Katharina Foerster

Universitätsklinikum Freiburg, Freiburg an der Elbe, Lower Saxony, Germany

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Publications (34)45.17 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A novel sensor for measuring arterial distension, pulse and pressure waveform is developed and evaluated. The system consists of a magnetic sensor which is applied and fixed to arterial vessels without any blood vessel constriction, hence avoiding stenosis. The measurement principle could be validated by in vitro experiments on silicone tubes, and by in vivo experiments in an animal model, thereby indicating the non-linear viscoelastic characteristics of real blood vessels. The sensor is capable to provide absolute measurements of the dynamically varying arterial diameter. By calibrating the sensor, a long-term monitoring system for continuously measuring blood pressure and other cardiovascular parameters could be developed based on the method described. This will improve diagnostics for high risk patients and enable a better, specific treatment.
    Biomedical Microdevices 07/2014; · 2.72 Impact Factor
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    ABSTRACT: Micro-Electrocorticography (µECoG) provides insights into the cortical organization with high temporal and spatial resolution desirable for the better understanding of neural information processing. Here we evaluated the use of µECoG for detailed cortical recording of somatosensory evoked potentials (SEP) in an ovine model. The approach to the cortex was planned using an MRI-based 3D model of the sheep's brain. We describe a minimally extended surgical procedure allowing placement of two different µECoG grids on the somatosensory cortex. With this small craniotomy the frontal sinus was kept intact, thus keeping the surgical site sterile and making this approach suitable for chronic implantations. We evaluated the procedure for chronic implantation of an encapsulated µECoG recording system. During acute and chronic recordings significant SEP responses in the triangle between the ansate, diagonal and coronal sulcus were identified in all animals. Stimulation of the nose, upper lip, lower lip and chin caused a somatotopic lateral-to-medial, ipsilateral response pattern. Using repetitive recordings of SEPs, this somatotopic pattern was reliably recorded for up to 16 weeks. The findings of this study confirm the previously postulated ipsilateral, somatotopic organization of the sheep's sensory cortex. High gamma band activity was spatially most specific in the comparison of different frequency components of the somatosensory evoked response. This study provides a basis for further acute and chronic investigations of the sheep's sensory cortex by characterizing its exact position, its functional properties and the surgical approach with respect to macro-anatomical landmarks. J. Comp. Neurol., 2014. © 2014 Wiley Periodicals, Inc.
    The Journal of Comparative Neurology 05/2014; · 3.66 Impact Factor
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    ABSTRACT: /st>Whereas the effects of various inspiratory ventilatory modifications in lung injury have extensively been studied, those of expiratory ventilatory modifications are less well known. We hypothesized that the newly developed flow-controlled expiration (FLEX) mode provides a means of attenuating experimental lung injury. /st>Experimental acute respiratory distress syndrome was induced by i.v. injection of oleic acid in 15 anaesthetized and mechanically ventilated pigs. After established lung injury ($P{\hbox{a}_{{{{\rm O}_{\rm 2}}}}/F{\small{\rm I}}_{{{\rm O}_{\rm 2}}}}$ratio <27 kPa), animals were randomized to either a control group receiving volume-controlled ventilation (VCV) or a treatment group receiving VCV with additional FLEX (VCV+FLEX). At predefined times, lung mechanics and oxygenation were assessed. At the end of the experiment, the pigs were killed, and bronchoalveolar fluid and lung biopsies were taken. Expression of inflammatory cytokines was analysed in lung tissue and bronchoalveolar fluid. Lung injury score was determined on the basis of stained tissue samples. /st>Compared with the control group (VCV; n=8), the VCV+FLEX group (n=7) demonstrated greater dynamic lung compliance and required less PEEP at comparable $F{{\small{\rm I}}_{{{\rm O}_{\rm 2}}}}$ (both P<0.05), had lower regional lung wet-to-dry ratios and lung injury scores (both P<0.001), and showed less thickening of alveolar walls (an indicator of interstitial oedema) and de novo migration of macrophages into lung tissue (both P<0.001). /st>The newly developed FLEX mode is able to attenuate experimental lung injury. FLEX could provide a novel means of lung-protective ventilation.
    BJA British Journal of Anaesthesia 04/2014; · 4.24 Impact Factor
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    ABSTRACT: We demonstrate by theory, as well as by ex vivo and in vivo measurements that impedance plethysmography, applied extravascularly directly on large arteries, is a viable method for monitoring various cardiovascular parameters, such as blood pressure, with high accuracy. The sensor is designed as an implant to monitor cardiac events and arteriosclerotic progression over the long term.
    Sensors (Basel, Switzerland). 01/2014; 14(8):14858-72.
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    ABSTRACT: A sensor system for continuous monitoring of blood pressure using an acceleration sensor implanted on an artery using minimally invasive techniques is described. The sensor relies on measurement of the reflected wave transit time (RWTT). This implantable system is fabricated on a flexible substrate using 2 mm × 2 mm acceleration sensors and a telemetric unit for transmission of the data. In vivo experiments show that the RWTT can be reliably determined from arterial acceleration signals. RWTT and systolic blood pressure are shown to be strongly coupled, with a correlation coefficient of 0.96, as determined from measurement of 1800 pulses with a mean deviation of the blood pressure of only 4.3%. The system was implanted in an animal and was able to telemetrically transmit acceleration plethysmographs with high quality out of the awake animal.
    Sensors and Actuators A Physical 01/2014; 206:151–158. · 1.84 Impact Factor
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    ABSTRACT: We recently presented a method for the quantitative measurement of the arterial input function which allows for determination of absolute cerebral blood flow (CBF) values without adjustable parameters. The aim of the present work is to estimate absolute CBF values by using this new technique and to compare it with the gold standard for cerebral perfusion, H215O positron emission tomography. Pigs (13) were comparatively investigated by each method performing multiple measurement runs. The reproducibility of both methods was assessed by a voxel-wise correlation of repeated measurements. An intersubject evaluation was performed on median whole-brain CBF estimates. The mean CBF (MRI) was 20±4mL/100g/min for gray matter, the mean CBF (positron emission tomography) was 24±6mL/100g/min for gray and white matter. The reproducibility for MRI correlated with r = 0.85 and P<0.0001, for positron emission tomography with r = 0.76 and P<0.0001. The correlation for the median whole-brain CBF in MRI and positron emission tomography was r = 0.60 and P = 0.04. The proposed method allows for determination of quantitative CBF without normalization factors. The relatively low estimates of absolute CBF most likely results from the higher age of the pigs as compared to other studies. The intermediate correlation between both methods is caused by physiological intraindividual fluctuations of the CBF and by a limited reproducibility of both methods. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 12/2013; · 3.27 Impact Factor
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    ABSTRACT: Sudden cardiac arrest is one of the leading causes of death. Conventional CPR techniques after cardiac arrest provide circulation with reduced and varying blood flow and pressure. We hypothesize that using pressure- and flow-controlled reperfusion of the whole body improves neurological recovery and survival after 15 min of normothermic cardiac arrest. Pigs were randomized in two experimental groups and exposed to 15 min of ventricular fibrillation (VF). After this period, the animals in the control group received conventional CPR with open chest compression (n=6), while circulation in the treatment group (n=6) was established with an extracorporeal life support system (ECLS) to control blood pressure and flow. Follow-up included the assessment of neurological recovery and magnetic resonance imaging (MRI) for up to 7 days. Five of the six animals in the control group died, one animal was resuscitated successfully. In the treatment group, 1/6 could not be separated from ECLS. Five out of the six pigs survived and were transferred to the animal facility. One animal was unable to walk and had to be sacrificed 30 hours after ECLS. The remaining 4 animals of the treatment group and the surviving pig from the control group showed complete neurological recovery. Brain MRI revealed no pathological changes. We were able to demonstrate a significant improvement in survival after 15 minutes of normothermic cardiac arrest. These results support our hypothesis that using an ECLS for pressure- and flow-controlled circulation after circulatory arrest is superior to conventional CPR.
    Perfusion 07/2013; · 0.94 Impact Factor
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    ABSTRACT: State-of-the-art cardiopulmonary resuscitation (CPR) restores circulation with inconsistent blood-flow and pressure. Extracorporeal life support (ECLS) following CPR opens the opportunity for "controlled reperfusion". In animal experiments investigating CPR with ECLS, systemic anticoagulation before induced cardiac arrest is normal, but a major point of dispute, since preliminary heparinization in patients undergoing unwitnessed cardiac arrest is impossible. In this study, we investigated options for ECLS after an experimental 15 minutes normothermic cardiac arrest, without preceding anticoagulation, in pigs. Neurological recovery was assessed by a scoring system, electroencephalography and brain magnetic resonance imaging. Additionally, brain histology was performed on day seven after cardiac arrest. We demonstrated that preliminary heparin administration was not necessary for survival or neurological recovery in this setting. Heparin flushing of the cannulae seemed sufficient to avoid thrombus formation. These findings may ease the way to using ECLS in patients with sudden cardiac arrest.
    Perfusion 07/2013; · 0.94 Impact Factor
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    ABSTRACT: We present the design and realization of a novel magnetic sensor system for in situ monitoring of cardiovascular parameters, such as arterial distension and pulse. The system is designed as an implantable, extravascular magnetic field sensor for continuously measuring these parameters. It is wrapped around an arterial blood vessel without constricting the artery, thus avoiding stenosis. In vitro measurements on silicone tubes show the predicted linear elastic properties. Successful in vivo experiments detect the viscoelastic behavior of real blood vessels and its correlation with blood pressure.
    Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS & EUROSENSORS XXVII), 2013 Transducers & Eurosensors XXVII: The 17th International Conference on Solid-State Sensors, Actuators and Microsystems; 06/2013
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    ABSTRACT: We introduce a minimally invasive, implantable system that uses pulse transit time to determine blood pressure. In contrast to previous approaches, the pulse wave is detected by a photoplethysmographic (PPG) signal, acquired with high quality directly on subcutaneous muscle tissue. Electrocardiograms (ECG) were measured with flexible, implantable electrodes on the same tissue. PPG detection is realized by a flat 20 mm x 6 mm optoelectronic pulse oximeter working in reflection mode. The optical sensor as well as the ECG electrodes can be implanted using minimally invasive techniques, with only a small incision into the skin, making long-term monitoring of blood pressure in day-to-day life for high-risk patients possible. The in vivo measurements presented here show that the deviation to intra-arterial reference measurements of the systolic blood pressure in a physiologically relevant range is only 5.5 mmHg, demonstrated for more than 12 000 pulses. This makes the presented sensor a grade B blood pressure monitor.
    Biomedical Microdevices 05/2013; · 2.72 Impact Factor
  • 42nd Annual Meeting of the German Society for Cardiovascular and Thoracic Surgery; 02/2013
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    ABSTRACT: State-of-the-art cardiopulmonary resuscitation (CPR) restores circulation with inconsistent blood-flow and pressure. Extracorporeal life support (ECLS) following CPR opens the opportunity for “controlled reperfusion”. In animal experiments investigating CPR with ECLS, systemic anticoagulation before induced cardiac arrest is normal, but a major point of dispute, since preliminary heparinization in patients undergoing unwitnessed cardiac arrest is impossible. In this study, we investigated options for ECLS after an experimental 15 minutes normothermic cardiac arrest, without preceding anticoagulation, in pigs. Neurological recovery was assessed by a scoring system, electroencephalography and brain magnetic resonance imaging. Additionally, brain histology was performed on day seven after cardiac arrest. We demonstrated that preliminary heparin administration was not necessary for survival or neurological recovery in this setting. Heparin flushing of the cannulae seemed sufficient to avoid thrombus formation. These findings may ease the way to using ECLS in patients with sudden cardiac arrest.
    Perfusion 01/2013; · 0.94 Impact Factor
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    ABSTRACT: An implantable sensor system for long-term monitoring of blood pressure is realized by taking advantage of the correlation between pulse transit time and blood pressure. The highly integrated implantable sensor module, fabricated using MEMS technologies, uses 8 light emitting diodes (LEDs) and a photodetector on chip level. The sensor is applied to large blood vessels, such as the carotid or femoral arteries, and allows extravascular measurement of highly-resolved photoplethysmograms. In addition, spectrophotometric approaches allow measurement of hemoglobin derivatives. For the calibration of blood pressure measurements, the sensor system has been successfully implemented in animal models.
    Biomedical Microdevices 09/2012; · 2.72 Impact Factor
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    ABSTRACT: Spectralphotometric measurement methods as, for example, pulse oximetry are established approaches for extracorporeal determination of blood constituents. We measure the dynamics of the arterial distension intracorporeally thus extending the scope of the method substantially. A miniaturized opto-electronic sensor is attached directly to larger arteries without harming the vessel. The transmitted light through the arteries shows a linear correlation with the pulsatile expansion in theory as well as in experiments. Intra-arterial blood pressure also shows a linear interrelationship with the optical signal. Measurements of blood vessel wall dynamics has great potential to quantify arteriosclerosis by this new and innovative approach.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:2359-62.
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    ABSTRACT: Cardiovascular disease caused 32.8% of deaths in the United States in 2008 [1]. The most important medical parameter is the arterial blood pressure. The origin of high or low blood pressure can mostly be found in the vessel compliance. With the presented implantable sensor, we are able to directly measure strain of arteries, as an indicator of arteriosclerosis. The sensor is designed as a cuff with integrated capacitive structures and is wrapped around arteries. With a new and innovative locking method, we could show that the system does not affect the arteries. This is demonstrated by theory as well as experimental in vivo investigations. Biocompatibility tests, confirmed by histological cuts and MRI measurements, showed that no stenosis, allergic reactions or inflammation occurs. The sensor shows excellent linear behavior with respect to stress and strain.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:535-8.
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    ABSTRACT: Imaging of cerebral perfusion by tracking the first passage of an exogenous paramagnetic contrast agent (termed dynamic susceptibility contrast, MRI) has been used in the clinical practice for about a decade. However, the primary goal of dynamic susceptibility contrast MRI to directly quantify the local cerebral blood flow remains elusive. The major challenge of dynamic susceptibility contrast MRI is to measure the contrast inflow to the brain, i.e., the arterial input function. The measurement is complicated by the limited dynamic range of MRI pulse sequences that are optimized for a good contrast in brain tissue but are suboptimal for a much higher tracer concentration in arterial blood. In this work, we suggest a novel method for direct arterial input function quantification. The arterial input function is measured in the carotid arteries with a dedicated plug-in to the conventional pulse sequence to enable resolution of T(2) on the order of a millisecond. The new technique is compatible with the clinical measurement protocols. Applied to the pig model (N = 13), the method demonstrates robustness of the arterial input function measurement. The cardiac output and cerebral blood volume, obtained without adjustable parameters, agree well with positron emission tomography measurements and values found in the literature. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 05/2012; · 3.27 Impact Factor
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    ABSTRACT: Myoblast-based therapy can improve cardiac function after infarction and is conventionally performed by direct injection. A scaffold-based transfer could overcome injection-associated problems. In upgrading this approach we transplanted skeletal myoblasts (SkM) overexpressing the prosurvival gene Akt1. SkM were transfected with pcDNA3-huda-Akt1 and seeded on polyurethane scaffolds. These scaffolds were transplanted in rats 2 weeks after myocardial infarction. Hemodynamics were analyzed before therapy and 6 weeks later. Infarction size and capillary density were performed thereafter. Additional groups received injections of Akt1-transfected or untransfected myoblasts, scaffolds seeded with untransfected myoblasts, or sham operation. Deterioration of global systolic left ventricular function could be inhibited by all therapeutic approaches. In addition, transplantation of Akt1-transfected cells, either scaffold-based or injected, was superior with regard to systolic properties of the left ventricular wall. This effect was accompanied by smaller infarction sizes and angiogenesis. Scaffolds with untransfected myoblasts yielded also smaller infarctions than injections of untransfected myoblasts. Both Akt groups profited with regard to dP/dt(min). In contrast, other diastolic parameters pointed at impaired relaxation and stiffer myocardium especially in the Akt1-scaffold group. In conclusion, SkM overexpressing Akt1 can maintain myocardial function after infarction, reduce infarction size, and induce neovascularization. Scaffold-based cell transfer does not augment this reverse remodeling capacity.
    Tissue Engineering Part A 01/2011; 17(1-2):205-12. · 4.64 Impact Factor
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    ABSTRACT: Cardiopulmonary bypass (CPB) may be associated with acute kidney injury (AKI). Inhaled carbon monoxide (CO) is cyto- and organ-protective. We hypothesized that pretreatment with inhaled CO prevents CPB-associated AKI. Pigs (n = 38) were nonrandomly assigned to SHAM, standard CPB, pretreatment with inhaled CO (250 ppm, 1 hour) before SHAM or CPB, to pretreatment with quercetin (an inhibitor of the heat shock response), and to pretreatment with SnPPIX (an inhibitor of endogenously derived CO), before CO inhalation and CPB. The primary outcome variables were markers of AKI (urea, uric acid, creatinine, cystatin C, neutrophil gelatinase-associated lipocalin, interleukin-6, tumor necrosis factor-alpha), which were determined 120 minutes after CPB. Secondary outcome variables were heat shock protein (HSP)-70 and heme oxygenase-1 protein expressions as indicators of CO-mediated heat shock response. Pretreatment with inhaled CO attenuated (all P < 0.001) CPB-associated, (1) increases in serum concentrations of cystatin C (64 +/- 14 vs 28 +/- 9 ng/mL), neutrophil gelatinase-associated lipocalin (391 +/- 65 vs 183 +/- 56 ng/mL), renal tumor necrosis factor-alpha (450 +/- 73 vs 179 +/- 110 pg/mL), and interleukin-6 (483 +/- 102 vs 125 +/- 67 pg/mL); (2) increase in renal caspase-3 activity (550 +/- 66 vs 259 +/- 52 relative fluorescent units); and (3) histological evidence of AKI. These effects were accompanied by activation of HSP-70 (196 +/- 64 vs 554 +/- 149 ng/mL, P < 0.001). Pretreatment with the heat shock response inhibitor quercetin counteracted the CO-associated biochemical and histological renoprotective effects (all P < 0.001), whereas the heme oxygenase inhibitor SnPPIX only partially counteracted the CO-associated renoprotection and the activation of the heat shock response. CO treatment before CPB was associated with evidence of renoprotection, demonstrated by fewer histological injuries and decreased cystatin C concentrations. The findings that the antiinflammatory and antiapoptotic effects of CO were accompanied by activation of HSP-70, which in turn were reversed by quercetin, suggest that renoprotection by pretreatment with inhaled CO before CPB is mediated by activation of the renal heat shock response.
    Anesthesia and analgesia 07/2010; 111(1):29-37. · 3.08 Impact Factor
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    ABSTRACT: Cardiopulmonary resuscitation is associated with high mortality and poor neurological recovery. Cardiopulmonary resuscitation can cause ischemia-reperfusion injury of the whole body and brain. We assessed the hypothesis that controlled reperfusion of the whole body with cardiopulmonary bypass would limit reperfusion injury after 15 minutes of normothermic cardiac arrest with better survival and neurological recovery. Eleven pigs were exposed to normothermic ischemia for 15 minutes by inducing ventricular fibrillation, followed by cardiopulmonary resuscitation (control group, n = 4) or 60 minutes of cardiopulmonary bypass (treatment group, n = 7). Conditions of reperfusion and the reperfusate were controlled with cardiopulmonary bypass. Animals were observed for up to 7 days, and neurological assessment (Neurological Deficit Score: 0, normal; 500, brain death), magnetic resonance imaging, and brain histology were performed. All animals in the control group died after 20 minutes of cardiopulmonary resuscitation (n = 4). All (n = 7) survived in the treatment group. Clinically apparent neurological recovery occurred within 24 hours; 1 fully conscious pig could not walk. The Neurological Deficit Score was 98 +/- 31 in all animals (n = 7) after 24 hours and decreased to 0 after 48 hours in 4 of 5 eligible animals; 1 animal had a Neurological Deficit Score of 110 after 3 days. Brain histology revealed hypoxic and apoptotic neurons with an inconclusive correlation regarding neurological recovery. Clinically apparent neurological recovery after a period of 15 minutes of cardiac arrest occurred with cardiopulmonary bypass instead of cardiopulmonary resuscitation for reperfusing the whole body. This approach contrasts with cardiopulmonary resuscitation, in which resuscitation has been reported as successful after only 3 to 5 minutes of cardiac arrest. Cardiopulmonary bypass might be a key to improve survival and neurological recovery after cardiac arrest.
    The Journal of thoracic and cardiovascular surgery 05/2010; 139(5):1325-32, 1332.e1-2. · 3.41 Impact Factor
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    ABSTRACT: We present a novel implantable multi-wavelength reflectance sensor for the measurement of blood pressure with pulse transit time (PTT). Continuous long-term monitoring of blood pressure and arterial oxygen saturation is vital for medical diagnostics and the ensuing therapy of cardiovascular diseases. Conventional cuff-based blood pressure monitors do not provide continuous data and put severe constraints on the patients' daily lives. An implantable sensor would eliminate such problems. The new biocompatible sensor is placed subcutaneously on blood perfused tissue. The PTT is calculated by photoplethysmograms and the ECG-signal, that is recorded with intracorporal electrodes. In addition, the sensor detects the arterial oxygen saturation. An ensuing spectralphotometric analysis of the light intensity changes delivers data on the concentration of dysfunctional hemoglobin derivatives. Experimental measurements showed a clear correlation between the estimated PTT and the systolic blood pressure reference. These initial results demonstrate the potential of the sensor as part of an fully implantable sensor system for the longterm-monitoring of cardiovascular parameters.
    Proc SPIE 04/2010;

Publication Stats

55 Citations
45.17 Total Impact Points

Institutions

  • 2011–2014
    • Universitätsklinikum Freiburg
      • Department of Radiology and Radiotherapy
      Freiburg an der Elbe, Lower Saxony, Germany
  • 2010–2014
    • University of Freiburg
      • Department of Microsystems Engineering (IMTEK)
      Freiburg, Baden-Württemberg, Germany