation suggest a state of uncoupled CBF and metabolism or "luxury perfusion" that could theoretically contribute to vasogenic edema, brain swelling, and cerebral herniation.

Adult↗
PubMed1995

Intraoperative urokinase infusion for embolic stroke during carotid endarterectomy.

Embolic stroke is an infrequent complication of carotid endarterectomy. Somatosensory evoked potential monitoring detected delayed acute neurological deterioration during endarterectomy performed on a 71-year-old woman. Intraoperative arteriography performed via an indwelling shunt revealed thrombus within the middle cerebral artery and distal branches. A microcatheter was placed into the internal carotid artery via the arteriotomy and advanced into the middle cerebral artery. Urokinase was infused into and around the thrombus until almost complete thrombolysis had been achieved. The patient recovered quickly and was discharged without neurological deficit.

Aged↗
PubMed1995

Temporary balloon test occlusion of the internal carotid artery: experience in 500 cases.

PURPOSE: To describe experience with 500 temporary balloon occlusions of the internal carotid artery, with particular emphasis on the techniques and complications. METHODS: Temporary occlusion of the internal carotid artery was accomplished endovascularly using various balloon-catheter combinations. These temporary balloon occlusions were combined, when possible, with cerebral blood flow analysis with stable xenon-enhanced CT. RESULTS: Complications related to this procedure occurred in 16 (3.2%) patients. Eight (1.6%) patients had asymptomatic complications. There were 8 who experienced neurologic changes. Six (1.2%) of these were transient; two (0.4%) were permanent. There were no deaths. CONCLUSIONS: Temporary balloon occlusion of the internal carotid artery, believed helpful in identifying patients at risk of stroke during abrupt carotid artery sacrifice, can be performed with an acceptably low complication rate.

Aortic Dissection↗
PubMed1994

Management of a giant middle cerebral artery fusiform serpentine aneurysm with distal clip application and retrograde thrombosis: case report and review of the literature.

Giant fusiform aneurysms are rare vascular anomalies that due to their size are often difficult to manage. We describe one such aneurysm that was managed with a superficial temporal to middle cerebral artery bypass followed by the application of a single clip just distal to the vascular dilation. Follow-up angiography has shown aneurysm obliteration by the process of retrograde thrombosis.

Adult↗
PubMed1994

The effect of arm exercise on regional cerebral blood flow in the subclavian steal syndrome.

Reversed vertebral blood flow distal to a subclavian obstruction is not uncommon and rarely leads to stroke. A small subgroup of these patients have obstruction in other portions of the extracranial or intracranial circulation, however, and cerebrovascular symptoms are induced by arm exercise, which may decrease regional cerebral blood flow--at times to critical levels--indicating a true "steal" syndrome. We evaluated six patients with symptomatic subclavian steal syndrome using stable xenon with computed tomography cerebral blood flow mapping. A decrease in flow from 13% to 90% in one or more regional vascular territories was found after arm exercise. Patients with a true "steal" syndrome may be at higher risk for stroke. Measuring regional cerebral blood flow may be a means of detecting patients who have a critical loss of flow reserves and who will be symptomatically improved by cerebral revascularization.

Acetazolamide↗
PubMed1994

Compartmentation of whole brain blood flow and oxygen and glucose metabolism in monkeys.

The cerebral metabolic rate of oxygen (CMRO2) has been functionally compartmentalized using the barbiturate thiopental into active CMRO2, associated with electroencephalographic (EEG) activity, and the balance, basal CMRO2, associated with the maintenance of neuronal viability. Previous measurements of these CMRO2 compartments were made in anesthetized animals. Our aim was to determine whether the same proportions for these compartments applied in unanesthetized monkeys. The active: basal distribution of the cerebral metabolic rate of glucose (CMRG) and cerebral flood flow (CBF) were also determined. Three measurements of whole-brain CBF (H2 clearance), CMRO2, and CMRG were made in six unanesthetized rhesus monkeys (Macaca mulatta). Thereafter, thiopental anesthesia was induced and maintained until an isoelectric EEG was obtained. Three additional measurements of CBF, CMRO2, and CMRG were made. Arterial blood pressure, end-tidal CO2, and arterial blood gas were measured with each set of measurements. Thiopental-induced isoelectric EEG resulted in a 47% reduction in CMRO2 from 5.95 +/- 0.54 to 3.10 +/- 0.51 ml/100 g/min (mean +/- SD); a 36% reduction in CBF from 76 +/- 21 to 48 +/- 14 ml/100 g/min; and a 61% reduction in CMRG from 8.09 +/- 2.78 to 3.13 +/- 0.77 mg/100 g/min. The oxygen-glucose index was 0.99 +/- 0.10 for the whole brain, 0.87 +/- 0.15 for the active, and 1.27 +/- 0.25 for the basal compartments. These results indicated an active:basal distribution of approximately 50:50 for CMRO2, 40:60 for CBF, and 60:40 for CMRG. The active:basal CMRO2 distribution corroborates earlier data and shows that relative to CMRO2, the active compartment is underperfused with a lower oxygen-glucose index compared with the basal compartment.

Anesthesia↗