Mark Ulbrich

The IMPACT shirt: textile integrated and portable impedance cardiography

Measurement of hemodynamic parameters such as stroke volume (SV) via impedance cardiography (ICG) is an easy, non-invasive and inexpensive way to assess the health status of the heart. We present a possibility to use this technology for monitoring risk patients at home. The IMPACT Shirt (IMPedAnce Cardiography Textile) has been developed with integrated textile electrodes and textile wiring, as well as with portable miniaturized hardware. Several textile materials were characterized in vitro and in vivo to analyze their performance with regard to washability, and electrical characteristics such as skin-electrode impedance, capacitive coupling and subjective tactile feeling. The small lightweight hardware measures ECG and ICG continuously and transmits wireless data via Bluetooth to a mobile phone (Android) or PC for further analysis. A lithium polymer battery supplies the circuit and can be charged via a micro-USB. Results of a proof-of-concept trial show excellent agreement between SV assessed by a commercial device and the developed system. The IMPACT Shirt allows monitoring of SV and ECG on a daily basis at the patients home.

Monitoring Change of Body Fluid during Physical Exercise using Bioimpedance Spectroscopy and Finite Element Simulations

Abstract Athletes need a balanced body composition in order to achieve maximum performance. Especially dehydration reduces power and endurance during physical exercise. Monitoring the body composition, with a focus on body fluid, may help to avoid reduction in performance and other health problems. For this, a potential measurement method is bioimpedance spectroscopy (BIS). BIS is a simple, non-invasive measurement method that allows to determine different body compartments (body fluid, fat, fat-free mass). However, because many physiological changes occur during physical exercise that can influence impedance measurements and distort results, it cannot be assumed that the BIS data are related to body fluid loss alone. To confirm that BIS can detect body fluid loss due to physical exercise, finite element (FE) simulations were done. Besides impedance, also the current density contribution during a BIS measurement was modeled to evaluate the influence of certain tissues on BIS measurements. Simulations were done using CST EM Studio (Computer Simulation Technology, Germany) and the Visible Human Data Set (National Library of Medicine, USA). In addition to the simulations, BIS measurements were also made on athletes. Comparison between the measured bioimpedance data and simulation data, as well as body weight loss during sport, indicates that BIS measurements are sensitive enough to monitor body fluid loss during physical exercise.

HeartCycle: Advanced sensors for telehealth applications

Current treatment of Cardiovascular Disease (CVD) - the most frequent cause of hospitalization for people over 65 - involves changes of diet and lifestyle, requiring in addition physical exercise to support these. Nowadays, patients receive sporadic feedback at doctor visits, or later on, when facing symptoms. The HeartCycle project aimed at providing 1) daily monitoring, 2) close follow up, 3) help on treatment routine and 4) decreasing non-compliance to treatment regimes. The present paper illustrates a new toolbox of advanced sensors developed within the HeartCycle project. Ongoing clinical studies support these developments.

A Thorax Simulator for Complex Dynamic Bioimpedance Measurements With Textile Electrodes

Bioimpedance measurements on the human thorax are suitable for assessment of body composition or hemodynamic parameters, such as stroke volume; they are non-invasive, easy in application and inexpensive. When targeting personal healthcare scenarios, the technology can be integrated into textiles to increase ease, comfort and coverage of measurements. Bioimpedance is generally measured using two electrodes injecting low alternating currents (0.5-10 mA) and two additional electrodes to measure the corresponding voltage drop. The impedance is measured either spectroscopically (bioimpedance spectroscopy, BIS) between 5 kHz and 1 MHz or continuously at a fixed frequency around 100 kHz (impedance cardiography, ICG). A thorax simulator is being developed for testing and calibration of bioimpedance devices and other new developments. For the first time, it is possible to mimic the complete time-variant properties of the thorax during an impedance measurement. This includes the dynamic real part and dynamic imaginary part of the impedance with a peak-to-peak value of 0.2 Ω and an adjustable base impedance (24.6 Ω ≥ Z0 ≥ 51.6 Ω). Another novelty is adjustable complex electrode-skin contact impedances for up to 8 electrodes to evaluate bioimpedance devices in combination with textile electrodes. In addition, an electrocardiographic signal is provided for cardiographic measurements which is used in ICG devices. This provides the possibility to generate physiologic impedance changes, and in combination with an ECG, all parameters of interest such as stroke volume (SV), pre-ejection period (PEP) or extracellular resistance (Re) can be simulated. The speed of all dynamic signals can be altered. The simulator was successfully tested with commercially available BIS and ICG devices and the preset signals are measured with high correlation (r = 0.996).

High spatial and temporal resolution 4D FEM simulation of the thoracic bioimpedance using MRI scans

In this work, a finite element model was created using MRI scans of the main author to analyze sources of the dynamic thoracic bioimpedance. This model can be used to identify limitations of impedance cardiography (ICG) in practice. Heart beat (8.3 ms temporal resolution) and aortic wave propagation (2.6 ms temporal resolution) were implemented. The static volume contains all major organs of the thorax in high spatial resolution. Simulations were successfully conducted and a high correlation (r = 0.9) between the simulated aortic ICG signal and a measured signal of the same subject was obtained.

A model-based approach for analysis of intracellular resistance variations due to body posture on bioimpedance measurements

Bioimpedance spectroscopy is a known option for measuring body fluid volume. However, it is prone to a variety of influence factors which prevent a wider use. One of these influencing factors is the body posture. It could be shown that the average intracellular resistance percentage changes when the subject changes position from lying to standing. Most authors explain this phenomenon by fluid shifts. Another possible reason is the stray capacitance between the body and the ground, because if a certain fraction of the injected current follows other paths than between the potential electrodes, the result will be wrong. This paper analyses the influence of different body postures on the measured intracellular resistance and the posture depending capacity. For this purpose, FEM simulations are used. Subsequently, an electrical equivalent model with capacitances was developed. With this model, it is possible to correct the measured impedance and to neglect the influence of the stray capacitance.

Bootstrap aggregating decision tree for motion classification based on a textile-integrated and wearable sensorarray

In this work a system for instant classification of motion patterns is presented. It is based on a non-contact magnetic induction monitoring device, which is textile-integrated, wearable, and able to measure pulse and respiratory activity. The proposed classificator is based on a decision tree algorithm generated by bootstrap aggregating. Its accurate classification performance is validated with the help of a data set comprising five exemplary motion patterns. Furthermore, the dependance of the misclassification error on the input sample length is investigated.

Evaluation of a new non-invasive measurement technique based on bioimpedance spectroscopy to estimate blood alcohol content: a pilot study

Abstract The gold standard for estimating blood alcohol content (BAC) after alcohol consumption is a blood sample analysis. An innovative technology to estimate BAC is based on impedance cardiography and bioimpedance spectroscopy (BIS). This study investigated whether it is possible to estimate increasing blood alcohol levels during a drinking trial with bioimpedance measurement techniques. Twenty-one healthy volunteers were assigned to a test (ethanol) group (ETH) or a reference group (H2O). After baseline measurements, the ETH group ingested 120 ml of vodka, followed by a resorption phase of 50 min. Then, bioimpedance and breath alcohol measurements were performed. Thereafter, 60 ml of vodka was ingested and another resorption phase of 50 min was followed by bioimpedance and breath alcohol measurements. This procedure was repeated until alcohol levels exceeded 0.4 mg/l. The H2O group performed in the same way with water. For all measurements, extracellular resistance (Re) and the base impedance (Z0) were computed. Regarding BIS, several parameters differed significantly between the ETH and the H2O group. Re increased in ETH (p=0.005), but not in the H2O group when comparing the first and last measurements. Z0 also increased significantly in the ETH group (p=0.001). To conclude, with BIS measurements, it is possible to measure increasing blood alcohol levels.