Are NIRS-derived cerebral autoregulation and ABPopt values different between hemispheres in hypoxic-ischemic brain injury patients following cardiac arrest?

PURPOSE: Near-infrared spectroscopy (NIRS) has been suggested as a non-invasive monitoring technique to set cerebral autoregulation (CA) guided ABP targets (ABPopt) in comatose patients with hypoxic-ischemic brain injury (HIBI) following cardiac arrest. We aimed to determine whether NIRS-derived CA and ABPopt values differ between left and right-sided recordings in these patients. METHODS: Bifrontal regional oxygen saturation (rSO2) was measured using INVOS or Fore-Sight devices. The Cerebral Oximetry index (COx) was determined as a CA measure. ABPopt was calculated using a published algorithm with multi-window weighted approach. A paired Wilcoxon signed rank test and intraclass correlation coefficients (ICC) were used to compare (1) systematic differences and (2) degree of agreement between left and right-sided measurements. RESULTS: Eleven patients were monitored. In one patient there was malfunctioning of the right-sided optode and in one patient not any ABPopt value was calculated. Comparison of rSO2 and COx was possible in ten patients and ABPopt in nine patients. The average recording time was 26 (IQR, 22-42) hours. The ABPopt values were not significantly different between the bifrontal recordings (80 (95%-CI 76-84) and 82 (95%-CI 75-84) mmHg) for the left and right recordings, p = 1.0). The ICC for ABPopt was high (0.95, 0.78-0.98, p < 0.001). Similar results were obtained for rSO2 and COx. CONCLUSION: We found no differences between left and right-sided NIRS recordings or CA estimation in comatose and ventilated HIBI patients. This suggests that in these patients without signs of localized pathology unilateral recordings might be sufficient to estimate CA status or provide ABPopt targets.

Definition of common carotid wall thickness affects risk classification in relation to degree of internal carotid artery stenosis: the Plaque At RISK (PARISK) study.

BACKGROUND: Mean or maximal intima-media thickness (IMT) is commonly used as surrogate endpoint in intervention studies. However, the effect of normalization by surrounding or median IMT or by diameter is unknown. In addition, it is unclear whether IMT inhomogeneity is a useful predictor beyond common wall parameters like maximal wall thickness, either absolute or normalized to IMT or lumen size. We investigated the interrelationship of common carotid artery (CCA) thickness parameters and their association with the ipsilateral internal carotid artery (ICA) stenosis degree. METHODS: CCA thickness parameters were extracted by edge detection applied to ultrasound B-mode recordings of 240 patients. Degree of ICA stenosis was determined from CT angiography. RESULTS: Normalization of maximal CCA wall thickness to median IMT leads to large variations. Higher CCA thickness parameter values are associated with a higher degree of ipsilateral ICA stenosis (p < 0.001), though IMT inhomogeneity does not provide extra information. When the ratio of wall thickness and diameter instead of absolute maximal wall thickness is used as risk marker for having moderate ipsilateral ICA stenosis (>50%), 55 arteries (15%) are reclassified to another risk category. CONCLUSIONS: It is more reasonable to normalize maximal wall thickness to end-diastolic diameter rather than to IMT, affecting risk classification and suggesting modification of the Mannheim criteria. TRIAL REGISTRATION: Clinical trials.gov NCT01208025 .

High resolution sonography in the evaluation of the peripheral nervous system in polyneuropathy--a review of the literature.

Clinical, laboratory and electrodiagnostic studies are the mainstay in the diagnosis of polyneuropathy. An accurate etiological diagnosis is of paramount importance to provide the appropriate treatment, prognosis and genetic counselling. High resolution sonography of the peripheral nervous system allows nerves to be readily visualized and to assess their morphology. Ultrasonography has brought pathophysiological insights and substantially added to diagnostic accuracy and treatment decisions amongst mononeuropathies. In this study the literature on its clinical application in polyneuropathy is reviewed. Several polyneuropathies have been studied by means of ultrasound: Charcot-Marie-Tooth, hereditary neuropathy with liability to pressure palsies, chronic inflammatory demyelinating polyneuropathy, Guillain-Barré syndrome, multifocal motor neuropathy, paraneoplastic polyneuropathy, leprosy and diabetic neuropathy. The most prominent reported pathological changes were nerve enlargement, increased hypo-echogenicity and increased intraneural vascularization. Sonography revealed intriguingly different patterns of nerve enlargement between inflammatory neuropathies and axonal and inherited polyneuropathies. However, many studies concerned case reports or case series and showed methodological shortcomings. Further prospective studies with standardized protocols for nerve sonography and clinical and electrodiagnostic testing are needed to determine the role of nerve sonography in inherited and acquired polyneuropathies.

Proximal Region of Carotid Atherosclerotic Plaque Shows More Intraplaque Hemorrhage: The Plaque at Risk Study.

BACKGROUND AND PURPOSE: Intraplaque hemorrhage contributes to lipid core enlargement and plaque progression, leading to plaque destabilization and stroke. The mechanisms that contribute to the development of intraplaque hemorrhage are not completely understood. A higher incidence of intraplaque hemorrhage and thin/ruptured fibrous cap (upstream of the maximum stenosis in patients with severe [≥70%] carotid stenosis) has been reported. We aimed to noninvasively study the distribution of intraplaque hemorrhage and a thin/ruptured fibrous cap in patients with mild-to-moderate carotid stenosis. MATERIALS AND METHODS: Eighty-eight symptomatic patients with stroke (<70% carotid stenosis included in the Plaque at Risk study) demonstrated intraplaque hemorrhage on MR imaging in the carotid artery plaque ipsilateral to the side of TIA/stroke. The intraplaque hemorrhage area percentage was calculated. A thin/ruptured fibrous cap was scored by comparing pre- and postcontrast black-blood TSE images. Differences in mean intraplaque hemorrhage percentages between the proximal and distal regions were compared using a paired-samples t test. The McNemar test was used to reveal differences in proportions of a thin/ruptured fibrous cap. RESULTS: We found significantly larger areas of intraplaque hemorrhage in the proximal part of the plaque at 2, 4, and 6 mm from the maximal luminal narrowing, respectively: 14.4% versus 9.6% (P = .04), 14.7% versus 5.4% (P < .001), and 11.1% versus 2.2% (P = .001). Additionally, we found an increased proximal prevalence of a thin/ruptured fibrous cap on MR imaging at 2, 4, 6, and 8 mm from the MR imaging section with the maximal luminal narrowing, respectively: 33.7% versus 18.1%, P = .007; 36.1% versus 7.2%, P < .001; 33.7% versus 2.4%, P = .001; and 30.1% versus 3.6%, P = .022. CONCLUSIONS: We demonstrated that intraplaque hemorrhage and a thin/ruptured fibrous cap are more prevalent on the proximal side of the plaque compared with the distal side in patients with mild-to-moderate carotid stenosis.

The reliability of transcranial duplex scanning in parkinsonian patients: comparison of different observers and ultrasound systems.

PURPOSE: To establish the inter-observer and intra-transducer reliability of "on-line" and "off-line" assessment of substantia nigra (SN) and raphe nuclei (RN) by transcranial duplex scanning (TCD) in a mixed study population. MATERIALS AND METHODS: Out-patient neurology department of the University Hospital Maastricht. In total 24 subjects were investigated: 9 patients with idiopathic Parkinson's disease, 10 with parkinsonism from yet unclear origin, 1 with essential tremor and 4 healthy volunteers. Each patient was assessed four times by two independent experienced sonographers using two different ultrasound devices: SONOS 5500 and iU22; both Philips, Eindhoven, The Netherlands. The echointensity of the SN is evaluated qualitatively and quantitatively and the RN only qualitatively. 1. In the "on-line" assessment we determined: a) the inter-observer agreement of the four possible combinations. b) the intra-observer agreement of both sonographers using two different ultrasound systems. 2. In the "off-line" assessment a third sonographer re-examined the stored images. We determined the inter-observer agreement of the third sonographer with the "on-line" assessment of the other two sonographers. Cohen's k value was calculated for the agreement. RESULTS: 1a) The "on-line" inter-observer agreement of the four possible combinations of sonographer and transducer was: kappa 0.23 - 0.39 for the qualitative evaluation of the SN, kappa 0.31 - 0.56 for the quantitative evaluation of the SN and kappa 0.03 - 0.15 for the evaluation of the RN. 1b) The "on-line" intra-observer agreement was: kappa 0.53 - 0.67 for the qualitative evaluation of the SN, kappa 0.55 - 0.76 for the quantitative evaluation of the SN and kappa 0.45 - 0.47 for the evaluation of the RN. 2. The "off-line" inter-observer agreement was: kappa 0.32 - 0.67 for the qualitative evaluation of the SN, kappa 0.53 - 0.61 for the quantitative evaluation of the SN and kappa 0.08 - 0.33 for the evaluation of the RN. CONCLUSION: For the SN we found mediocre accordance comparing both observers "on-line" with each other as well as comparing an "off-line" observer with both "on-line" observers. On the whole, the inter-observer and intra-observer agreement were moderate to substantial for the evaluation of the SN. "On-line" and "off-line" comparisons yielded comparable results. The agreement for the evaluation of the RN, on the contrary, was considerably lower. Our findings indicate that this TCD technique is not yet ready for the application in large population screenings.

Early control of distal internal carotid artery during carotid endarterectomy: does it reduce cerebral microemboli?

AIM: According to the results of the large trials on carotid endarterectomy (CEA), this type of surgery is only warranted if perioperative mortality and morbidity are kept considerably low. Less attention has been paid to methods of cerebral protection during CEA, although intraoperative transcranial Doppler (TCD) can visualise intracerebral microemboli (MES) during routine carotid dissection, although MES occur throughout the CEA, only those during dissection are related to neurological outcome. Prevention of MES by means of early control of the distal internal carotid artery dislodging from the carotid artery plaque during dissection is very likely the mechanism behind an eventual benefit from this approach. Hence, the amount of MES might serve as a surrogate parameter for the risk of periprocedural neurological events. So, the aim of the present study was to evaluate whether early control of the distal carotid artery during CEA is capable of reducing the number of MES by means of a prospective randomised trial. METHODS: Twenty-eight patients (29 procedures) could be prospectively included in our study. Before surgery we randomly assigned the patients to two groups: group A (N.=12): CEA by means of early control of the distal internal carotid artery; group B (N.=17): CEA with dissection of the total carotid bifurcation before clamping the arteries. Periprocedurally, we continuously monitored the cerebral blood flow in the ipsilateral middle cerebral artery by means of TCD. Pre- and postoperative morbidity were independently verified by a neurologist <2 days before and not later than five days after the procedure. Values of microembolic signs during dissection were summarised with arithmetic means and standard deviations. For further analysis non parametric Wilcoxon test was performed between both methods. P-values <0.05 were considered as statistically significant. Wilcoxon test was performed to compare both methods concerning clamp- and procedure times. RESULTS: We performed EEA 26 times, in three patients a longitudinal arteriotomy with endarterectomy and patchplasty was performed, in one of these patients a shunt was necessary. In 12 twelve patients MES occurred during the dissection before clamping. Eight of these patients belonged to group B and four patients to group A. The mean number of MES during dissection for group A was 2.4 (SD 4.6; 5-15) and for group B 3.9 (SD 7.1; 2-28). There is no statistically significant difference in the Wilcoxon-test; P=0.4375. There was no patient showing reperfusion syndrom or clinical signs of a new cerebral infarction or any other neurological deficit. There were no other major complications like myocardial infarction or death as well as no minor complications like periphereal nerve lesions, bleeding or wound healing disturbance. CONCLUSION: In this prospective, randomised trial early control of the distal internal carotid artery did not reduce the occurrence of MES during dissection of the carotid bifurcation. Also, the total number of MES throughout the procedure and postoperatively was comparable between both groups. The procedure related times as well as the clinical outcome did not differ significantly. Thus, early control of the distal internal carotid artery has got no advantage but also no disadvantage as compared to the traditional CEA technique. However, a limitation of the study is the small number of patients included.

[Intraoperative neuromonitoring for prevention of neurological complications in aortic surgery]. / Intraoperatives Neuromonitoring zur Prävention neurologischer Komplikationen bei Aortenbogen- und thorakoabdomineller Aortenchirurgie.

AIM: Stroke and paraplegia are devastating complications of thoracic and thoracoabdominal aortic surgery. The aim of this study was to analyse the value of transcranial Doppler ultrasound (TCD), electroencephalogram (EEG) and motor-evoked potentials (MEP) in preventing neurological complications. Moreover, the principles, technology and surgical protocols are described. PATIENTS AND METHODS: In 2009, 22 patients (4 females, 18 males) underwent thoracic or thoracoabdominal open aortic repair. We performed 2 arches with descending aortic replacement, 5 arches with TAAA repair, 2 type II, 9 type III, 3 type IV and one type V TAAA aortic repair. In 6 patients, the neuromonitoring included TCD, EEG and MEPs. In 15 patients only MEP monitoring was necessary. In one patient who was operated on in an emergency setting, neuromonitoring was not performed. The surgical approach was a left thoracotomy in 3 and a left thoracolaparotomy in 19 patients. The surgical protocol included cerebrospinal fluid drainage (n=22), moderate (n=19) or deep hypothermia (n=2), and extracorporeal circulation (n=21) with retrograde aortic perfusion and selective cerebral and/or viscerorenal perfusion. RESULTS: In 21 patients, the neuromonitoring could be established successfully. Using TCD and EEG, a relevant cerebral ischaemia during supraaortic clamping was excluded. With a mean distal arterial pressure of 60 mmHg, the MEPs remained adequate in 15 patients (68.2%). Increasing of the blood pressure restored the MEPs in one patient. In 5 patients (22.7%), a reimplantation of segmental arteries (n=4) or of the left subclavian artery (n=1) re-established spinal cord perfusion, as indicated by restored MEPs. We had no absent MEPs at the end of the procedures. Delayed paraparesis developed in 2 patients with a haemodynamic instability during the postoperative course. Paraplegia was not observed. CONCLUSION: TCD, EEG and MEPs are reliable techniques to unmask cerebral or spinal cord ischaemia during aortic surgery. Immediate operative strategies based on neuromonitoring information prevent neurological complications in aortic surgery.

The role of procalcitonin as predictor for neurological deficits after carotid endarterectomy.

AIM: Outcome of carotid endarterectomy (CEA) is defined by mortality rate as well as the neurological outcome due to cerebral ischemia. Thus the aim of this study was to evaluate the role of the acute phase protein procalcitonin (PCT) as a predictor for neurological deficits after carotid endarterectomy. METHODS: Fifty-five patients with high grade stenosis of the internal carotid artery and interdisciplinary consensus for endarterectomy were followed. Neurological examination was performed before and after the procedure to analyze perioperative neurological deficits. Blood samples were obtained before and after CEA and procalcitonin was analyzed in 55 consecutive patients (65.5% symptomatic/34.5% asymptomatic). RESULTS: No perioperative or in-hospital death was observed. Major complications did not occur, two patients suffered from bleeding requiring surgical intervention and one patient had a temporary peripheral facial nerve lesion. Postoperative neurological examination revealed no new deficit, there was no significant change of PCT (level pre- and post-CEA (the mean preoperative PCT was 0.25 ng/mL [SD 0.78, min 0.1, max 4.3]; the mean postoperative PCT was 0.11 ng/mL [SD 0.06, min 0.1, max 0.5]). There was no association found between perioperative neurological deficit and PCT. CONCLUSIONS: The present study demonstrates that there is still not sufficient evidence to recommend PCT measurement as a predictor for perioperative neurological deficit during CEA.

Measurement of common carotid artery intima-media thickness in clinical practice: comparison of B-mode and RF-based technique.

PURPOSE: The common carotid artery intima-media thickness (CCA-IMT) is usually measured using B-mode ultrasound images. A different approach for CCA-IMT detection is based on radio frequency (RF) multiple M-line analysis. MATERIALS AND METHODS: The present study explores the relationship between B-mode and RF measurement of CCA-IMT, as well as the reproducibility of both methods in 136 patients recently diagnosed with cardiovascular disease. Within one session, repeated measurements were made in the distal CCA bilaterally, using the B-mode (averaged over 10 mm) and RF technique (averaging 12 M-lines over 14 mm). RESULTS: The two methods correlate well (Pearson r = 0.765). The CCA-IMT values measured with B-mode and RF were 0.779 +/- 0.196 mm and 0.734 +/- 0.172 mm, respectively. B-mode CCA-IMT is significantly larger than RF CCA-IMT (mean difference of 0.045 mm, SEM 7.8 microm; t = 5.82; p < 0.001). In the multivariate regression analysis, carotid artery stenosis, inhomogeneous IMT and diabetes mellitus were the main predictors of differences between B-mode and RF CCA-IMT. The intrapatient variation for B-mode and RF-based CCA-IMT is comparable (0.05 +/- 0.04 mm and 0.07 +/- 0.05 mm, respectively). CONCLUSION: CCA-IMT values measured with RF and B-mode have similar reproducibility and exhibit acceptable correlation, but RF CCA-IMT is significantly smaller. The difference between both methods is mainly due to advanced atherosclerosis. Hence, both methods can be used reliably to measure CCA-IMT in clinical practice.

Spinal cord functional MRI at 3 T: gradient echo echo-planar imaging versus turbo spin echo.

The purpose of this study was to evaluate and compare turbo spin echo (TSE) with gradient echo echo-planar imaging (GE-EPI) pulse sequences for functional magnetic resonance imaging (fMRI) of spinal cord activation at 3 T field strength. Healthy volunteers underwent TSE and GE-EPI spinal fMRI. The activation paradigm comprised the temporal alternation of finger motion and rest. Pulse sequences were optimized to obtain sufficient image quality and optimal sensitivity to small T(2) or T(2)* relaxation time changes. Spinal cord activation measured by the two pulse sequences was evaluated with respect to spatial distribution of activation, signal sensitivity, and reproducibility. For the GE-EPI sequence, fMRI activation was maximal in the spinal cord segments at the levels of the fifth cervical down to the first thoracic vertebra. For the TSE sequence, fMRI measurements showed no distinct location with maximal activation. Percentage signal change and number of activated voxels were approximately twice as high for GE-EPI compared to TSE fMRI. Reproducibility of the signal changes was much better for GE-EPI than for TSE imaging. To conclude, multi-subjects averaged GE-EPI is more location specific for blood-oxygen-level-dependent (BOLD) activation, more sensitive, and is suggested to be more reproducible than TSE fMRI.

Thoracoabdominal aortic aneurysm repair in patients with marfan syndrome.

OBJECTIVE: We assessed the surgical outcome of descending thoracic aortic aneurysm repair (DTAA) and thoracoabdominal aortic aneurym (TAAA) repair in patients with Marfan syndrome. METHODS: During a six year period, 206 patients underwent DTAA and TAAA repair. In 22 patients, Marfan syndrome was confirmed. The median age was 40 years with a range between 18 and 57 years. The extend of the aneurysms included 6 DTAA (1 with total arch, 2 with distal hemi-arch), 11 type II TAAA (2 with total arch, 3 with distal hemi-arch), 4 type III and one type IV TAAA. All patients suffered from previous type A (n=6) or type B (n=16) aortic dissection and 15 already underwent aortic procedures like Bentall (n=7) and ascending aortic replacement (n=8). All patients were operated on according to the standard protocol with cerebrospinal fluid drainage, distal aortic and selective organ perfusion and monitoring motor evoked potentials. In patients undergoing simultaneous arch replacement (via left thoracotomy), transcranial Doppler and EEG assessed cerebral physiology during antegrade brain perfusion. In four patients circulatory arrest under moderate hypothermia was required. RESULTS: In-hospital mortality did not occur. Major postoperative complications like paraplegia, renal failure, stroke and myocardial infarction were not encountered. Mean pre-operative creatinine level was 125mmol/L, which peaked to a mean maximal level of 130 and returned to 92mmol/L at discharge. Median intubation time was 1.5 days (range 0.33-30 days). Other complications included bleeding requiring surgical intervention (n=1), arrhythmia (n=2), pneumonia (n=2) and respiratory distress syndrome (n=1). At a median follow-up of 38 months all patients were alive. Using CT surveillance, new or false aneurysms were not detected, except in one patient who developed a visceral patch aneurysm six years after open type II repair. CONCLUSION: Surgical repair of descending and thoracoabdominal aortic aneurysms provides excellent short- and mid-term results in patients with Marfan syndrome. In this series, a surgical protocol with cerebrospinal fluid drainage, distal aortic and selective organ perfusion and monitoring motor evoked potentials resulted in low morbidity and absent mortality. These outcomes of open surgery should be considered when discussing endovascular aneurysm repair in Marfan patients.

Dynamic cerebral autoregulation and cerebrovascular reactivity: a comparative study in lacunar infarct patients.

The major purpose of this study was to simultaneously evaluate dCA before and shortly after cerebral vasodilatation evoked by infusion of acetazolamide (ACZ). It was questioned if and to what degree dCA was changed after ACZ infusion. Using 15 mg kg(-1) ACZ infusion cerebrovascular reactivity (CVR) was assessed in 29 first ever lacunar stroke patients (19 M/10 F). During the CVR-test, the electrocardiogram, non-invasive finger arterial blood pressure (ABP) and middle cerebral artery blood flow velocity (CBFV) were recorded. DCA based on spontaneous blood pressure variations was evaluated in 24 subjects by linear transfer function analysis. Squared coherence, gain and phase angle in the frequency range of autoregulation (0.04-0.16 Hz) were compared before and after ACZ infusion. After ACZ infusion, median phase angle decreased significantly (p < 0.005 Wilcoxon) to 0.77 rad compared to a pre-test baseline value of 1.05 rad, indicating less efficient dCA due to ACZ. However, post-test phase values are still mostly within the normal range. Poor and statistically non-significant correlations were found between CVR and absolute dCA phase angle. It can be concluded that CVR testing with body weight adjusted infusion of ACZ lowers dCA performance but by no means exhausts dCA, suggesting that in this way maximal CVR is not determined. Characterizing dCA based on transfer function analysis of ABP to CBFV needs no provocation and adverse patient effects are minimal. The poor correlation between CVR and dCA phase angle supports an interpretation that CVR and dCA study different mechanisms of cerebrovascular control.

Orthogonal B-Mode Evaluation of Common Carotid Artery Plaques Reveals the Absence of Outward Remodeling.

To properly assess morphologic and dynamic parameters of arteries and plaques, we propose the concept of orthogonal distance measurements, that is, measurements made perpendicular to the local lumen axis rather than along the ultrasound beam (vertical direction for a linear array). The aim of this study was to compare orthogonal and vertical artery and lumen diameters at the site of a plaque in the common carotid artery (CCA). Moreover, we investigated the interrelationship of orthogonal diameters and plaque size and the association of artery parameters with plaque echogenicity. In 29 patients, we acquired a longitudinal B-mode ultrasound recording of plaques at the posterior CCA wall. After semi-automatic segmentation of end-diastolic frames, diameters were extracted orthogonally along the lumen axis. To establish inter-observer variability of diameters obtained at the location of maximal plaque thickness, a second observer repeated the analysis (subset N = 21). Orthogonal adventitia-adventitia and lumen diameters could be determined with good precision (coefficient of variation: 1%-5%. However, the precision of the change in lumen diameter from diastole to systole (distension) at the site of the plaque was poor (21%-50%). The orthogonal lumen diameter was significantly smaller than the vertical lumen diameter (p <0.001). Surprisingly, the plaques did not cause outward remodeling, that is, a local increase in adventitia-adventitia distance at the site of the plaque. The intra- and inter-observer precision of diastolic-systolic plaque compression was poor and of the same order as the standard deviation of plaque compression. The orthogonal relative lumen distension was significantly lower for echogenic plaques, indicating a higher stiffness, than for echolucent plaques (p <0.01). In conclusion, we illustrated the feasibility of extracting orthogonal CCA and plaque dimensions, albeit that the proposed approach is inadequate to quantify plaque compression.

Surgical repair of thoracoabdominal aortic aneurysms.

Morbidity and mortality following thoracoabdominal aortic aneurysm (TAAA) repair are tremendous. Preoperative assessment is essential in detecting cardiac and pulmonary risk factors in order to reduce cardiopulmonary complications. Paraplegia and renal failure are main determinants of postoperative mortality and therefore gained substantial attention during the last decades. Left heart bypass, cerebrospinal fluid (CSF) drainage and epidural cooling have significantly reduced paraplegia rate, however, this dreadful event still occurs in up to 25% of patients undergoing type II repair. Renal failure has been partly prevented by means of retrograde aortic perfusion and cooling but renal failure still remains a significant problem. We have evaluated the effects of protective measures aiming for reduction of paraplegia and renal failure. Monitoring motor evoked potentials (MEPs) is an accurate technique to assess spinal cord integrity during TAAA repair, guiding surgical strategies to prevent paraplegia. Selective volume- and pressure controlled perfusion is a technique to continuously perfuse the kidneys during aortic cross clamping and subsequent circulatory exclusion In patients with atherosclerotic thoracoabdominal aortic aneurysms, blood supply to the spinal cord depends on a highly variable collateral system. In our experience, monitoring MEPs allowed detection of cord ischemia, guiding aggressive surgical strategies to restore spinal cord blood supply and reduce neurologic deficit: overall paraplegia rate was less than 3%. We believe that these protective measures should be included in the surgical protocol of TAAA repair, especially in type II cases. Renal and visceral ischemia can be reduced significantly by continuous perfusion during aortic cross clamping in TAAA repair. Not only sufficient volume flow but also adequate arterial pressure appears to be essential in maintaining renal function.Obviously, endovascular modalities have been successfully applied in TAAA patients, the majority of which as part of hybrid procedures. Technological innovation will eventually cause a shift from open to minimal invasive surgical repair. At present, however, open surgery is considered the gold standard for TAAA repair, especially in (relatively) young patients and patients suffering from Marfan's disease.

Cognitive deterioration in adult epilepsy: Does accelerated cognitive ageing exist?

A long-standing concern has been whether epilepsy contributes to cognitive decline or so-called 'epileptic dementia'. Although global cognitive decline is generally reported in the context of chronic refractory epilepsy, it is largely unknown what percentage of patients is at risk for decline. This review is focused on the identification of risk factors and characterization of aberrant cognitive trajectories in epilepsy. Evidence is found that the cognitive trajectory of patients with epilepsy over time differs from processes of cognitive ageing in healthy people, especially in adulthood-onset epilepsy. Cognitive deterioration in these patients seems to develop in a 'second hit model' and occurs when epilepsy hits on a brain that is already vulnerable or vice versa when comorbid problems develop in a person with epilepsy. Processes of ageing may be accelerated due to loss of brain plasticity and cognitive reserve capacity for which we coin the term 'accelerated cognitive ageing'. We believe that the concept of accelerated cognitive ageing can be helpful in providing a framework understanding global cognitive deterioration in epilepsy.

Technical aspects of neurostimulation: Focus on equipment, electric field modeling, and stimulation protocols.

Neuromodulation is a field of science, medicine, and bioengineering that encompasses implantable and non-implantable technologies for the purpose of improving quality of life and functioning of humans. Brain neuromodulation involves different neurostimulation techniques: transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), vagus nerve stimulation (VNS), and deep brain stimulation (DBS), which are being used both to study their effects on cognitive brain functions and to treat neuropsychiatric disorders. The mechanisms of action of neurostimulation remain incompletely understood. Insight into the technical basis of neurostimulation might be a first step towards a more profound understanding of these mechanisms, which might lead to improved clinical outcome and therapeutic potential. This review provides an overview of the technical basis of neurostimulation focusing on the equipment, the present understanding of induced electric fields, and the stimulation protocols. The review is written from a technical perspective aimed at supporting the use of neurostimulation in clinical practice.

Somatosensory cortex responses to median nerve stimulation: fMRI effects of current amplitude and selective attention.

OBJECTIVES: The aim of this study was to localize and to investigate response properties of the primary (SI) and the secondary (SII) somatosensory cortex upon median nerve electrical stimulation. METHODS: Functional magnetic resonance imaging (fMRI) was used to quantify brain activation under different paradigms using electrical median nerve stimulation in healthy right-handed volunteers. In total 11 subjects were studied using two different stimulus current values in the right hand: at motor threshold (I(max)) and at I(min) (1/2 I(max)). In 7 of these 11 subjects a parametric study was then conducted using 4 stimulus intensities (6/6, 5/6, 4/6 and 3/6 I(max)). Finally, in 10 subjects an attention paradigm in which they had to perform a counting task during stimulation with I(min) was done. RESULTS: SI activation increased with current amplitude. SI did not show significant activation during stimulation at I(min). SII activation did not depend on current amplitude. Also the posterior parietal cortex appeared to be activated at I(min). The I(min) response in SII significantly increased by selective attention compared to I(min) without attention. At I(max) significant SI activity was observed only in the contralateral hemisphere, the ipsilateral cerebellum, while other areas possibly showed bilateral activation. CONCLUSIONS: Distributed activation in the human somatosensory cortical system due to median nerve stimulation was observed using fMRI. SI, in contrast to SII, appears to be exclusively activated on the contralateral side of the stimulated hand at I(max), in agreement with the concept of SI's important role in processing of proprioceptive input. Only SII remains significantly activated in case of lower current values, which are likely to exclusively stimulate the sensible fibres mediating cutaneous receptor input. Selective attention only enhances SII activity, indicating a higher-order role for SII in the processing of somatosensory input.

Functional MR imaging of the cervical spinal cord by use of median nerve stimulation and fist clenching.

BACKGROUND AND PURPOSE: Findings of blood oxygen level-dependent (BOLD) functional MR (fMR) imaging of the cervical spinal cord, obtained by using a fist-clenching motor task, have been sporadically reported. Because spinal activation by sensory stimuli has a potential at least equal to that of fist clenching, its feasibility was assessed. Whether stimulation of the median nerve could evoke an fMR imaging response at 1.5 T in the cervical spinal cord was investigated, and the response pattern was compared with that obtained by fist clenching. METHODS: A dynamic cardiac-gated T2*-weighted imaging sequence was used to quantify cervical spinal cord activation under two paradigms with different numbers of subjects. Seven subjects underwent electrical median nerve stimulation at the elbow sufficient to elicit a maximal compound muscle action potential in the flexor carpi radialis muscle. Eleven subjects performed self-paced fist clenching. Cord activation was measured in the sagittal and transverse imaging planes. RESULTS: In the sagittal view, five of seven subjects had an fMR imaging response in the lower cervical spinal cord upon median nerve stimulation, whereas seven of 11 subjects showed activation with the fist-clenching task. Within the cord, the measured fMR imaging response level was approximately 8-15% with respect to the baseline signal level. In the transverse imaging plane, significant fMR imaging responses could be measured in only two of six and six of nine subjects with median nerve stimulation or fist clenching, respectively. A consistent cross-sectional localization of the activity measured in the spinal cord was not detected, either in terms of the right and left sides or in terms of the posterior and anterior directions. CONCLUSION: In the sagittal plane, median nerve stimulation at the elbow can evoke an fMR imaging response in the lower cervical spinal cord. The activation pattern was comparable with that obtained by fist clenching. The localization of the segmental fMR imaging activation (C4 through T1) is consistent with the known functional neuroanatomy for both paradigms. In the transverse plane, reliable fMR imaging responses were obtained much less frequently, and assignment of distinct areas of the spinal cord to the stimulation methods used was not possible.

A new algorithm for off-line automated emboli detection based on the pseudo-wigner power distribution and the dual gate TCD technique.

Research on microembolic signals (MES) using the dual-gate technique has shown promising results, when the time difference (Deltat) of a MES in two sample volumes (SVs) placed serially has been measured manually. On the other hand, the computerized discrimination of MES and artefacts has been reported not to be superior to algorithms based on a single SV. Therefore, a dataset containing MES as well as four types of artefacts was made to test a preliminary version of a new algorithm for automated emboli detection. We monitored 20 patients during carotid endarterectomy (n = 17) and heart surgery (n = 3). Two transcranial Doppler (TCD) signals with a partial overlap of the SVs were recorded online and analysed off-line with an algorithm based on three consecutive steps: 1. Is there an intensity increase in both channels (64-point FFT; 50% overlap)? 2. What is the expected time difference (Deltat), with the velocity measured in channel 1 as the calculation basis? 3. What is the 'exact' Deltat (pseudo-Wigner power function)? Two human experts decided whether a signal was a MES or belonged to one of the four artefact groups. Of a total of 97 MES, 28% (n = 27) could not be detected in the distal channel. Thus, 72% (n = 70) of the MES were present in both channels and could be analysed based on the abovementioned criteria. Of these 70 MES, 87% (n = 61) were correctly identified off-line. We assessed artefact rejection for four different types of artefacts: changes of TCD settings, probe movement, low flow artefacts and electrocautery. The reliability of artefact rejection was 98% for setting changes (n = 382), 96% for probe movement (n = 477) and 98% for low flow artefacts (n = 91), but only 68% for electrocautery (n = 264). These preliminary results are promising, but need careful interpretation: 28% of the MES were not detectable in the distal SV, probably due to a poor signal-to-noise ratio (SNR) and anatomical restrictions. Electrocautery signals were insufficiently rejected. However, even an artefact rejection of 96% can be insufficient if the number of MES is very small compared to the number of artefacts.