Katharina Foerster

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

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Publications (44)84.9 Total impact

  • [Show abstract] [Hide abstract] ABSTRACT: Objectives: In mechanical ventilation, normoventilation in terms of PCO2 can be achieved by titration of the respiratory rate and/or tidal volume. Although a linear relationship has been found between changes in respiratory rate and resulting changes in end-tidal cO2 (ΔPetCO2) as well as between changes in respiratory rate and equilibration time (teq) for mechanically ventilated patients without lung injury, it is unclear whether a similar relationship holds for acute lung injury or altered hemodynamics. Design: We performed a prospective randomized controlled animal study of the change in PetCO2 with changes in respiratory rate in a lung-healthy, lung-injury, lung-healthy + altered hemodynamics, and lung-injury + altered hemodynamics pig model. Setting: University research laboratory. Subjects: Twenty mechanically ventilated pigs. Interventions: Moderate lung injury was induced by injection of oleic acid in 10 randomly assigned pigs, and after the first round of measurements, cardiac output was increased by approximately 30% by constant administration of noradrenalin in both groups. Measurements and main results: We systematically increased and decreased changes in respiratory rate according to a set protocol: +2, -4, +6, -8, +10, -12, +14 breaths/min and awaited equilibration of Petco2. We found a linear relationship between changes in respiratory rate and ΔPetCO2 as well as between changes in respiratory rate and teq. A two-sample t test resulted in no significant differences between the lung injury and healthy control group before or after hemodynamic intervention. Furthermore, exponential extrapolation allowed prediction of the new PetCO2 equilibrium and teq after 5.7 ± 5.6 min. Conclusions: The transition between PetCO2 equilibria after changes in respiratory rate might not be dependent on moderate lung injury or cardiac output but on the metabolic production or capacity of cO2 stores. Linear relationships previously found for lung-healthy patients and early prediction of PetCO2 equilibration could therefore also be used for the titration of respiratory rate on the PetCO2 for a wider range of pathologies by the physician or an automated ventilation system.
    No preview · Article · Dec 2015 · Critical Care Medicine
  • [Show abstract] [Hide abstract] 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.
    No preview · Article · Dec 2014 · Magnetic Resonance in Medicine
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    [Show abstract] [Hide abstract] 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.
    Full-text · Article · Nov 2014 · The Journal of Comparative Neurology
  • No preview · Article · Oct 2014 · Biomedizinische Technik/Biomedical Engineering
  • [Show abstract] [Hide abstract] ABSTRACT: In mechanical ventilation, normoventilation in terms of the carbon dioxide partial pressure can be achieved by titration of the respiratory rate and/or tidal volume by the physician or an automated ventilation system. The timing of repeated adjustments needs to be tuned to the equilibration time of the biological system. While a linear relation has been found between changes in the respiratory rate (Delta RR) and resulting changes in the end-tidal CO2 partial pressure (Delta PetCO(2)) as well as between changes in Delta RR and the equilibration time (t(eq)) for mechanically ventilated patients without lung injury, it is unclear if a similar relation holds for acute lung injury or altered hemodynamics. We carried out a systematic study of the change in end-tidal CO2 partial pressure with respiratory rate in 20 mechanically ventilated pigs divided into two groups, one acute lung injury and one lung-healthy control group, before and after hemodynamic intervention. We systematically increased and decreased the respiratory rate according to a set protocol: Delta RR=+ 2, -4, + 6, -8, + 10, -12, + 14 breaths/min and awaited equilibration of the end-tidal CO2 partial pressure. We found a linear relation between Delta RR and Delta PetCO(2) as well as between Delta RR and t(eq). A two-sample T-test resulted in no significant changes between the lung injured and healthy control group before or after hemodynamic intervention. We conclude that the linear relationships previously found for lung healthy patients could also be used for the titration of the respiratory rate on the end-tidal CO2 partial pressure in severe lung injury and/or altered hemodynamics.
    No preview · Conference Paper · Oct 2014
  • [Show abstract] [Hide abstract] ABSTRACT: Complete alveolar recruitment is the main goal of lung-protective ventilation strategy which is reached either (i) by intermittent recruitment maneuvers or (ii) by titration of the end-expiratory pressure (PEEP) on the basis of the analysis of the patient individual lung mechanics. We investigated the relationship between PEEP and alveolar recruitability both in healthy and injured lungs in mechanically ventilated pigs (n=20). The animals were allocated in random order to lunghealthy control group (n=10) or to the lung-injury group (n=10). Acute lung injury was induced by systemic application of oleic acid. All animals were mechanically ventilated in the pressure-controlled mode (PCV) and undergoing two PEEP-wave maneuvers during the entire intervention. The volume-dependent intratidal compliance was calculated using the gliding-SLICE method. The alveolar recruitability was analyzed by the comparison of the volume-dependent intratidal compliance at the identical PEEP-levels which were realized two times per maneuver, during the increasing and during the decreasing PEEP-sequence of the PEEP-wave maneuver. We found in 97% of all lung-injured animals an increase of the compliance by the decremental PEEP trial with respect to the incremental one. Hence, the recruitability in lung-injured animals is significantly larger than in lung-healthy animals. We conclude that alveolar recruitability is higher in acute lung injury and one should pay attention on the recruitment state in the clinical setting of acute lung injury. From the methodical point of view we conclude that our method of compliance difference analysis between the situation preceding and following a recruitment maneuver allows non-invasive analysis of alveolar recruitability.
    No preview · Conference Paper · Oct 2014
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    [Show abstract] [Hide abstract] 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.
    Preview · Article · Aug 2014 · Sensors
  • [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.
    No preview · Article · Jul 2014 · Biomedical Microdevices
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    [Show abstract] [Hide abstract] 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.
    Full-text · Article · Apr 2014 · BJA British Journal of Anaesthesia
  • [Show abstract] [Hide abstract] 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.
    No preview · Article · Feb 2014 · Sensors and Actuators A Physical
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    [Show abstract] [Hide abstract] ABSTRACT: Introduction Bi-Directional brain-computer-interfaces (BCI) have the potential of treating a variety of conditions such as movement and mood disorders. Furthermore, they can allow heavily impaired patients to communicate with their environment. In our work, we describe the technological platform of an implant with the potential of being used for both applications and the outcomes of pilot chronic animal studies. Materials and Methods The device interfaces with the cortex by a grid-type electrode array, suitable for high-resolution electrocorticography (Micro-ECoG) as well as for electrical stimulation. The grid electrode consist of a 4 x 8 array Pt/Ir electrodes, having a diameter of 1.1 mm and a centre-to-centre distance of 4 mm. It is fabricated from multiple layers of silicone rubber, Parlyene-C polymer, and Pt/Ir foil, which were cut to shape layer-by-layer using an automated laser. The result is a flexible printed circuit board with integrated stretchable tracks which run to an edge of the grid, forming weld-pads for the electrode cable to be spot-welded to. The cable has a length of 50 cm and is made from individual MP35N wires of 0.07 mm diameter bundled in silicone rubber tubing of 1.8 mm diameter. The electrode cable is soldered to the electrical feed-through contacts of the ceramic package which hermetically encloses the implant electronics. The ceramic package is casted in silicone rubber, lectrically insulating the cable contacts. The electronics amplify (200x) and digitize (1kS/s, 16bit) the ECoG signals from 16 electrodes and permit voltage-controlled electrical stimulation of max. 17 V via 8 electrodes. The implant communicates at 1Mbit/s with a body-external transceiver unit (BETU) through an infrared optical link. Power is inductively supplied to the implant by a 16 MHz alternating magnetic field generated by the BETU. The BETU is powered by and communicates with a laptop computer using a USB link.
    Full-text · Conference Paper · Nov 2013
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    [Show abstract] [Hide abstract] 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.
    Full-text · Article · Jul 2013 · Perfusion
  • [Show abstract] [Hide abstract] 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.
    No preview · Article · Jul 2013 · Perfusion
  • [Show abstract] [Hide abstract] 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.
    No preview · Conference Paper · Jun 2013
  • [Show abstract] [Hide abstract] 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.
    No preview · Article · May 2013 · Biomedical Microdevices
  • [Show abstract] [Hide abstract] 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.
    No preview · Article · Mar 2013 · Magnetic Resonance in Medicine
  • No preview · Conference Paper · Feb 2013
  • [Show abstract] [Hide abstract] 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.
    No preview · Article · Jan 2013 · Perfusion
  • [Show abstract] [Hide abstract] 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.
    No preview · Article · Sep 2012 · Biomedical Microdevices
  • [Show abstract] [Hide abstract] 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.
    No preview · Article · Aug 2012 · Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference