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Biomedical subjects

H Yonas

Publications and source records attributed to H Yonas.

At least 55 records · Page 3Linked to original sources
PubMed1998

Correlation of transcranial Doppler sonography mean flow velocity with cerebral blood flow in patients with intracranial pathology.

Several studies suggest that relative changes in cerebral blood flow (CBF) may be assessed via transcranial Doppler sonography (TCD). The present study investigates the correlation between changes in TCD-mean flow velocity (Vm) and changes in CBF in patients with a variety of types of intracranial pathology undergoing cerebrovascular reactivity tests. After informed consent was obtained, 32 patients presenting with stenoses of brain-supplying arteries (n = 13), cerebral vascular malformations (n = 6), surgical decompression for subarachnoid hemorrhage (n = 2), brain edema after closed head injury (n = 8), or hepatic encephalopathy (n = 3) were studied. The patients were divided into two groups for different reactivity tests. Patients in group 1 (awake or sedated, n = 18) received a 1-g dose of acetazolamide intravenously. In group 2 (n = 14), mechanical ventilation was adjusted to produce a 20% decrease in arterial CO2 tension compared with baseline. Regional CBF was measured using xenon-enhanced computed tomography (Xe-CT). Xe-CT scans at the levels of the basal ganglia and the lateral ventricles were performed during a 4.5-min xenon wash-in period. Bilateral flow velocity was measured in the middle cerebral artery using a 2-MHz pulsed TCD system. Mean arterial blood pressure, heart rate, and end-tidal CO2 were continuously recorded during the procedure. After baseline measurements and either alteration of CO2 or application of acetazolamide, the cerebrovascular reactivity was assessed at 20 min by a second measurement of CBF, TCD, and all other physiologic variables. The correlation coefficient for relative changes of MCA territory CBF versus Vm and for the overall population was r = 0.82. In groups 1 and 2, the r values were 0.39 and 0.5, respectively. Correlation coefficients did not exceed r = 0.4 in any subgroup-classification based on diagnosis. The close correlation between changes in CBF and Vm (r = 0.82) in patients with heterogeneous intracranial pathology seems to show that TCD is a measure of CBF. However, in groups 1 and 2 and in subgroups formed of patients classified according to diagnoses, data dispersion suggests that the actual correlation is weaker. Relation of changes in Vm to those in CBF may depend on the underlying diagnosis. These data indicate that the correlation between Vm and CBF may vary with intracranial pathology.

Acetazolamide↗
PubMed1998

Relation between cerebral blood flow and neurologic deficit resolution in acute ischemic stroke.

BACKGROUND AND OBJECTIVE: Early intervention remains the key to acute ischemic stroke therapy. Many patients whose deficits would later resolve without intervention are exposed to the risks of stroke treatment without benefit. The purpose of this study was to determine whether patients with transient deficits could be distinguished from patients with evolving strokes on the basis of acute cerebral blood flow (CBF) measurements before any clinical distinction could be made. METHODS: Fifty-three patients who presented with acute hemispheric stroke symptoms and who underwent xenon-enhanced CT (XeCT) CBF studies within 8 hours of onset of symptoms (and before any clinical improvement) were studied. RESULTS: Eight patients (15%) had a complete resolution of their symptoms within 24 hours (not related to treatment). All eight patients with deficits that resolved had normal CBF in the symptomatic vascular territories (mean time to XeCT = 3 hours, 51 min). Mean CBF in the regions of interest of the symptomatic vascular territories of patients who had deficits that resolved was 35.4 +/- 8.1 mL x 100 g(-1) x min(-1) compared with 17.3 +/- 9.3 mL x 100 g(-1) x min(-1) of patients with evolving strokes (p = 0.00058). CONCLUSIONS: Patients with ischemic neurologic deficits that will later resolve can be acutely distinguished from patients with evolving cortical infarctions using XeCT CBF measurements. CBF measurements may assist in the triage of patients for acute stroke therapy by selecting patients with a favorable prognosis and may not benefit from therapy but would still be exposed to the potential risks and expense of treatment.

Acute Disease↗
PubMed1998

Relationship between cerebral blood flow and the development of swelling and life-threatening herniation in acute ischemic stroke.

OBJECT: The purpose of this study was to determine whether cerebral blood flow (CBF) measurements in acute stroke could be correlated with the subsequent development of cerebral edema and life-threatening brain herniation. METHODS: Twenty patients with aggressively managed acute middle cerebral artery (MCA) territory strokes who underwent xenon-enhanced computerized tomography (Xe-CT) CBF scanning within 6 hours of onset of symptoms were retrospectively reviewed. The relationship among CBF and follow-up CT evidence of edema and clinical evidence of brain herniation during the 36 to 96 hours following stroke onset was analyzed. Initial CT scans displayed abnormal findings in 11 patients (55%), whereas the Xe-CT CBF scans showed abnormal findings in all patients (100%). The mean CBF in the symptomatic MCA territory was 10.4 ml/100 g/minute in patients who developed severe edema compared with 19 ml/100 g/minute in patients who developed mild edema (p < 0.05). The mean CBF in the symptomatic MCA territory was 8.6 ml/100 g/minute in patients who developed clinical brain herniation compared with 18 ml/100 g/minute in those who did not (p < 0.01). The mean CBF in the symptomatic MCA territory that was 15 ml/100 g/minute or lower was significantly associated with the development of severe edema and herniation (p < 0.05). CONCLUSIONS: Within 6 hours of acute MCA territory stroke, Xe-CT CBF measurements can be used to predict the subsequent development of severe edema and progression to clinical life-threatening brain herniation. Early knowledge of the anatomical and clinical sequelae of stroke in the acute phase may aid in the triage of such patients and alert physicians to the potential need for more aggressive medical or neurosurgical intervention.

Acute Disease↗
PubMed1998

Cerebral monitoring by means of oximetry and somatosensory evoked potentials during carotid endarterectomy.

OBJECT: Cerebral ischemia that occurs during carotid endarterectomy is commonly monitored by means of somatosensory evoked potentials (SSEPs) and electroencephalography (EEG). The authors conducted this study to determine whether cerebral ischemia could also be reliably detected by cerebral oximetry. METHODS: Twenty-nine patients who underwent carotid endarterectomy were monitored by means of SSEPs, EEG, and cerebral oximetry with a model NIRO500 (20 patients) or INVOS3100A (nine patients) oximeter. Changes in amplitude of SSEPs were graded as follows: 0, no change; 1, decrease of less than 50%; 2, decrease of greater than 50%; and 3, 100% decrease. As measured with the NIRO500 oximeter, closing the common caro-tid artery decreased mean oxyhemoglobin levels twice as much (p < 0.005) in the group with SSEPs of 1 to 3 (-13.11+/-5.59 microM [mean+/-standard deviation], 12 patients) as in the group with SSEPs of 0 (-6.22+/-5.59 microM, eight patients). The rise in deoxyhemoglobin was also greater (p < 0.05). Two of nine patients monitored with the INVOS3100A oximeter had SSEPs of 1 and 3, and their regional saturation of oxygen (rSO2) values fell by -11.50 and -11.51, respectively. In the remaining seven patients with SSEPs of 0, the rSO2 ranged between -2.00 and -6.10 with no overlap with the group with SSEPs of I to 3. The increase in oxyhemoglobin monitored using the NIRO500 oximeter and rSO2 monitored using the INVOS3100A machine after opening the external carotid artery was less than that seen after opening the internal carotid artery. Both types of oximeters could detect cerebral ischemia but whereas false negatives occurred with the NIRO500, none was observed with the INVOS3100A. Extracranial contamination was also four times less frequent with the INVOS3100A than with the NIRO500 monitor. CONCLUSIONS: The results indicate that at least as measured with the INVOS3100A instrument, a decrease in rSO2 of -10 or more or a decrease below an rSO2 of 50 is indicative of cerebral ischemia of sufficient severity to decrease the amplitude of SSEPs.

Brain Ischemia↗
PubMed1997

Finite element methods in the simulation and analysis of intracranial blood flow.

This paper presents an introduction to the use of finite element methods in the simulation and analysis of intracranial blood flow and lays the foundation for more detailed clinically oriented studies. An overview of finite element theory is provided and includes the formulation of both the continuous and discrete equations of viscous fluid flow. A discussion of appropriate assumptions and boundary conditions governing arterial blood flow is presented. Two-dimensional, rigid-walled models are developed for flow in a straight artery, a 90 degrees curved artery and a bifurcated artery. For each model, a description of the finite element mesh, numerical solution and computational results are presented. This paper is the first in a series which will detail computational analysis of the relationship between pressure, velocity development of intracranial aneurysms and therapeutic approaches to aneurysm management. The goals of this research are to investigate the fluid dynamics that arise as a result of pulsatile flow in the arteries of the circle of Willis, relate these hemodynamics to the formation of aneurysms, develop a computational understanding of the effects of various therapies on blood flow related to aneurysms, and to develop and utilize patient specific computer simulations for treatment planning.

Cerebrovascular Circulation↗
PubMed1997

Cerebrovascular response in infants and young children following severe traumatic brain injury: a preliminary report.

To further describe the pathophysiologic processes that occur in infants and young children after severe traumatic brain injury (TBI), we retrospectively reviewed the cerebral blood flow (CBF) values and 6-month Glasgow Outcome Scores (GOS) in 30 children < or = 8 years old (25 were < or = 4 years old) with a Glasgow Coma Score (GCS) on admission of < or = 8. Twelve females and 18 males (mean age 2.1 years, range 1 month to 8 years) underwent 61 CBF studies using stable xenon computed tomography at variable times from admission to 9 days after TBI. In 12 patients, PaCO2 was manipulated an average of 8.4 torr (range 5-11 torr) and a second CBF study performed to determine CO2 vasoreactivity (CO2VR), defined as the percent change in CBF per torr change in PaCO2. CBF on admission (n = 13)was 25.1+/-7.7 ml/100 g/min (mean +/- SEM) and was < or = 20 ml/100 g/min in 10 of 13 patients (77%). By 24 h and for up to 6 days after TBI, the mean CBF increased to 55.3+/-3.4 ml/100 g/min (range 2-95) which differed significantly from the admission CBF value (p < 0.05); a CBF of >70 ml/100 g/min tended to be associated with a good outcome. Poor outcome (GOS < or = 3) was seen uniformly in children under the age of 1 year and in patients with a CBF of < or = 20 ml/100 g/min any time after TBI. Poor outcome was seen in 85% of children under the age of 24 months, but in only 41% of children > or = 24 months old. Mean CO2VR was 2.1+/-0.6%/torr PaCO2 and ranged from 0.02 to 5.98%. Mean CO2VR tended to differ between good and poor outcome children (3.2+/-0.9 and 1.17+/-0.2%, respectively) and a CO2VR of < or = 2% was significantly associated with a poor outcome. Younger age, low CBF in the early period after TBI, and a CO2VR of <2% was associated with a poor outcome in this subgroup of children. Young children (<24 months) may represent a particular high-risk group with early hypoperfusion after severe TBI. This finding may be a key factor in the pathophysiology and outcome in this age group, and may need to be addressed in our future therapeutic protocols.

Age Factors↗
PubMed1997

Quantitative cerebral blood flow determinations in acute ischemic stroke. Relationship to computed tomography and angiography.

BACKGROUND AND PURPOSE: The advent of new modalities to treat acute ischemic stroke presents the need for accurate, early diagnosis. In acute ischemic stroke, CT scans are frequently normal or reveal only subtle hypodense changes. This study explored the utility and increased sensitivity of xenonenhanced CT (XeCT) in the diagnosis of acute cerebral ischemia and investigated the relationship between cerebral blood flow (CBF) measurements and early CT and angiographic findings in acute stroke. METHODS: The CT scans, XeCT scans, and angiograms of 20 patients who presented within 6 hours of acute anterior circulation ischemic strokes were analyzed. RESULTS: CT scans were abnormal in 11 (55%) of 20 patients. XeCT scans were abnormal in all 20 (100%) patients, showing regions of interest with CBF < 20 (mL/100 g per minute) in the symptomatic middle cerebral artery (MCA) territories. The mean CBF in the symptomatic MCA territories was significantly lower than than of the asymptomatic MCA territories (P < .0005). In patients with basal ganglia hypodensities, the mean symptomatic MCA territory CBF was significantly lower than that of patients who did not exhibit these early CT findings (P < .05). The mean symptomatic MCA territory CBF in patients with angiographic M1 occlusions was significantly lower than that of patients whose infarcts were caused by MCA branch occlusions (P < .01). CONCLUSIONS: These results show that XeCT is more sensitive than CT in detecting acute strokes and that CBF measurements correlate with early CT and angiographic findings. XeCT may allow for the hyperacute identification of subsets of patients with acute ischemic events who are less likely to benefit and more likely to derive complications from aggressive stroke therapy.

Acute Disease↗
PubMed1997

Effect of transluminal angioplasty on cerebral blood flow in the management of symptomatic vasospasm following aneurysmal subarachnoid hemorrhage.

In this study the authors have examined the effects of transluminal angioplasty on cerebral blood flow (CBF) in the management of intractable vasospasm following aneurysmal subarachnoid hemorrhage (SAH). Fourteen consecutively enrolled patients underwent attempted angioplasty with or without intraarterial infusion of papaverine. Twelve patients underwent pre- and postangioplasty xenon-enhanced computerized tomography (Xe-CT) scanning to measure regional CBF in 55 to 65 regions of interest (ROIs) per patient. Angioplasty was possible in 13 (93%) of 14 patients, with angiographically demonstrated improvement in all 13. Twelve (92%) of the 13 patients were neurologically improved following angioplasty; seven (58%) of the 12 patients who improved had a complete reversal of all delayed ischemic deficits. Angioplasty significantly decreased the mean number of ROIs at risk (11.4 ROIs pre- and 0.9 ROIs postangioplasty) (p < 0.00005, t-test). All patients had a reduction in the number of ROIs at risk after angioplasty; six (50%) of 12 no longer had any ROIs remaining at risk after angioplasty. Angioplasty significantly increased the mean CBF within at-risk ROIs (13 ml/100 g/minute pre- and 44 ml/100 g/minute postangioplasty) (p < 0.00005, t-test). All patients experienced an improvement in mean CBF in at-risk ROIs after angioplasty, with the mean CBF improving to above 20 ml/100 g/minute in all cases. No differences in the degree of improvement were found in patients who received intraarterial papaverine compared with those who did not. In the majority of patients with refractory vasospasm following SAH, angioplasty effectively dilated spastic arteries, reversed delayed neurological deficits, and significantly improved CBF in areas of brain at risk of infarction.

Adult↗
PubMed1997

Regional parenchymal enhancement with mixed cavernous/venous malformations of the brain. Case report.

With improvements in imaging technology, the detection of both cavernous malformations and venous malformations has increased markedly in recent years. Although much has been learned about the association of cavernous and venous malformations, important questions regarding the true nature of such a relationship remain unanswered. It has been proposed that certain venous malformations produce local venous hypertension with resultant microhemorrhage, growth factor release, and creation of cavernous malformations. The authors report on two patients with cerebellopontine venous malformations associated with cavernous malformations. Both patients demonstrated persistent regional parenchymal enhancement associated with the vascular malformations. In addition, both patients had significant clinical symptoms referable to the region of affected brain. This previously undescribed finding may represent an imaging correlate to the complex interaction among venous malformations, venous hypertension, and cavernous malformations.

Adult↗
PubMed1996

Construction of 3-D arterial volume meshes from magnetic resonance angiography.

Finite element methods are well-suited for solving problems in arterial fluid dynamics, primarily due to their ability to handle flows in complex geometries. However, in order to use these computational methods to develop realistic models of pulsatile flow in intracranial arteries and associated aneurysms, it is necessary to construct a 3-D mesh, or grid, that accurately duplicates the arterial geometry of interest. In this paper, we present an efficient method to accurately develop realistic 3-D computational meshes of human intracranial arteries and aneurysms from serial magnetic resonance angiography images. However, these techniques may be applied to any other form of imaging data including computed tomographic angiography. First, raw grayscale images are segmented, converted to their binary form and arterial contours are extracted at each image slice. Next, the arterial contours are stacked and cubic splines are computed along the axial direction. This creates an affect similar to smooth integration in the axial direction and provides a set of points that define the 3-D arterial surface geometry. Then, surface patches are constructed and merged. A surface mesh is then computed with the ability to locally vary the mesh density as desired. Finally, nodal points on the surface mesh are used to compute the finite element volume mesh. The 3-D volume mesh accurately describes the arterial geometry and is used to develop patient-specific computational fluid dynamic models of flow phenomena in intracranial arteries and aneurysms. These flow models are then suitable for investigating the hemodynamics of intracranial aneurysm formation and test the end-effects of various medical and surgical treatments.

Algorithms↗
PubMed1996

Norepinephrine activation of basal cerebral metabolic rate for oxygen (CMRO2) during hypothermia in rats.

In an earlier study on the effect of mild hypothermia (34 degrees C) on the cerebral metabolic rate for oxygen (CMRO2) in rats, we used norepinephrine (NE) to support arterial blood pressure while inducing isoelectricity on the electroencephalogram (EEG) with thiopental (TP). Even with administration of sufficient TP to reduce a fully active EEG to an isoelectric EEG, CMRO2 was often unchanged. Based on this observation, we hypothesized that NE had activated CMRO2 despite thiopental coma. Therefore, we studied the effect of NE compared with donor blood (DB) infusion to maintain arterial blood pressure during TP-induced isoelectric EEG on whole-brain CBF (H2 clearance) and CMRO2 during normothermia (38 degrees C) and mild hypothermia (34 degrees C) in rats during 70% N2O/30% O2 analgesia. Cerebral blood flow (CBF) and CMRO2 were measured in four groups of rats at 38 degrees C followed by measurements at either 38 degrees C (two groups) or 34 degrees C (two groups) and during TP-induced EEG isoelectricity. Within each of the two groups at 38 degrees C and 34 degrees C, arterial pressure was sustained by either DB (n = 10) or NE (n = 9) infusion. At 38 degrees C, CMRO2 in the DB and NE groups was 7.92 +/- 1.05 and 6.4 +/- 0.80 mL x 100 g-1.min-1 and decreased to 50% of normal (3.95 +/- 0.70 and 3.32 +/- 0.40 mL x 100 g-1.min-1, respectively) during TP isoelectricity for a functional:basal CMRO2 distribution of 50% +/- 4% and 50% +/- 4%. At 34 degrees C, CMRO2 values in the DB and NE groups were 6.31 +/- 1.41 and 5.41 +/- 2.02 mL x 100 g-1.min-1, respectively. During TP-induced isoelectricity, CMRO2 values in both groups were reduced to 2.37 +/- 0.43 and 3.55 +/- 1.27 mL x 100g-1.min-1, respectively, resulting in a functional:basal CMRO2 distribution of 61%:38% in the DB group and the reverse, or 27%:73%, in the Ne group. Basal CMRO2 was significantly (P < 0.05) larger in the NE-infused rats. These results suggest that NE infusion, by increasing CMRO2 during mild hypothermia, could nullify its protective effects in the ischemic brain.

Adrenergic alpha-Agonists↗
PubMed1996

The relationship of blood velocity as measured by transcranial doppler ultrasonography to cerebral blood flow as determined by stable xenon computed tomographic studies after aneurysmal subarachnoid hemorrhage.

Transcranial doppler (TCD) ultrasonography is often used to guide the management of patients with subarachnoid hemorrhage (SAH). However, the correlation between increased blood velocity as measured by TCD ultrasonography and angiographic vasospasm was established before the routine use of hypervolemia/hemodilution and administration of nimodipine and did not address blood flow. The relationship of blood velocity as measured by TCD ultrasonography and local cerebral blood flow (LCBF) in SAH managed with these modalities is unknown. Patients presenting with aneurysmal SAH between January 1992 and September 1993 who underwent TCD ultrasonography and xenon computed tomographic (Xe/CT) LCBF studies within 12 hours were retrospectively studied. Fifty patients underwent a total of 94 paired studies, encompassing 709 vascular territories. All were treated with nimodipine and hypervolemia/hemodilution. Hematocrit, blood pressure, and partial carbon dioxide pressure were similar at the time of TCD ultrasonography and Xe/CT measurement of LCBF. When LCBF in the middle cerebral artery (MCA) was < or = 31 ml/100 g/min, the corresponding peak systolic velocity measured by TCD ultrasonography was 119 cm/s, whereas those > 31 ml/100 g/min had a velocity of 169 cm/s (P = 0.006). High LCBF was associated with high velocity in all vascular territories, reaching significance in all but the internal carotid artery. At the time of each study, 41 neurological examinations were focal and 53 were nonfocal. The Xe/CT measurement of LCBF in the MCA contralateral to a deficit was significantly less than in territories without corresponding clinical deficits (P = 0.01), whereas peak systolic velocities in the MCA were not significantly different (P = 0.71). Territories with increases in blood velocity in the MCA of > 50 cm/s/24 h did not have statistically different LCBF (P = 0.183). Our results suggest that increased blood velocity revealed by TCD ultrasonography correlates with increased LCBF and not with ischemia. No difference in LCBF was found in territories with and without rapid increases in blood velocity in the MCA. Furthermore, although focal neurological deficits corresponded with decreased contralateral LCBF in the MCA, increased velocity did not correlate with neurological findings. Therapeutic decisions based solely on blood velocity revealed by TCD ultrasonography might be inappropriate and potentially harmful. Xe/CT studies of LCBF are useful in guiding the management of SAH.

Aneurysm, Ruptured↗
PubMed1996

Physiological diagnosis and surgical treatment of recurrent limb shaking: case report.

OBJECTIVE AND IMPORTANCE: Although recurrent limb shaking has been observed in patients with carotid occlusion, its cause, method of diagnosis, and definitive treatment have yet to be fully elucidated. This report examines the cerebrovascular physiology of a patient with recurrent limb shaking by means of xenon-enhanced computed tomographic (XeCT) scanning. By measuring cerebral blood flow (CBF) and cerebrovascular reserve capacity, we were able to confirm both the clinical diagnosis and the response to treatment on physiological grounds. CLINICAL PRESENTATION: The patient is a 49-year-old man who presented with frequent brief attacks of left arm and leg shaking that occurred at standing or coughing. After cervical radiation therapy for a laryngeal carcinoma, he was found to have bilateral carotid occlusion with minimal collateral development. XeCT scans revealed borderline ischemic perfusion and lack of cerebrovascular reserve in response to an acetazolamide vasodilatory challenge. INTERVENTION: The patient underwent a right superficial temporal artery to middle cerebral artery bypass to augment cerebral perfusion. CONCLUSION: After the procedure, the patient's limb shaking attacks ceased. The postoperative XeCT scan showed improved CBF and a return of cerebrovascular reserve capacity. Recurrent limb shaking is a manifestation of decreased CBF. Quantitative XeCT CBF studies coupled with vasodilatory challenge is an important way to assess patients with cerebrovascular disorders and thus identify individuals who will benefit from cerebral revascularization.

Arm↗