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Biomedical subjects

R Scherer

Publications and source records attributed to R Scherer.

At least 19 recordsLinked to original sources
PubMed2003

Critical decision-speed and information transfer in the "Graz Brain-Computer Interface".

The "Graz Brain-Computer Interface (BCI)" transforms changes in oscillatory EEG activity into control signals for external devices and feedback. These changes are induced by various motor imageries performed by the user. For this study, 2 different types of motor imagery (movement of the right vs. left hand or both feet) were classified by processing 2 bipolar EEG-channels (derived at electrode positions C3 and C4). After a few sessions, within some weeks, 4 young paraplegic patients learned to control the BCI. In accordance with the participants, decision-speed (trial length) was varied and the information transfer rate (ITR) was calculated for each run. All experimental runs have been feedback-runs employing a simple computer-game-like paradigm. A falling ball had to be led into a randomly marked target halfway down the screen. The horizontal position was controlled by the BCI-output signal and the trial length was varied by the investigator across runs. The goal was to find values for trial length enabling a maximum ITR. Three out of 4 participants had good results after a few runs. Analysis of their last 2 experimental sessions, each containing between 10 and 16 runs, showed that the trial length can be reduced to values around 2 s to obtain the highest possible information transfer. Attainable ITRs were between 5 and 17 bit/min depending on the participant's performance and condition.

Adult↗
PubMed2003

Graz-BCI: state of the art and clinical applications.

The Graz-brain-computer interface (BCI) is a cue-based system using the imagery of motor action as the appropriate mental task. Relevant clinical applications of BCI-based systems for control of a virtual keyboard device and operations of a hand orthosis are reported. Additionally, it is demonstrated how information transfer rates of 17 b/min can be acquired by real time classification of oscillatory activity.

Amyotrophic Lateral Sclerosis↗
PubMed2000

[Injury pattern and overuse stress syndrome in young sport climbers].

The rapidly growing interest in sports climbing in recent years among young climbers raises the question about the risk of injuries and overstrain syndromes in this group. This paper investigates injuries and overstrain syndromes of 99 adolescent climbers aged between 8 and 19 years. The authors interviewed climbers from Austria, Germany and Switzerland. Besides the type and pattern of injuries and overstrain syndromes, the level and duration of climbing, intensity of training and gender were recorded as potential risk factors. 47 climbers were asked about setting up fingers on small holds, which is considered a main reason for epiphyseal injuries of fingers in the literature. Injuries and overstrain syndromes, as well as their frequency and pattern are reported and classified. Descriptive data analysis and statistical models are used to assess the influence of risk factors. Among the potential risk factors only the climbing level has a significant influence on the risk of injuries and overstrain syndromes (p = 0.0427). Furthermore the risk of injuries and overstrain syndromes in the area of the fingers is significantly higher for climbers who reported setting up fingers on small holds (OR = 8.24, p = 0.0022). Finally we found a higher frequency of injuries and overstrain syndromes in lower extremities (43% of all injury and overstrain occurrences) and a lower frequency of injuries and overstrain syndromes in general (43% of all the climbers under investigation) compared to other studies. As a result special guidelines for training and competition are given. In order to increase the accuracy of the reports and to investigate long-term effects we recommend a study with clinical assessment and a longer period of observation.

Adolescent↗
PubMed1999

Blood flow in distal end-to-side anastomoses with PTFE and a venous patch: results of an in vitro flow visualisation study.

OBJECTIVES: non-physiological flow behaviour plays a significant role in the development of distal anastomotic intimal hyperplasia. To investigate flow patterns in four anastomotic types of femoral end-to-side distal bypass graft anastomoses, a flow visualisation study was performed. METHODS: transparent 1:1 casted replicas of distal vascular graft anastomoses created by conventional technique, Miller-cuff, Taylor- and Linton-patch were fabricated. A pulsatile mock circulation with a high-speed video system was constructed. Flow pattern was determined at mean Reynolds numbers 100-500. Migrations of the stagnation points on the bottom of the anastomoses at mean Reynolds numbers 100, 230, and 350 were measured. RESULTS: a vortex forms during early systole and increases to maximum systole in all anastomoses. During the diastolic phase the vortex moves in the Miller-cuff distally to the toe of the anastomosis and remains standing, while in the other anastomotic types the vortex moves proximally to the heal of the junction and breaks down. The shift of the stagnation point in the Miller-cuff was considerably smaller than in the other anastomoses. CONCLUSION: conventional, Linton and Taylor anastomoses show similar flow patterns. The Miller-cuff with its wider cavity shows lower shift of the bottom stagnation point, but a persistent washout of the anastomotic cavity, which may contribute to its reported good clinical performance.

Anastomosis, Surgical↗
PubMed1999

Combined antithrombin III and C1-esterase inhibitor treatment decreases intravascular fibrin deposition and attenuates cardiorespiratory impairment in rabbits exposed to Escherichia coli endotoxin.

OBJECTIVE: To assess the effect of a combined antithrombin III and C1-esterase inhibitor treatment on intravascular organ fibrin deposition and cardiorespiratory changes following intravenous Escherichia coli endotoxin (lipopolysaccharide [LPS] 80 microg/kg i.v.) exposure. DESIGN: Prospective, randomized trial. SETTING: Research laboratory of a university medical center. SUBJECTS: Anesthetized, instrumented and mechanically ventilated rabbits ([Chbb:CH); n = 40). INTERVENTIONS: Endotoxin was given to 30 animals. Ten animals received no inhibitor (endotoxin control group). The other animals were either treated by high-dose (300 units/kg; n = 10) or low-dose (100 units/kg; n = 10) combined antithrombin III and C1-esterase inhibitor administration. Ten rabbits (time control group) were given placebo (sodium chloride 0.9%). Cardiorespiratory variables were assessed at baseline, 120 mins, and 240 mins after endotoxin or placebo administration. Four hours after endotoxin injection, liver, lung, and kidney tissue samples were examined for intravascular fibrin deposition by light microscopy. MEASUREMENTS AND MAIN RESULTS: Inhibitor treatment significantly decreased clot formation in lungs and livers without, however, demonstrating a clear dose-dependent effect. Combined antithrombin III/C1-esterase treatment attenuated the decrease of mean arterial pressure and cardiac output observed following endotoxin injection. Blood pressure improvement was significantly dependent on dosage administered. CONCLUSION: Combination of antithrombin III and C1-esterase inhibitor treatment during early endotoxin shock decreased organ fibrin deposition and improved cardiovascular stability.

Animals↗
PubMed1998

Auxiliary liver transplantation with arterialization of the portal vein for acute hepatic failure.

Six adult patients suffering from acute hepatic failure and with a high urgent status underwent heterotopic auxiliary liver transplantation. In four of these patients, the portal vein of the liver graft was arterialized in order to leave the native liver and the liver hilum untouched and to be able to place the liver graft wherever space was available in the abdomen. The arterial blood flow via the portal vein was tapered by the width of the anastomosis. Two patients died, one of sepsis on postoperative day 17 (POD), the other after 3 months due to a severe CMV pneumonia. There were no technically related deaths. The native liver showed early regeneration in all cases. In one patient, the auxiliary graft was removed 6 weeks after transplantation. Four weeks later, he had to undergo orthotopic retransplantation due to a recurrent fulminant failure of the recovered native liver. This patient is alive more than 1 year after the operation. We conclude that heterotopic auxiliary liver transplantation with portal vein arterialization is a suitable approach to bridging the recovery of the acute failing native liver.

Acute Disease↗
PubMed1997

Secretion of brain natriuretic peptide in patients with aneurysmal subarachnoid haemorrhage.

BACKGROUND: Subarachnoid haemorrhage is commonly associated with natriuresis and hyponatraemia. One possible explanation for these features is a defect in the central regulation of renal sodium reabsorption with increased secretion of a natriuretic factor. We investigated whether excess sodium secretion in patients with subarachnoid haemorrhage is related to increased secretion of natriuretic peptides or to the presence of digoxin-like immunoreactive substances. METHODS: We measured the plasma concentrations of digoxin-like immunoreactive substances (by a fluorescence polarisation immunoassay) and natriuretic peptides, aldosterone, renin, and antidiuretic hormone (by radioimmunoassay) in ten patients with aneurysmal subarachnoid haemorrhage, ten patients undergoing elective craniotomy for cerebral tumours, and 40 healthy controls of similar age and sex distribution. Samples were collected before surgery, 1 h, 4 h, and 12 h after surgery, then daily until 7 days postoperatively in the two groups of patients. FINDINGS: All patients with subarachnoid haemorrhage, but none of the tumour patients, showed increased urine output and urinary excretion of sodium (p = 0.018 for comparison of means of curves to 7 days). The patients with subarachnoid haemorrhage had much higher plasma concentrations of brain natriuretic peptide (BNP) than controls, on admission (mean 15.1 [SE 3.8] vs 1.6 [1.0] pmol/L, p < 0.001) and throughout the study period, accompanied by lower than normal aldosterone concentrations and normal plasma concentrations of atrial and C-type natriuretic peptides (ANP, CNP). The patients with tumours had similar plasma concentrations of ANP, BNP, and CNP to the controls. We did not detect digoxin-like immunoreactive substances in either group of patients. INTERPRETATION: Salt-wasting of central origin may induce hyponatraemia in patients with aneurysmal subarachnoid haemorrhage, possibly as a result of increased secretion of BNP with subsequent suppression of aldosterone synthesis.

Brain Neoplasms↗
PubMed1997

[Intraoperative heat conservation. A lot of hot air?].

Thermoregulation and its impairment by anaesthesia and surgery has recently been brought back into focus by researchers and clinicians. All volatile and IV anaesthetics, opioids, as well as spinal and epidural anaesthesia increase the inter-threshold range of thermoregulation from 0.2 degree C to 4 degrees C between vasodilation and vasoconstriction. Thermoregulatory vasoconstriction and shivering occurs in anaesthetized patients at lower core temperatures than in awake subjects. Following induction of general or spinal/epidural anaesthesia, core temperature decreases significantly due to internal redistribution of body heat from the core thermal compartment to peripheral tissues. About 1 h after induction of general anaesthesia and initial redistribution hypothermia, a real reduction in body heat occurs as heat loss exceeds metabolic heat production. Heat loss is further increased due to low operating room temperatures, evaporation from open body cavities, and cold IV fluids. Peripheral thermoregulatory vasoconstriction is triggered by core temperatures between 33 degrees C and 35 degrees C, and is able to slow heat loss. However, body heat content continues to decrease even though core temperatures remain nearly constant. During spinal or epidural anaesthesia thermoregulation remains intact in the unblocked body segments, leading to reduced real heat loss when compared to general anaesthesia. Inadvertent hypothermia markedly decreases drug metabolism. Coagulation is impaired by cold-induced defects of platelet function. Hypothermia reduces neutrophil phagocytosis and oxidative killing capacity, causing wound infections. Postoperative hypothermia represents an unnecessary stress for the circulatory system, elevating plasma catecholamines and leading to myocardial ischaemia and arrhythmias. These hypothermia-related morbidities therefore have consequences reaching fare into the postoperative period. Prevention of inadvertent hypothermia is always indicated. Forced-air warming is the most effective and safest method to prevent perioperative hypothermia.

Body Temperature↗
PubMed1997

The influence of antithrombin III (AT III) substitution to supranormal activities on systemic procoagulant turnover in patients with end-stage chronic liver disease.

OBJECTIVE: Since antithrombin III (AT III) substitution to normal activities could not be shown to have major beneficial effects in patients with end-stage chronic liver disease in a variety of clinical settings, we tested the hypothesis that substitution to supranormal activities decreases systemic procoagulant turnover better in this patient group. DESIGN: Controlled prospective clinical study. SETTING: Operating rooms at a University Hospital. PATIENTS: Twenty-four patients with histologically verified liver cirrhosis consecutively scheduled for liver transplantation. INTERVENTIONS: Nineteen patients were given an antithrombin III concentrate to achieve either 100% (n = 10) or 175% (n = 9) AT III activity. Control patients (n = 5) received saline 0.9% instead. MEASUREMENTS AND RESULTS: Molecular markers of coagulation activation, platelet count and aggregability, and global coagulation variables were measured prior to AT III infusion and 60 min thereafter. In both AT III-treated groups thrombin-antithrombin III-complex increased significantly (p < 0.005), whereas prothrombin fragment F1 + 2, soluble fibrin and D-dimer concentrations, as well as other variables, did not show major changes. CONCLUSIONS: Despite thrombin inhibition by AT III in patients with end-stage chronic liver disease, systemic procoagulant turnover was not significantly decreased 60 min after AT III application even to supranormal activities. Replenishment of the inhibitory antithrombin III pool, decreased in chronic liver disease, should not be expected to slow down the baseline consumptive component of the haemostatic disorder in this patient group.

Adult↗
PubMed1997

[Post-traumatic cerebrospinal rhinorrhea].

PURPOSE: Since frontobasal fractures after severe head trauma may cause serious late-term complications such as meningitis, their recognition and operative treatment are essential. Therefore, we analysed the importance of rhinoliquorrhoea as an early symptom of such fractures by comparison with neuroradiological methods. MATERIAL AND METHODS: In all patients undergoing operative revision of frontobasal fractures during a 7-year period, the clinical symptoms, results of neuroradiological examinations, concomitant injuries, as well as operative results, were studied retrospectively. RESULTS: 45 patients out of 688 with severe head injury showed frontobasal fractures (6.5%). The most common cause of these injuries were traffic accidents (55%) and precipitated falls or plunges (35%). Posttraumatic rhinoliquorrhoea was seen in 41 of 45 patients (91%), and 30 showed external periorbital injuries (66%). In 8 patients (18%) the frontobasal fractures could not be visualised by facultatively performed neuroradiological methods (coronary CT-scan, CT-cisternography, subarachnoid space scintigraphy). 15 patients (33%) were secondarily transferred to our institution, two of them more than two years after the causative injury. All patients were operated on successfully within 14 days after admission. CONCLUSION: Traffic accidents and precipitated falls or plunges are the main causes of head injuries with frontobasal fractures and about 2/3 of these patients show external periorbital injuries. Rhinoliquorrhoea as an early symptom allows diagnosis of frontobasal fractures in 90% of all cases rather than neuroradiological methods which failed to demonstrate frontobasal fractures in about 20% of our patients. Therefore, recognition of rhinoliquorrhoea in patients with severe head injury is essential.

Adolescent↗
PubMed1997

Participation in the Ischemic Optic Neuropathy Decompression Trial: sex, race, and age.

BACKGROUND: The Ischemic Optic Neuropathy Decompression Trial (IONDT) is a randomized, single masked, multicenter trial designed to assess the safety and efficacy of optic nerve decompression surgery compared with careful follow-up in patients 50 years or older with non-arteritic anterior ischemic neuropathy (NAION). OBJECTIVES: To examine and evaluate the sex, race, and age distributions of the screened, and subsequently enrolled, IONDT population, especially the proportions of female, minority, and elderly patients, and demographic characteristics of clinical center investigators, the geographical location of IONDT Clinical Centers, and the referral patterns of local physicians. SETTING: Twenty-five U.S. clinical centers. PARTICIPANTS: There were 1,681 referrals to the Clinical Centers; an Eligibility Screening Form providing demographic information was completed for 1,152. FINDINGS: Forty-three percent (495/1,152) of screened cases were women. Seven percent (85/1,152) were minorities: 33 African-Americans, 34 Hispanics, 17 Asians, and 1 Native-American. The average age was 66 +/- 10 years with a range of 22-92 years of age. Of the 1,152 referred patients, 305 were eligible for randomization; 258 (85%) of these agreed to participate in the trial. The demographic makeup of the randomized IONDT patients was similar to that of the screened population. CONCLUSIONS: Women and the elderly are well represented in the IONDT. Because the number of participating minorities was low, we cannot reliably assess their level of participation. Both a low incidence of NAION in minorities and a low referral rate of minorities to clinical trials are plausible explanations for our findings.

Adult↗
PubMed1996

[Percutaneous puncture technique for portofemorosubclavicular venovenous bypass in orthotopic liver transplantation].

UNLABELLED: Portofemoro-axillary bypass systems are commonly used to treat adverse haemodynamic effects during the anhepatic phase of orthotopic liver transplantation (OLT). However, low shunt flows may reduce the efficacy of these bypass systems. In order to improve veno-venous bypass management, a percutaneous cannulation technique (PCT) was used to insert large-bore catheters (21 F) into the left femoral and subclavian veins. This study prospectively addresses the complications of the PCT in 195 adult patients undergoing 203 OLTs. METHODS: The left femoral and subclavian veins were cannulated preoperatively with 21 F single-lumen catheters (DLP, Grand Rapids, MN, USA) using a Seldinger technique. Intra-operatively, the centrifugal pump (Biopump, Biomedicus, Minnesota, USA) and the portal part of the bypass were connected with the femoral and subclavian catheters. Coagulation profiles, shunt flows, haemodynamic parameters, and complications during OLT associated with the bypass system were recorded. RESULTS: Percutaneous cannulation of the left subclavian and femoral veins was successful in 198 (97.6%) patients. Mean portofemoro-subclavian shuntflow was 4.3 (SD 1.3 l min-1). Although cardiac index (shunt 3.91 [SD 1.1] vs pre-shunt 4.42 [SD 1.0] l min-1 m-2, P < 0.05) and oxygen delivery (shunt 496 [SD 111] vs. pre-shunt 562 [SD 153] ml ml-1.m-2, P < 0.05) were not maintained at pre-shunt levels, renal perfusion pressure stayed above 50 mm Hg during the anhepatic phase. Two intra-operative air embolism (0.98%) and one myocardial infarction (0.49%) at the beginning of the anhepatic phase were observed. There were no bleeding complications. CONCLUSIONS: The portofemoro-subclavian bypass can be performed by percutaneous cannulation without additional complications in patients undergoing OLT. Although haemorrhagic complications following central venous catheterisation are reported to occur in patients with haemostatic defects, none of them was observed in this study. Two events of air embolism and one cardiac arrest could not be related to the PCT. In conclusion, femoro-subclavian percutaneous cannulation is a simple, rapid, and safe alternative to commonly used veno-venous bypass systems.

Adult↗
PubMed1996

[Anxiolysis, sedation, and stress reduction following oral premedication with midazolam in adults. A comparison with dipotassium clorazepate and placebo].

Benzodiazepines are the most commonly used anxiolytic agents. Among the benzodiazepines, midazolam has the advantage of a short elimination half-life, which is especially useful in outpatient surgery. However, in contrast to other commonly prescribed benzodiazepines, such as chlorazepate dipotassium, oral premedication with midazolam has not been thoroughly investigated. Therefore, the present study was performed to compare anxiolysis, sedation and stress reduction with midazolam and clorazepate dipotassium in adults. METHODS. After IRB approval and informed consent had been obtained, 85 patients scheduled for breast biopsy were studied. The patients were chosen at random to receive either 7.5 mg midazolam (n = 29), 20 mg clorazepate dipotassium (n = 28) or placebo (n = 28) preoperatively. Before premedication, immediately prior to surgery and postoperatively in the recovery room, the following parameters were determined with visual analogue scales (VAS): "asthenia," "depression," oral salivation, muscle tension, motoric restlessness and sweating of the palms. In addition, anxiety (STAI-G-X-1, Spielberger), heart rate and arterial blood pressure were measured. Before patients underwent surgery, the degree of sedation was evaluated by the anaesthesiologist. RESULTS. Clorazepate dipotassium and midazolam both caused a reduction in anxiety as compared with the placebo (P < 0.05). Only clorazepate dipotassium reduced anxiety postoperatively (P < 0.05). Neither midazolam nor clorazepate dipotassium caused a reduction in "asthenia" and "depression." Midazolam was more effective in preventing increased blood pressure than clorazepate dipotassium and the placebo (P < 0.05). Furthermore, after premedication with midazolam, salivation, muscle tension, motoric restlessness and sweating of the palms remained stable, in contrast to the results after premedication using clorazepate dipotassium or placebo (P < 0.05). CONCLUSIONS. The anxiolytic effects of 7.5 mg midazolam and 20 mg clorazepate dipotassium were similar after oral application. However, the anxiolytic effect of midazolam is shorter-lived than that of clorazepate dipotassium. In contrast to clorazepate dipotassium, midazolam produced no increase in arterial blood pressure and stabilized oral salivation, production in the palms, muscle tension and motoric restlessness.

Adult↗
PubMed1996

Velocity distributions in glottal models.

Velocity distributions within three models of the human larynx, namely, a rigid plexiglas model, an excised canine larynx, and a computational model are investigated with experimental and theoretical analyses. A plexiglas wind tunnel with interchangeable glottal constrictions was used as a two-dimensional steady-flow model to measure velocity and pressure for various glottal shapes. A canine excised larynx was used as a prototype pulsatile flow model to study pressure and velocity variations during phonation. Results of the plexiglas modelling indicated a parabolic laminar velocity profiles upstream of the glottal constriction and turbulent and asymmetric velocity profile downstream of the glottal constriction. The time-averaged velocities of the excised larynx had similarities with the plexiglas model results, and instabilities and asymmetries were also demonstrated by the computational method.

Animals↗