Multi-Sensor Adjustment of the Invasive Blood Pressure Measurement to Compensate changes in Body Posture

Duration: 01.10.2012 - 31.03.2016
Project Leader: Prof. Dr.-Ing Horst Hellbrück
Staff: Martin Mackenberg

Motivation

Invasive pressure measuring of arterial blood pressure and central venous pressure is a standard procedure in critical neuro surgery or heart surgery. Altitude of the blood pressure sensor is the same as the reference point, which might be the right auricle with patient in supine position. Permanent changes in position of the patient during minimally invasive procedures or changes of height during radiologic interventions require permanent manual adjustment due to incorrect display of blood pressure.

Objective

Automatic correction of the intravasal measured blood pressure related to the position of the patient is crucial. This is done by adapting the reference point and the pressure transducer with accuracy of +/- 1cm. A 2-sensor-system (reference point patient and pressure transducer) is preferred. Therefore it is planned to compare various methods for position determination based on a Body-Area-Network (BAN = wireless sensor network). Moreover, goals of this project are to combine, prototypically implement and evaluate the various methods.

Approach

Multisensor and application-optimized measurement setups are based on orientation sensors to measure 3D angles in space and 3D localization e.g. by using ultra-wide-band (UWB) systems. Involving additional sensor technology in the table or patient is leading to an adaptive, intelligent and reliable system. This project benefits from the complement of the expertizes of the areas wireless sensors (FHL, ITM), positioning and navigation (FHL, ITM) and monitoring in anesthesia (UK S-H).

Project Partners

  • Uni Lübeck - Institute of Telematics
  • UK-SH, Campus Lübeck - Klinik für Anästhesiologie und Intensivmedizin
  • Ubisense AG, Düsseldorf

Publications


Refereed Articles and Book Chapters
[2016] Reflection and transmission of ultra-wideband pulses for detection of vascular pressure variation and spatial resolution within soft tissues (Martin Mackenberg, Klaas Rackebrandt, Christian Bollmeyer, Philipp Wegerich, Hartmut Gehring, Horst Hellbrück), In Biomedical Physics & Engineering Express, volume 2, 2016. [bib] [pdf] [abstract]
Ultra-wideband signals have a variety of applications. An upcoming medical application is the detection of the heart rate of patients. However, current UWB systems provide poor resolution and are only able to detect vessels with a large diameter, e.g. the aorta. The detection and quantification of vascular dilation of thinner vessels is essential to develop wearable ultra-wideband based devices for real-time detection of cardiovascular conditions of the extremities. The reflection and transmission processes of those signals within inhomogeneous bodies are complex and their prediction is challenging. In this paper, we present an experimental setup (UWB system; phantom) for the detection of vascular dilation within soft tissues. Furthermore, we suggest a theoretical simulation model for the prediction of the reflection of ultra-wideband pulses and compare these simulated predictions to results of measurements within the phantom. The results verify that we are able to identify vascular dilation within the simulation model and the experimental setup, depending on the depth of the vessel (20 mm, 40 mm, 60 mm).
[2015] Entwicklung einer kompakten Sensorplattform für prototypischen Einsatz in der Medizintechnik (Christian Bollmeyer, Martin Mackenberg, Hartmut Gehring, Horst Hellbrück), In ImpulsE (submitted), volume 20, 2015. [bib]
[2013] Höhenbestimmung mittels Luftdrucksensoren und differentieller Messung für Indoor-Anwendungen (Christian Bollmeyer, Tim Esemann, Hartmut Gehring, Horst Hellbrück), In ImpulsE, volume 17, 2013. [bib]
Refereed Conference Papers
[2015] Indoor Localization based on Bi-Phase Measurements for Wireless Sensor Networks (Mathias Pelka, Christian Bollmeyer, Horst Hellbrück), In 2015 IEEE Wireless Communications and Networking Conference (WCNC): - Track 3: Mobile and Wireless Networks (IEEE WCNC 2015 - Track 3- Mobile and Wireless Networks), 2015. [bib] [abstract]
Indoor localization is important for medical and industrial application as well as for wireless emergency and security systems. For such applications an accuracy within a few meters is desired. Available radio based systems within that accuracy are neither cost effective nor easy to deploy. In this work, we suggest an approach called biphase measurement based on phase measurements with two frequencies to determine the location of a tag. We design and build a complete indoor positioning system based on bi-phase measurements with easy to deploy wireless sensor nodes. The wireless sensor nodes shape anchors and tags and communicate results to a location engine of the indoor positioning system. Our implementation comprises lowcost IEEE802.15.4 radio chips with built-in support for phase measurements unit for both, anchor and tags. We compute the position of the tag based on distance estimation retrieved with bi-phase measurements. We evaluate our indoor positioning system providing first measurement results for accuracy and precision and discuss trade-off between scalability, real-time and accuracy.
[2015] Wireless Medical Sensors - Context, Robustness and Safety (Christian Bollmeyer, Mathias Pelka, Hartmut Gehring, Horst Hellbrück), In 49th annual conference of the German Society for Biomedical Engineering (BMT 2015), 2015. [bib]
[2014] Accurate Radio Distance Estimation by Phase Measurements with Multiple Frequencies (Mathias Pelka, Christian Bollmeyer, Horst Hellbrück), In The Fifth International Conference on Indoor Positioning and Indoor Navigation 2014 (IPIN 2014), 2014. [bib] [abstract]
Indoor localization is beneficial for logistics, industrial applications and for several consumer applications. In the area of logistics, e.g. warehouses, localization accuracy within a few meters is desired. Available radio based systems within that accuracy are neither cost effective nor easy to deploy. Distance estimations are one possible method for localization. In this work, we propose phase measurements between two wireless sensor nodes for distance estimation. We introduce a mathematical model to estimate distances from phase measurements with multiple frequencies and provide a systematic analysis of possible sources of errors. Additionally, we derive requirements, e.g. resolution and speed for a phase measurement unit to reach certain accuracy. To proof our theoretical results, we present evaluation results based on our implementation. Our implementation comprises a low cost IEEE 802.15.4 hardware with a built-in phase measurement unit. We implement the developed algorithm for distance estimation in our wireless sensor network and use two wireless sensor nodes to perform a phase measurement. The contribution of the paper comprises a new model for phase measurements to estimate distances and a preliminary evaluation with our hardware.
[2014] Experimental Evaluation & Optimization of a UWB Localization System for Medical Applications (Christian Bollmeyer, Horst Hellbrück, Hartmut Gehring), In 48th annual conference of the German Society for Biomedical Engineering (BMT 2014), 2014. [bib]
[2014] Evaluation of Radio Based, Optical and Barometric Localization for Indoor Altitude Estimation in Medical Applications (Christian Bollmeyer, Mathias Pelka, Hartmut Gehring, Horst Hellbrück), In The Fifth International Conference on Indoor Positioning and Indoor Navigation, 2014. [bib] [abstract]
The advances of electronics provide options for improved monitoring of patients in clinical environment.Medical applications like blood pressure monitoring require precise and wireless altitude measurement in indoor environment. An error of only a few centimeters may lead to mistreatment of patients.Furthermore, user requirements like small form factor, usability and robust operation are important in the medical field.Existing evaluations of indoor localization systems focus on accuracy analysis of x- and y-coordinates and not on the z-coordinate (altitude). In this paper, we define evaluation criteria for altitude estimation in medical applications. We compare an Ultra-Wide-Band indoor localization system, an optical Microsoft Kinect camera system and our own development of a wireless barometric sensor against these criteria. We present a comparative measurement setup, results and a final evaluation of the three systems in an indoor environment.
[2013] Precise Indoor Altitude Estimation based on differential barometric Sensing for wireless Medical Applications (Christian Bollmeyer, Tim Esemann, Hartmut Gehring, Horst Hellbrück), In Body Sensor Networks Conference 2013 (BSN2013), 2013. [bib] [abstract]
Some medical applications require precise information of position and orientation of a patient as changes affect pressure condition inside the body. In this paper we focus on altitude estimation, where altitude is a distance, in vertical direction, between a reference and a point of a human body. We suggest equipping wireless sensor nodes with high resolution pressuresensors to calculate the altitude with the barometric formula. We implement a body sensor network based on IEEE 802.15.4 and synchronization mechanism with a reference. Pressure variations due to environmental effects are compensated by cancellation with this differential measurement setup. We demonstrate the need for differential measurements and show with a series of measurements that environmental pressure variations have no significant effect on the proposed altitude estimation. Compared to existing systems, our solution is cost effective, easy to deploy and provides a flexible tradeoff between precision and location lag by adjusting a filter constant.
Refereed Workshop Papers
[2013] A Reusable and Extendable Testbed for Implementation and Evaluation of Cooperative Sensing (Tahir Akram, Tim Esemann, Torsten Teubler, Horst Hellbrück), In The 8th ACM International Workshop on Performance Monitoring, Measurement and Evaluation of Heterogeneous Wireless and Wired Networks PM2HW2N'13, 2013. [bib] [abstract]
Cooperative sensing has been identi?ed as a potential improvement for cognitive radios to perceive their radio environment. In the past, algorithms have been developed by analysis and simulations exclusively. With cheaper hardware experimental platforms have been used for evaluation purpose recently. Simulations lack realistic propagation models for radio transmission but are reproducible compared to experimental evaluation done by hand. The effects of reduced detection probability and false alarms are not realistic in these simulations. In this paper, we suggest a reusable and extendable automated testbed software and instructions for deployment of own testbeds. Primary users as well as secondary users with cooperating cognitive radios can be flexibly deployed in the testbed within seconds. The advantage is that a series of even long lasting measurements including automatic logging of results can be easily repeated. Results can be assessed on the fly during the ongoing evaluation by accessing debug output remotely. The testbed supports stationary, portable, and in the future mobile radio devices for flexible scenarios as well as monitoring devices for debugging. The testbed and the radio devices are validated by deploying primary and secondary user in a small scenario whose outcome was analyzed beforehand. The results are as predicted and show the usefulness of this approach.
Other Publications
[2015] Comparison and Performance Evaluation of Indoor Localization Algorithms based on an Error Model for an Optical System (Z. Lifang, M. Pelka, C. Bollmeyer, H. Hellbrück), GRIN (T. M. Buzug et. al., ed.), 2015. [bib]
[2014] Localization of Heart Reference Point of a Lying Patient with Microsoft Kinect Sensor (Q. Ma, C. Bollmeyer, Y. Zhu, H. Hellbrück), GRIN (T. M. Buzug et. al., ed.), 2014. [bib]
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