Design of Bioimpedance Spectroscopy Instrument With Compensation Techniques for Soft Tissue Characterization

Development and Characterization of Interstitial-Fluid-Mimicking Solutions for Pre-Clinical Assessment of Hypoxia

Asphyxia, a leading cause of illness and death in newborns, can be improved by early detection and management. Arterial blood gas (ABG) analysis is commonly used to diagnose and manage asphyxia, but it is invasive and carries risks. Dermal interstitial fluid (ISF) is an alternative physiological fluid that can provide valuable information about a person's health. ISF is more sensitive to severe hypoxia and metabolic disorders compared to blood, making it an attractive option for minimally invasive asphyxia detection using biosensors. However, obtaining ISF samples from humans is challenging due to ethical concerns and sampling difficulties. To address this, researchers are developing ISF-mimicking solutions as substitutes for early testing and evaluation of biosensors. This paper focuses on the development of these solutions for bench-based testing and validation of continuous asphyxia-monitoring biosensors. With an understanding of the factors influencing system quality and performance, these solutions can aid in the design of biosensors for in vivo monitoring of dermal ISF. Monitoring interstitial fluid pH levels can provide valuable insights into the severity and progression of asphyxia, aiding in accurate diagnosis and informed treatment decisions. In this study, buffer solutions were prepared to mimic the pH of ISF, and their electrical properties were analyzed. The results suggest that certain buffers can effectively mimic metabolic acidosis associated with asphyxia (pH < 7.30), while others can mimic metabolic alkalosis (pH > 7.45). Overall, this research contributes to the development of ISF-mimicking solutions and lays the groundwork for biosensor systems that monitor dermal ISF in real time.

Novel 3D printed probe for bioimpedance spectroscopic measurement of oral mucosa: design and testing with ex vivo porcine oral tissues

Three-dimensional (3D) printing has a high potential in various biomedical applications. We hypothesize that 3D printing could be a viable option to construct novel bioimpedance spectroscopic (BIS) sensors suitable for electrochemical characterization of oral mucosal tissues. Previous BIS studies have relied on hand-made probes possessing significant limitations related to their single patient disposable use, large inter-probe differences, and weak reproducibility of measurement. There is also uncertainty related to the effect of varying loading pressure between the probe and biological tissue. Here, we introduce three differently sized rectangular shaped 3D printed probes and test those using a four-terminal measurement principle on various porcine oral tissue samples. We find that constructing a fully 3D printed probe is a challenging task, prone to issues relating to short-circuiting or electrochemical corrosion. However, our final prototype version, constructed with silver-coated copper electrodes, showed favorable characteristics in BIS experiments. All three differently sized probes were able to differentiate between different tissue types with excellent reproducibility. The effect of loading pressure was found to be almost negligible when using small- and medium-sized probes. However, further studies are needed to measure tissues with uneven surfaces, such as palatinum, and to avoid manual or (electro)chemical surface-finishing steps.

Compensating the Influence of Tremors on Impedance Measurements Through Fourier Analysis. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2023;2023:1-4. [PMID: 38082760 DOI: 10.1109/embc40787.2023.10340912] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Electrical mpedance measurements are a promising method for detecting structural changes in tissue and can be used in oncology to differentiate between healthy and tumorous tissue areas. The impedance measurements are so sensitive that they are not only affected by changes in the tissue itself, but also by a fluctuating contact force between sensor and tissue. In this work, the correlation between impedance measurements and movements during the measuring process, such as physiological tremors, are analyzed. To do this, impedance measurements are taken on pig bladders and the sensor-tissue contact force is simultaneously recorded. The tremor frequencies are directly visible in the Fourier transform of the impedance measurement. To counteract these effects, a Butterworth filter is used to filter out tremor frequencies and remove unwanted artefacts. Additionally, placing an spring on top of the impedance sensor helped to achieve a steadier contact force between sensor and tissue to also remove low frequency disturbances in the impedance measurements.Clinical relevance- This approach can help to obtain more reliable impedance measurements on tissue both for ex vivo and in vivo applications.

Smart Bioimpedance Spectroscopy Device for Body Composition Estimation

The purpose of this work is to describe a first approach to a smart bioimpedance spectroscopy device for its application to the estimation of body composition. The proposed device is capable of carrying out bioimpedance measurements in multiple configurable frequencies, processing the data to obtain the modulus and the bioimpedance phase in each of the frequencies, and transmitting the processed information wirelessly. Another novelty of this work is a new algorithm for the identification of Cole model parameters, which is the basis of body composition estimation through bioimpedance spectroscopy analysis. Against other proposals, the main advantages of the proposed method are its robustness against parasitic effects by employing an extended version of Cole model with phase delay and three dispersions, its simplicity and low computational load. The results obtained in a validation study with respiratory patients show the accuracy and feasibility of the proposed technology for bioimpedance measurements. The precision and validity of the algorithm was also proven in a validation study with peritoneal dialysis patients. The proposed method was the most accurate compared with other existing algorithms. Moreover, in those cases affected by parasitic effects the proposed algorithm provided better approximations to the bioimpedance values than a reference device.