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Biomedical subjects

F Viñuela

Publications and source records attributed to F Viñuela.

At least 73 records · Page 4Linked to original sources
PubMed1995

Epilepsy associated with cerebral arteriovenous malformations: a multivariate analysis of angioarchitectural characteristics.

PURPOSE: To identify the morphological vascular characteristics of cerebral arteriovenous malformations (AVMs) that predict a clinical presentation of epilepsy. METHOD: Fifteen angioarchitectural characteristics of brain AVMs were selected for assessment in 100 consecutive patients referred to our institution for endovascular treatment. In this population, 47% of the AVMs were diagnosed as a consequence of epilepsy. The angioarchitectural characteristics and population demographics were statistically analyzed by means of multivariate analysis. RESULTS: The following six parameters were found to be the most predictive of epilepsy: cortical location of the AVM, feeding by the middle cerebral artery, cortical location of the feeder, absence of aneurysms, presence of varix/varices in the venous drainage, and association of varix and absence of intranidal aneurysms. Three factors were not among the most predictive factors of epilepsy but were significantly associated with the onset of seizures: AVM feeding by the external carotid artery, a temporal cortical location, and a parietal cortical location. CONCLUSION: Detailed analysis of the angioarchitecture of intracranial AVMs has helped us identify features that strongly correlate with epilepsy. This may aid in future understanding of the physiopathologic mechanisms in epilepsy associated with AVMs, and in identifying goals of treatment for epileptogenic AVMs.

Adolescent↗
PubMed1995

Quantitation of intracranial aneurysm neck size from diagnostic angiograms based on a biomathematical model.

Accurate measurement of the aneurysm neck size from diagnostic angiograms is crucial in the consideration and implementation of interventional embolotherapeutic procedures. Due to inherent problems in angiography, aneurysm morphology and location, and obstruction by overlying structures, accurate measurement of the aneurysm neck size is difficult. We are proposing a method for the angiographic measurement of aneurysm neck size based on a biomathematical model of an aneurysm. A biomathematical model of an intracranial saccular aneurysm was developed based on Laplace's law for a spherical elastic object, given by: Stress = Pressure x Radius/2 x Wall thickness. In addition, another biomechanical parameter used to describe an elastic sphere is the strain: Strain = delta R/Ri = (R-Ri)/Ri where R is the current aneurysm radius and Ri is the initial radius prior to aneurysm development. The stress and strain of an elastic structure are used to describe the elastic modulus, E: E = stress/strain = [PR/2h]/[(R-Ri)/Ri] = [PRRi]/[2hR-2hri]. It is assumed at this point that no additional tissue growth occurs through the developmental course of the aneurysm. The expression for E is now solved for Ri which, in essence, represents the radius of the aneurysm neck: Ri = [2hER]/[PR + 2hE]. Thus, the diameter of the neck, Dn, is given by Dn = 2 + i = 2 ([2hER]/[PR + 2hE]). During diagnostic angiography, the radius, R, and pressure, P, are easily obtained during the examination procedure. However, it is not possible to angiographically determine the elastic modulus, E, and the wall thickness, h. In this case, the following average values are used: E = 1.0 MPa and h = 50 microns. From the diagnostic angiograms and hospital records of 23 patients, the aneurysm neck size was determined using the biomathematical model and compared to the results obtained from the correlative relationship between the measured and accepted ratios of neck size to diameter of parent artery. The neck diameter as measured from the accepted ratios of neck size to parent artery diameter for the 23 patients ranged from 1.5 mm to 8.7 mm. The angiographically measured neck sizes were in excellent agreement with those obtained from the biomathematical model, particularly for the wide-necked aneurysms, as evidenced by the fact that all but two chi 2 values were < 1.0. We have described a simple yet accurate method for obtaining aneurysm neck size measurements from diagnostic angiograms using a biomathematical model. The model requires knowledge of only the aneurysm radius and blood pressure and becomes particularly important in characterizing wide-necked aneurysms.

Adult↗
PubMed1994

Experimental saccular aneurysms. I. Review of surgically-constructed models and their laboratory applications.

Experimental models of intracranial saccular aneurysms are a useful contribution to our basic understanding of these lesions. Currently, the commonest in use are those constructed surgically in laboratory animals. We review the numerous surgical techniques available since the 1950s, and the research applications and uses of experimental aneurysms. Further development and use of such models is greatly encouraged in future pathophysiological, hemodynamic, and therapeutic investigations of intracranial saccular aneurysms.

Animals↗
PubMed1994

Experimental saccular aneurysms. II. A new model in swine.

A new technique for surgical construction of experimental lateral saccular aneurysms on the common carotid artery of swine is described. It involves end-to-side suturing of an isolated segment of vein to an artery. During a short period of parent artery clamping, an elliptical arteriotomy is fashioned through the open-ended vein graft, the open end of which is subsequently tied and clamps are removed to form an aneurysmal vein pouch. The principal advantage of this technique is the short period of vascular clamping necessary to isolate a segment of the parent artery. This prevents severe endothelial injury and prolonged postoperative vasospasm, both of which may promote intra-aneurysmal thrombosis. Narrow- or wide-necked aneurysms can be created. Steps in the surgical construction of this model are detailed, and specific advantages of using swine are highlighted.

Animals↗
PubMed1994

Saccular aneurysms in moyamoya disease: endovascular treatment using electrically detachable coils.

Moyamoya disease (MMD) often presents with subarachnoid hemorrhage due to rupture of saccular aneurysms. We describe three patients with cerebrovascular features of MMD in whom four aneurysms of the posterior circulation were endovascularly occluded by electrothrombosis using the recently developed Guglielmi electrically detachable coils (GDC). Near total occlusion was achieved in three aneurysms. Subtotal occlusion was achieved in one aneurysm. This patient developed complications related to the neuroleptic anesthesia administered for the procedure. The particular hazards of anesthesia and aneurysmal surgery in MMD are discussed, and comparison is made with the benefits of using the GDC. Initial experience suggests that this endovascular approach is safe and effective in the treatment of saccular aneurysms in MMD. However, follow-up is necessary to assess long-term persistence of aneurysm obliteration.

Adult↗
PubMed1994

A nonlinear mathematical model for the development and rupture of intracranial saccular aneurysms.

Mathematical models of aneurysms are typically based on Laplace's law which defines a linear relation between the circumferential tension and the radius. However, since the aneurysm wall is viscoelastic, a nonlinear model was developed to characterize the development and rupture of intracranial spherical aneurysms within an arterial bifurcation and describes the aneurysm in terms of biophysical and geometric variables at static equilibrium. A comparison is made between mathematical models of a spherical aneurysm based on linear and nonlinear forms of Laplace's law. The first form is the standard Laplace's law which states that a linear relation exists between the circumferential tension, T, and the radius, R, of the aneurysm given by T = PR/2t where P is the systolic pressure. The second is a 'modified' Laplace's law which describes a nonlinear power relation between the tension and the radius defined by T = ARP/2At where A is the elastic modulus for collagen and t is the wall thickness. Differential expressions of these two relations were used to describe the critical radius or the radius prior to aneurysm rupture. Using the standard Laplace's law, the critical radius was derived to be Rc = 2Et/P where E is the elastic modulus of the aneurysm. The critical radius from the modified Laplace's law was R = [2Et/P]2At/P. Substituting typical values of E = 1.0 MPa, t = 40 microns, P = 150 mmHg, and A = 2.8 MPa, the critical radius is 4.0 mm using the standard Laplace's law and 4.8 mm for the modified Laplace's law.(ABSTRACT TRUNCATED AT 250 WORDS)

Aneurysm, Ruptured↗
PubMed1994

A nonlinear mathematical model for the development and rupture of intracranial fusiform aneurysms.

Laplace's law, which describes a linear relation between the tension and the radius, is often used to characterize the mechanical response of the aneurysm wall to distending pressures. However, histopathological studies have confirmed that the wall of the fully developed aneurysm consists primarily of collagen and is subject to large increases in tension for small increases in the radius, i.e., a nonlinear relationship exists between the tension within the aneurysm wall and the radius. Thus, a nonlinear version of Laplace's law is proposed to accurately describe the development and rupture of a fusiform saccular aneurysm. The fusiform aneurysm was modelled as a thin-walled ellipsoidal shell with a major axis radius, Ra, minor axis radius, Rb, circumferential tension, S0, and meridional tension, S phi, with phi defining the angle from the surface normal. Using both linear and nonlinear models, differential expressions of the volume distensibility evaluated at 90 degrees were used to determine the critical radius of the aneurysm along the minor axis from S0 and S phi in terms of the following geometric and biophysical variables; A, elastic modulus of collagen; E, elastic modulus of the aneurysm (elastin and collagen); t, wall thickness; P, systolic pressure; and Ra. For typical physiological values of A = 2.8 MPa, E = 1.0 MPa, T = 40 microns, P = 150 mmHg, and Ra = 4Rb, the linear model yielded critical radii of 4.0 mm from S phi and 2.2 mm from S0. The resultant critical radius was 4.56 mm. Using the same values, the critical radii from the tension components of the nonlinear model were 3.5 mm from S phi and 1.9 mm from S0.(ABSTRACT TRUNCATED AT 250 WORDS)

Aneurysm, Ruptured↗
PubMed1994

Aneurysms related to cerebral arteriovenous malformations: superselective angiographic assessment in 58 patients.

PURPOSE: To report the comprehensive superselective angiographic characteristics of aneurysms associated with cerebral arteriovenous malformations. METHOD: One hundred consecutive patients referred for cerebral arteriovenous malformation embolization underwent preembolization superselective angiography. Superselective angiograms were obtained after microcatheterization of arteriovenous malformation pedicles, and assessed for number and location of aneurysms related to the malformation. A chi 2 test was conducted to correlate these parameters with the onset of intracranial hemorrhage. RESULTS: Aneurysms were demonstrated in 58 of 100 patients. Single aneurysms were found in 24 patients and multiple aneurysms in 34. Presence and number of aneurysms were found to correlate significantly with a clinical presentation of hemorrhage. CONCLUSION: Superselective angiography was found to be of paramount importance in elucidating the precise and detailed angioarchitecture of brain arteriovenous malformations.

Adolescent↗
PubMed1994

Potential toxic effects of superselective injection of amobarbital sodium on microvasculature: a study in an animal model.

PURPOSE: To determine whether microvascular damage occurs from superselective intraarterial injection of amobarbital sodium using the swine endovascular embolization model. METHODS: Thirty-four swine underwent percutaneous femoral puncture for superselective catheterization of the proximal artery of the rete. Varying concentrations of amobarbital sodium were prepared (12.5 to 100 mg/mL solution) in either normal saline or sterile water (105 mOsm/L to 1138 mOsm/L) of which one concentration was infused slowly into one ipsilateral rete. Control infusions were also performed. Histopathologic changes were evaluated at 30 minutes and 10 days after infusion, using standard light and electron microscopy techniques. RESULTS: Moderate vasospasm occurred only in three swine at 100 mg/mL amobarbital sodium in normal saline. Light microscopy showed no significant histologic changes in the retia at any of the tested concentrations of amobarbital sodium. Electron microscopy showed ultrastructural alterations in the intima only at the higher amobarbital sodium concentrations. CONCLUSIONS: Concerns for inducing significant damage to cerebral microvasculature by superselective injection of amobarbital sodium at the usually recommended concentrations and doses are probably not justified.

Amobarbital↗
PubMed1994

An experimental arteriovenous malformation model in swine: anatomic basis and construction technique.

We assessed the feasibility of creating an experimental arteriovenous malformation model in swine by diverting and increasing blood flow through bilateral retia mirabilia. This was achieved by surgical formation of a large right-sided carotid-jugular fistula, in combination with endovascular occlusion of several neck arteries ipsilateral to the fistula. Using this technique, 11 of 13 swine demonstrated an acute-phase angiographic simulation of an arteriovenous malformation. There was rapid circulatory diversion from the left ascending pharyngeal artery ("feeder"), across both retia ("nidus"), and fast retrograde flow into the right ascending pharyngeal and common carotid arteries ("draining vein") toward the fistula. The relevant vascular anatomy of the swine head and neck is outlined, and steps in the construction of this arteriovenous malformation model are detailed.

Anastomosis, Surgical↗
PubMed1994

Endovascular occlusion of intracranial aneurysms with electrically detachable coils: correlation of aneurysm neck size and treatment results.

PURPOSE: To devise a method to measure aneurysm neck size on angiographic films, and to correlate the sizes obtained with the extent of endovascular aneurysm occlusion, performed with electrically detachable coils. METHODS: The angiograms of 79 intracranial aneurysms treated by endovascular occlusion using electrically detachable coils were retrospectively analyzed. A method using the average reported caliber of the major intracranial vessels was applied to determine the aneurysm neck sizes on the diagnostic angiograms. The cases were divided into two groups according to neck size, 4 mm being the discriminative value for small and wide necks. The posttreatment angiogram of each case was analyzed to evaluate the degree of occlusion achieved by the technique. RESULTS: Necks were successfully measured in 95% of the aneurysms. Complete aneurysm thrombosis was observed in 85% of the small-necked aneurysms and in 15% of the wide-necked aneurysms. CONCLUSIONS: Accurate angiographic measurements of neck diameter can be obtained in most aneurysms. The size of an aneurysm neck correlates well with the results of the endovascular treatment. Small-necked aneurysms can be satisfactorily occluded with this technique. In wide-necked aneurysms this technique should be reserved for lesions having a high surgical risk.

Aneurysm, Ruptured↗
PubMed1994

Experimental models of bifurcation and terminal aneurysms: construction techniques in swine.

We report our preliminary experience in the surgical construction of five experimental bifurcation and terminal aneurysm models in swine. We used unilateral neck vessels to construct models in which the relative directions and sizes of the parent and daughter arteries could be varied by surgery, resulting in aneurysms with high morphologic similarity to human intracranial lesions. Steps in the construction of each model are detailed.

Anastomosis, Surgical↗
PubMed1994

An in vivo arteriovenous malformation model in swine: preliminary feasibility and natural history study.

PURPOSE: To assess the feasibility, natural history, and preliminary physiologic validation of creating an in vivo arteriovenous malformation model in swine. METHODS: A transorbital puncture technique into the cavernous sinus was used to create an arteriovenous communication between the rostral rete and the cavernous sinus in eight swine. Short-term patency and hemodynamic behavior were assessed clinically and by serial angiography. Acute phase physiologic characterization of four models was also performed, using intravascular pressure and Doppler blood flow velocity measurements. RESULTS: Large arteriovenous shunts between the rostral rete and cavernous sinus were consistently produced, which mimicked the angiographic features of cerebral arteriovenous malformations in humans. Classic changes in intraarterial and intravenous pressures and blood flow velocities were also observed. Early pathophysiologic evolution occurred in two animals, consisting of recruitment of previously unseen collateral vessels. Spontaneous occlusion of the arteriovenous shunt occurred in most animals within 7 days because of a rigorous fibroblastic response. CONCLUSIONS: A simple technique for creating an arteriovenous malformation model in swine is now possible and is promising for future studies.

Animals↗
PubMed1994

Combined stent implantation and endosaccular coil placement for treatment of experimental wide-necked aneurysms: a feasibility study in swine.

PURPOSE: To assess the feasibility of combining stent implantation in the parent artery with endosaccular coil placement for the treatment of experimentally created wide-necked aneurysms. METHODS: Wide-necked aneurysms were surgically created on the common carotid artery in 12 swine. A metal stent was endovascularly implanted across each aneurysm neck and its effect documented anigiographically. If the aneurysm remained patent, a microcatheter was introduced into the aneurysm through the stent mesh. Electrically detachable coils were delivered into the aneurysm sac to produce thrombosis. RESULTS: After stent implantation, one carotid artery thrombosed and two aneurysms spontaneously occluded. In the other 9 cases, coils were deposited through the stent to occlude the aneurysm. Complete aneurysm packing was possible in all 9 cases. The presence of the stent allowed placement of small coils near the aneurysm neck, thus contributing to the safe occlusion of small remnants in the final stages of aneurysm packing. CONCLUSION: The combination of stent implantation and coil placement is feasible in the treatment of experimental wide-necked saccular aneurysms. The stent maintains patency of the parent artery while allowing aneurysm occlusion by endosaccular coil placement through the stent's mesh. Occlusion of small aneurysm remnants is possible with no fear of coil hernation or migration into the parent artery. Long-term studies will be necessary before application to treatment of selected intracranial aneurysms.

Aneurysm↗
PubMed1994

Technical feasibility and histopathologic studies of ethylene vinyl copolymer (EVAL) using a swine endovascular embolization model.

PURPOSE: To study the safety, technical efficacy, and histopathology of the ethylene vinyl alcohol copolymer (EVAL) embolic mixture in an animal model. METHODS: Microcatheterization of the rete was performed in 29 swine. The clinical, angiographic, and histopathologic consequences of superselective injection of the two principal embolic mixture components (EVAL and dimethyl sulfoxide [DMSO]) were evaluated. Necropsy and standard histologic preparation were used for pathologic analysis. RESULTS: Significant technical difficulties and adverse outcomes occurred. The EVAL mixture was difficult to see under fluoroscopy and prematurely polymerized during one embolization, resulting in catheter occlusion. However, polymerized EVAL did not adhere to the catheter. DMSO damaged the plastic hubs of the microcatheters. Infusions of DMSO always caused immediate, moderate to severe vasospasm and frequently caused either subarachnoid hemorrhage or stroke. Histopathologic findings of both DMSO and DMSO plus EVAL were similar, producing variable endothelial denuding, thrombosis, and disruption of internal elastic lamina in the acute stage. An intense, mixed inflammatory response, organized thrombus, and transmural necrosis with extravasation were seen in the subacute and chronic stages. CONCLUSIONS: Despite having some desirable features as an embolic agent, significant problems were encountered with EVAL; the most important of which is that one of the principal components of the embolic mixture, DMSO, seems to be very angiotoxic.

Animals↗
PubMed1994

Intracranial aneurysms. Guglielmi electrothrombotic coils.

It is estimated that approximately 2% of the entire population harbors an intracranial aneurysm; most of these patients, however, will never become symptomatic. The incidence of aneurysmal rupture as a cause of subarachnoid hemorrhage is 10 per 100,000 per year. The primary purpose of treatment for ruptured aneurysms is to prevent the often fatal rebleeding.

Adult↗
PubMed1994

Technical feasibility and performance studies of a Doppler guide wire for potential neuroendovascular applications.

PURPOSE: To conduct technical feasibility and performance studies on a new Doppler-tipped, 0.014-inch micro-guide wire for potential neuroendovascular applications. METHODS: In vivo microcatheterizations of brachiocephalic arteries were performed in two swine using the 0.014-inch Doppler guide wire and a commonly used microcatheter. A standardized, bench-top method of evaluating basic mechanical properties of micro-guide wires was also used to compare the 0.014-inch Doppler guide wire with a commonly used micro-guide wire. RESULTS: The 0.014-inch Doppler guide wire had similar steerability, tractability, torque control, and distal tip flexibility to the commonly used micro-guide wire in the in vivo simulations. Frequent micro-guide wire exchanges were possible without loss of superselective positioning of the microcatheter. Bench-top testing showed the 0.014-inch Doppler guide wire to have comparable distal tip flexibility and stiffness to the commonly used micro-guide wire. CONCLUSION: The comparable subjective and objective mechanical properties of the 0.014-inch Doppler guide wire to that of a commonly used micro-guide wire further establishes the possibility of clinical implementation of the device.

Animals↗