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Biomedical subjects

L N Hopkins

Publications and source records attributed to L N Hopkins.

At least 37 records · Page 2Linked to original sources
PubMed2001

Carotid endarterectomy: can we select surgical candidates at high risk for stroke and low risk for perioperative complications?

DESPITE EVIDENCE OF the efficacy of carotid endarterectomy from the large randomized multicenter trials completed in the 1990s, the physician who treats patients with carotid artery stenosis still is faced with a difficult management decision. More recently, subgroup analyses have been conducted of asymptomatic and symptomatic patients enrolled in these trials to identify clinical and radiological factors that increase the rates of morbidity and mortality associated with surgery, as well as those that increase the risk of stroke without surgery. Knowledge of these factors is important to recommend the best course of action for the individual patient. In this article, we summarize the conclusions of some of the subgroup analyses from the major carotid endarterectomy trials.

Carotid Stenosis↗
PubMed2001

Who should be screened for asymptomatic carotid artery stenosis? Experience from the Western New York Stroke Screening Program.

OBJECTIVE: Identification of significant asymptomatic carotid artery stenosis (ACAS) is important because of the stroke-risk reduction observed with carotid endarterectomy. The authors developed and validated a simple scoring system based on routinely available information to identify persons at high risk for ACAS using data collected during a community health screening program at various sites in western New York. A total of 1331 unselected volunteers without previous stroke, transient ischemic attack, or carotid artery surgery were evaluated by personal interview and duplex ultrasound. The main outcome measure was carotid artery stenosis > 60% by duplex ultrasound. In the derivation set (n = 887), 4 variables were significantly associated with ACAS > 60%: age > 65 years (odds ratio [OR] = 4.1, 95% confidence interval [CI] = 2.6-6.7), current smoking (OR = 2.0, 95% CI = 1.2-3.5), coronary artery disease (OR = 2.4, 95% CI = 1.5-3.9), and hypercholesterolemia (OR = 1.9, 95% CI = 1.2-2.9). Three risk groups (low, intermediate, and high) were defined on the basis of total risk score assigned on the basis of the strength of association. The scheme effectively stratified the validation set (n = 444); the likelihood ratio and posttest probability for ACAS in the high-risk group were 3.0 and 35%, respectively, and in the intermediate and low-risk groups were 1.4 and 20% and 0.4 and 7%, respectively. Routinely available information can be used to identify persons in the community at high risk for ACAS. Doppler ultrasound screening in this subgroup may prove to be cost-effective and have an effect on stroke-free survival.

Aged↗
PubMed2001

Determination of blood flow velocity and transit time in cerebral arteriovenous malformation using microdroplet angiography.

Advancement in imaging and biomedical technology has improved the use of catheter-based transarterial embolization (occlusive therapy) of cerebral arteriovenous malformations (AVMs). Among a variety of embolic agents, liquid adhesives (acrylates) have proven to be more successful in permanent obliteration of AVMs. The use of liquid adhesives requires the experience and skill of the operator. However, acquiring accurate information on blood flow and transit times through the AVM prior to embolization can optimize the treatment. In addition, knowledge of the polymerization time and behavior of the acrylate enables a complete and safe occlusion of the arteriovenous transition within the AVM nidus. Standard commercially available iodine-based contrast agents seem to be insufficient to determine AVM transit times from angiograms. For a more accurate assessment of AVM transit times, the use of a nonsoluble contrast agent (Ethiodol) and a high-speed digital subtraction angiography (DSA) is suggested. Small amounts (<20 microl) of Ethiodol were infused to create microdroplets and traced using DSA at 15 fps. Transit time, defined as the time interval required for a droplet to reach the venous part of the AVM after being flushed from the tip of the catheter, could be accurately calculated. Postprocessing was used to calculate trajectories and velocities of microdroplets.

Angiography, Digital Subtraction↗
PubMed2001

Role of conventional angiography in evaluation of patients with carotid artery stenosis demonstrated by Doppler ultrasound in general practice.

BACKGROUND AND PURPOSE: Previous studies have suggested that patients with carotid stenosis who are candidates for endarterectomy can be effectively identified on the basis of carotid Doppler ultrasound alone. Before widespread acceptance of this policy, the accuracy of carotid Doppler ultrasound outside selected centers and clinical trials needs to be evaluated. We performed a 12-month prospective study to evaluate the accuracy of Doppler ultrasound in identifying patients for carotid intervention in general practice settings. METHODS: Each patient referred to our endovascular service for diagnostic angiography to evaluate for carotid stenosis was interviewed and examined by a neurologist. Subjects consisted of symptomatic patients with >/=50% stenosis and asymptomatic patients with >/=60% stenosis by Doppler ultrasound. Information pertaining to demographic and cerebrovascular risk factors and the results of the carotid Doppler ultrasound were recorded. The severity of stenosis on angiograms was measured with North American Symptomatic Carotid Endarterectomy Trial criteria by a blinded observer. The results of both studies were compared to determine the relative accuracy of ultrasound results. RESULTS: Of 130 patients (mean age, 69+/-8.8 years) who met Doppler ultrasound criteria, 22 (17%) and 8 patients (6%) were found to have 30% to 49% or <30% stenosis by angiography, respectively. The positive predictive value of carotid Doppler ultrasound for identifying appropriate symptomatic candidates for carotid intervention (angiographic stenosis >/=50%) was 80%, with a false-positive value of 20%. The positive predictive value of carotid Doppler ultrasound for identifying appropriate asymptomatic candidates for carotid intervention (angiographic stenosis >/=60%) was 59%, with a false-positive value of 41%. Carotid endarterectomy or angioplasty and stent placement were undertaken subsequently in 60 (46%) of the patients. In 94 patients who underwent cerebral angiography alone, no complications were observed. CONCLUSIONS: The present accuracy of carotid Doppler ultrasound in general practice does not justify its use as the sole basis of selecting appropriate patients for carotid intervention. Given the relatively low rate of associated morbidity with present day techniques, additional confirmatory studies such as angiography should be performed in every patient before a decision regarding intervention is made.

Aged↗
PubMed2001

Fatal progression of posttraumatic dural arteriovenous fistulas refractory to multimodal therapy. Case report.

The authors report the case of a man who suffered from progressive, disseminated posttraumatic dural arteriovenous fistulas (DAVFs) resulting in death, despite aggressive endovascular, surgical, and radiosurgical treatment. This 31-year-old man was struck on the head while playing basketball. Two weeks later a soft, pulsatile mass developed at his vertex, and the man began to experience pulsatile tinnitus and progressive headaches. Magnetic resonance imaging and subsequent angiography revealed multiple AVFs in the scalp, calvaria, and dura, with drainage into the superior sagittal sinus. The patient was treated initially with transarterial embolization in five stages, followed by vertex craniotomy and surgical resection of the AVFs. However, multiple additional DAVFs developed over the bilateral convexities, the falx, and the tentorium. Subsequent treatment entailed 15 stages of transarterial embolization; seven stages of transvenous embolization, including complete occlusion of the sagittal sinus and partial occlusion of the straight sinus; three stages of stereotactic radiosurgery; and a second craniotomy with aggressive disconnection of the DAVFs. Unfortunately, the fistulas continued to progress, resulting in diffuse venous hypertension, multiple intracerebral hemorrhages in both hemispheres, and, ultimately, death nearly 5 years after the initial trauma. Endovascular, surgical, and radiosurgical treatments are successful in curing most patients with DAVFs. The failure of multimodal therapy and the fulminant progression and disseminated nature of this patient's disease are unique.

Adult↗
PubMed2001

Endovascular treatment of intracranial aneurysms by using Guglielmi detachable coils in awake patients: safety and feasibility.

OBJECT: Embolization of intracranial aneurysms performed using Guglielmi detachable coils (GDCs) is performed with the patient in a state of general anesthesia at most centers. Such an approach does not allow intraprocedural evaluation of the patient's neurological status and carries additional risks associated with general anesthesia and mechanical ventilation. At the authors' institution, GDC embolization of intracranial aneurysms is performed in awake patients after administration of sedative and analgesic agents (midazolam, fentanyl, morphine, and/or hydromorphone). To determine the feasibility and safety of this approach, the authors have retrospectively reviewed their clinical experience. METHODS: The authors reviewed the medical records of all patients in whom GDC embolization for the treatment of intracranial aneurysms was undertaken between February 1, 1990 and October 31, 1999. Clinical presentation, medical comorbidities, anesthetic agents used, intraprocedural complications, and final procedural outcome were recorded for each patient. Guglielmi detachable coil embolization was attempted in the awake patient in 150 procedures. Among 92 procedures for unruptured aneurysms, 75 (82%) were completed without complications. Four procedures were completed with complications. Of the 92 procedures, 13 were aborted due to patient uncooperativeness (one patient), complications (three patients), morphological characteristics of the aneurysm or surrounding vessels that made embolization technically difficult (eight patients), or vasospasm (one patient). Among 58 procedures for ruptured aneurysms, the procedure was completed without complication in 48 cases (83%). The procedure was completed with complications in five cases and two patients required induction of general anesthesia during the procedure. Five procedures were aborted because morphological characteristics of the aneurysm or surrounding vessels made embolization technically difficult (two patients) or because of aneurysm rupture (two patients) or the appearance of a transient neurological deficit (one patient). CONCLUSIONS: Embolization of intracranial aneurysms performed using GDCs in the awake patient appears to be safe and feasible and allows intraprocedural evaluation of the patient. Potential advantages, including decreased cardiopulmonary morbidity rates, shorter hospital stay, and lower hospital costs, still require confirmation by a direct comparison with other anesthetic procedures.

Adult↗
PubMed2001

Europium fluorescence to visualize N-butyl 2-cyanoacrylate in embolized vessels of an arteriovenous malformation swine model.

BACKGROUND AND PURPOSE: Standard tissue staining using the lipid dye Oil-Red-O has been previously applied to stain vessel specimens, which were embolized with a mixture of n-butyl 2-cyanoacrylate (NBCA) and oil (Lipiodol). That technique, however, results in nonspecific and nonquantitative staining that does not provide the necessary differentiation between NBCA and Lipiodol. We present an innovative staining procedure that quantifies NBCA within treated tissues. METHODS: An arteriovenous malformation (AVM) model in swine was used to evaluate the polymerization characteristics of various ratios of Lipiodol/NBCA/glacial acetic acid (GAA) mixtures. To determine the depth of NBCA penetration within the AVM model and to characterize the polymerization patterns of various mixtures within the vessel, histologic cross- and longitudinal sections were prepared for microscopy. These paraffin-embedded tissue sections were stained with a europium aryl-beta-diketone complex (TEC) to improve differentiation between NBCA and Lipiodol. Quantification of NBCA and Lipiodol within the lumen of rete cross-sections was accomplished using image analysis software to determine percent luminal area occluded by embolization. RESULTS: Upon application of TEC, intense europium fluorescence was seen when the tissue samples were excited by low-power UV light (excitation at 365 nm; emission at 614 nm). The area of europium intensity within the lumen corresponded to NBCA concentration, and addition of GAA aided the NBCA distribution throughout the lumen without affecting fluorescence intensity. It was seen that NBCA could be easily differentiated from Lipiodol and that quantification could be readily performed on these sections because of the improved differentiation. For the case of a 50:50 (vol. %) mixture with an added 20 microL of GAA, luminal area distribution of Lipiodol, NBCA, and blood products was 42.6 +/- 3.5%, 33.8 +/- 5.7%, and 23.7 +/-2.7%, respectively. CONCLUSION: The rare earth metal europium, when added as a fluorescent chelate compound to histologic tissue sections, allowed for differentiation between NBCA and Lipiodol with good detail. These results have facilitated further characterization of NBCA polymerization for the use of AVM embolization.

Animals↗
PubMed2001

Using the flexibility index to compare batch and continuous activated sludge processes.

This paper considers the question of which is better: the batch or the continuous activated sludge processes? It is an important question because dissension still exists in the wastewater industry as to the relative merits of each of the processes. A review of perceived differences in the processes from the point of view of two related disciplines, process engineering and biotechnology, is presented together with the results of previous comparative studies. These reviews highlight possible areas where more understanding is required. This is provided in the paper by application of the flexibility index to two case studies. The flexibility index is a useful process design tool that measures the ability of the process to cope with long term changes in operation.

Bioreactors↗
PubMed2001

An overview of the posters presented at Watermatex 2000. III: Model selection and calibration/optimal experimental design.

This paper presents an overview of the posters presented in sessions 7 and 8 of the Watermatex 2000 conference. These posters present two aspects of modelling biological processes--model selection and calibration. Special attention is given to the papers on OED (Optimal Experimental Design), which is a method of optimising the data collection for model selection and calibration. The presence of these presentations at the conference highlights the continuing significance of modelling and stresses the requirement of improvements in modelling techniques. The papers provide some contribution to this end.

Calibration↗
PubMed2001

Operating space diagrams: a tool for designers of wastewater treatment plants.

Recent years have seen the introduction of new and varied designs of activated sludge plants. With increasing needs for higher efficiencies and lower costs, the possibility of a plant that operates more effectively has created the need for tools that can be used to evaluate and compare designs at the design stage. One such tool is the operating space diagram. It is the aim of this paper to present this tool and demonstrate its application and relevance to design using a simple case study. In the case study, use of the operating space diagram suggested changes in design that would improve the flexibility of the process. It also was useful for designing suitable control strategies.

Computer Simulation↗
PubMed2000

Horner's syndrome after carotid artery stenting: case report.

BACKGROUND: Angioplasty and stenting of various lesions of the carotid artery is gaining in popularity. Our knowledge of the efficacy and limitations of this promising technology is incomplete. Although Horner's syndrome and its variants have been described after traumatic, spontaneous, or surgical carotid dissection, it has not been reported after carotid artery stenting. CASE DESCRIPTION: A 36-year-old woman presented with left neck and ear pain and a 3-year history of rushing noises in her left ear. Angiography demonstrated evidence of dissection of the left internal carotid artery at the skull base with a pseudoaneurysm. The pseudoaneurysm was treated with a 6-mm diameter self-expanding stent in a 4-mm diameter left internal carotid artery. A few hours later, she developed partial Horner's syndrome with a subtle ipsilateral ptosis and miosis without anhidrosis. Angiography performed on the next day did not demonstrate further dissection or aneurysm growth but did show distention of the artery wall because of the stent. She did not develop any further sequelae. CONCLUSION: This case suggests that stretching of the artery wall may result in stretching of surrounding structures. The sympathetic fibers surrounding the internal carotid artery are clearly sensitive to this degree of stretch. Possible complications associated with stretch injury must be considered when choosing the stent diameter.

Adult↗
PubMed2000

A grading scale to predict outcomes after intra-arterial thrombolysis for stroke complicated by contrast extravasation.

OBJECTIVE: Contrast extravasation after intra-arterial thrombolysis for stroke occurs frequently and is identifiable on a computed tomographic (CT) scan, but it is often unrecognized or misdiagnosed. Few articles describing this phenomenon have been published. The clinical outcomes of patients after contrast extravasation are poorly understood. We designed a grading system to predict outcomes after contrast extravasation and tested the grading scale prospectively. METHODS: We studied 27 patients who had contrast extravasation exhibited on a CT scan immediately after intra-arterial thrombolysis. The National Institutes of Health Stroke Scale was used to quantify neurological examinations preoperatively, postoperatively, and at follow-up an average of 3 months later. A grading scale from 0 to 10 was developed from a retrospective analysis of the first 18 patients using odds ratios and Fisher's exact test. The grading system was then applied prospectively to the next 9 consecutive patients. RESULTS: Six components of the grading system were weighted approximately proportional to corresponding odds ratios: 1) incomplete recanalization (3 points), 2) prolonged angiographic blush (2 points), 3) hyperdensity greater than 150 Hounsfield units (2 points), 4) lesion volume greater than 50 cc exhibited on a CT scan (1 point), 5) lesion in eloquent parenchyma (1 point), and 6) hypodensity demonstrated on an immediate postoperative CT scan (1 point). The contrast extravasation grades for each outcome category (excellent, fair, poor, died) increased in stepwise fashion. There was a direct linear correlation between the assigned grade and National Institutes of Health Stroke Scale score improvement at follow-up. CONCLUSION: This grading system should prove useful as a preliminary guide for predicting outcomes of patients with contrast extravasation after intra-arterial thrombolysis for stroke. Further analysis in a large cohort of prospective patients is necessary to ensure extensibility.

Adult↗
PubMed2000

Abciximab as an adjunct to high-risk carotid or vertebrobasilar angioplasty: preliminary experience.

OBJECTIVE: Abciximab, a platelet glycoprotein IIb/IIIa receptor inhibitor, has been shown to reduce the risk of ischemic events associated with coronary intervention. However, its role in neurointerventional procedures needs to be defined. We prospectively evaluated our initial experience with the use of abciximab in a series of high-risk patients undergoing carotid, basilar, or vertebral artery angioplasty. METHODS: Patients were given an intravenous abciximab bolus (0.25 mg/kg), followed by infusion (10 microg/min) for a period ranging from 12 to 24 hours, as an adjunct to angioplasty in 20 procedures (19 patients). These patients were considered to be at high risk for thromboembolic events because of recent ischemic symptoms and/or complex lesion morphology. Before, immediately after, and 24 hours after the procedure, each patient was evaluated by a neurologist for the presence of new neurological deficits. Any bleeding or other complications during hospitalization were also recorded. Bleeding was defined as major (hemoglobin decrease >5 g/dl), minor (hemoglobin decrease 3-5 g/dl), or insignificant. RESULTS: Angioplasty was performed in the internal carotid artery (n = 13), vertebral artery (n = 4), or basilar artery (n = 2). Stents were placed across 13 lesions. In one patient, angioplasty could not be performed owing to technical difficulties; however, abciximab was administered because of extensive lesion manipulation. Intraprocedural heparin was given in 19 procedures (35-86 U/kg intravenously) and partially reversed in 6 procedures. Low-dose intra-arterial thrombolytic agents were administered in seven patients before the lesion was crossed. Two patients experienced transient neurological deficits either during (n = 1) or immediately after (n = 1) the procedure. Another patient had complete occlusion of the right vertebral artery after angioplasty with complete recanalization after 24 hours of abciximab infusion. Major or minor bleeding was not observed in any patient. Insignificant bleeding was observed in eight patients. Thrombocytopenia was observed in one patient who received concomitant administration of intravenous heparin and abciximab infusion. CONCLUSION: We observed a low frequency of neurological events in high-risk patients undergoing angioplasty with or without stent placement. Abciximab seems to be a relatively safe adjunct for carotid or vertebrobasilar endovascular intervention either alone or in combination with low-dose thrombolytics. Partial reversal of intraprocedural heparin should be considered to reduce the risk of postprocedural bleeding.

Abciximab↗
PubMed2000

Prevention and treatment of thromboembolic and ischemic complications associated with endovascular procedures: Part I--Pathophysiological and pharmacological features.

Thromboembolic and ischemic complications frequently occur during and after endovascular procedures, because of associated arterial injury and the thrombogenic characteristics of arterial catheters, contrast agents, and implanted devices such as coils and stents. Platelet adhesion, activation, and aggregation occurring at the site of arterial injury are mediated by local factors, including thromboxane A2 (inhibited by aspirin) and adenosine diphosphate (inhibited by ticlopidine and clopidogrel). Concomitantly, thrombin is formed by serial activation of clotting factors via contact with subendothelial tissue factor. Thrombin cleaves fibrinogen into fibrin. Thrombin activation is indirectly blocked by heparin and its analogs. However, after thrombin is clot-bound (with fibrin), it is relatively protected from heparin and is effectively blocked only by direct thrombin inhibitors (hirudin and its analogs). The final common pathway in clot formation is the binding of fibrinogen to platelets via platelet glycoprotein IIb/IIIa receptors, which is inhibited by antibodies to platelet IIb/IIIa receptors. New treatment modalities, such as the use of direct thrombin inhibitors and antibodies to platelet glycoprotein IIb/IIIa, seem to be more effective for prophylaxis and treatment than conventional anticoagulation and antiplatelet therapies.

Angioplasty, Balloon↗
PubMed2000

Prevention and treatment of thromboembolic and ischemic complications associated with endovascular procedures: Part II--Clinical aspects and recommendations.

We reviewed the incidence, risk factors, and clinical features of thromboembolic and ischemic events associated with diagnostic cerebral angiography, endovascular treatment of aneurysms using coils or balloons, angioplasty and stent placement to treat extracranial carotid artery stenosis, and embolization of arteriovenous malformations using glue or other embolic agents. We performed a cumulative analysis to determine the frequency and characteristics of these events and a subset analysis (whenever possible) to determine the benefits of various strategies for complication avoidance. Of the 1,547 patients who underwent Guglielmi detachable coil treatment, thromboembolic events were observed for 127 (8.2%), consisting of asymptomatic events for 12 patients, transient ischemic attacks for 29, and strokes for 86. The outcomes for the 86 patients with strokes were categorized as full recovery for 15, good recovery for 27, partial recovery for 19, no recovery for 11, death for 12, and undetermined outcome for 2. Of the 834 patients who underwent carotid angioplasty and stent placement, thromboembolic events were observed for 73 (8.8%), consisting of transient ischemic attacks for 26 patients and strokes for 47. The outcomes for the patients with strokes were categorized as full recovery for 20, good recovery for 15, partial recovery for 6, no recovery for 2, and death for 4. High rates of thromboembolic events were also observed with balloon occlusion of aneurysms (11%) or parent arteries (19%) and carotid angioplasty alone (5.9%). Arteriovenous malformation embolization was associated with an ischemic event/procedure rate of 9.4%. High rates of thromboembolic and ischemic complications, with subsequent morbidity and death, are associated with most endovascular procedures. Further research and the formulation of standard preventive guidelines may help to reduce these risks and improve the overall success of these procedures.

Angioplasty, Balloon↗
PubMed2000

Transradial approach for vertebral artery stenting: technical case report.

OBJECTIVE: We report the technique of transradial vertebral artery stenting for two patients in whom severe supra-aortic ectasia prevented ready access to the right vertebral artery origin. METHODS: An Allen test was performed to verify ulnar artery collateral flow in the hand. After the administration of local anesthesia, a 6-French sheath was introduced into the radial artery. To allay induced spasm, a mixture of heparin (5000 IU/ml), verapamil (2.5 mg), nitroglycerine (400 microg/ml, 0.25 ml), and lidocaine (2%, 1.0 ml) was infused through the introducer sheath. A microguidewire was positioned across the vertebral artery lesion, followed by placement of a balloon-expandable stent. RESULTS: Postdeployment angiography revealed improved vertebrobasilar system flow. There were no complications related to the radial artery. The patients tolerated the procedure without difficulty and were immediately ambulatory. CONCLUSION: This novel approach should be considered for endovascular procedures for which access to the vertebral artery origin via the femoral approach is limited.

Aged↗
PubMed2000

Effects of a mixture of a low concentration of n-butylcyanoacrylate and ethiodol on tissue reactions and the permanence of arterial occlusion after embolization.

OBJECTIVE: Cyanoacrylates are the most commonly used liquid embolic agents. For embolization of arteriovenous malformations, a mixture of a low concentration of n-butylcyanoacrylate (NBCA) and Ethiodol (Savage Laboratories, Melville, NY) has been recommended for deeper penetration of the nidus. Dilution of NBCA, however, might result in different degrees of tissue reaction and might influence the permanence of vessel occlusion, with an increased risk of vessel recanalization. We compared tissue reactions induced by different NBCA/Ethiodol mixtures and analyzed the permanence of their embolic effects. METHODS: NBCA was diluted with Ethiodol to prepare the following standard solutions: Mixture A, low concentration (NBCA/Ethiodol ratio of 20:80); Mixture B, high concentration (50:50). The study was designed in two parts, because tissue reactions after embolization are considered to be a combination of foreign body reactions to solidified material and reactions to the injured blood vessel. Foreign body reactions were studied by intramuscularly injecting both glue mixtures into the backs of 18 rats. Specimens were obtained at various times after implantation. Immunohistochemical analysis and esterase staining were used to detect macrophages and neutrophils, respectively. The densities of these inflammatory cells were calculated and statistically compared. To study the degree of vascular wall injury and the permanence of embolic effects, the renal arteries in 48 rabbits were embolized with NBCA Mixture A or B. Six specimens for each group were obtained at various times after embolization. RESULTS: There was no significant difference in foreign body reactions between groups treated with Mixtures A and B, at any time. However, the macrophage density was larger for both groups at 3 months versus 3 days and for the group treated with Mixture B at 3 months versus 2 weeks. There was no difference in the degree of vessel wall injury. None of the embolized vessels demonstrated evidence of recanalization. CONCLUSION: The low concentration of NBCA induced a tissue response similar to that of the high-concentration form. Embolized vessels exhibited no greater incidence of recanalization. Therefore, embolization of arteriovenous malformations with diluted NBCA may be safe.

Animals↗