Staff

Dr. rer. nat. Jens Kirchner

Contact

  • Mail:
  • Phone: 09131/85-27196
  • Fax: Neu:09131/85-28730
  • Room: 01.196
  • Neu: Wetterkreuz 15
    91058 Erlangen

About Jens Kirchner

Biography

Jens Kirchner studied Physics at Friedrich-Alexander University Erlangen-Nürnberg (FAU) and at University of St. Andrews, Scotland, between 1999 and 2004. In 2008, he received his doctoral degree from FAU in 2004, with his thesis about stochastic modelling of cardiological time series. Between 2008 and 2015, he worked for Biotronik SE & Co. KG in Erlangen and Berlin in research and development of implantable sensors. He joined the Institute for Electronics Engineering in 2015, where he leads the Medical Electronics group.

Areas of Interest

  • Implantable and wearable sensors
  • Monitoring of chronic diseases
  • Analysis and modelling of vital parameters
  • Simulation of multi-physics systems

Open thesis projetcs

See studOn or just call me!

Lectures Summer term 2018

Lectures Winter term 2018

Publications

2019

  • L. Grebenstein, J. Kirchner, R. Stavracakis Peixoto, W. Zimmermann, W. Wicke, A. Ahmadzadeh, V. Jamali Kooshkghazi, G. Fischer, R. Weigel, A. Burkovski, and R. Schober, "Biological Optical-to-Chemical Signal Conversion Interface: A Small-scale Modulator for Molecular Communications" in 5th ACM International Conference on Nanoscale Computing and Communication 2018, Reykjavik, Iceland, 2019 (to be published). [DOI] [Bibtex]
    @inproceedings{grebenstein2018,
    abstract = {Although many exciting applications of molecular communication (MC) systems are envisioned to be at microscale, the available MC testbeds reported in the literature so far are mostly at macroscale. This may partially be due to the fact that controlling an MC system at microscale is quite challenging. To link the macroworld to the microworld, we propose a biological signal conversion interface that can also be seen as a microscale modulator. This interface translates an optical signal, which can be easily controlled using a light-emitting diode (LED), into a chemical signal by changing the pH of the environment. The modulator is realized using Escherichia coli bacteria that express the light-driven proton pump gloeorhodopsin from Gloeobacter violaceus and, upon inducing external light stimuli, can locally change their surrounding pH level by exporting protons into the environment. Based on measurement data from a testbed, we develop an analytical model for the induced chemical signal as a function of the applied optical signal. Finally, using a pH sensor as detector, we show for an example scenario that the proposed setup is able to successfully convert an optical signal representing a sequence of binary symbols into a chemical signal with a bit rate of 1 bit/min.},
    author = {Grebenstein, Laura and Kirchner, Jens and Stavracakis Peixoto, Renata and Zimmermann, Wiebke and Wicke, Wayan and Ahmadzadeh, Arman and Jamali Kooshkghazi, Vahid and Fischer, Georg and Weigel, Robert and Burkovski, Andreas and Schober, Robert},
    language = {English},
    booktitle = {5th ACM International Conference on Nanoscale Computing and Communication 2018},
    cris = {https://cris.fau.de/converis/publicweb/publication/203247813},
    year = {2019},
    month = {09},
    day = {05},
    doi = {10.1145/3233188.3233203},
    eventdate = {2018-09-05/2018-09-07},
    faupublication = {yes},
    keywords = {Molecular communication; bacteriorhodopsi},
    note = {unpublished},
    peerreviewed = {Yes},
    title = {Biological Optical-to-Chemical Signal Conversion Interface: A Small-scale Modulator for Molecular Communications},
    type = {Konferenzschrift},
    venue = {Reykjavik, Iceland},
    }
  • H. Shinoda, D. Anzai, J. Kirchner, G. Fischer, and J. Wang, "A Study on Nonlinear Effect of Low-Frequency Modulated Radio Signals on Stimulus Response", IEICE Transactions on Communications, 2019. [Bibtex]
    @article{shinoda2019,
    abstract = {Stimulus response caused by low-frequency electromagnetic exposure can be used to realize effective medical treatments. However, it is well known that the membrane potential of nerve cells exhibits nonlinearity, particularly in the case of modulated signals, it is important to analyze the nonlinear stimulation effect based on a nerve cell model. This paper adopts the Frankenhaeuser–Huxley (FH) model as the nerve cell model, and evaluates the stimulus response based on the FH model when nerve cells are exposed to low-frequency modulated radio signals such as On-Off Keying (OOK) modulation. This paper investigated the nonlinear effect of the stimulus intensity from the viewpoint of the spike frequency with different modulation parameter values including the induced amplitude and duty cycle. It was confirmed that action potential (AP) rate was higher with OOK-type radio signals than with unmodulated signals. 
    }, author = {Shinoda, Hiroki and Anzai, Daisuke and Kirchner, Jens and Fischer, Georg and Wang, Jianqing}, cris = {https://cris.fau.de/converis/publicweb/publication/208638084}, year = {2019}, month = {06}, day = {30}, faupublication = {yes}, issn = {0916-8516}, journaltitle = {IEICE Transactions on Communications}, keywords = {Low-frequency stimulation; Frankenhaeuser-Huxley model; Nonlinear Response; On-Off keying modulation}, peerreviewed = {Yes}, shortjournal = {IEICE T COMMUN}, title = {A Study on Nonlinear Effect of Low-Frequency Modulated Radio Signals on Stimulus Response}, type = {Article in Journal}, }
  • L. Grebenstein, J. Kirchner, R. Stavracakis Peixoto, W. Zimmermann, F. Irnstorfer, W. Wicke, A. Ahmadzadeh, V. Jamali Kooshkghazi, G. Fischer, R. Weigel, A. Burkovski, and R. Schober, "Biological Optical-to-Chemical Signal Conversion Interface: A Small-scale Modulator for Molecular Communications", IEEE Transactions on Nanobioscience, 2019. [DOI] [Bibtex]
    @article{grebenstein2019,
    abstract = {Although many exciting applications of molecular communication (MC) systems are envisioned to be at microscale, the MC testbeds reported in the literature so far are mostly at macroscale. This may partially be due to the fact that controlling an MC system at microscale is challenging. To link the macroworld to the microworld, we propose and demonstrate a biological signal conversion interface that can also be seen
    as a microscale modulator. In particular, the proposed interface transduces an optical signal, which is controlled using a lightemitting diode (LED), into a chemical signal by changing the pH of the environment. The modulator is realized using Escherichia coli bacteria as microscale entity expressing the light-driven
    proton pump gloeorhodopsin from Gloeobacter violaceus. Upon inducing external light stimuli, these bacteria locally change their surrounding pH level by exporting protons into the environment. To verify the effectiveness of the proposed optical-to-chemical signal converter, we analyze the pH signal measured by a
    pH sensor, which serves as receiver. We develop an analytical parametric model for the induced chemical signal as a function of the applied optical signal. Using this model, we derive a trainingbased channel estimator which estimates the parameters of the proposed model to fit the measurement data based on a least square error approach. We further derive the optimal maximum likelihood detector and a suboptimal low-complexity detector to recover the transmitted data from the measured received signal. It is shown that the proposed parametric model is in good agreement with the measurement data. Moreover, for an example scenario, we show that the proposed setup is able to successfully convert an optical signal representing a sequence of binary symbols into a chemical signal with a bit rate of 1 bit/min and recover the transmitted data from the chemical signal using the proposed estimation and detection schemes. The proposed modulator may form the basis for future MC testbeds and applications at microscale.
    }, author = {Grebenstein, Laura and Kirchner, Jens and Stavracakis Peixoto, Renata and Zimmermann, Wiebke and Irnstorfer, Florian and Wicke, Wayan and Ahmadzadeh, Arman and Jamali Kooshkghazi, Vahid and Fischer, Georg and Weigel, Robert and Burkovski, Andreas and Schober, Robert}, cris = {https://cris.fau.de/converis/publicweb/publication/205157325}, year = {2019}, month = {04}, day = {15}, doi = {10.1109/TNB.2018.2870910}, faupublication = {yes}, issn = {1536-1241}, journaltitle = {IEEE Transactions on Nanobioscience}, keywords = {Diffusive molecular communications; experimental testbed; statistical modeling; E. coli bacteria; light-driven proton pump}, peerreviewed = {Yes}, shortjournal = {IEEE T NANOBIOSCI}, title = {Biological Optical-to-Chemical Signal Conversion Interface: A Small-scale Modulator for Molecular Communications}, type = {Article in Journal}, }

2018

  • D. M. A. Ahmed, J. Kirchner, and G. Fischer, "Signal Transmission with Intra-body and Inter-body Communications (Simulation-based Models)" in 13th EAI International Conference on Body Area Networks (BODYNETS 2018), Oulu, Finland, 2018 (to be published). [Bibtex]
    @inproceedings{ahmed2018,
    abstract = {In this paper, we investigate two types of data transmission in human body communication (HBC) with galvanic coupling: Intra-body communication along a human arm and inter-body communication between
    two arms in touch. For the former, the effect of bending the arm is investigated, too. The arms were modeled
    as five-layers concentric cylinders of different types of tissue. For simulation, the finite element method (FEM) COMSOL Multiphysics5.3a software was used. The influence of different HBC key parameters including applied frequency, distance between transmitter (TX) and receiver (RX), bending, contact area between the contiguous models, and induced current were investigated. The results show that the transmission loss increases with the increase of the transmission length and operating frequency. The electrical potential is directly proportional to the induced current. Bending helps to improve the detected signal in the cases of short distance between TX and RX around the curvature. For distant transceivers, both straight and bended models tend to behave in a close manner. However, no joints are added to the model. The signal degradation in inter-body communication is considerably higher compared to intra-body communication at the same horizontal distance between TX and RX. At frequencies above 200 kHz, both inter-body and intra-body communication give close values when the contact area between the arms covers the distance between TX and RX electrodes. In addition, by increasing the contact area and avoiding gaps between the models, the detected signal is improved. The results illustrate the main determinants of information transmission between both sensors within a body-sensors-network and between different person.
    }, author = {Ahmed, Doaa Mahmoud Ahmed and Kirchner, Jens and Fischer, Georg}, language = {English}, booktitle = {13th EAI International Conference on Body Area Networks (BODYNETS 2018)}, cris = {https://cris.fau.de/converis/publicweb/publication/203249033}, year = {2018}, month = {10}, day = {02}, eventdate = {2018-10-02/2018-10-03}, faupublication = {yes}, keywords = {Cole-Cole expressions; dielectric properties; human tissue; finite element model; galvanic coupling; human body communication; inter-body communication; intra-body communication}, note = {unpublished}, peerreviewed = {Yes}, title = {Signal Transmission with Intra-body and Inter-body Communications (Simulation-based Models)}, type = {Konferenzschrift}, venue = {Oulu, Finland}, }
  • J. Kirchner, S. Faghih-Naini, P. Agdemir, and G. Fischer, "Sensor Selection for Classification of Physical Activity in Long-Term Wearable Devices" in 2018 IEEE SENSORS, New Delhi, India, 2018 (to be published). [Bibtex]
    @inproceedings{kirchner2018c,
    abstract = {Classification of physical activity based on the kNN algorithm is assessed with different combinations of sensors
    (from accelerometer, gyroscope, barometer) with respect to classification accuracy, power consumption and computation time. For that purpose, a wearable sensor platform is proposed and a study with 20 subjects is conducted. The combination of accelerometer and barometer is found to provide the best trade-off for the
    three criteria: It provides an F1 score of 94.96 ± 1.73 %, while computation time and power consumption are reduced by 45 % and 88 %, respectively, compared to the full sensor set.
    }, author = {Kirchner, Jens and Faghih-Naini, Samira and Agdemir, Pinar and Fischer, Georg}, language = {English}, booktitle = {2018 IEEE SENSORS}, cris = {https://cris.fau.de/converis/publicweb/publication/203246503}, year = {2018}, month = {10}, day = {28}, eventdate = {2018-10-28/2018-10-31}, faupublication = {yes}, keywords = {Activity classification; wearable devices; sensors; accelerometer; gyroscope; barometer; knn; machine learning; power consumption; computation time; F1 score; sensitivity; precision}, note = {unpublished}, peerreviewed = {Yes}, title = {Sensor Selection for Classification of Physical Activity in Long-Term Wearable Devices}, type = {Konferenzschrift}, venue = {New Delhi, India}, }
  • J. Kirchner, N. Ebel, S. Kinner, G. Fischer, S. Werner, D. W. Schubert, and M. Weyand, "Inductive transcutaneous energy transfer for cardiac assist devices – pushing the limits" in 22. Chirurgische Forschungstage, Erlangen, Germany, 2018. [Bibtex]
    @inproceedings{kirchner2018,
    abstract = {Background / Purpose
    Power supply is an essential component of active implants. To provide energy across the skin barrier, inductive energy transfer is well established in low-power devices like Cochlea implants. However, current designs are not applicable to high-power implants like cardiac assist devices due to strong tissue heating, caused by local spots of high magnetic field strength associated with large heat dissipation. Here, we propose a system design that overcomes this problem.

    Methods
    To avoid the “hot spots”, the magnetic field is guided and thus homogenized by composite coil cores based on liquid silicon rubber (LSM), which permits to design appropriate gradients of permeability. Furthermore, the frequency is kept below 1 MHz to reduce dielectric losses within the body. LSM is a biocompatible material, whose flexibility allows adaption to the body surface to minimize the gap between extracorporeal and implanted coil. For analysis and optimization of coil and coil core design, the FEM software COMSOL Multiphysics® 5.3 was used.

    Results
    The simulations showed that with the proposed coil and coil core design the magnetic fields can be homogenized such that 24 W can be transferred with an efficiency of 98.8% and a temperature increase in the tissue of only 0.8°C.

    Conclusions
    These findings suggest the possibility to make inductive energy transfer applicable also for high‑power active implants such as ventricular assist devices, reducing the number of complications of VAD-patients.}, author = {Kirchner, Jens and Ebel, Nina and Kinner, Sarah and Fischer, Georg and Werner, Siegfried and Schubert, Dirk W. and Weyand, Michael}, language = {English}, booktitle = {22. Chirurgische Forschungstage}, cris = {https://cris.fau.de/converis/publicweb/publication/203249510}, year = {2018}, month = {09}, day = {06}, eventdate = {2018-09-06/2018-09-08}, faupublication = {yes}, keywords = {Inductive energy transfer; transcutaneous energy transfer; cardiac assist device}, peerreviewed = {Yes}, title = {Inductive transcutaneous energy transfer for cardiac assist devices – pushing the limits}, type = {Abstract zum Poster}, venue = {Erlangen, Germany}, }
  • J. Kirchner and G. Fischer, "Vital Sign Sensors for Artificial Intelligence and Deep Learning" in 52nd Annual Conference of the German Society for Biomedical Engineering, Aachen, Germany, 2018. [Bibtex]
    @inproceedings{kirchner2018a,
    abstract = {Up to now vital data of patients are mostly acquired during clinical or ambulant examination. Here, the sensors are carefully placed by trained personal and movements of the patient are well controlled, e.g. during exercise ECG on a recumbent ergometer. In this way, misplacement of the sensors as well as motion artifacts are avoided, and physical load is well defined, such that high quality data is ensured that can be use for diagnostic purposes.
    Such a clinical or ambulant examination, however, captures only a short moment in time and is not representative for daily life. More preferable from the perspective of the treating physician would be data collected on a regular basis from daily routine work of the subjects. In such a situation, however, sensors may not be placed properly by the patient and movements are not well controlled any more, so data quality can be compromised.
    Hence, the validity of the sensor data has to be assessed and taken into account during data analysis in order to derive reasonable conclusions. Therefore, a wearable sensor system for daily life must be multimodal to allow machine learning algorithms to clean the acquired sensor data from artefacts. Artificial intelligence and deep learning system can then identify corrupt data segments, substract artefact patterns and by that clean up sensor data.
    The talk will highlight the trade-off between usability and integratability of a sensor system into daily life versus the validity of data obtained. This challenge will be illustrated by a multimodal sensor platform for elderly and dementia care that was developed during the course of the Medical Valley excellence cluster funded by German Federal Ministry of Education and Research (BMBF).
    Another example discussed in the talk are ECG circuit concepts that make the sensor more robust and compatible with daily life. Special focus will be put on capacitive ECG. Here, movement artefacts can be cleaned up if the movement during ECG aquisition is known, which can be done, e.g., by EMG or acceleration/gyroscopic sensors. Apart from that, these sensors allow to interpret the captured ECG data with respect to the current load to the body and thus provide context
    information.
    In conclusion, a combination of advancements in both sensor hardware/circuitry and multimodal sensor processing by artificial intellifence is needed to make the sketched vision real.
    }, author = {Kirchner, Jens and Fischer, Georg}, language = {English}, booktitle = {52nd Annual Conference of the German Society for Biomedical Engineering}, cris = {https://cris.fau.de/converis/publicweb/publication/203247152}, year = {2018}, month = {09}, day = {26}, eventdate = {2018-09-26/2018-08-28}, faupublication = {yes}, keywords = {Vital signs; artificial intelligence; deep learning}, peerreviewed = {Yes}, title = {Vital Sign Sensors for Artificial Intelligence and Deep Learning}, type = {Abstract zum Vortrag}, venue = {Aachen, Germany}, }
  • M. Chen, D. Anzai, J. Kirchner, G. Fischer, and J. Wang, "Development of EOG-based Input System and Study on Improving Methods of Eye Movement Detection", IEICE Transactions on Communications, vol. Title of Special Issue: Healthcare, Medical Information and Communication Technology for Safe and Secure Society, 2018. [Bibtex]
    @article{chen2018,
    author = {Chen, Minghui and Anzai, Daisuke and Kirchner, Jens and Fischer, Georg and Wang, Jianqing},
    cris = {https://cris.fau.de/converis/publicweb/publication/202231321},
    year = {2018},
    month = {07},
    day = {02},
    faupublication = {yes},
    issn = {0916-8516},
    journaltitle = {IEICE Transactions on Communications},
    keywords = {EOG},
    peerreviewed = {Yes},
    shortjournal = {IEICE T COMMUN},
    title = {Development of EOG-based Input System and Study on Improving Methods of Eye Movement Detection},
    type = {Review article},
    volume = {Title of Special Issue: Healthcare, Medical Information and Communication Technology for Safe and Secure Society},
    }
  • J. Kirchner, M. Arnold, and G. Fischer, "Analysis of the Movement of ICD Leads During Cardiac Contraction as Determinant of Intracardiac Impedance" in 40th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Honolulu, HI, USA, 2018 (to be published). [Bibtex]
    @inproceedings{kirchner2018b,
    abstract = {Intracardiac impedance (ICI) has been proposed as an indicator of cardiac status in heart failure patients. We introduce a biophysical model of the measurement setup and apply it to the movement of ICD leads reconstructed from clinical-routine X-ray recordings in a study population of 12 patients. Tilting of the right ventricular lead is found to be a major determinant of ICI changes during cardiac contraction with a mean contribution of 42+-23%. The relative position between right and left ventricular lead is the second major contributor (40+-22%).
    However, the contributions of the components of movement strongly differ between the patients.
    The proposed method provides means for a better interpretation of ICI measurements and for an improvement of its performance for monitoring heart failure status.}, author = {Kirchner, Jens and Arnold, Martin and Fischer, Georg}, language = {English}, booktitle = {40th Annual International Conference of the IEEE Engineering in Medicine and Biology Society}, cris = {https://cris.fau.de/converis/publicweb/publication/111732544}, year = {2018}, month = {07}, day = {17}, eventdate = {2018-07-17/2018-07-21}, faupublication = {yes}, note = {unpublished}, peerreviewed = {Yes}, title = {Analysis of the Movement of ICD Leads During Cardiac Contraction as Determinant of Intracardiac Impedance}, type = {Journal Article}, venue = {Honolulu, HI, USA}, }
  • H. Unterweger, J. Kirchner, W. Wicke, A. Ahmadzadeh, D. M. A. Ahmed, V. Jamali Kooshkghazi, C. Alexiou, G. Fischer, R. Weigel, and R. Schober, "Experimental Molecular Communication Testbed Based on Magnetic Nanoparticles in Duct Flow" in 19th IEEE International Workshop on Signal Processing Advances in Wireless Communications, Kalamata, Greece, 2018 (to be published). [Bibtex]
    @inproceedings{unterweger2018,
    abstract = {Simple and easy to implement testbeds are needed to further advance molecular communication research. To this end, this paper presents an in-vessel molecular communication testbed using magnetic nanoparticles dispersed in an aqueous suspension as they are also used for drug targeting in biotechnology. The transmitter is realized by an electronic pump for injection via a Yconnector. A second pump provides a background flow for signal propagation. For signal reception, we employ a susceptometer, an electronic device including a coil, where the magnetic particles move through and generate an electrical signal. We present experimental results for the transmission of a binary sequence and the system response following a single injection. For this flowdriven particle transport, we propose a simple parameterized mathematical model for evaluating the system response. 
    }, author = {Unterweger, Harald and Kirchner, Jens and Wicke, Wayan and Ahmadzadeh, Arman and Ahmed, Doaa Mahmoud Ahmed and Jamali Kooshkghazi, Vahid and Alexiou, Christoph and Fischer, Georg and Weigel, Robert and Schober, Robert}, language = {English}, booktitle = {19th IEEE International Workshop on Signal Processing Advances in Wireless Communications}, cris = {https://cris.fau.de/converis/publicweb/publication/203248614}, year = {2018}, month = {06}, day = {25}, eventdate = {2018-06-25/2018-06-28}, faupublication = {yes}, keywords = {Molecular communication; magnetic nanoparticles}, note = {unpublished}, peerreviewed = {Yes}, title = {Experimental Molecular Communication Testbed Based on Magnetic Nanoparticles in Duct Flow}, type = {Konferenzschrift}, venue = {Kalamata, Greece}, }
  • L. Grebenstein, J. Kirchner, R. Stavracakis Peixoto, G. Fischer, R. Weigel, R. Schober, and A. Burkovski, "The First Cell Phone in Molecular Communications: A Pilot Model of a Biological Transmitter" in 3rd Workshop on Molecular Comunications, Ghent, Belgium, 2018. [Bibtex]
    @inproceedings{grebenstein2018a,
    abstract = {In the past years, Molecular Communications were studied mainly from a communication engineering and theoretical point of view. To design nano- to micro-sized signaling networks, reliable communication-theoretical models and experimental testbeds are still missing. Inspired by microbial cells we established an organic, molecular signal converter as a modulator for MC signals. The transmitter is a bacterial cell expressing the light-driven proton pump gloeorhodopsin. In recent test runs, we were able to send short messages encoded in a light signal and converted to pH variation with a rate of 2 bits/min with the help of living bacteria.
    }, author = {Grebenstein, Laura and Kirchner, Jens and Stavracakis Peixoto, Renata and Fischer, Georg and Weigel, Robert and Schober, Robert and Burkovski, Andreas}, booktitle = {3rd Workshop on Molecular Comunications}, cris = {https://cris.fau.de/converis/publicweb/publication/203289422}, year = {2018}, month = {04}, day = {04}, eventdate = {2018-04-04/2018-04-06}, faupublication = {yes}, peerreviewed = {Yes}, title = {The First Cell Phone in Molecular Communications: A Pilot Model of a Biological Transmitter}, type = {Konferenzschrift}, url = {https://www.molecularcommunications.eu/abstracts/MolCom_2018_paper_16.pdf}, venue = {Ghent, Belgium}, }
  • L. Grebenstein, J. Kirchner, R. Stavracakis Peixoto, W. Zimmermann, F. Irnstorfer, W. Wicke, A. Ahmadzadeh, V. Jamali Kooshkghazi, G. Fischer, R. Weigel, A. Burkovski, and R. Schober, "Biological Optical-to-Chemical Signal Conversion Interface: A Small-scale Modulator for Molecular Communications", IEEE Transactions on Nanobioscience, 2018. [Bibtex]
    @article{grebenstein2018b,
    abstract = {Although many exciting applications of molecular communication (MC) systems are envisioned to be at microscale, the MC testbeds reported in the literature so far are mostly at macroscale. This may partially be due to the fact that controlling an MC system at microscale is challenging. To link the macroworld to the microworld, we propose and demonstrate a biological signal conversion interface that can also be seen as a microscale modulator. In particular, the proposed interface transduces an optical signal, which is controlled using a light-emitting diode (LED), into a chemical signal by changing the pH of the environment. The modulator is realized using Escherichia coli bacteria as microscale entity expressing the light-driven proton pump gloeorhodopsin from Gloeobacter violaceus. Upon inducing external light stimuli, these bacteria locally change their surrounding pH level by exporting protons into the environment. To verify the effectiveness of the proposed optical-to-chemical signal converter, we analyze the pH signal measured by a pH sensor, which serves as receiver. We develop an analytical parametric model for the induced chemical signal as a function of the applied optical signal. Using this model, we derive a training-based channel estimator which estimates the parameters of the proposed model to fit the measurement data based on a least square error approach. We further derive the optimal maximum likelihood detector and a suboptimal low-complexity detector to recover the transmitted data from the measured received signal. It is shown that the proposed parametric model is in good agreement with the measurement data. Moreover, for an example scenario, we show that the proposed setup is able to successfully convert an optical signal representing a sequence of binary symbols into a chemical signal with a bit rate of 1 bit/min and recover the transmitted data from the chemical signal using the proposed estimation and detection schemes. The proposed modulator may form the basis for future MC testbeds and applications at microscale. 
    }, author = {Grebenstein, Laura and Kirchner, Jens and Stavracakis Peixoto, Renata and Zimmermann, Wiebke and Irnstorfer, Florian and Wicke, Wayan and Ahmadzadeh, Arman and Jamali Kooshkghazi, Vahid and Fischer, Georg and Weigel, Robert and Burkovski, Andreas and Schober, Robert}, cris = {https://cris.fau.de/converis/publicweb/publication/203819343}, year = {2018}, faupublication = {yes}, issn = {1536-1241}, journaltitle = {IEEE Transactions on Nanobioscience}, keywords = {Diffusive molecular communications; experimental testbed; statistical modeling; E. coli bacteria; light-driven proton pump}, peerreviewed = {Yes}, shortjournal = {IEEE T NANOBIOSCI}, title = {Biological Optical-to-Chemical Signal Conversion Interface: A Small-scale Modulator for Molecular Communications}, type = {Article in Journal}, }

2017

  • J. Kirchner, S. Souilem, and G. Fischer, "Wearable System for Measurement of Thoracic Sounds with a Microphone Array" in IEEE SENSORS 2017, Glasgow, UK, 2017, pp. 1-3. [DOI] [Bibtex]
    @inproceedings{kirchner2017b,
    abstract = {Acoustic signals from the thorax provide diagnostic information about the heart, the respiratory and the digestive system. This information is useful for both the detection of acute illness, e.g. in elderly care, and for the monitoring of chronic diseases. Here, a wearable system for long-term capture of thoracic sounds is proposed that comprises four microphones for physiological signals and one for noise from the surrounding. The performance of the prototype is evaluated in comparison to a reference stethoscope and under different wearing conditions. Combining the microphones will provide means for cancellation of environmental noise, fusion of acoustic signals from different physiological sources as well as focusing on a particular source by use of beamforming.},
    author = {Kirchner, Jens and Souilem, Sara and Fischer, Georg},
    language = {English},
    publisher = {IEEE},
    booktitle = {IEEE SENSORS 2017},
    cris = {https://cris.fau.de/converis/publicweb/publication/109573904},
    year = {2017},
    month = {12},
    day = {25},
    doi = {10.1109/ICSENS.2017.8234248},
    eventdate = {2017-10-30/2017-11-01},
    faupublication = {yes},
    keywords = {wearable system; long-term capture; microphones; physiological signals; acoustic signals; microphone array; diagnostic information; elderly care; wearing conditions; physiological sources; thoracic sounds measurement; chronic diseases monitoring; heart; microphones; prototypes; biomedical monitoring; stethoscope; acoustics; acoustic signals; wearable system; thorax; heart sounds; sensor array},
    pages = {1--3},
    peerreviewed = {Yes},
    title = {Wearable System for Measurement of Thoracic Sounds with a Microphone Array},
    type = {Konferenzschrift},
    url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8234248&isnumber=8233862},
    venue = {Glasgow, UK},
    }
  • J. Kirchner, M. Arnold, and G. Fischer, "Reconstruction of 3D-Movement of ICD Leads from Clinical-Routine X-Ray Movies" in 2017 IEEE International Symposium on Signal Processing and Information Technology (ISSPIT), Bilbao, Spain, 2017, pp. 399-404. [DOI] [Bibtex]
    @inproceedings{kirchner2017c,
    abstract = {A technique is proposed to reconstruct the threedimensional movement of leads of implantable cardioverter defibrillators from X-ray movies obtained as part of clinical routine during implantation. The technique is applied to data from 16 patients. 12 of them provide results with a sufficient accuracy of less than 2.5 mm in terms of half of the minimum distance of the projection lines and when compared to the length of the shock coil as reference. From the reconstructed 3D data, the movement along and perpendicular to the lead axes as well as tilt are obtained. Such data will prove useful in research on material fatigue and cardiac sensors integrated into the leads.},
    author = {Kirchner, Jens and Arnold, Martin and Fischer, Georg},
    language = {English},
    booktitle = {2017 IEEE International Symposium on Signal Processing and Information Technology (ISSPIT)},
    cris = {https://cris.fau.de/converis/publicweb/publication/111729464},
    year = {2017},
    month = {12},
    day = {18},
    doi = {10.1109/ISSPIT.2017.8388676},
    eventdate = {2017-12-18/2017-12-20},
    faupublication = {yes},
    keywords = {cardiology; defibrillators; diagnostic radiography; image reconstruction; medical image processing; prosthetics; reconstructed 3D data; lead axes; implantable cardioverter defibrillators; three-dimensional movement; clinical-routine X-ray movies; ICD leads; 3D-movement; shock coil; projection lines; minimum distance; motion pictures; electric shock lead; heart; X-ray imaging; image reconstruction; signal processing; ICD; lead; cardiac movement; X-ray movie; 3D reconstruction; implantation},
    pages = {399--404},
    peerreviewed = {Yes},
    title = {Reconstruction of 3D-Movement of ICD Leads from Clinical-Routine X-Ray Movies},
    type = {Article in Journal},
    url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8388676&isnumber=8388305},
    venue = {Bilbao, Spain},
    }
  • D. M. A. Ahmed, J. Kirchner, and G. Fischer, "Wave Propagation with Human Body Communications in BANs" in 2017 IEEE MTT-S International Conference on Numerical Electromagnetic and Multiphysics Modeling and Optimization for RF, Microwave, and Terahertz Applications (NEMO), Sevilla, Spain, 2017, pp. 16-18. [DOI] [Bibtex]
    @inproceedings{ahmed2017,
    abstract = {Today's interest in health assistance systems, sport activities and remote patient monitoring require distributing various types of sensors at specific places across the human body. These sensors might be used to measure temperature, blood pressure level, blood glucose level and the like. This implies collecting the data generated at the distributed sensors in a wireless Body Area Network (BAN) and fusing these data at a central processing unit, which transfers the data, if needed, to a hospital or medical center for diagnosing. Whereas, transmission could be done for real time or stored data depending on the application scenario. However, sending data wirelessly is typically a very energy intensive task implying large batteries. Hence, BAN networks have been developed by IEEE 802.15.Task Group (TG6) to serve a variety of applications including medical, consumer lifestyle and entertainment applications at low power consumption. Human Body Communication is a non-RF propagation system in BAN network that utilizes the human body as a transmission medium to transfer data between several points inside, on or sometimes near the human body using electrodes, rather than antennas based on near field communication and quasistatic field approximations.},
    author = {Ahmed, Doaa Mahmoud Ahmed and Kirchner, Jens and Fischer, Georg},
    language = {English},
    booktitle = {2017 IEEE MTT-S International Conference on Numerical Electromagnetic and Multiphysics Modeling and Optimization for RF, Microwave, and Terahertz Applications (NEMO)},
    cris = {https://cris.fau.de/converis/publicweb/publication/108446624},
    year = {2017},
    month = {07},
    day = {03},
    doi = {10.1109/NEMO.2017.7964172},
    eventdate = {2017-05-17/2017-05-19},
    faupublication = {yes},
    isbn = {9781509048373},
    keywords = {Body Area Communication; Galvanic Coupling; Human Arm Model},
    pages = {16--18},
    peerreviewed = {Yes},
    title = {Wave Propagation with Human Body Communications in BANs},
    type = {Konferenzschrift},
    venue = {Sevilla, Spain},
    }
  • D. M. A. Ahmed, J. Kirchner, and G. Fischer, "Wave Propagation with HBC in a Human Arm Model" in 2017 IEEE International Symposium on Medical Measurements and Applications (MeMeA), Rochester, MN, USA, 2017, pp. 448-452. [DOI] [Bibtex]
    @inproceedings{ahmed2017a,
    abstract = {Today’s interest in health assistance systems, sport activities, person’s vital signs observing and remote patient monitoring require distributing various types of sensors at specific places across the human body. These sensors might be used to measure temperature, blood pressure level, blood glucose level and the like. This implies collecting the data generated at the distributed sensors in a wireless Body Area Network (BAN) and fusing these data at an access point (e.g. wristwatch) and then to a central processing unit (i.e., PC) for diagnosing, as shown in Fig. 1. However, sending data wirelessly is typically a very energy intensive task implying large batteries. Hence, BAN networks have been developed by IEEE 802.15.Task Group (TG6) to serve a variety of applications including medical, consumer lifestyle and the like at a low power consumption. Human Body Communications (HBC) is one technique used in BAN networks that utilizes the human body as a transmission medium to transfer data between sensors on, in or at the proximity of the human body using electrodes (i.e., electrical conductors).},
    author = {Ahmed, Doaa Mahmoud Ahmed and Kirchner, Jens and Fischer, Georg},
    language = {English},
    booktitle = {2017 IEEE International Symposium on Medical Measurements and Applications (MeMeA)},
    cris = {https://cris.fau.de/converis/publicweb/publication/109721304},
    year = {2017},
    month = {07},
    day = {20},
    doi = {10.1109/MEMEA.2017.7985918},
    eventdate = {2017-05-07/2017-05-10},
    faupublication = {yes},
    isbn = {9781509029846},
    keywords = {Body Area Communication; Galvanic Coupling; Human Arm Model},
    pages = {448--452},
    peerreviewed = {Yes},
    title = {Wave Propagation with HBC in a Human Arm Model},
    type = {Konferenzschrift},
    venue = {Rochester, MN, USA},
    }
  • J. Kirchner and G. Fischer, "Monitoring of Cardiac Diseases by Use of a Wearable Sensor Platform with Capacitive ECG" in 39th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), Jeju Island, Korea (Republic of), 2017. [Bibtex]
    @inproceedings{kirchner2017a,
    abstract = {The concept of a wearable sensor platform in the form of a patch for fixation at a patient’s chest is described. It is used for monitoring of cardiac diseases, which is illustrated with the detection of atrial fibrillation.},
    author = {Kirchner, Jens and Fischer, Georg},
    language = {English},
    booktitle = {39th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC)},
    cris = {https://cris.fau.de/converis/publicweb/publication/109722184},
    year = {2017},
    month = {07},
    day = {11},
    eventdate = {2017-07-11/2017-07-15},
    faupublication = {yes},
    keywords = {Wearable Sensors; Cardiac diseases; Atrial fibrillation},
    peerreviewed = {Yes},
    title = {Monitoring of Cardiac Diseases by Use of a Wearable Sensor Platform with Capacitive ECG},
    type = {Abstract zum Vortrag},
    venue = {Jeju Island, Korea (Republic of)},
    }
  • J. Kirchner, S. Schild, and G. Fischer, "Detection of Paroxysmal Atrial Fibrillation: A Computationally Efficient Algorithm for Use in a Wearable Telemedical System" in 2017 IEEE International Sympium on Medical Measurements and Applications (MeMeA), Rochester, MN, USA, 2017, pp. 320-325. [DOI] [Bibtex]
    @inproceedings{kirchner2017,
    abstract = {For early detection of the sporadic events of paroxysmal atrial fibrillation (AF), long-term ECG monitoring and data evaluation are required. To allow energy-efficient on-device preprocessing of the data, an as simple as possible algorithm is sought. The proposed approach is based on heart frequency data only and makes use of the increased heart rate variation with the occurrence of AF. Criteria for the choice of the free parameters of this method are derived, and it is shown that, under these conditions, results are insensitive against variations of these parameters. If a compromise between sensitivity and specificity is sought, i.e. equality of these values, 89.4% are obtained in average. If instead sensitivity alone is optimized, i. e. for use with additional AF detection strategies, an average value of 99.6% is reached with specificity 38.4%. The algorithm forms the first step in the development of a computationally and thus energy efficient signal processing module for the purpose of reducing the amount of data that has to be stored or transmitted and then evaluated by the treating physician.},
    author = {Kirchner, Jens and Schild, Stefanie and Fischer, Georg},
    language = {English},
    booktitle = {2017 IEEE International Sympium on Medical Measurements and Applications (MeMeA)},
    cris = {https://cris.fau.de/converis/publicweb/publication/109658824},
    year = {2017},
    month = {05},
    day = {07},
    doi = {10.1109/MEMEA.2017.7985896},
    eventdate = {2017-05-07/2017-05-10},
    faupublication = {yes},
    keywords = {paroxysmal atrial fibrillation detection; wearable telemedical system; sporadic event detection; long-term ECG monitoring; energy-efficient on-device data preprocessing; heart frequency data; atrial fibrillation detection strategy; energy efficient signal processing; Sensitivity; Heart rate; Electrocardiography; Optimization; Medical services; Paroxysmal Atrial Fibrillation; Electrocardiogram; Heart Rate Variability; Cardiac Diseases; Diagnostic Monitoring},
    pages = {320--325},
    peerreviewed = {Yes},
    title = {Detection of Paroxysmal Atrial Fibrillation: A Computationally Efficient Algorithm for Use in a Wearable Telemedical System},
    type = {Konferenzschrift},
    url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7985896&isnumber=7985834},
    venue = {Rochester, MN, USA},
    }

2016

  • J. Kirchner, N. Roth, A. Meyer, and G. Fischer, "ECG Measurement by Use of Passive Capacitively Coupled Electrodes" in Proc. IEEE Sensors Conf., Orlando, FL, USA, 2016. [DOI] [Bibtex]
    @inproceedings{kirchner2016,
    abstract = {The prototype of a capacitive ECG measurement device with purely passive signal transmission between electrodes and differential amplifier is presented. This design is intended to improve transmission symmetry and thus common-mode rejection. The feasibility of the approach is demonstrated by measurements with different materials between body surface and electrodes. The ECG module shall be incorporated in a mobile sensor platform in the form of a plaster for the monitoring of chronic diseases.},
    author = {Kirchner, Jens and Roth, Nils and Meyer, Andreas and Fischer, Georg},
    booktitle = {Proc. IEEE Sensors Conf.},
    cris = {https://cris.fau.de/converis/publicweb/publication/109800504},
    year = {2016},
    month = {10},
    day = {30},
    doi = {10.1109/ICSENS.2016.7808736},
    eventdate = {2016-10-30/2016-11-02},
    eventtitle = {IEEE Sensors},
    faupublication = {yes},
    keywords = {electrocardiogram; ECG; capacitive electrodes; passive channel; chronic disease monitoring},
    peerreviewed = {Yes},
    title = {ECG Measurement by Use of Passive Capacitively Coupled Electrodes},
    venue = {Orlando, FL, USA},
    }
  • J. Kirchner, J. Nehring, G. A. Guarin Aristizabal, I. Nasr, B. Lämmle, M. Dietz, R. Weigel, D. Kissinger, and A. Hagelauer, "SiGe Integrated Broadband Wireless Sensors for Biomedical Applications" in 9th Sin-German Joint Symposium on Opto- and Microelectronic Devices and Circuits (SODC2016), Changchun, 2016, pp. 77-78. [Bibtex]
    @inproceedings{kirchner2016a,
    author = {Kirchner, Jens and Nehring, Johannes and Guarin Aristizabal, Gustavo Adolfo and Nasr, Ismail and Lämmle, Benjamin and Dietz, Marco and Weigel, Robert and Kissinger, Dietmar and Hagelauer, Amelie},
    booktitle = {9th Sin-German Joint Symposium on Opto- and Microelectronic Devices and Circuits (SODC2016)},
    cris = {https://cris.fau.de/converis/publicweb/publication/120010484},
    year = {2016},
    month = {09},
    faupublication = {yes},
    pages = {77--78},
    peerreviewed = {unknown},
    title = {SiGe Integrated Broadband Wireless Sensors for Biomedical Applications},
    venue = {Changchun},
    }
  • A. Meyer, J. Kirchner, and G. Fischer, "EKG-Messung mittels passiver kapazitiv gekoppelter Elektroden" in Analogworkshop 2016, Hannover, 2016. [Bibtex]
    @inproceedings{meyer2016,
    abstract = {Hintergrund

    Kapazitiv gekoppelte Elektroden zur EKG-Erfassung erschließen seit einigen Jahren Anwendungsgebiete jenseits der klinischen Routine: Während dort zumeist galvanisch gekoppelte, insbesondere Nasselektroden zum Einsatz kommen, die direkten Hautkontakt erfordern und wegen des austrocknenden Elektrolytgels nur für kurze Messungen geeignet sind, erlauben kapazitive Elektroden Langzeit-Messungen und die Integration in Alltagsgegenstände wie Kleidung, Autositze oder Betten.

    Stand der Technik ist dabei eine aktive Ausführung, bei der direkt an der Elektrode das anliegende Signal verstärkt wird, bevor es in einem Differenzverstärker mit dem Signal einer zweiten Elektrode zusammengeführt wird. Allerdings führen in diesem Ansatz die Toleranzen der verwendeten aktiven Bauelemente zu asymmetrischem Übertragungsverhalten in den beiden Kanälen, sodass die Gleichtaktunterdrückung wesentlich beeinträchtigt wird.
    Um diesem Problem entgegenzuwirken und den Gleichlauf der Pfade von Elektrode bis Differenzverstärker zu verbessern, wurde ein EKG-System mit rein passiven Kanälen entwickelt.

    Methoden

    Für die Aufnahme der Messsignale wurden möglichst großflächige Elektroden mit jeweils 20cm2 Fläche verwendet. Da zwischen Elektrode und Differenzverstärker auf eine Verstärkung der Einzelsignale verzichtet wurde, ist auf dieser Strecke eine möglichst verlust- und störungsfreie Übertragung entscheidend. Hierfür wurde die jeweilige Leitung mit einer Ummantelung versehen, die auf demselben Potential wie die zugehörige Elektrode gehalten wird. Hierdurch werden äußere Störeinflüsse aktiv abgeschirmt, gleichzeitig werden durch den Bootstrap effektiv keine durch die Elektroden und die Signalleitungen hervorgerufenen parasitischen Eingangskapazitäten wirksam.

    Ferner wurde ein Differenzverstärker mit möglichst geringer Eingangskapazität und hoher CMRR gewählt. Um die Gleichtaktunterdrückung im Gesamtsystem zusätzlich zu erhöhen, wurde eine Bezugspotentialsteuerung eingesetzt. Hierbei wird die Common-Mode-Störung über eine dritte Elektrode invertiert und verstärkt in den Körper des Patienten zurückgespeist (sog. "driven right leg circuit").

    Schließlich wurde eine Baseline-Drift, hervorgerufen durch Ladungsansammlungen an den Elektroden, mittels langsamem Feedback korrigiert, indem Gleichspannungsanteile am Ausgang des Instrumentenverstärkers als Referenzspannung an diesen zurückgegeben werden.

    Ergebnisse

    Mit den beschriebenen Maßnahmen wurde ein stabiles EKG-Signal erhalten, das in der ersten Verstärkerstufe um einen Faktor 100, in der zweiten um einen Faktor 2000 verstärkt werden konnte.

    Exemplarische Messungen durch ein Baumwoll-T-Shirt hindurch zeigten in jedem Herzzyklus des aufgenommenen EKGs deutlich den QRS-Komplex, der sich zur Detektion von Arrhythmien eignet, sowie die T-Welle. Die P-Welle war vereinzelt zu erkennen. Vergleichbare Ergebnisse wurden bei Messungen durch Papier und Plastikfolie hindurch erzielt.

    Fazit

    Das entwickelte System ermöglicht die kontaktlose Messung der elektrischen Herzaktivität durch verschiedene Materialien hindurch und erzielte dabei rausch- und interferenzärmere Ergebnisse als vergleichbare Systeme mit kapazitiv gekoppelten Elektroden in aktiver Ausführung. Das System eignet sich damit für diverse Anwendungsbereiche, beispielsweise für den Einsatz auf einem Rückenpflaster oder zur Integration in Kleidung.}, author = {Meyer, Andreas and Kirchner, Jens and Fischer, Georg}, publisher = {Leibniz Universität Hannover}, booktitle = {Analogworkshop 2016}, cris = {https://cris.fau.de/converis/publicweb/publication/123114244}, year = {2016}, month = {03}, day = {03}, eventdate = {2016-03-03/2016-03-04}, eventtitle = {Analogworkshop 2016}, faupublication = {yes}, keywords = {ECG; capacitatively coupled electrode}, peerreviewed = {No}, title = {EKG-Messung mittels passiver kapazitiv gekoppelter Elektroden}, type = {Abstract zum Vortrag}, venue = {Hannover}, }

2015

  • J. Kirchner, S. Paule, C. Beckendorf, S. Achenbach, and M. Arnold, "Circadian and circaseptan rhythms in implant-based thoracic impedance", Physiological Measurement, vol. 36, iss. 7, pp. 1615-1628, 2015. [DOI] [Bibtex]
    @article{kirchner2015,
    abstract = {

    Thoracic impedance (TI) denotes the electrical resistance that is measured between the right ventricular lead and the can of an implantable cardioverter-defibrillator. It is used in medical diagnostics for fluid load monitoring in heart failure patients. We analysed TI for diurnal and weekly components that go along with the recurrent patterns of daily life.

    TI was measured in 53 patients over 280d each with a resolution of 1h. Information about the patients' professional occupation and typical sleeping rhythm was sought. Periodic signal components were identified in the amplitude spectrum, and their main characteristics were derived by cosinor analysis. The typical daily and weekly pattern were reconstructed by Fourier filtering.

    The Fourier spectrum indicates a strong circadian and a weaker circaseptan component in TI. The latter is significantly elevated in patients who regularly go to work, on error level p < 0.05. Cosinor analysis states a significant circadian rhythm in all patients (p < 0.001), with MESOR 61.8Ohm, amplitude 1.9Ohm, and acrophase 17.5h. A significant weekly rhythm is found in 25 patients (p < 0.05), with amplitude 0.31Ohm and acrophase typically on Wednesday. Both rhythms typically obtain their maximum during the 'active' phase of the period in daily life, i.e. in the afternoon and on working days, respectively, while the minimum is reached in the 'recreative' phase.

    Circadian and circaseptan variation are hence prevalent components of TI, which can induce impedance changes of several Ohms and thus be an error source for daily TI measurements.

    }, author = {Kirchner, Jens and Paule, Stefan and Beckendorf, Claudia and Achenbach, Stephan and Arnold, Martin}, cris = {https://cris.fau.de/converis/publicweb/publication/203475017}, year = {2015}, month = {06}, day = {18}, doi = {10.1088/0967-3334/36/7/1615}, faupublication = {yes}, issn = {0967-3334}, journaltitle = {Physiological Measurement}, number = {7}, pages = {1615--1628}, peerreviewed = {Yes}, shortjournal = {PHYSIOL MEAS}, title = {Circadian and circaseptan rhythms in implant-based thoracic impedance}, type = {Article in Journal}, url = {http://stacks.iop.org/0967-3334/36/i=7/a=1615}, volume = {36}, }

2014

  • C. Beckendorf, J. Kirchner, S. Paule, S. Achenbach, and M. Arnold, "Circadian variation in thoracic impedance", Clinical Research in Cardiology Supplements, vol. 103, iss. Suppl. 1, 2014. [DOI] [Bibtex]
    @article{beckendorf2014,
    abstract = {Introduction: Thoracic impedance (TI) is the electrical resistance measured between the right ventricular shock coil and the can of an implantable cardioverter-defibrillator. As it is known to decrease on lung congestion, it has been proposed as a marker of worsening of cardiac status in heart failure patients. However, the diagnostic value of TI is limited by various confounding factors and the extent of physiologic variability is poorly understood. We therefore analyzed circadian variation of TI.

    Methods: In 54 patients with an implanted ICD (n = 47) or CRT-D (n = 7) device (85% male, 66 ± 11 years, NYHA class I-IV, EF 31 ± 14 %), TI was measured with an hourly resolution. The resulting 24 TI values per day were transmitted via home monitoring. For each patient, data from an observation interval of 28 days were averaged separately for each time of the day. Intra-day variability was correlated to each individual patient´s daily routine, which was determined by a questionnaire.

    Results: Daily mean thoracic impedance of all 54 subjects was 61.0 ± 6.2 Ω (range: 43.8-71.8 Ω). Intra-day variation was present in all subjects, ranging from 1.1 to 8.4 Ω and with 3.2 ± 1.7 Ω in average. The typical day-curve (see figure) exhibits a clear minimum in the early morning (average lowest TI: -1.9 ± 1.4 Ω below mean) and a plateau in the afternoon (maximum height: 1.3 ± 1.0 Ω above mean).

    The phases of the day with large changes in TI - nighttime and morning hours till noon - are strongly correlated with the patients going to bed and getting up from bed, respectively: After both events, TI exhibits a trend in negative respectively positive direction (p < 0.001, Page trend test), which leads to significant changes of TI over at least 6 hours (p < 0.001 for all measurement times, Wilcoxon signed-rank test).


    Figure: circadian variation of the thoracic impedance of a heart failure patient.

    Conclusion: Thoracic impedance exhibits a strong circadian variation, which amounts to 7 % of its absolute value and seems to be based on the sleep-wake rhythm. Therefore, daily TI values from a single measurement time per day are prone to errors of the same size, particularly when measured in high-dynamic phases. More appropriate is the use of either the mean or an extremal value of the TI day-curve from several equidistant measurements.}, author = {Beckendorf, Claudia and Kirchner, Jens and Paule, Stefan and Achenbach, Stephan and Arnold, Martin}, language = {English}, booktitle = {80. Jahrestagung der Deutsche Gesellschaft für Kardiologie- Herz- und Kreislaufforschung}, cris = {https://cris.fau.de/converis/publicweb/publication/203476665}, year = {2014}, month = {04}, day = {23}, doi = {10.1007/S00392-014-1100-9}, eventdate = {2014-04-23/2014-04-26}, faupublication = {yes}, issn = {1861-0706}, journaltitle = {Clinical Research in Cardiology Supplements}, number = {Suppl. 1}, peerreviewed = {Yes}, title = {Circadian variation in thoracic impedance}, type = {Article in Journal}, url = {http://www.abstractserver.de/dgk2014/ft/abstracts/V164.HTM}, venue = {Mannheim, Germany}, volume = {103}, }

2012

  • J. Kirchner, M. Arnold, C. Beckendorf, S. Paule, and G. Czygan, "Heart failure monitoring with implantable defibrillators", Biomedizinische Technik. Biomedical engineering, vol. 57, iss. SI-1 Track-N, pp. 1079-1082, 2012. [DOI] [Bibtex]
    @article{kirchner2012,
    abstract = {Heart failure is one of the most frequent diseases and a leading cause for hospital admission and death in Germany and other  industrialized  countries.  Two  types  of  impedance  sensors  are  presented  that  promise  to  allow  improved  disease monitoring and hence better therapy adaptation in heart failure patients  with an implanted defibrillator: thoracic impedance to estimate the lung fluid status of the patient, and intracardiac impedance for assessment of cardiac hemodynamics.
    }, author = {Kirchner, Jens and Arnold, Martin and Beckendorf, Claudia and Paule, Stefan and Czygan, Gerald}, language = {English}, cris = {https://cris.fau.de/converis/publicweb/publication/203477687}, year = {2012}, doi = {10.1515/BMT-2012-4256}, faupublication = {yes}, issn = {1862-278X}, journaltitle = {Biomedizinische Technik. Biomedical engineering}, number = {SI-1 Track-N}, pages = {1079--1082}, peerreviewed = {Yes}, title = {Heart failure monitoring with implantable defibrillators}, type = {Article in Journal}, url = {https://www.degruyter.com/view/j/bmte.2012.57.issue-s1-N/bmt-2012-4256/bmt-2012-4256.xml}, volume = {57}, }
  • A. Urbaszek, J. Kirchner, A. van Ooyen, and O. Skerl, "Hemodynamic Monitoring with an Implantable Pressure Monitor is Improved by Additional Detection of Heart Sounds", Biomedizinische Technik. Biomedical engineering, vol. 57, iss. SI-1 Track-L, pp. 740-742, 2012. [DOI] [Bibtex]
    @article{urbaszek2012,
    abstract = {Early diagnosis of cardiac decompensation is essential to improve therapy of heart failure as one of the  most  cost-intensive chronic diseases worldwide. This can be achieved by remote monitoring of pulmonary artery pressure. An implantable pressure sensor system is developed in a joint research project (COMPASS), funded by the BMBF. The application of pulse contour analysis, which is well established for stroke volume estimation based on aortic blood pressure, to pulmonary artery pressure (PAP) is challenging due to different signal morphology and limited signal resolution. Especially the incisure in the pressure signal which marks valve closure is often not visible. Therefore, it was investigated whether valve closure can be detected by additional use of heart sounds more reliably. Blood pressure of an anesthetized Rhoen sheep was measured in the pulmonary artery with the mplantable pressure monitor COMPASS and, for reference, additionally with commercial pressure catheters (Millar Instruments) in the pulmonary artery, aorta, left and right ventricles. Heart sounds were detected with a 3D accelerometer fixed at the animal’s chest. For reference, valve opening and closure were derived from left ventricular pressure. With PAP only, 6.3% of all cardiac cycles were unusable for PCA at low and medium heart rates, as either valve opening or closure were missed or not correctly identified. At very high heart rates the loss rate increased up to 87%. When both PAP and accelerometer data were used, the loss rate was reduced to 0.1% ... 0.4% for all heart rates. Combining blood pressure analysis with heart sounds improves the detection of valve opening and closure and thus SV estimation, especially at high heart rates. 
    }, author = {Urbaszek, Albrecht and Kirchner, Jens and van Ooyen, André and Skerl, Olaf}, language = {English}, cris = {https://cris.fau.de/converis/publicweb/publication/203479323}, year = {2012}, doi = {10.1515/BMT-2012-4358}, faupublication = {no}, issn = {1862-278X}, journaltitle = {Biomedizinische Technik. Biomedical engineering}, number = {SI-1 Track-L}, pages = {740--742}, peerreviewed = {Yes}, title = {Hemodynamic Monitoring with an Implantable Pressure Monitor is Improved by Additional Detection of Heart Sounds}, type = {Article in Journal}, url = {https://www.degruyter.com/view/j/bmte.2012.57.issue-s1-L/bmt-2012-4358/bmt-2012-4358.xml}, volume = {57}, }

2011

  • J. Kirchner, A. van Ooyen, S. Ershov, and O. Skerl, "Enhancement of pulse contour analysis in the pulmonary artery by use of heart sounds" in IEEE SENSORS 2011, Limerick, Ireland, 2011, pp. 1792-1795. [DOI] [Bibtex]
    @inproceedings{kirchner2011,
    abstract = {Pulse contour analysis (PCA) estimates cardiac stroke volume on a beat-to-beat basis from the systolic time interval of arterial blood pressure. Hence, identification of the ejection time intervals plays a crucial role. However, this is an intricate task when pulmonary artery pressure (PAP) measured with an implantable pressure sensing device is used. The feature marking the end of systole is rather indistinct and thus often not detectable in low-resolution signals. We therefore suggest using additional information from heart sounds, which are indicative of beginning and end of systole, respectively. The potential benefit of this approach was evaluated with data from an animal experiment. Blood pressure was recorded with a pressure transducer catheter and heart sounds with a prototype accelerometer. Using PAP only, 6.1% of all cycles were unusable for PCA. With additional use of heart sounds, however, a detection rate of 100.0% was achieved.},
    author = {Kirchner, Jens and van Ooyen, André and Ershov, Sergey and Skerl, Olaf},
    language = {English},
    booktitle = {IEEE SENSORS 2011},
    cris = {https://cris.fau.de/converis/publicweb/publication/203475875},
    year = {2011},
    month = {10},
    day = {28},
    doi = {10.1109/ICSENS.2011.6127104},
    eventdate = {2011-10-28/2011-10-31},
    faupublication = {no},
    keywords = {blood pressure measurement; blood vessels; catheters; pressure sensors; pressure transducers; prosthetics; pulse contour analysis enhancement; PCA enhancement; heart sound; cardiac stroke volume estimation; arterial blood pressure systolic time interval; ejection time intervals identification; pulmonary artery pressure measurement; PAP measurement; implantable pressure sensing device; pressure transducer catheter; prototype accelerometer; heart; blood pressure; arteries; biomedical monitoring; accelerometers; sensors},
    pages = {1792--1795},
    peerreviewed = {Yes},
    title = {Enhancement of pulse contour analysis in the pulmonary artery by use of heart sounds},
    type = {Konferenzschrift},
    url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6127104&isnumber=6126898},
    venue = {Limerick, Ireland},
    }
  • J. Kirchner, A. van Ooyen, M. Pfennig, T. Schmitz-Rode, and A. Urbaszek, "Estimating cardiac output from pulmonary arterial pressure" in Biomedizinische Technik. Biomedical engineering, vol. 56, iss. s1, Freiburg, Germany, 2011. [DOI] [Bibtex]
    @inproceedings{kirchner2011a,
    abstract = {Introduction
    Cardiac output (CO) and stroke volume (SV) are fundamental physiologic parameters for diagnosis and monitoring of congestive  heart  failure.  Methods  for  estimating  these  quantities  from  continuous  blood  pressure  measurements,  typically from aortic pressure, are known as pulse contour analysis (PCA). In an acute animal study, different methods of PCA were evaluated for applicability to continuously calculating CO and SV from pulmonary arterial blood pressure.

    Methods
    Acute experiments were performed with anesthetized Rhoen sheep with high-rate paced rhythm. Cardiac output was varied by a stepwise increase of dobutamine dosage, accompanied by constant administration of saline solution. Blood pressure was measured continuously in the left and right ventricle as well as in the aorta and the pulmonary artery by use of two pressure transducer catheters (Micro-Tip, Millar instruments). As a reference, CO was determined by use of the thermodilution method (Vigilance Monitor, Edwards Lifesciences). Stroke volume was determined by use of several methods from literature, including the use of pulse pressure, pressure integral and triangular approximations of pressure area. Cardiac output was calculated by multiplication by heart rate.

    Results
    All estimates of CO from PCA exhibit an excellent agreement with the measurement protocol, i.e. increased CO when contractility is raised. These observations are further supported by comparison to (dP/dt)max, which is regarded as a measure of contractility. The different methods show very similar behavior and vary only in the relative changes. The results from PCA agree well with the reference measurement with the thermodilution method. Calculated CO even shows a significantly quicker response to changes in physiologic condition compared to the Vigilance measurements.

    Conclusion
    Estimations of CO and SV from PCA reflect changes in physiologic condition on a beat-to-beat basis. Continuous monitoring of cardiac condition, particularly detection of a worsening of heart failure, is feasible using measurements of pulmonary arterial pressure. }, author = {Kirchner, Jens and van Ooyen, André and Pfennig, Michael and Schmitz-Rode, Thomas and Urbaszek, Albrecht}, language = {English}, booktitle = {Biomedizinische Technik. Biomedical engineering, vol. 56, iss. s1}, cris = {https://cris.fau.de/converis/publicweb/publication/203488399}, year = {2011}, month = {09}, day = {27}, doi = {10.1515/BMT.2011.345}, eventdate = {2011-09-27/2011-09-30}, eventtitle = {45. DGBMT Jahrestagung (BMT 2011)}, faupublication = {no}, peerreviewed = {Yes}, title = {Estimating cardiac output from pulmonary arterial pressure}, type = {Abstract zum Vortrag}, url = {https://www.degruyter.com/view/j/bmte.2011.56.issue-s1/bmt.2011.824/bmt.2011.824.xml}, venue = {Freiburg, Germany}, }
  • C. Rockstroh, J. Kirchner, T. Krämer, and B. Hensel, "Assessing the Severity of Congestive Heart Failure by New Parameters of Circadian variation" in Biomedizinische Technik. Biomedical engineering, vol. 56, iss. s1, Freiburg, Germany, 2011. [DOI] [Bibtex]
    @inproceedings{rockstroh2011,
    abstract = {Introduction
    Circadian variation reflects the overall activity of a patient and thus promises to particularly indicate changes in cardiac function in patients with congestive heart failure (CHF). A model that allows reconstructing parameters of the day-night rhythm with a minimal set of presuppositions is provided by the non-stationary Langevin equation. The clinical applicability of these parameters was evaluated.

    Methods
    We analyzed 24-h RR-interval time series, which are publicly available at PhysioNet.org. The study populations included patients with normal sinus rhythm as well as with mild to medium CHF. From the Langevin model, parameters were derived that correspond to heart rates typical for day and night phases, respectively, to the difference between these values and to sleeping duration. Additionally, standard parameters of heart rate variability in time domain were computed, which serve as gold standard for cardiologic time series analysis. In order to estimate the impact of measurement artifacts on the method, analysis was performed both on raw and filtered signals.

    Results
    The Langevin parameters discriminate between patients with normal sinus rhythm and those suffering from mild CHF as well as the standard HRV parameters. When applied to patient groups with mild and medium CHF, respectively, the new approach performs even better than the gold standard. Hence, both the onset and worsening of heart failure are indicated by the new parameters. In contrast to the standard HRV parameters, these results remain unaltered if the raw instead of the filtered signal is used. These results indicate that the parameters from circadian variation are robust against measurement artifacts. Sensitivity to clinical cofounders is unlikely, due to tests with medium CHF patients from different databases showing no significant differences.

    Conclusion
    The Langevin approach to circadian variation provides robust markers for changes in cardiac condition,  which are hence suitable for clinical use.
    }, author = {Rockstroh, Christian and Kirchner, Jens and Krämer, Thomas and Hensel, Bernhard}, language = {English}, booktitle = {Biomedizinische Technik. Biomedical engineering, vol. 56, iss. s1}, cris = {https://cris.fau.de/converis/publicweb/publication/203480068}, year = {2011}, month = {09}, day = {27}, doi = {10.1515/BMT.2011.517}, eventdate = {2011-09-27/2011-09-30}, eventtitle = {45. DGMBT Jahrestagung (BMT 2011)}, faupublication = {yes}, peerreviewed = {Yes}, title = {Assessing the Severity of Congestive Heart Failure by New Parameters of Circadian variation}, type = {Abstract zum Vortrag}, url = {https://www.degruyter.com/view/j/bmte.2011.56.issue-s1/bmt.2011.851/bmt.2011.851.xml}, venue = {Freiburg, Germany}, }

2009

  • J. Kirchner, W. Meyer, and B. Hensel, "Non-stationary Langevin Equation in Cardiology" in IFMBE Proceedings 25/4, München, Germany, 2009. [DOI] [Bibtex]
    @inproceedings{kirchner2009,
    abstract = {As a model for RR-interval time series, a nonstationary linear Langevin equation is used. Approximating the time-dependent point of equilibrium by a piecewise constant function, an algorithm is presented to reconstruct the amplitudes of this trend. From these quantities a measure of activity is defined, which is shown to be an indicator of a deterioration of cardiac performance such as involved by congestive heart failure.},
    author = {Kirchner, Jens and Meyer, Wolfgang and Hensel, Bernhard},
    editor = {Dössel O., Schlegel W.C.},
    language = {English},
    publisher = {Springer},
    booktitle = {IFMBE Proceedings 25/4},
    cris = {https://cris.fau.de/converis/publicweb/publication/203478913},
    year = {2009},
    month = {09},
    day = {07},
    doi = {10.1007/978-3-642-03882-2_84},
    eventdate = {2009-09-07/2009-09-12},
    eventtitle = {World Congress on Medical Physics and Biomedical Engineering},
    faupublication = {yes},
    isbn = {9783642038822},
    keywords = {Congestive Heart Failure; Langevin Equation; NYHA Class; Cardiac Performance; Circadian Variation},
    peerreviewed = {Yes},
    title = {Non-stationary Langevin Equation in Cardiology},
    type = {Article in Journal},
    url = {https://link.springer.com/chapter/10.1007/978-3-642-03882-2_84},
    venue = {München, Germany},
    }

2008

  • J. Kirchner, "Nicht-stationäre Langevin-Gleichungen als Modell kardiologischer Zeitreihen", 2008. [Bibtex]
    @phdthesis{kirchner2008,
    abstract = {Kardiologische Signale, insbesondere RR-Intervall-Zeitreihen, entstehen aus einem Antagonismus zwischen extern induzierten, zufälligen Störungen und internen Regelungen des Herz-Kreislauf-Systems. Dieser wird hier durch den Langevin-Ansatz eingefangen, die Beschreibung einer Messgröße durch eine Bewegungsgleichung mit einer deterministischen und einer stochastischen Kraft. Dazu werden zwei Modelle abgeleitet, die als grundlegende Neuerung eine Zeitabhängigkeit der Gleichgewichtslage, hervorgerufen von langfristigen Belastungsänderungen, wie auch erstmals im Bereich der Kardiologie Korrelationen auf kleinen Zeitskalen erfassen. Zur Rekonstruktion der Funktionen, die diese Charakteristika quantifizieren, – der Wirkungsfunktion und des Trends – werden neue Methoden vorgestellt und anhand eigens zu diesem Zweck aufgezeichneter Elektrokardiogramme auf ihre praktische Umsetzbarkeit getestet. Hierbei wird auch gezeigt, dass sich sowohl im regulativ-korrelierten als auch im aktivitätsbestimmt-dekorrelierten Skalenbereich Informationen über den Gesundheitszustand des Herzens gewinnen lassen: Der hierzu eingeführte Skalenfaktor der Wirkungsfunktion sowie das Aktivitätsmaß weisen hoch signifikante Unterschiede zwischen Patienten mit kongestiver Herzinsuffizienz und gesunden Probanden auf. Des Weiteren werden die Auswirkungen einer Veränderung der Gleichgewichtslage auf statistische und darauf aufbauende Signalanalysen untersucht, wodurch die Erklärung mehrerer in der Literatur vorgestellter Phänomene ermöglicht wird. Um im Gegenzug derartige, durch Instationaritäten hervorgerufene Effekte zu vermeiden, wird als Instrument zur Datenvorverarbeitung ein Algorithmus zur Trennung von Phasen unterschiedlicher Belastungen vorgestellt. Durch die genannten Ergebnisse gibt die Arbeit Aufschluss darüber, bei welchen Fragestellungen und mit welchen Zeitkonstanten die verwendeten Modelle und alle daraus abgeleiteten Konzepte angewandt werden dürfen; in konstruktiver Funktion werden Anwendungen in der Datenanalyse und der medizinischen Diagnostik vorgestellt.},
    author = {Kirchner, Jens},
    institution = {FAU Erlangen-Nürnberg},
    language = {German},
    cris = {https://cris.fau.de/converis/publicweb/publication/203477286},
    year = {2008},
    entrysubtype = {Dissertation},
    faupublication = {yes},
    keywords = {Kardiologie; Kardiovaskuläres System; Langevin-Gleichung; Nichtstationäre Zeitreihenanalyse; Stochastischer Prozess},
    peerreviewed = {automatic},
    title = {Nicht-stationäre Langevin-Gleichungen als Modell kardiologischer Zeitreihen},
    type = {Dissertation},
    }

2007

  • J. Kirchner, W. Meyer, M. Elsholz, and B. Hensel, "Nonstationary Langevin equation: Statistical properties and application to explain effects observed in cardiological time series", Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, vol. 76, iss. 2, 2007. [DOI] [Bibtex]
    @article{kirchner2007,
    abstract = {Using the Langevin equation we develop the model of a stochastic process subject to a given time-dependent regulatory mechanism. The effects of this nonstationarity on the statistical properties of the time series, i.e., on global and conditional probability densities and on the moments of the distribution, are derived. Application of these results on simple model trends allows one to approximate cardiological data and thus to explain effects recently observed in the reconstruction of the deterministic part of the Langevin equation for time series of heart rate.},
    author = {Kirchner, Jens and Meyer, Wolfgang and Elsholz, Markus and Hensel, Bernhard},
    language = {English},
    cris = {https://cris.fau.de/converis/publicweb/publication/203478286},
    year = {2007},
    doi = {10.1103/PHYSREVE.76.021110},
    faupublication = {yes},
    issn = {1550-2376},
    journaltitle = {Physical Review E - Statistical, Nonlinear, and Soft Matter Physics},
    number = {2},
    peerreviewed = {Yes},
    title = {Nonstationary Langevin equation: Statistical properties and application to explain effects observed in cardiological time series},
    type = {Article in Journal},
    url = {https://link.aps.org/doi/10.1103/PhysRevE.76.021110},
    volume = {76},
    }

2005

  • J. Kirchner, W. Meyer, J. Schwab, and B. Hensel, "Measures of complexity derived from automata theory for characterising cardiological time series", Biomedizinische Technik. Biomedical engineering, vol. 50, iss. Suppl. 1, part 1, pp. 137-138, 2005. [Bibtex]
    @article{kirchner2005,
    abstract = {In order to obtain information about the regulatory mechanisms of the human cardiovascular system, measures of complexity are used to characterise heart rate variability. A method introduced by Crutchfield and Young [1] for constructing an abstract automaton, which produces a given time series, is applied to cardiological data. We use measures of complexity derived from this model to detect differences between patients with congestive heart failure (CHF) and a reference group of healthy persons.
    }, author = {Kirchner, Jens and Meyer, Wolfgang and Schwab, Jörg and Hensel, Bernhard}, language = {English}, cris = {https://cris.fau.de/converis/publicweb/publication/203543434}, year = {2005}, faupublication = {yes}, issn = {1862-278X}, journaltitle = {Biomedizinische Technik. Biomedical engineering}, number = {Suppl. 1, part 1}, pages = {137--138}, peerreviewed = {Yes}, title = {Measures of complexity derived from automata theory for characterising cardiological time series}, type = {Article in Journal}, volume = {50}, }

2004

  • J. Kirchner, "Untersuchung von Komplexitätsmaßen zur Charakterisierung kardiologischer Zeitreihen," Diplomarbeit , FAU Erlangen-Nürnberg, 2004. [Bibtex]
    @thesis{kirchner2004,
    author = {Kirchner, Jens},
    institution = {FAU Erlangen-Nürnberg},
    cris = {https://cris.fau.de/converis/publicweb/publication/203477042},
    year = {2004},
    entrysubtype = {Diplomarbeit},
    faupublication = {yes},
    peerreviewed = {automatic},
    title = {Untersuchung von Komplexitätsmaßen zur Charakterisierung kardiologischer Zeitreihen},
    type = {Diplomarbeit},
    }

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