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PurposeDeep brain stimulation (DBS), an effective treatment for movement disorders, usually involves lead implantation while the patient is awake and sedated. Recently, there has been interest in performing the procedure under general anesthesia (asleep). This report of a consecutive cohort of DBS patients describes anesthesia protocols for both awake and asleep procedures.MethodsConsecutive patients with Parkinson’s disease received subthalamic nucleus (STN) implants either moderately sedated or while intubated, using propofol and remifentanil. Microelectrode recordings were performed with up to five trajectories after discontinuing sedation in the awake group, or reducing sedation in the asleep group. Clinical outcome was compared between groups with the UPDRS III.ResultsThe awake group (n = 17) received 3.5 mg/kg/h propofol and 11.6 μg/kg/h remifentanil. During recording, all anesthesia was stopped. The asleep group (n = 63) initially received 6.9 mg/kg/h propofol and 31.3 μg/kg/h remifentanil. During recording, this was reduced to 3.1 mg/kg/h propofol and 10.8 μg/kg/h remifentanil. Without parkinsonian medications or stimulation, 3-month UPDRS III ratings (ns = 16 and 52) were 40.8 in the awake group and 41.4 in the asleep group. Without medications but with stimulation turned on, ratings improved to 26.5 in the awake group and 26.3 in the asleep group. With both medications and stimulation, ratings improved further to 17.6 in the awake group and 15.3 in the asleep group. All within-group improvements from the off/off condition were statistically significant (all ps 0.05).ConclusionThe above anesthesia protocols make possible an asleep implant procedure that can incorporate sufficient microelectrode recording. Together, this may increase patient comfort and improve clinical outcomes.

Four unidirectional fiber reinforced SiCN ceramic matrix composites were manufactured by means of polymer infiltration and pyrolysis. Two carbon fibers (T800H and Granoc XN90) as well as two silicon carbide fibers (Tyranno ZMI and SA3) without fiber coating were chosen. As matrix precursor, a poly(methylvinyl)silazane was investigated and utilized. The composites with the SA3 and the XN90 fiber had the highest tensile strengths of 478 and 288 MPa, respectively. It is considered that these high modulus fibers with the low modulus SiCN matrix create weak matrix composites. After exposure to air (T = 1200 °C, 10 h), a significant decrease of the mechanical properties was found, caused by the burnout of carbon fibers and the oxidation through open pores stemming from the PIP process and SiCN/SiCN interfaces in case of the SiC fiber based composites.

SiC/SiCN ceramic matrix composites (CMCs) are promising candidates for components of aero-engines. To evaluate the properties of these CMCs under realistic conditions, a quasi-flat panel with effusion cooling holes was investigated in a high pressure combustor rig. A Tyranno SA3 fabric-based SiC/SiCN composite with high strength and strain to failure was manufactured via polymer infiltration and pyrolysis process. Due to its weak matrix no fiber coating was necessary for damage tolerant behavior. The cooling holes in the panel were introduced via laser drilling. An outer coating of CVD-based SiC was finally applied for enhanced oxidation resistance. The specimen was tested in the combustor rig and the cooling effectiveness was evaluated. The microstructure of laser machined holes was studied via microscopy and energy-dispersive X-ray spectroscopy. The macrostructure was investigated via computing tomography scans before and after the combustor test. Material performances at higher temperatures were estimated via a material performance index. Local microstructure modifications were observed after laser drilling. No crack formation was observed in the CMC panels after rig tests. The measured global cooling effectiveness of 0.76 and the analytical performance evaluation demonstrate the potential benefit of SiC/SiCN materials in combustor applications.

Damage-tolerant ceramic matrix composites (CMC) are prone to high temperature applications under severe environmental conditions and usually utilize carbon or ceramic fibres (e.g. SiC) as reinforcements of ceramic matrices with inherent low elongation to break compared to common metals. However, CMC reveal an elongation to break and stiffness similar to the ceramic matrices, and thus need a fibre coating in order to improve the elongation to break length and thus to achieve damage tolerance of the composite. In addition, such fibers often expose a low ductility during failure. As a consequence, design criteria for components of such CMC materials are limited by the low strain of failure. In order to overcome this problem, we follow the idea of a reinforcement concept of a ceramic matrix reinforced by refractory metal fibres to reach pseudo ductile behaviour during failure. Tungsten (W) and molybdenum (Mo) fibers were chosen as reinforcement in SiCN CMC manufactured by polymer infiltration and pyrolysis process. These fibres are commercially available since they are widespread used in light bulbs, etc. , and possess an intrinsic higher elongation to break, compared to ceramic fibres, as well as high stiffness even at high temperatures. W/SiCN and Mo/SiCN composites were manufactured via filament winding and resin transfer moulding of commercially available polysilazanes, pyrolysed and re-densified by multiple reinfiltration and pyrolysis steps. These composites were investigated with respect to microstructure, flexural and tensile strength. Single fibre strengths for W and Mo were investigated and compared to the strength of the composites. Tensile strengths of 206 and 156 MPa as well as bending strengths of 427 and 312 MPa were achieved for W/SiCN and Mo/SiCN composites, respectively. W fibre became brittle across the entire cross section, while the Mo fibre showed a superficial, brittle reaction zone but kept ductile on the inside.

Currently, there is no known time frame when the patients are the most responsive during awake craniotomy. The aim of this work is therefore to determine when the patient has the shortest reaction time and so to extrapolate the optimal time window for cortical mapping. In this analytic observational study, our group has recorded the reaction times of 35 patients undergoing an awake craniotomy and compared them with the preoperative baseline. The operations were performed according to a "sleep-awake-awake" protocol. Data collection was performed in parallel with standard methods for evaluation of language and cognitive functions. The preoperative reaction times of our patient cohort (average ± SD = 510 ± 124 ms) were significantly shorter than those measured during the operation 786 ± 280 ms, p .001. A one-factor ANOVA within subjects showed a significant increase in reaction times; p .001. Post hoc comparisons on a Bonferroni-corrected α-error level of .05 showed significant differences between the reaction speed during the 0-10 min time frame and the preoperative baseline, as well as the intraoperative reaction times during the 20-30 min, 30-40 min, and the t 40 min time frames. In conclusion, measurement of intraoperative reaction speed seems to be a technically feasible method that is well tolerated by the patients. The intraoperative reaction speed performance was shown to be significantly slower than on the day before the operation. The patients seem to be the slowest directly after extubation and gradually wake up during the awake phase. The poorest wakefulness is demonstrated during the first 20 min after extubation.

SiC/SiC ceramics consist of silicon carbide fibres embedded in a silicon carbide matrix. As an alternative to classic CVI and PIP routes, Liquid Silicon Infiltration (LSI) was chosen as a technique with short process times to obtain composites with low porosity. Silicon carbide composites show good thermal shock resistance, a low coefficient of thermal expansion and excellent physical and chemical stability at elevated temperatures and are therefore regarded as promising candidates for various applications in jet engines and in power engineering. To build up the matrix, different phenolic resin based carbon precursors were infiltrated in fibre preforms and thermally cured, pyrolysed and siliconized. The aim is to obtain a high carbon yield during pyrolysis and to control the pore morphology in a way that the following liquid silicon infiltration leads to a complete reaction of the carbon matrix with silicon to SiC. The siliconization behaviour and conversion into SiC in dependence of pore morphology and chosen precursor is analysed.At the same time a functional fibre coating has to be developed which protects the fibres from liquid silicon and simultaneously provides a weak fibre matrix bonding. A LPCVD-SiNx fibre coating has been chosen and is investigated in fibre composites especially in terms of protection and reactivity in different atmospheres during pyrolysis and siliconization.

Uncoated SiC fibres in SiC/SiC composites manufactured by the liquid-silicon infiltration (LSI) process show a strong degradation as a result of silicon attack. The goal of this research is the development of a SiNx-based fibre coating, which acts as a barrier against the liquid silicon. The coating is applied by means of low-pressure chemical vapour deposition (LPCVD) utilising the gaseous precursors silane (SiH4) and ammonia (NH3) on a commercial SiC multifilament yarn. The result is an amorphous fibre coating with an increasing coating thickness and a variable chemical composition from the middle of the yarn to the edges. The coated fibres exhibit a reduced characteristic Weibull strength in comparison to the uncoated fibres. In order to examine the stability of the films, the coated fibres undergo a heat treatment at 1450 °C in different environments (vacuum, argon and nitrogen). In all environments, the amorphous SiNxcoatings crystallise to the trigonal Si3N4. Depending on the coating thickness cracks and defects develop. However, the best results and the lowest amount of damaging occurs during the treatment in nitrogen.

Liquid Silicon Infiltration (LSI) is a technique to manufacture non-oxide ceramic matrix composites such as C/C-SiC or SiC/SiC. In the beginning of this three-step process, fiber preforms are shaped and impregnated with phenolic resins. After curing, the preforms are pyrolyzed to convert the polymer matrix to a porous carbon matrix. This porosity is then used to infiltrate liquid silicon by capillary forces. Simultaneously, an exothermic reaction of silicon and carbon creates a silicon carbide matrix. Generally the liquid silicon reacts with any carbon and even with SiC present in the form of fibers, fiber coatings or matrix. Therefore, especially the fibers must be protected from Si attack effectively. The morphology of silicon carbide was observed to be heavily driven by Ostwald ripening. This can be suppressed by the addition of boron to the melt. The initially formed SiC crystals in C/C-SiC composites are hereby prevented from grain coarsening, resulting in almost completely preserved C/C blocks. For the manufacture of SiC/SiC composites, the silicon boron alloys allow an effective preservation of the nanocrystalline SiC-fibers. Thus, the use of Si based B containing alloys helps effectively to moderate and control the aggressive reaction during LSI process.

A damage tolerant weak matrix SiC fiber reinforced composite was developed by utilising a polyvinylsilazane in the polymer infiltration and pyrolysis (PIP) process. The polysilazane was infiltrated via resin transfer moulding in a layup of SA3 fabrics, thermally cured and pyrolyzed. This process was repeated until a residual open porosity of below 5% was reached. During pyrolysis the polyvinylsilazane converts to an amorphous SiCN matrix. In combination with the high modulus Tyranno SA3 SiC fibers a weak matrix composite is created. To protect the composite in oxidative environment at high temperatures, an exterior SiC coating by means of chemical vapour deposition was applied. The polyvinylsilazane was investigated in terms of differential scanning calorimetry and measurement of viscosity to find the ideal temperatures for the polymer infiltration step. Specimens of the precursor were cured and pyrolyzed. The densification during pyrolysis was investigated in terms of He gas pycnometry and X-ray diffraction. The composite was characterized by SEM, CT and mercury intrusion porosimetry. To determine the suitability of the SiC/SiCN composite for high temperature applications, samples were oxidized and tested by means of 3-point bending.

Hypersonic airliner would be exposed to temperatures that are beyond the limits of classical aircraft materials. In order to handle this problem the latest developments of new materials and composite structures suitable for high temperature application need to be taken into account. The focus of the European Research program ATLLAS is on advanced light-weight, high-temperature material development strongly linked to a high-speed passenger aircraft design. ATLLAS stands for Aerodynamic and Thermal Load Interactions with Lightweight Advanced Materials for High Speed Flight. The 4 years program ATLLAS-II is a logical continuation project built upon the experience and technology development gained within ATLLAS-I. The corresponding work related to combustor structures and material integration deals with the opportunity to investigate at academic level, both in basic and relevant environment, different solutions possibly usable to ensure the long range cruise of a high speed airliner. Different materials (UTHC, CMC, metallic) and different cooling techniques (radiation, convective, transpiration) are studied. Available numerical or semi-empirical tools are used to prepare the test, to design the different architectures. A pin fin experiment allows to better know the pressure drop and the heat transfer for different channel patterns with thermal cristal techniques. The ERBURIGK long duration test facility allows to characterize different ceramic matrix composite uncooled samples and will allow to realize, at small scale, a long duration (several hours) investigation of cooled ceramic structure in PTAH-SOCAR technology. A multifunctional metallic transpiration cooled HSS panel using Hollow Spheres Stacking as core material was designed and preliminary tested in cold conditions with GN2 and in hot conditions with infra red lamps under 1 MW/m² heat flux. CMC and UHTC materials are used to design, manufacture and test generic fin injectors usable in high speed combustors. Industrial hypersonic METHYLE test facility is used to test in relevant Mach 6 combustor environment HSS panel as well as advanced fin injectors. Hot and cold permeability of composites is documented with GN2 and GH2. Numerical models are used in accordance with the experiments, some examples are given in the present paper.

Specific phenolic resin samples have been developed as the carbon precursor for SiC/C composites. Liquid phenolic resins suitable for fiber-infiltration in the resin transfer moulding (RTM) process are synthesized by using versatile combination of the aromatic component (phenol, naphthalen-2-ol) with various formaldehyde equivalents such as methanal, 1,3,5,7tetraazatricyclo [3.3.1.13,7] decane (urotropine), and 1,3,5-trioxane, under different reaction conditions. Room temperature liquid resoles (RTLR) are obtained by using an excess of the formaldehyde component over phenol (≥2) under basic conditions. Upon heating RTLR can form a crosslinked network even without addition of a hardening reagent. In addition, novolacs are synthesized under acidic conditions using a phenol/formaldehyde ratio ≥1. Nitrogen-containing resins contain nitrogen due to reaction of phenol with urotropine. Novolacs and nitrogen-containing resins are solids at room temperature and not self-curing. To infiltrate these both resins into SiC fibers in the RTM process, they are dissolved in 2furanmethanol (furfuryl alcohol FA) and urotropine which is added as curing-agent. Both, the molecular weight and the amount of the dissolved phenolic resin have an influence on the viscosity and the carbon yield after pyrolysis which is important for this application. The aim was to create different phenolic resins for the fabrication in the RTM process and to characterize the carbon after pyrolysis with respect to the structure and porosity as these are key parameters to generate a stoichiometric SiC matrix by LSI.

Hypersonic airliner would be exposed to temperatures that are beyond the limits of classical aircraft materials. In order to handle this problem the latest developments of new materials and composite structures suitable for high temperature application need to be taken into account. The focus of the European Research program ATLLAS is on advanced light-weight, high-temperature material development strongly linked to a high-speed passenger aircraft design. ATLLAS stands for Aerodynamic and Thermal Load Interactions with Lightweight Advanced Materials for High Speed Flight. The 4 years program ATLLAS-II is a logical continuation project built upon the experience and technology development gained within ATLLAS-I. The corresponding work related to combustor structures and material integration deals with the opportunity to investigate at academic level, both in basic and relevant environment, different solutions possibly usable to ensure the long range cruise of a high speed airliner. Different materials (UTHC, CMC, metallic) and different cooling techniques (radiation, convective, transpiration) are studied. Available numerical or semi-empirical tools are used to prepare the test, to design the different architectures. A pin fin experiment allows to better know the pressure drop and the heat transfer for different channel patterns with thermal cristal techniques. The ERBURIG-K long duration test facility allow to characterize different ceramic matrix composite uncooled samples and will allow to realize, at small scale, a long duration (several hours) investigation of cooled ceramic structure in PTAH-SOCAR technology. A multifonctionnal metallic transpiration cooled HSS panel using Hollow Spheres Stacking as core material was designed and preliminary tested in cold conditions with GN2 and in hot conditions with infra lamps under 1 MW/m² heat flux. CMC and UHTC materials are used to design, manufacture and test generic fin injectors usable in high speed combustors. Industrial hypersonic METHYLE test facility is used to test in relevant Mach 6 combustor environment HSS panel as well as advanced fin injectors. Hot and cold permeability of composites is documented with GN2 and GH2. Numerical models are used in accordance with the experiments, some examples are given in the present paper.

Purpose: We developed a monitoring system to detect spinal cord ischemia during aortic cross-clamping (AXC). This system was used to prospectively determine in which patients ischemia occurs, in which patients reimplantation of intercostal arteries is unnecessary or mandatory, and when reperfusion of intercostal arteries (ICAs) is urgent. Methods: Two hundred sixty patients underwent thoracoabdominal aortic aneurysm (TAA) repair with simple AXC. In 167 patients, two electrocatheters were placed before the onset of anaesthesia at level L1/L2 (stimulation) and level T5/T6 (recording) within the epidural space. During surgery, spinal cord function was monitored by recording spinal somatosensory evoked potentials (sSSEP). According to the extent of aortic replacement, most patients were expected to have a high risk of paraplegia. Results: In group A (59 patients), sSSEP remained normal throughout surgery, and in 54 of these patients ICAs were not reattached outside the proximal aortic anastomosis. In the other five patients ICAs were reimplanted separately because of possible anatomic relation to spinal cord blood supply. No patient in group A had postoperative neurologic deficit. In group B (54 patients) sSSEP remained normal until 15 minutes after AXC but were impaired thereafter. Nineteen patients had early reimplantation of ICAs. Of the 19, three had paraparesis and two had paraplegia. Neurologic deficit developed in the patients without early reimplantation of ICAs. In four patients separate reimplantation of ICAs was performed late in the procedure because of incomplete sSSEP recovery. Subsequently, the sSSEP returned to normal and only one of the four patients had mild paraparesis. The total rate of neurologic deficits in this group was 13% (paraplegia, 3.5%; paraparesis, 9.5%). All 54 patients in group C showed rapid loss of sSSEP within 15 minutes of AXC. In 28 patients ICAs were reimplanted only within the proximal anastomosis. Twenty-one of these patients showed prompt signal recovery after blood-flow release into the reimplanted ICAs, and none had neurologic deficit. Seven patients had no or very late and incomplete sSSEP recovery. Of the seven, three had paraplegia and four had paraparesis. In 26 patients ICAs were reimplanted separately to the proximal anastomosis. This was done early during the procedure in 17 patients, of whom 13 had full recovery of sSSEP and normal neurologic status. Four patients had incomplete or no recurrence of sSSEP, followed by paraplegia in one and paraparesis in three. In nine patients ICAs were reimplanted after the aortic replacement had been completed because sSSEP recovery was not satisfactory. In all patients in this subgroup sSSEP returned to normal. Six patients had a normal neurologic status and three had mild paraparesis. The total neurologic complication rate in group C was 26% (paraplegia, 7.5%; paraparesis, 18.5%). Conclusion: The risk of ischemic spinal cord injury during replacement for TAA can be assessed continuously by monitoring the sSSEP directly from the spinal cord. Patients without sSSEP changes during aortic reconstruction do not require ICA reattachment and will not have neurologic deficit. Patients who lose sSSEP after AXC are at risk for paraplegia. Patients with impairment or loss of sSSEP >15 minutes after AXC have some collateral vessels, and must have ICAs reimplanted only if sSSEP do not return within normal recovery time after blood-flow release into the proximal anastomosis. Loss of sSSEP within 15 minutes of AXC shows poor collateralization and mandates early restoration of spinal cord blood supply. If the surgeon can achieve the return of sSSEP to normal by subsequent separate reimplantation of ICAS, paraplegia will not occur and paraparesis will be rare and mild. Spinal cord monitoring is a valuable guide to detect whether the spinal cord is at risk and to take measures against paraplegia. (J VASC SURG 1996;23:230-40.)

Background Most new perioperative myocardial ischemic episodes occur in the absence of hypertension or tachycardia. The ability of alpha 2-adrenoceptor agonists to inhibit central sympathetic outflow may benefit patients with coronary artery disease by increasing the myocardial oxygen supply and -demand ratio. Methods A randomized double-blind study design was used in 297 patients scheduled to have elective vascular surgical procedures to evaluate the effects of 2 micrograms/kg-1 oral clonidine (n = 145) or placebo (n = 152) on the incidence of perioperative myocardial ischemic episodes, myocardial infarction, and cardiac death. Continuous real-time S-T segment trend analysis (lead II and V5) was performed during anesthesia and surgery and correlated with arterial blood pressure and heart rate before and during ischemic events. Dose requirements for vasoactive and antiischemic drugs to control blood pressure and heart rate as well as episodes of myocardial ischemia (i.e., catecholamines, beta-adrenoceptor antagonists, nitrates, and systemic vasodilators) and fluid volume load were recorded. Results Administration of clonidine reduced the incidence of perioperative myocardial ischemic episodes from 39% (59 of 152) to 24% (35 of 145) (P < 0.01). Hemodynamic patterns, percentage of ischemic time, and the number of ischemic episodes per patient did not differ. Nonfatal myocardial infarction developed after operation in four patients receiving placebo compared with none receiving clonidine (day 2 to 21; P = 0.07). The incidence of fatal cardiac events (1 vs. 2) was not different. Dose requirements for vasoactive and antiischemic drugs did not differ between the groups, but the amount of presurgical fluid volume was slightly greater in patients receiving clonidine (951 +/- 388 vs. 867 +/- 381 ml; P < 0.03). Conclusion A small oral dose of clonidine, given prophylactically, can reduce the incidence of perioperative myocardial ischemic episodes without affecting hemodynamic stability in patients with suspected or documented coronary artery disease.

Polymer-derived ceramic nanocomposites (PDC-NCs) can be synthesized via thermal conversion of suitable single-source precursors, leading in a first step to amorphous single-phase ceramics, which subsequently undergo phase separation pro- cesses to furnish bi- or multiphase ceramic nanocomposites. PDC-NCs have been shown to be excellent candidate materials suitable for applications at ultrahigh-temperatures and under harsh environments. [1,2] In the present work, amorphous SiHf(B)CN-based PDC-NCs were synthesized via cross-link- ing and ceramization of a polysilazane which was chemically modified by Hf(NEt2)4 and borane dimethylsulfide complex (BH3.SMe2). High-temperature annealing of the obtained amorphous SiHf(B)CN ceramics in nitrogen atmosphere led to HfN/Si(B)CN nanocom-posites; whereas HfB2/Si(B)CN was obtained upon annealing in argon atmosphere. The presented results emphasize a convenient preparative approach to nanos- tructured ultrahigh-temperature stable materials starting from a greatly flexible/compliant single-source precursor.

To reduce the incidence of misleading assessments, and to derive criteria for critical spinal cord ischemia during thoracic or thoracoabdominal aortic aneurysm repair, the authors epidurally stimulated and recorded somatosensory evoked potentials (ESEP) below and above, respectively, the spinal segment at risk (electrospinogram).Epidural somatosensory evoked potentials were analyzed in 100 consecutive patients undergoing resection of aortic aneurysms using two bipolar catheters (stimulation at the L2 level and recording at the T3 level) for the following criteria: 1) the time until ESEP disappeared completely after cross clamping, 2) the duration of complete ESEP loss during and after cross clamping, and 3) the time until ESEP recovered after declamping. Postoperatively, neurologic deficits were evaluated by a neurologist who was unaware of the ESEP recordings.Three types of patients could be identified. First, thirty-one patients neither showed ESEP loss nor neurologic deficits. Second, ESEP loss occurring later than 15 min after cross clamping was associated with a neurologic deficit in 2 of 29 patients (6.9%). And, third, 12 of 40 patients (30%) presented a neurologic deficit when ESEP loss occurred within 15 min after cross clamping. Further indicators of an impending risk were a total ESEP loss greater than 40 min (sensitivity 100%, specificity 68%, positive predictive value [PPV] 35%, and negative predictive value [NPV] 100%), and a recovery of ESEP later than 20 min after declamping (sensitivity 93%, specificity 86%, PPV 52%, and NPV 99%).Epidural somatosensory evoked potentials appeared to be a reasonable intraoperative predictor of postoperative neurologic outcome, and informs surgeons and anesthesiologists about the impending danger at an early state of the operation.

Background To reduce the incidence of misleading assessments, and to derive criteria for critical spinal cord ischemia during thoracic or thoracoabdominal aortic aneurysm repair, the authors epidurally stimulated and recorded somatosensory evoked potentials (ESEP) below and above, respectively, the spinal segment at risk (electrospinogram). Methods Epidural somatosensory evoked potentials were analyzed in 100 consecutive patients undergoing resection of aortic aneurysms using two bipolar catheters (stimulation at the L2 level and recording at the T3 level) for the following criteria: 1) the time until ESEP disappeared completely after cross clamping, 2) the duration of complete ESEP loss during and after cross clamping, and 3) the time until ESEP recovered after declamping. Postoperatively, neurologic deficits were evaluated by a neurologist who was unaware of the ESEP recordings. Results Three types of patients could be identified. First, thirty-one patients neither showed ESEP loss nor neurologic deficits. Second, ESEP loss occurring later than 15 min after cross clamping was associated with a neurologic deficit in 2 of 29 patients (6.9%). And, third, 12 of 40 patients (30%) presented a neurologic deficit when ESEP loss occurred within 15 min after cross clamping. Further indicators of an impending risk were a total ESEP loss greater than 40 min (sensitivity 100%, specificity 68%, positive predictive value [PPV] 35%, and negative predictive value [NPV] 100%), and a recovery of ESEP later than 20 min after declamping (sensitivity 93%, specificity 86%, PPV 52%, and NPV 99%). Conclusions Epidural somatosensory evoked potentials appeared to be a reasonable intraoperative predictor of postoperative neurologic outcome, and informs surgeons and anesthesiologists about the impending danger at an early state of the operation.

In order to develop SiC/SiC ceramic matrix composites with a low porosity, liquid silicon infiltration (LSI) was chosen as a technique, characterized by short processing times. To create the matrix, a tailored phenolic resin containing s-naphthol units was synthesized and infiltrated in wound fiber preforms, thermally cured, pyrolysed and siliconized. The aim is to obtain a high carbon yield during pyrolysis and to create a dense carbon foam between the SiC fibers. Instead of a classic liquid silicon infiltration via capillary forces through a carbon block-like microstructure, this foam promotes a softer infiltration with less fiber degradation and a maximized carbon conversion to near stoichiometric SiC. To protect the SiC fibers from an attack of the liquid silicon and to simultaneously provide a weak fiber matrix bonding, a BNx/SiNx fiber coating was chosen. The coating was applied by means of low-pressure chemical vapor deposition (LPCVD) using gaseous chlorine free precursors.