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PubMed1998

Compensatory and excess retrieval: two types of endocytosis following single step depolarizations in bovine adrenal chromaffin cells.

1. Endocytosis following exocytosis evoked by single step depolarizations was examined in bovine adrenal chromaffin cells using high resolution capacitance measurements in perforated-patch voltage clamp recordings. 2. Endocytosis was detected as a smooth exponential decline in membrane capacitance to either the pre-stimulus level ('compensatory retrieval') or far below the pre-stimulus level ('excess retrieval'). During excess retrieval, > 10% of the cell surface could be internalized in under 5 s. 3. Compensatory retrieval was equal in magnitude to stimulus-evoked exocytosis for membrane additions > 100 fF (about fifty large dense-cored vesicles). In contrast, excess retrieval surpassed both the stimulus-evoked exocytosis, and the initial capacitance level recorded at the onset of phase-tracking measurements. Cell capacitance was not maintained at the level achieved by excess retrieval but slowly returned to pre-stimulus levels, even in the absence of stimulation. 4. A large percentage of capacitance increases < 100 fF, usually evoked by 40 ms depolarizations, were not accompanied by membrane retrieval. 5. Compensatory retrieval could occur with any amount of Ca2+ entry, but excess retrieval was never triggered below a threshold Ca2+ current integral of 70 pC. 6. The kinetics of compensatory and excess retrieval differed by an order of magnitude. Compensatory retrieval was usually fitted with a single exponential function that had a median time constant of 5.7 s. Excess retrieval usually occurred with double exponential kinetics that had an extremely fast first time constant (median, 670 ms) and a second time constant indistinguishable from that of compensatory retrieval. 7. The speed of compensatory retrieval was Ca2+ dependent: the largest mono-exponential time constants occurred for the smallest amounts of Ca2+ entry and decreased with increasing Ca2+ entry. The Ca2+ dependence of mono-exponential time constants was disrupted by cyclosporin A (CsA), an inhibitor of the Ca(2+)- and calmodulin-dependent phosphatase calcineurin. 8. CsA also reduced the proportion of responses with excess retrieval, but this action was caused by a shift in Ca2+ entry values below the threshold for activation. The lower total Ca2+ entry in the presence of CsA was due to an increase in the rate of Ca2+ current inactivation rather than a reduction in peak amplitude. 9. Our data suggest that compensatory and excess retrieval represent two independent, Ca(2+)-regulated mechanisms of rapid membrane internalization in bovine adrenal chromaffin cells. Alternatively, there is a single membrane internalization mechanism that can switch between two distinct modes of behaviour.

Adrenal Glands↗

PubMed2005

Heat-induced retrieval of immunogold labeling for nucleobindin and osteoadherin from Lowicryl sections of bone.

The main purpose of this study was to examine whether antigens can be retrieved by heating Lowicryl sections of paraformaldehyde-fixed (PFF) tissues. Thus the intensity of the immunogold signal for two bone proteins (Nucleobindin (Nuc) and osteoadherin (OSAD)) was compared in retrieved and non-retrieved sections of PFF rat bone. As an additional experiment, the effect of antigen retrieval (for Nuc) in sections of tissue primary stabilized by high pressure freezing with subsequent freeze substitution (HPF-FS) was studied. Finally, the tissue distribution patterns of Nuc labeling were compared in non-retrieved HPF-FS sections to that of retrieved and non-retrieved PFF sections. Antigen retrieval in Lowicryl sections of PFF tissues showed significantly enhanced labeling intensity for both proteins in all compartments where they are known to occur. Retrieved PFF Lowicryl sections showed only minor ultrastructural differences compared to non-retrieved ones. Retrieval of HPF-FS sections exhibited no enhancement of labeling but rather a slight reduction, which was significant in the cytoplasm and in cartilage. Furthermore, striking ultrastructural differences were observed in retrieved HPF-FS sections compared to non-retrieved ones with loss of coherence and structure in sections subjected to heating. Comparison of the distribution patterns of Nuc in the sections of PFF and HPF-FS tissues showed discrepancy in most compartments. Antigen retrieval by heating Lowicryl sections of PFF tissues significantly enhances immunogold labeling in all cell compartments where the bone proteins are known to occur. However, the procedure may distort the tissue distribution pattern of bone proteins.

Acrylic Resins↗

PubMed2001

Günther Tulip Retrievable Vena Cava Filter: results from the Registry of the Canadian Interventional Radiology Association.

PURPOSE: To report data collected by the Canadian Registry of the Günther Tulip Retrievable Filter (GTF). MATERIALS AND METHODS: Between February 1998 and December 2000, 90 patients at eight hospitals underwent implantation of 91 GTFs. There were 45 male patients and 45 female patients, age 17-88 years, with a mean age of 49 years. Indications for filter placement were pulmonary embolism (PE) or deep vein thrombosis (DVT) with a contraindication to anticoagulation in 83 patients, prophylaxis after massive PE in one, prophylaxis for proximal free-floating thrombus in one, and prophylaxis with no DVT or PE in six patients (major trauma, n = 4; high preoperative risk, n = 2). GTF retrieval was attempted in selected patients from a right internal jugular vein approach. RESULTS: One GTF was inadvertently placed in the right iliac vein and could not be retrieved. There were no other major placement complications. GTF retrieval was attempted in 52 patients (53 GTFs); 52 GTFs were successfully retrieved from 51 patients. Implantation times were 2-25 days (mean, 9 d). Of these 51 patients, 37 underwent follow-up for 5-420 days (mean, 103 d) after filter retrieval. Four patients (8% of retrieved GTFs) required reinsertion of a permanent filter 17-167 days (mean, 78 d) after GTF retrieval as a result of bleeding from anticoagulation (n = 2) or because the patient required further surgery (n = 2). One other patient had recurrent DVT 230 days after retrieval; no PE or other complication was documented in the retrieval group. GTFs were not retrieved from 39 patients for various reasons. Of these 39 patients, 25 underwent follow-up 7-420 days (mean, 85 d) after filter placement. Two patients developed filter occlusion (5%); no other complications were documented. CONCLUSION: The GTF has a broad range of utility: it can be used as a permanent filter or retrieved after implantation periods of 15 days and possibly longer. However, indications for retrieval require further study, as does the maximum implantation time.

Adolescent↗

PubMed2006

Outcomes with retrievable inferior vena cava filters: a multicenter study.

PURPOSE: To retrospectively review the outcomes after placement and retrieval of retrievable inferior vena cava (IVC) filters at two academic medical centers. MATERIALS AND METHODS: All patients who underwent retrievable filter placement between May 2001 and December 2005 were included. Hospital records at both institutions were reviewed, and relevant data were collected concerning the placement and retrieval of all removable filters. RESULTS: A total of 197 patients underwent placement of a retrievable IVC filter. Of those, 143 patients (72.5%) had Günther Tulip filters (GTFs) placed, and 54 patients (27.5%) had Recovery filters placed. A total of 94 patients underwent attempted filter retrieval, accounting for just less than half of all retrievable filters placed during the study period (47.7%). Retrievals were successful in 80 patients (85.1%). Half the retrieval failures (n = 7) were the result of thrombus within the filter, and technical difficulties (eg, filter embedded in IVC wall, tilted filter) were the cause of retrieval failure in the other half. There was no significant difference in retrieval failure rates between the GTF and Recovery filter (16.4% vs 9.5%, respectively). GTFs were removed after a median implantation time of 11 days (range, 1-139 d), whereas Recovery filters were removed after a median implantation time of 28 days (range, 6-117 d). CONCLUSIONS: Placement and retrieval of nonpermanent IVC filters can be performed safely with a high technical success rate. In patients at high risk for venous thromboembolism and contraindication to anticoagulation, retrievable filters may be used aggressively to prevent the potentially devastating outcome of pulmonary embolism.

Humans↗

PubMed2004

A similarity learning approach to content-based image retrieval: application to digital mammography.

In this paper, we describe an approach to content-based retrieval of medical images from a database, and provide a preliminary demonstration of our approach as applied to retrieval of digital mammograms. Content-based image retrieval (CBIR) refers to the retrieval of images from a database using information derived from the images themselves, rather than solely from accompanying text indices. In the medical-imaging context, the ultimate aim of CBIR is to provide radiologists with a diagnostic aid in the form of a display of relevant past cases, along with proven pathology and other suitable information. CBIR may also be useful as a training tool for medical students and residents. The goal of information retrieval is to recall from a database information that is relevant to the user's query. The most challenging aspect of CBIR is the definition of relevance (similarity), which is used to guide the retrieval machine. In this paper, we pursue a new approach, in which similarity is learned from training examples provided by human observers. Specifically, we explore the use of neural networks and support vector machines to predict the user's notion of similarity. Within this framework we propose using a hierarchal learning approach, which consists of a cascade of a binary classifier and a regression module to optimize retrieval effectiveness and efficiency. We also explore how to incorporate online human interaction to achieve relevance feedback in this learning framework. Our experiments are based on a database consisting of 76 mammograms, all of which contain clustered microcalcifications (MCs). Our goal is to retrieve mammogram images containing similar MC clusters to that in a query. The performance of the retrieval system is evaluated using precision-recall curves computed using a cross-validation procedure. Our experimental results demonstrate that: 1) the learning framework can accurately predict the perceptual similarity reported by human observers, thereby serving as a basis for CBIR; 2) the learning-based framework can significantly outperform a simple distance-based similarity metric; 3) the use of the hierarchical two-stage network can improve retrieval performance; and 4) relevance feedback can be effectively incorporated into this learning framework to achieve improvement in retrieval precision based on online interaction with users; and 5) the retrieved images by the network can have predicting value for the disease condition of the query.

Algorithms↗

PubMed2001

Percutaneous retrieval of the Tulip vena cava filter: feasibility, short- and long-term changes--an experimental study in dogs.

PURPOSE: To evaluate experimentally the retrievability of the Tulip inferior vena cava (IVC) filter in an in vivo study. Changes which accompany venous healing after filter retrieval were investigated. METHODS: In 12 dogs, 23 filters were inserted percutaneously into the lumbar and intrahepatic segments of the IVC. Two weeks (n = 21 filters) or 3 weeks (n = 2 filters) after insertion, filter retrieval was attempted through an 11 Fr coaxial retrieval sheath system placed via the jugular vein. Follow-up studies before and after filter retrieval included cavography, computed tomography and intravascular ultrasound of the IVC. Seven dogs were killed immediately after filter retrieval to confirm short-term changes of the IVC, and 5 dogs were killed 6 months after filter retraction to evaluate long-term changes of the IVC related to filter retrieval. Post-mortem examinations and histologic specimens of the IVC were obtained to evaluate caval wall abnormalities secondary to filter removal. RESULTS: All but one filter were successfully retrieved 2 weeks post-implantation. However, 3 weeks after insertion, filter retrieval was impossible. There were no complications caused by filter extraction. Follow-up studies after filter retrieval revealed no significant changes in the integrity, morphology or composition of the IVC and pericaval tissue. Histologic examination 6 months after filter retrieval revealed only flimsy fibrotic intimal plaques at the sites of former hook insertion. CONCLUSION: The Tulip filter allows percutaneous insertion and retrieval up to 14 days after insertion, suggesting that it may be useful for either permanent or temporary prophylaxis against pulmonary embolism.

Animals↗

PubMed1999

Kidney damage during organ retrieval: data from UK National Transplant Database. Kidney Advisory Group.

BACKGROUND: Kidney damage at organ retrieval is believed to be an increasing problem that is under reported. We aimed to identify the true rate of such damage and assess the effects on transplant survival. METHODS: Data from the UK National Transplant Database were analysed on all cadaveric kidneys donated over a 5-year period in the UK. Records indicated whether kidneys had been retrieved by a liver or renal surgical team and whether damage was noted at the time of retrieval or at the transplant procedure. Multivariate Cox's regression models were fitted to 1-year and 3-year transplant-survival data in those kidneys that were transplanted between 1992 and 1994. FINDINGS: Of 9014 kidneys retrieved, 96 could not be transplanted because of damage sustained at retrieval. Damage was reported in 1726 (19%) kidneys although by both donor and recipient centres in only 270 (3%). 1070 (62%) of the damaged organs were from donors aged 40 years or older. Reported kidney damage was more likely for retrievals of kidney only by a renal team (503 [26%]) than for multiorgan retrieval (454 [21%]), the proportion was lower when a liver team retrieved both liver and kidneys (415 [17%]). 794 (14%) kidneys retrieved and retained locally were reported as damaged, compared with 932 (29%) kidneys which had been exported. Donors' age had a significant effect on both 1-year and 3-year transplant survival (p<0.01 for both) but kidney damage did not (1 year p=0.40; 3 year p=0.81). INTERPRETATION: Despite the high rate of damage to kidneys at retrieval, most of the organs can be transplanted with no adverse effect on transplant survival. Kidney damage is least likely to occur with kidneys from young donors, and when liver teams or centres undertaking more than 50 retrievals per year do the retrieval.

Adolescent↗

PubMed2004

Retrieving physiotherapy patient records in selected health care facilities in South Africa--is record keeping compromised?

PURPOSE: The purpose of this study was to evaluate the process and feasibility of retrieving patient records in a variety of physiotherapy care settings in the Gauteng province in the Republic of South Africa. METHODS: Thirteen public and private health care facilities providing physiotherapy services were studied. Multiple methods of data collection (facility walk-through observation aided by a researcher designed checklist, in-depth interviews and attempting to retrieve physiotherapy records) were employed to evaluate the process of retrieving physiotherapy patient records, determine physiotherapy record retrieval rates and to determine the factors that were influencing record retrieval. RESULTS: The process of retrieving physiotherapy records was arduous and multi-faceted, with some health care facilities allowing patients to take their records home. A final retrieval rate of 46% (36.3% - 100%) was obtained. An odds ratio calculation revealed that it was 13.09 (CI: 8.99 - 19.13; p<0.001) times more possible to retrieve records of patients treated in private physiotherapy care settings (87.4% retrieval rate) than in public sector physiotherapy care settings (34.67% retrieval rate). CONCLUSIONS: This study concludes that the process of retrieving physiotherapy records was arduous and lacked uniformity in public sector hospitals. Further a low physiotherapy record retrieval rate was obtained.

Community Health Services↗

PubMed1997

The effect of age on retrieval of local anesthetic solution from the epidural space.

UNLABELLED: We conducted this prospective study to determine whether advancing age is correlated with retrieval of local anesthetic solution from the epidural space. Three hundred forty-six patients (ASA physical status I or II, 20-93 yrs of age, 177 female and 169 male patients) undergoing epidural anesthesia were enrolled. The epidural space was identified by a loss of resistance technique using air, and a catheter was introduced 3 cm. Three milliliters of 2% lidocaine with epinephrine was injected as a study dose by hand at a rate of 1 mL/s with the patient in the supine position. The syringe was immediately aspirated to retrieve the local anesthetic solution. A retrieved volume of 0.5 mL or more with a glucose concentration less than 6 mg/dL was defined as retrieval positive, and a volume of less than 0.5 mL was defined as retrieval negative. There was a significant correlation between age and retrieval volume among all the patients (Y = 0.008X-0.222, P < 0.0001) with a significant increase in the positive retrieval incidence and volume from the patients in their 50s (11%, 0.6 +/- 0.3 mL) to the patients in their 60s (26%, 1.0 +/- 0.6 mL) (P < 0.05 for both). The incidence of positive retrieval and the retrieval volume were greater in the patients in their 60s and older (30%, 1.1 +/- 0.63 mL) than in the younger than 60 (10%, 0.6 +/- 0.3 mL) (P < 0.0001 and P < 0.001). The glucose concentration was 2.3 +/- 1.2 mg/dL in the positive cases. We conclude that there is a weak positive correlation between age and the local anesthetic solution retrieved from the epidural space. IMPLICATIONS: We conducted a study in 346 patients to determine whether advancing age could be correlated with retrieval of local anesthetic solution from the epidural space. We found a weak positive correlation between advanced age and the amount of solution retrievable from the epidural space. Further studies are required to determine whether this phenomenon may call for dose adjustments in patients aged more than 60 yrs.

Adult↗

PubMed2005

[Does oocyte retrieval influence the following morphological quality of embryos?].

OBJECTIVE: To verify that the number of retrieved oocytes influence the following morphological quality of transferred embryos and the success of IVF treatment. DESIGN: A retrospective study. SETTING: Clinic of assisted medicine and gynecology, Zlin. METHODS: By observing the collection is composed of 837 IVF cycles with embryotransfer, which were practised between June 2002 and December 2004. To observe the number of retrieved oocytes, following morfological quality of transferred embryos, (number of clinical pregnancies). RESULTS: We found that in cycles with more retrieved oocytes (7 oocytes and more), there were embryos of first morphological quality transferred significantly more frequently (59.2% cycles, p < 0.001) than in cycles with 1-6 retrieved oocytes. Morphologicaly abnormal embryos were found in cycles with more retrieved oocytes (7 oocytes and more) and transferred significantly less frequently (13.1% cycles, p < 0.001) than in cycles with 1-6 retrieved oocytes (34.8% cycles). We have found that on the retrieval of 16-18 oocytes, there were embryos of first morphological quality transferred in 67.4% cycles of treatment (p = 0.002). The number of cycles with transferred morphological abnormal embryos is decreasing in relation with increase of oocyte retrieval (p = 0.002). Most of clinical pregnancies were achieved in IVF cycles with retrieval of 16-18 oocytes (clinical pregnancies was achieved in 50.0% cycles, p < 0.001). CONCLUSION: The results show that the number of retrieved oocytes was influenced following morphological quality of transferred embryos. In IVF cycles with more retrieved oocytes there are transferred embryos of first morphological quality more frequently. These embryos have higher implantation potential. The number and quality retrieved oocytes are possibly more effective with type and dosing of hormonal stimulation, which should be suitable for every patient.

Adult↗

PubMedDate not supplied

The granularity of medical narratives and its effect on the speed and completeness of information retrieval.

OBJECTIVE: Using electronic rather than paper-based record systems improves clinicians' information retrieval from patient narratives. However, few studies address how data should be organized for this purpose. Information retrieval from clinical narratives containing free text involves two steps: searching for a labeled segment and reading its content. The authors hypothesized that physicians can retrieve information better when clinical narratives are divided into many small, labeled segments ("high granularity"). DESIGN: The study tested the ability of 24 internists and 12 residents at a teaching hospital to retrieve information from an electronic medical record--in terms of speed and completeness--when using different granularities of clinical narratives. Participants solved, without time pressure, predefined problems concerning three voluminous, inpatient case records. To mitigate confounding factors, participants were randomly allocated to a sequence that was balanced by patient case and learning effect. RESULTS: Compared with retrieval from undivided notes, information retrieval from problem-partitioned notes was 22 percent faster (statistically significant), whereas retrieval from notes divided into organ systems was only 11 percent faster (not statistically significant). Subdividing segments beyond organ systems was 13 percent slower (statistically significant) than not subdividing. Granularity of medical narratives affected the speed but not the completeness of information retrieval. CONCLUSION: Dividing voluminous free-text clinical narratives into labeled segments makes patient-related information retrieval easier. However, too much subdivision slows retrieval. Study results suggest that a coarser granularity is required for optimal information retrieval than for structured data entry. Validation of these conclusions in real-life clinical practice is recommended.

Cross-Over Studies↗

PubMed1980

Answer-passage retrieval by text searching.

Passage retrieval (already operational for lawyers) has advantages in output form over reference retrieval and is economically feasible. Previous experiments in passage retrieval for scientists have demonstrated recall and false retrieval rates as good or better than those of present reference retrieval services. The present experiment involved a greater variety of forms of retrieval question. In addition, search words were selected independently by two different people for each retrieval question. The search words selected, in combination with the computer procedures used for passage retrieval, produced average recall ratios of 72 and 67%, respectively, for the two selectors. The false retrieval rates were (except for one predictably difficult question) respectively 13 and 10 falsely retrieved sentences per answer-paper retrieved.

Abstracting and Indexing↗

PubMed2001

Comparative electrophysiological and hemodynamic measures of neural activation during memory-retrieval.

The spatial and temporal characteristics of the brain processes underlying memory retrieval were studied with both event-related potentials (ERP) and positron emission tomography (PET) techniques. Subjects studied lists of 20 words and then performed episodic (old/new judgment) or semantic (living/nonliving decision) retrieval tasks on multiple four-item test lists, each lasting 10 sec. The PET and ERP measurements at test were assessed in relation to both the task (episodic vs. semantic) and the item (old vs. new or living vs. nonliving). Episodic retrieval was associated with increased blood flow in the right frontal lobe (Brodmann Area 10) and a sustained, slowly developing positive ERP shift recorded from the right frontopolar scalp. Semantic retrieval was associated with increased blood flow in the left frontal (Area 45) and temporal (Area 21) lobes but no clear ERP concomitant. The two retrieval tasks also differed from each other in the ERPs to single items in an early (300-500 ms) time window. Item-related comparisons yielded convergent results mainly if the retrieved information was relevant to the given task (e.g., old/new items during episodic retrieval and living/nonliving items during semantic retrieval). Episodically retrieved old items were associated with increased blood flow in the left medial temporal lobe and a transient increase in the amplitude of the late positive component (500-700 ms) of the ERP. Semantically retrieved living items were associated with increased blood flow in the left frontal cortex and anterior cingulate and a transient late frontal slow wave (700-1,500 ms) in the ERPs. These results indicate that the brain regions engaged in memory retrieval are active in either a sustained or transient manner. They map task-related processes to sustained and item-related processes to transient neural activity. But they also suggest that task-related factors can transiently affect early stages of item processing.

Adult↗

PubMed1999

Math-Fact Retrieval as the Cognitive Mechanism Underlying Gender Differences in Math Test Performance.

Males from select populations receive better scores on standardized math achievement tests than females. The research reported in this article evaluates the hypothesis that the reason for these differences is that males are faster at retrieving basic math facts. Studies 1-3 demonstrate that math-fact retrieval predicts performance on math achievement tests with students in grades 5-8 and in college. Studies 4-6 show that males and females in grades 2-8 and in college have different patterns of math-fact retrieval performance and that males at the high positive end of the retrieval distribution are faster than comparable females. Study 5 also demonstrates that math-fact retrieval varies in three populations (Anglo-American, Chinese-American, Hong Kong Chinese) and that speed of retrieval improves with practice. Studies 7-9 tested the hypothesis that males are faster than females on retrieval tasks in general. Study 7 showed that there were no gender differences on simple retrieval tasks, and Studies 8 and 9 showed that females were slightly faster than males on verbal-processing tasks. The General Discussion indicates that the math-fact retrieval hypothesis is consistent with previous research. It also relates the math-fact retrieval hypothesis to theories of cognitive performance and introduces the practice and engagement hypothesis. This hypothesis explains the origin of gender differences in math and reading and relates those differences to the existing literature on gender differences in academic performance. The article concludes with a description of needed future research and a discussion of the educational implications of the math-fact retrieval hypothesis. Copyright 1999 Academic Press.

Journal Article↗

PubMed2005

The control of memory retrieval: insights from event-related potentials.

Effective performance on episodic retrieval tasks requires the ability to flexibly adapt to changing retrieval demands ('retrieval orientations'; [M.D. Rugg, E.L. Wilding, Retrieval processing and episodic memory, Trends Cogn. Sci. 4 (2000) 108-115]). We used event-related potentials (ERP) to examine whether maintaining a specific retrieval orientation and changing flexibly between different retrieval demands are mediated by the same brain systems or whether dissociable aspects of cognitive control are involved. Sixteen participants performed two recognition memory tasks. One required mere old/new decisions for words (general task), whereas the other task required the additional retrieval of each word's study font typeface (specific task). Furthermore, the participants either were asked to perform the same task continuously or to switch between the two tasks after every second test word. ERPs elicited by correctly rejected new (unstudied) words were analyzed. This enabled us to examine the ERP correlates of having adapted and maintained a task instruction as required during continuous blocks and of flexibly changing between retrieval demands during alternating blocks. The ERP analysis revealed more positive-going ERP slow waves for alternating blocks than for continuous blocks over bilateral frontal recording sites. This effect started around 250 ms after the test word and extended for several hundred milliseconds. As it was present for trials requiring a switch to the other task or to stay on the same task between 500 and 750 ms and no differences between the latter two trial types were obtained, it can be assumed that it is more related to general coordination requirements in alternating blocks, rather than to the actual control required to switch the retrieval task set. In addition, contrasting ERPs for the two task types revealed more positive-going ERP slow waves in the specific task than in the general task in the continuous blocks at lateral frontal recording sites between 250 and 700 ms. Together, these findings suggest that there are electrophysiologically dissociable aspects of cognitive control, namely for adapting and maintaining a retrieval orientation and for flexibly changing between varying retrieval demands.

Adult↗

PubMed1998

Preliminary report on prediction of spinal cord ischemia in endovascular stent graft repair of thoracic aortic aneurysm by retrievable stent graft.

OBJECTIVE: To predict spinal cord ischemia after endovascular stent graft repair of descending thoracic aortic aneurysms, temporary interruption of the intercostal arteries (including the aneurysm) was performed by placement of a novel retrievable stent graft (Retriever) in the aorta under evoked spinal cord potential monitoring. METHODS: From February 1995 to October 1997, endovascular stent graft repair of descending thoracic aortic aneurysms was performed in 49 patients after informed consent was obtained. In 16 patients with aneurysms located in the middle and distal segment of the descending aorta, the Retriever was placed temporarily before stent graft deployment. The Retriever consisted of two units of self-expanding zigzag stents connected in tandem with stainless steel struts. Each strut was collected in a bundle fixed to a pushing rod, and the stent framework was lined with an expanded polytetrafluoroethylene sheet. The Retriever was delivered beyond the aneurysm through a sheath and was retracted into the sheath 20 minutes later. A stent graft for permanent use was deployed in patients whose predeployment test results with the Retriever were favorable. Evoked spinal cord potential was monitored throughout placement of the Retriever and stent grafting until the next day. RESULTS: The Retriever was placed in 17 aneurysms in 16 patients. There were no changes in amplitude or latency of evoked spinal cord potential records obtained before or during Retriever placement. After withdrawal of the Retriever, all aneurysms were excluded from circulation immediately after permanent stent grafting. There were no changes in evoked spinal cord potential, nor were neurologic deficits seen after stent graft deployment in any patient. CONCLUSIONS: These results suggest that predeployment testing with the Retriever under evoked spinal cord potential monitoring is promising as a predictor of spinal cord ischemia in candidates for stent graft repair of thoracic aortic aneurysms.

Aged↗

PubMed1999

Improved bidirectional retrieval of sparse patterns stored by Hebbian learning.

The Willshaw model is asymptotically the most efficient neural associative memory (NAM), but its finite version is hampered by high retrieval errors. Iterative retrieval has been proposed in a large number of different models to improve performance in auto-association tasks. In this paper, bidirectional retrieval for the hetero-associative memory task is considered: we define information efficiency as a general performance measure for bidirectional associative memory (BAM) and determine its asymptotic bound for the bidirectional Willshaw model. For the finite Willshaw model, an efficient new bidirectional retrieval strategy is proposed, the appropriate combinatorial model analysis is derived, and implications of the proposed sparse BAM for applications and brain theory are discussed. The distribution of the dendritic sum in the finite Willshaw model given by Buckingham and Willshaw [Buckingham, J., & Willshaw, D. (1992). Performance characteristics of associative nets. Network, 3, 407-414] allows no fast numerical evaluation. We derive a combinatorial formula with a highly reduced evaluation time that is used in the improved error analysis of the basic model and for estimation of the retrieval error in the naive model extension, where bidirectional retrieval is employed in the hetero-associative Willshaw model. The analysis rules out the naive BAM extension as a promising improvement. A new bidirectional retrieval algorithm - called crosswise bidirectional (CB) retrieval - is presented. The cross talk error is significantly reduced without employing more complex learning procedures or dummy augmentation in the pattern coding, as proposed in other refined BAM models [Wang, Y. F., Cruz, J. B., & Mulligan, J. H. (1990). Two coding strategies for bidirectional associative memory. IEEE Trans. Neural Networks, 1(1), 81-92; Leung, C.-S., Chan, L.-W., & Lai, E. (1995). Stability, capacity and statistical dynamics of second-order bidirectional associative memory. IEEE Trans. Syst. Man Cybern., 25(10), 1414-1424]. The improved performance of CB retrieval is shown by a combinatorial analysis of the first step and by simulation experiments: it allows very efficient hetero-associative mapping, as well as auto-associative completion for sparse patterns - the experimentally achieved information efficiency is close to the asymptotic bound. The different retrieval methods in the hetero-associative Willshaw matrix are discussed as Boolean linear optimization problems. The improved BAM model opens interesting new perspectives, for instance, in information retrieval it allows efficient data access providing segmentation of ambiguous user input, relevance feedback and relevance ranking. Finally, we discuss BAM models as functional models for reciprocal cortico-cortical pathways, and the implication of this for a more flexible version of Hebbian cell-assemblies.

Journal Article↗

PubMed2000

Günther Tulip filter: preliminary clinical experience with retrieval.

PURPOSE: The Günther Tulip filter is a permanent filter that has a hook to permit retrieval. The authors report their preliminary clinical evaluation of the filter with regard to feasibility and safety of retrieval. MATERIALS AND METHODS: Nine men and six women who ranged in age from 17 to 79 years (mean, 51 years) underwent treatment with use of the Günther Tulip filter. Patients judged to require caval interruption for < 14 days were selected to receive the filter and retrieval was planned for all patients. Indications for filter placement were: recent pulmonary embolism (PE) or proximal deep vein thrombosis (DVT) with a contraindication to anticoagulation (11 patients), massive PE treated with thrombolytic therapy (one patient), PE with heparin-induced thrombocytopenia (one patient), and prophylaxis after major trauma (two patients). Patients were followed for inferior vena cava (IVC) thrombosis, bleeding, and recurrent DVT or PE. RESULTS: In all nine patients in whom it was attempted, the filter was successfully snared and retrieved via a jugular approach. The mean implantation period was 8.6 days (range, 5-13 days). Retrieval required 2.2-13 minutes (mean 5.3 minutes) of fluoroscopy. No caval injuries occurred as a result of retrieval. All retrieved filters had strands of organized thrombus on the filter struts. The patients were followed for 52-285 days (mean, 115 days) after retrieval. One patient developed a recurrent DVT 230 days after retrieval. No other patients developed a recurrent DVT and no patients developed IVC thrombosis, bleeding, or PE. Six filters were not retrieved: five because of an ongoing contraindication to anticoagulation and one because the patient died of causes unrelated to the filter. CONCLUSION: This preliminary study confirms the feasibility and safety of retrieval of the Günther Tulip filter up to 13 days after implantation.

Adolescent↗