Results of the North American Complex Abdominal Aortic Debranching (NACAAD) Registry

BACKGROUND

Hybrid debranching repair of pararenal and thoracoabdominal aortic aneurysms was initially designed as a better alternative to standard open repair, addressing the limitations of endovascular repair involving the visceral aorta. We reviewed the collective outcomes of hybrid debranching repairs using extra-anatomic, open surgical debranching of the renal-mesenteric arteries, followed by endovascular aortic stenting.

METHODS

Data from patients who underwent hybrid repair in 14 North American institutions during 10 years were retrospectively reviewed. Society of Vascular Surgery scores were used to assess comorbidity risk. Early and late outcomes, including mortality, morbidity, reintervention, and patency were analyzed.

RESULTS

A total of 208 patients (118 male; mean age, 71±8 years old) were treated by hybrid repair with extraanatomic reconstruction of 657 renal and mesenteric arteries (mean 3.2 vessels/patient). Mean aneurysm diameter was 6.6±1.3 cm. Thoracoabdominal aortic aneurysms were identified in 163 (78%) patients and pararenal aneurysms in 45 (22%). A single-stage repair was performed in 92 (44%) patients. The iliac arteries were the most common source of inflow (n=132; 63%), and most (n=150; 72%) had 3 or more bypasses. There were 30 (14%) early deaths, ranging widely across sites (0%-21%). A Society of Vascular Surgery comorbidity score >15 was the primary predictor of early mortality (P<0.01), whereas mortality was 3% in a score ≤9. Early complications occurred in 140 (73%) patients and included respiratory complications in 45 patients (22%) and spinal cord ischemia in 22 (11%), of whom 10 (45%) fully recovered. At 5 years, survival was 61±5%, primary graft patency was 90±2%, and secondary patency was 93±2%. The most significant predictor of late mortality was renal insufficiency (P<0.0001).

CONCLUSIONS

Mortality after hybrid repair and visceral debranching is highly variable by center, but strongly affected by preoperative comorbidities and the centers' experience with the technique. With excellent graft patency at 5 years, the outcomes of hybrid repair done at centers of excellence and in carefully selected patients may be comparable (or better) than traditional open or even totally endovascular approaches. However, in patients already considered as high-risk for surgery, it may not offer better outcomes.

Increased climate pressure on the agricultural frontier in the Eastern Amazonia-Cerrado transition zone

Several large-scale drivers of both anthropogenic and natural environmental changes are interacting nonlinearly in the transition zone between eastern Amazonia and the adjacent Cerrado, considered to be another Brazilian agricultural frontier. Land-use change for agrobusiness expansion together with climate change in the transition zone between eastern Amazonia and the adjacent Cerrado may have induced a worsening of severe drought conditions over the last decade. Here we show that the largest warming and drying trends over tropical South America during the last four decades are observed to be precisely in the eastern Amazonia-Cerrado transition region, where they induce delayed wet-season and worsen severe drought conditions over the last decade. Our results evidence an increase in temperature, vapor pressure deficit, subsidence, dry-day frequency, and a decrease in precipitation, humidity, and evaporation, plus a delay in the onset of the wet season, inducing a higher risk of fire during the dry-to-wet transition season. These findings provide observational evidence of the increasing climatic pressure in this area, which is sensitive for global food security, and the need to reconcile agricultural expansion and protection of natural tropical biomes.

Elective Resection of Symptomatic Arteriovenous Fistulae and Grafts in Patients with Functioning Renal Allografts at A High Volume Transplant Hospital

OBJECTIVE

Patients with functioning renal allografts may need ligation of pre-existing hemodialysis conduits. Chronic immunosuppression for renal allografts may adversely affect wound healing and perioperative complications following these procedures. We sought to analyze outcomes following elective ligation and resection of symptomatic arteriovenous (AV) access in immunosuppressed patients with renal allografts no longer requiring dialysis at a high-volume renal transplant hospital.

METHODS

We retrospectively reviewed procedure codes for hemodialysis access resection and revision from 2014-2020 at a single academic tertiary care hospital. Patients who underwent complete or subtotal dialysis access resection with a functioning renal allograft were included for analysis of preoperative, operative, and postoperative outcomes. We performed descriptive statistics, and student's t-test using Microsoft Excel.

RESULTS

Thirty-four patients met inclusion criteria. The majority were male, 56%, and the most common causes of renal failure were hypertension and diabetes, respectively. Ligation and resection of proximal upper extremity access was performed in 68%. The mean operative time was 126 minutes with pain being the most common indication for intervention. Four patients required arterial reconstruction. Mean postoperative follow-up was 13 months. Arm pain and swelling resolved in 100% and 88% of patients following AV access resection, respectively. No impairment in mean postoperative glomerular filtration rates were noted. One patient required hemodialysis and died three months after fistula resection following complications from treatment of a newly diagnosed neuroendocrine tumor and subsequent fungemia, CONCLUSION: Elective operative resection of symptomatic AV access may be performed safely in immunosuppressed patients with functioning renal transplants. The risk of allograft impairment and/or failure as a result of AV access resection in our series was low. Elective ligation and resection can be achieved with low mortality, excellent symptomatic relief, and few wound complications despite chronic immunosuppression.

Mutacytin-1, a New C-Type Lectin-Like Protein from the Venezuelan Cuaima (Lachesis muta muta Linnaeus, 1766) (Serpentes: Viperidae) Snake Venom Inducing Cardiotoxicity in Developing Zebrafish (Danio rerio) Embryos

Envenomation by the Venezuelan bushmaster snake (Lachesis muta muta) (Serpentes: Viperidae) is characterized by local and cardiac alterations. This study investigates the in vivo cardiac dysfunction, tissue destruction, and cellular processes triggered by Lachesis muta muta snake crude venom and a C-type lectin (CTL)-like toxin named Mutacytin-1 (MC-1). The 28 kDa MC-1 was obtained by molecular exclusion, ion exchange, and C-18 (checking pureness) reverse-phase chromatographies. N-terminal sequencing of the first eight amino acids (NNCPQ LLM) revealed 100% identity with Mutina (CTL-like) isolated from Lachesis stenophrys, which is a Ca²⁺-dependent-type galactoside-binding lectin from Bothrops jararaca and CTL BpLec from Bothrops pauloensis. The cardiotoxicity in zebrafish of MC-1 was evaluated by means of specific phenotypic expressions and larvae behavior at 5, 15, 30, 40 and 60 min post-treatment. The L. muta muta venom and MC-1 also produced heart rate/rhythm alterations, circulation modifications, and the presence of thrombus and apoptotic phenomenon with pericardial damages. Acridine orange (100 μg/mL) was used to visualize apoptosis cellular process in control and treated whole embryos. The cardiotoxic alterations happened in more than 90% of all larvae under the action of L. muta muta venom and MC-1. The findings have demonstrated the potential cardiotoxicity by L. muta muta venom, suggesting the possibility of cardiovascular damages to patients after bushmaster envenoming.

Spatio-temporal patterns of thermal anomalies and drought over tropical forests driven by recent extreme climatic anomalies

The recent 2015-2016 El Niño (EN) event was considered as strong as the EN in 1997-1998. Given such magnitude, it was expected to result in extreme warming and moisture anomalies in tropical areas. Here we characterize the spatial patterns of temperature anomalies and drought over tropical forests, including tropical South America (Amazonia), Africa and Asia/Indonesia during the 2015-2016 EN event. These spatial patterns of warming and drought are compared with those observed in previous strong EN events (1982-1983 and 1997-1998) and other moderate to strong EN events (e.g. 2004-2005 and 2009-2010). The link between the spatial patterns of drought and sea surface temperature anomalies in the central and eastern Pacific is also explored. We show that indeed the EN2015-2016 led to unprecedented warming compared to the other EN events over Amazonia, Africa and Indonesia, as a consequence of the background global warming trend. Anomalous accumulated extreme drought area over Amazonia was found during EN2015-2016, but this value may be closer to extreme drought area extents in the other two EN events in 1982-1983 and 1997-1998. Over Africa, datasets disagree, and it is difficult to conclude which EN event led to the highest accumulated extreme drought area. Our results show that the highest values of accumulated drought area over Africa were obtained in 2015-2016 and 1997-1998, with a long-term drying trend not observed over the other tropical regions. Over Indonesia, all datasets suggest that EN 1982-1983 and EN 1997-1998 (or even the drought of 2005) led to a higher extreme drought area than EN2015-2016. Uncertainties in precipitation datasets hinder consistent estimates of drought severity over tropical regions, and improved reanalysis products and station records are required.This article is part of a discussion meeting issue 'The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications'.

Differentiation of Ecuadorian National and CCN-51 cocoa beans and their mixtures by computer vision

BACKGROUND

Ecuador exports two major types of cocoa beans, the highly regarded and lucrative National, known for its fine aroma, and the CCN-51 clone type, used in bulk for mass chocolate products. In order to discourage exportation of National cocoa adulterated with CCN-51, a fast and objective methodology for distinguishing between the two types of cocoa beans is needed.

RESULTS

This study reports a methodology based on computer vision, which makes it possible to recognize these beans and determine the percentage of their mixture. The methodology was challenged with 336 samples of National cocoa and 127 of CCN-51. By excluding the samples with a low fermentation level and white beans, the model discriminated with a precision higher than 98%. The model was also able to identify and quantify adulterations in 75 export batches of National cocoa and separate out poorly fermented beans.

CONCLUSION

A scientifically reliable methodology able to discriminate between Ecuadorian National and CCN-51 cocoa beans and their mixtures was successfully developed. © 2017 Society of Chemical Industry.

Technical modifications for endovascular infrarenal AAA repair for the angulated and dumbbell-shaped neck: the precuff Kilt technique

BACKGROUND

High risk surgical patients with abdominal aortic aneurysms and difficult infrarenal necks continue to be challenged when performing endovascular repair. Although fenestrated and branched endografts may ultimately be the main method of repair for these patients, their current limited availability has prompted the use of alternative endovascular techniques to enhance success of endovascular aortic aneurysm repair in patients with "dumbbell" shaped and angulated necks.

METHODS

A retrospective review of all patients who underwent endovascular abdominal aneurysm repair with a predeployed aortic cuff (Kilt) at University of California, Los Angeles between January 2009 and April 2010 was performed.

RESULTS

Four patients underwent initial Kilt placement before endovascular abdominal aortic aneurysm (AAA) repair. The mean age of these patients was 78.0 + 7.0 years. All were American Society of Anesthesiologists class 3 patients with multiple medical comorbidities. All of them had angulated and dumbbell-shaped necks. Median follow-up period was 11 months (8-18 months). All patients had postoperative computed tomography at 1 and 6 months because of their high-risk neck anatomy. One patient was found to have a large type I endoleak on computed tomography 1 month postoperatively. He required placement of an additional aortic cuff and Palmaz stent, after which the endoleak was found to have resolved. There were no open conversions, aneurysm sac enlargement, or perioperative deaths.

CONCLUSION

Short-term follow-up suggests that the Kilt technique may be useful in certain high-risk patients with traditionally unfavorable anatomy for endovascular abdominal aortic aneurysm repair. It can be performed with minimal patient morbidity, even in high-risk patients. Anatomic features most amenable to this technique include dumbbell-shaped and angulated infrarenal necks.

Antibody and cytokine responses in BALB/c mice immunized with the excreted/secreted proteins of Giardia intestinalis: the role of cysteine proteases

The mechanisms involved in the induction of the immune response in humans or experimental hosts infected with Giardia intestinalis are not well understood. The results of previous studies indicate that the parasite induces a mixed Th1/Th2 response and that, in experimentally infected mice, the parasite's excreted/secreted (E/S) proteins contain cysteine proteases that are recognised by the murine immune system. In the present study, the possible effects of the E/S proteases of G. intestinalis on the host's humoral and cellular immune responses were investigated in BALB/c mice immunized with the parasite's E/S proteins. High titres of specific IgG(1), IgG(2a) and IgE antibodies were detected after immunization with native E/S proteins. Spleen cells stimulated with such proteins in vitro showed a significant antigen-specific proliferative response accompanied by the production of high concentrations of interleukin-4 (IL-4), interleukin-5 (IL-5) and interleukin-10 (IL-10) but little secretion of interferon-gamma (IFN-gamma). When, before use, the proteases in the E/S proteins were inhibited, by heat treatment or the addition of E-64, they elicited much lower titres of specific IgG(1) and IgE in mice while, in splenocytes in vitro, they triggered much lower production of IL-4, IL-5 and IL-10 and reduced antigen-specific proliferation. Since E-64 only inhibits cysteine proteases, these results indicate that the excreted/secreted cysteine proteases of G. intestinalis may be involved in the induction and regulation of a specific immune response in the infected host.

Nonlinear local electrovascular coupling. II: From data to neuronal masses

In the companion article a local electrovascular coupling (LEVC) model was proposed to explain the continuous dynamics of electrical and vascular states within a cortical unit. These states produce certain mesoscopic reflections whose discrete time series can be reconstructed from electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). In this article we develop a recursive optimization algorithm based on the local linearization (LL) filter and an innovation method to make statistical inferences about the LEVC model from both EEG and fMRI data, i.e., to estimate the unobserved states and the unknown parameters of the model. For a better understanding, the LL filter is described from a Bayesian point of view, providing the particulars for the case of hybrid data (e.g., EEG and fMRI), which could be sampled at different rates. The dynamics of the exogenous synaptic inputs going into the cortical unit are also estimated by introducing a set of Gaussian radial basis functions. In order to study the dynamics of the electrical and vascular states in the striate cortex of humans as well as their local interrelationships, we applied this algorithm to EEG and fMRI recordings obtained concurrently from two subjects while passively observing a radial checkerboard with a white/black pattern reversal. The EEG and fMRI data from the first subject was used to estimate the electrical/vascular states and parameters of the LEVC model in V1 for a 4.0 Hz reversion frequency. We used the EEG data from the second subject to investigate the changes in the dynamics of the electrical states when the frequency of reversion is varied from 0.5-4.0 Hz. Then we made use of the estimated electrical states to predict the effects on the vasculature that such variations produce.

Realistically Coupled Neural Mass Models Can Generate EEG Rhythms

We study the generation of EEG rhythms by means of realistically coupled neural mass models. Previous neural mass models were used to model cortical voxels and the thalamus. Interactions between voxels of the same and other cortical areas and with the thalamus were taken into account. Voxels within the same cortical area were coupled (short-range connections) with both excitatory and inhibitory connections, while coupling between areas (long-range connections) was considered to be excitatory only. Short-range connection strengths were modeled by using a connectivity function depending on the distance between voxels. Coupling strength parameters between areas were defined from empirical anatomical data employing the information obtained from probabilistic paths, which were tracked by water diffusion imaging techniques and used to quantify white matter tracts in the brain. Each cortical voxel was then described by a set of 16 random differential equations, while the thalamus was described by a set of 12 random differential equations. Thus, for analyzing the neuronal dynamics emerging from the interaction of several areas, a large system of differential equations needs to be solved. The sparseness of the estimated anatomical connectivity matrix reduces the number of connection parameters substantially, making the solution of this system faster. Simulations of human brain rhythms were carried out in order to test the model. Physiologically plausible results were obtained based on this anatomically constrained neural mass model.

Minimally invasive distal limb bypasses. Techniques and results

As endovascular procedures increasingly become the procedures of choice for limb salvage, a subset of patients remains that requires open arterial reconstruction due to anatomic or pathologic reasons. Traditional greater saphenous vein harvest performed during open bypass for peripheral occlusive arterial disease is associated with long surgical incisions, increased operative times devoted to wound closure, and wound complications such as infection and dehiscence. Endoscopic conduit harvest, used with excellent results in coronary artery bypass surgery, can also be used in minimally invasive arterial bypass for limb salvage with certain technical modifications. These approaches to complex limb salvage procedures may result in shortened operating room time, shorter length of stay, reduced readmissions for wound complications, and ultimately, decreased costs to the health care system. The treating surgeon must continue to stay up to date with these approaches and be aware of pertinent issues regarding open and minimally invasive arterial interventions, as well as endovascular approaches.

Palsies of the fifth cervical nerve root after cervical decompression: prevention using continuous intraoperative electromyography monitoring

OBJECT

A desire to prevent complications resulting from spinal surgery led to the development of intraoperative monitoring. Intraoperative electromyography (EMG) provides useful diagnostic information regarding nerve root function during spinal and peripheral nerve surgeries. The C-5 nerve root is considered particularly vulnerable to injury during cervical surgery. Despite advances in techniques, the incidence of postoperative C-5 palsy has not changed.

METHODS

The authors reviewed prospectively collected data obtained in 161 patients who underwent 171 cervical procedures. In 116 procedures, operative monitoring was modified to include continuous C-5 EMG from the deltoid muscle. In cases in which spontaneous C-5 activity occurred, an appropriate change in operative manipulation was made. A historical control group consisted of a retrospective review of 55 procedures that were monitored using conventional techniques. In the retrospective cohort, four (7.3%) of 55 patients presented after undergoing surgery for C-5 nerve root palsy. In each patient conventional monitoring revealed unremarkable findings. In the prospective cohort, intraoperative spontaneous EMG activity necessitated a change in either positioning or operative technique in three cases. Only one patient (0.9%) experienced postoperative C-5 palsy. Postoperative C-5 palsy occurred in no patient in whom there was no intra-operative evidence of root irritation (p < 0.03, chi-square test).

CONCLUSIONS

The incidence of postoperative C-5 palsies was reduced from 7.3% to 0.9% due to intraoperative continuous EMG monitoring. No patient suffered a postoperative C-5 palsy when intraoperative evidence of root irritation was absent.

Reducing the noneducational and nonclinical workload of the surgical resident; defining the role of the health technician

PURPOSE

Recent controversy over excessive resident work hours has prompted surgical educators and program directors to search for more efficient methods to limit the nonclinical and noneducational workload of surgical residents. Health technicians were employed at a large Veteran's Administration Medical Center to allow residents more time for direct patient care in the clinics and wards and in educational activities.

METHODS

In a two-week period, daily data cards were collected from each intern and health technician identifying total hours spent in work, operations, clinics, and conferences. Each intern recorded the number and type of tasks performed and those tasks assigned to the health technician. The number and type of task performed were tabulated and averaged for each health technician and physician.

RESULTS

Each intern (n = 3) and health technician (n = 8) completed 100% of the required data forms. In a control survey, each intern worked a mean of 16.9 hours per weekday and 5.0 hours per weekend day. With the addition of the health technicians, interns worked 12.9 hours per weekday and 6.8 hours per weekend day (when the health technicians were not present). Following the addition of the health technicians, resident time in the operating room increased from 3.3 hours per week to 9.8 hours per week. Each health technician aided the intern by performing an average of 20.25 tasks per day.

CONCLUSIONS

This study shows that health technicians can be effective in reducing the overall hours and workload of surgical residents and increasing time spent in the operating room. Consideration should be given to including the health technician as integral members of the health care team in the teaching hospital.

Complications after laparoscopic gastric bypass: a review of 3464 cases

HYPOTHESIS

The type and frequency of complications after open Roux-en-Y gastric bypass (GBP) have changed with the development of laparoscopic technique.

BACKGROUND

The number of laparoscopic GBP cases performed in the United States has increased dramatically during the past several years. We compared the type and frequency of complications after laparoscopic and open GBP.

METHODS

We searched MEDLINE from January 1, 1994, through December 31, 2002, using the keywords morbid obesity, laparoscopy, bariatric surgery, and gastric bypass. We selected studies on laparoscopic or open GBP with more than 50 patients and published in the English language for analysis. We excluded studies with reoperative Roux-en-Y GBP cases or other bariatric procedures. The type and frequency of postoperative complications were recorded from each study. We used chi2 and Fisher exact tests to determine statistical significance.

RESULTS

Ten laparoscopic GBP studies with 3464 patients and 8 open GBP studies with 2771 patients were considered. The mean of the reported average age for patients undergoing laparoscopic GBP was 41 years compared with 43 years for open GBP. The mean percentages of female patients were 87% for laparoscopic GBP and 82% for open GBP; the mean reported average body mass index (calculated as weight in kilograms divided by the square of height in meters), 48.7 and 49.5, respectively. Compared with open GBP, laparoscopic GBP was associated with a decrease in the frequency of iatrogenic splenectomy, wound infection, incisional hernia, and mortality; however, there was an increase in the frequency of early and late bowel obstruction, gastrointestinal tract hemorrhage, and stomal stenosis. There were no significant differences in the frequency of anastomotic leak, pulmonary embolism, or pneumonia.

CONCLUSIONS

The type and frequency of postoperative complications after laparoscopic and open GBP are different. Certain complications increase with laparoscopic GBP, probably owing to the learning curve of this complex procedure, whereas other complications decrease because of the advantages of the smaller access incision.

Minimal deviation melanoma

Minimal deviation melanomas (MDM) are poorly characterized, uncommon naevomelanocytic tumours that are thought to represent part of the continuum from benign atypical naevi to frank malignant melanomas. Exactly where on that continuum they stand and who is most affected remains controversial. The few studies classifying MDM pointed to a less aggressive nature. Furthermore, it is thought that MDM affects patients in the fourth and fifth decades of life. In a recent review conducted at our institution, medical records of all patients with melanoma diagnosed at a tertiary care university medical center between January 1997 and May 2000 were reviewed to identify those with MDM. Those with MDM were examined to determine subtype, age and sex distributions, and location of tumour and findings were compared to those in the published literature. Unlike previous studies, the mean age of patients with MDM was 27 years with 20/31 being under 30 years old. Our results support prior findings that MDM is less aggressive than typical malignant melanomas in that only 1/5 undergoing lymphatic mapping had a positive node. Despite its description more than 30 years ago, MDM remains a poorly understood pathologic entity. Further study in such techniques as sentinel lymph node mapping and determination of angiogenesis factors is warranted to give insight as to what features predict an aggressive nature and to identify prognostic factors.

Iodine-131 treatment of thyroid papillary carcinoma in patients undergoing dialysis for chronic renal failure: a dosimetric method

Until recently, the therapeutic protocol widely accepted for ablation of the thyroid remnant and for metastases of thyroid papillary carcinoma was the administration of 131I after surgery. However, at present, some data question the usefulness of such treatment in patients considered low risk. The treatment with radioiodine in patients suffering from end-stage renal disease (ESRD) undergoing hemodialysis requires controlled dosages and individualized administration guidelines. The need to include these patients on the waiting list for a renal transplantation, once they have overcome the disease, and the higher prevalence of thyroid carcinoma in ESRD patients makes this an increasingly significant problem. The cases reported in the literature are few and the therapeutic models followed are very difficult. In this paper we propose a therapeutic model that provides the highest thyroid ablative dosage, minimizing radiation exposure to the rest of the organs. The main difference between our protocol and that already described is the performance of daily hemodialysis during the first 5 days of treatment, as well as the administration of a dose of 131I equivalent to that administered to patients who show normal renal function.

Testing non-linearity and directedness of interactions between neural groups in the macaque inferotemporal cortex

Information processing in the visual cortex depends on complex and context sensitive patterns of interactions between neuronal groups in many different cortical areas. Methods used to date for disentangling this functional connectivity presuppose either linearity or instantaneous interactions, assumptions that are not necessarily valid. In this paper a general framework that encompasses both linear and non-linear modelling of neurophysiological time series data by means of Local Linear Non-linear Autoregressive models (LLNAR) is described. Within this framework a new test for non-linearity of time series and for non-linearity of directedness of neural interactions based on LLNAR is presented. These tests assess the relative goodness of fit of linear versus non-linear models via the bootstrap technique. Additionally, a generalised definition of Granger causality is presented based on LLNAR that is valid for both linear and non-linear systems. Finally, the use of LLNAR for measuring non-linearity and directional influences is illustrated using artificial data, reference data as well as local field potentials (LFPs) from macaque area TE. LFP data is well described by the linear variant of LLNAR. Models of this sort, including lagged values of the preceding 25 to 60 ms, revealed the existence of both uni- and bi-directional influences between recording sites.

Nonlinear EEG analysis based on a neural mass model

The well-known neural mass model described by Lopes da Silva et al. (1976) and Zetterberg et al. (1978) is fitted to actual EEG data. This is achieved by reformulating the original set of integral equations as a continuous-discrete state space model. The local linearization approach is then used to discretize the state equation and to construct a nonlinear Kalman filter. On this basis, a maximum likelihood procedure is used for estimating the model parameters for several EEG recordings. The analysis of the noise-free differential equations of the estimated models suggests that there are two different types of alpha rhythms: those with a point attractor and others with a limit cycle attractor. These attractors are also found by means of a nonlinear time series analysis of the EEG recordings. We conclude that the Hopf bifurcation described by Zetterberg et al. (1978) is present in actual brain dynamics.

Measuring the dissimilarity between EEG recordings through a non-linear dynamical system approach

A new measure of dissimilarity between two EEG segments is proposed. It is derived from the application of the mathematical concept of distance between series of one-step predictions according to the estimated non-linear autoregressive functions. The non-linear autoregressive estimation is performed by non-parametric regression using kernel estimators. The possibility of applying this measure for automatic classification of EEG segments is explored. For this purpose multidimensional scaling and cluster analyses are applied on the basis of the calculated dissimilarity measures. In particular, its application to different EEG segments with delta activity and also with alpha waves reveals high agreement with visual classification by EEG specialists.

Modeling the electroencephalogram by means of spatial spline smoothing and temporal autoregression

A spatial-temporal model for the description of electroencephalographic (EEG) data is introduced that combines smooth reconstruction in the spatial domain and autoregressive representation in the time domain. Its spatial aspect is formulated in a general framework that covers interpolation, smoothing, and regression. Contrary to the multivariate time series models used for EEG analysis up to date, the introduced model provides a smooth spatial reconstruction of the EEG cross-spectrum, keeping the condition of nonnegative definiteness. As an instance of practical importance, the case in which the spatial reconstruction is based on spherical splines is developed in detail. Illustrative examples are presented that show the flexibility of the model to describe both normal and abnormal EEG data.

High resolution quantitative EEG analysis

High resolution spectral methods are explored as an alternative to broad band spectral parameters (BBSP) in quantitative EEG analysis. In a previous paper (Valdes et al. 1990b) regression equations ("Developmental surfaces") were introduced to characterize the age-frequency distribution of the mean and standard deviation of the log spectral EEG power in a normative sample. These normative surfaces allow the calculation of z transformed spectra for all derivations of the 10/20 system and z maps for each frequency. Clinical material is presented that illustrates how these procedures may pinpoint frequencies of abnormal brain activity and their topographic distribution, avoiding the frequency and spatial "smearing" that may occur using BBSP. The increased diagnostic accuracy of high resolution spectral methods is demonstrated by means of receiver operator characteristic (ROC) curve analysis. Procedures are introduced to avoid type I error inflation due to the use of more variables in this type of procedure.