Katharina Foerster

Successful resuscitation after prolonged periods of cardiac arrest: A new field in cardiac surgery

OBJECTIVE 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. METHODS 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. RESULTS 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. CONCLUSION 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.

An implantable optical blood pressure sensor based on pulse transit time

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.

Arterial input function measurements for bolus tracking perfusion imaging in the brain

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 T2 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, 2013.

Superior neurologic recovery after 15 minutes of normothermic cardiac arrest using an extracorporeal life support system for optimized blood pressure and flow

Objective: 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. Methods: 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. Results: 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. Conclusion: 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.

Mapping of sheep sensory cortex with a novel microelectrocorticography grid.

Microelectrocorticography (µECoG) provides insights into the cortical organization with high temporal and spatial resolution desirable for better understanding of neural information processing. Here we evaluated the use of µECoG for detailed cortical recording of somatosensory evoked potentials (SEPs) in an ovine model. The approach to the cortex was planned using an MRI‐based 3D model of the sheeps 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. With 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 sheeps 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 sheeps sensory cortex by characterizing its exact position, its functional properties, and the surgical approach with respect to macroanatomical landmarks. J. Comp. Neurol. 522:3590–3608, 2014.

Implantable sensor for blood pressure determination via pulse transit time

High blood pressure (BP), also known as hypertension, is the most common cardiovascular disease and one of the leading causes of death in industrial countries. Clinical research is looking for a possibility to monitor blood pressure continuously. Standard non-invasive cuff-based BP measurement devices have proven ill-suited for a continuous long-term monitoring as they severely restrain the patients mobility. With conventional intravascular sensors, patients run a very high risk of developing thrombosis. The implantable sensor system for continuous BP measurement presented here avoids this risk since it is positioned at the arterys exterior. This paper shows that BP can be determined by measuring the pulse transit time (PTT) entirely inside the body. In vivo measurements with the sensor attached to a domestic pigs carotid artery have clearly shown that the systolic blood pressure and the estimated PTT correlate. This was verified in the physiological BP range of 94-144 mmHg.

Implantable multi sensor system for in vivo monitoring of cardiovascular parameters

A novel implantable sensor for continuous long-term monitoring of various cardiovascular parameters is presented. An optical arterial blood oxygen saturation sensor and a piezoelectric blood pressure sensor have been developed using a silicone-based fabrication technology. An elastic silicone stripe houses the sensors and is wrapped around an arterial blood vessel. Due to this choice of a soft material, no necking of the vessel or influence on the blood flow occur even at large dilatations of 10 %. The pulse oximetric sensor is able to measure oxygen saturations in the physiologically relevant range of 65 % – 100 % (psO2) with a precision of ±1 %. The piezoelectric blood pressure sensor uses a 70 μm cellular polypropylene (PP) layer which responds to the dilatation of the blood vessel with a sensitivity of 0.75 mV/mmHg.

In vivo monitoring of blood oxygenation using an implantable MEMS-based sensor

We present a novel implantable, but extravascular, optical sensor for continuous long-term monitoring of vital medical parameters such as arterial blood oxygen saturation, pulse and respiratory frequencies. The biocompatible sensor uses a silicone-based manufacturing technique. It consists of two elastic silicone stripes that house the optoelectronic devices. These flexible stripes can be wrapped around an arterial blood vessel without constricting the vessel or influencing the blood flow - even at large dilatations of 10 %. In vivo experiments on domestic pigs have shown that real-time measurements with this sensor deliver excellent data.

Determination of vessel wall dynamics by optical microsensors

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.

Arterial strain measurement by implantable capacitive sensor without vessel constriction

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.