Cuffless Blood Pressure in clinical practice: challenges, opportunities and current limits.

Background: Cuffless blood pressure measurement technologies have attracted significant attention for their potential to transform cardiovascular monitoring.Methods: This updated narrative review thoroughly examines the challenges, opportunities, and limitations associated with the implementation of cuffless blood pressure monitoring systems.Results: Diverse technologies, including photoplethysmography, tonometry, and ECG analysis, enable cuffless blood pressure measurement and are integrated into devices like smartphones and smartwatches. Signal processing emerges as a critical aspect, dictating the accuracy and reliability of readings. Despite its potential, the integration of cuffless technologies into clinical practice faces obstacles, including the need to address concerns related to accuracy, calibration, and standardization across diverse devices and patient populations. The development of robust algorithms to mitigate artifacts and environmental disturbances is essential for extracting clear physiological signals. Based on extensive research, this review emphasizes the necessity for standardized protocols, validation studies, and regulatory frameworks to ensure the reliability and safety of cuffless blood pressure monitoring devices and their implementation in mainstream medical practice. Interdisciplinary collaborations between engineers, clinicians, and regulatory bodies are crucial to address technical, clinical, and regulatory complexities during implementation. In conclusion, while cuffless blood pressure monitoring holds immense potential to transform cardiovascular care. The resolution of existing challenges and the establishment of rigorous standards are imperative for its seamless incorporation into routine clinical practice.Conclusion: The emergence of these new technologies shifts the paradigm of cardiovascular health management, presenting a new possibility for non-invasive continuous and dynamic monitoring. The concept of cuffless blood pressure measurement is viable and more finely tuned devices are expected to enter the market, which could redefine our understanding of blood pressure and hypertension

A Feasibility Study of the Suitability of an AD5933-based Spectrometer for EBI Applications

Projecte final de carrera realitzat en col.laboració amb University of BoräsElectrical Bioimpedance (EBI) measurements have proven their validity in several medical applications like body composition analysis and detection of melanoma among others. The successful application of EBI technology on the field of medicine has lead the way for applications in the field of personal healthcare and body performance in the field of sports. Due to the widespread use of the EBI technology and rising of new EBI applications requiring system portability or even suitable to wear, the manufacturer Analog devices has introduced in the market the first integrated system dedicated to measure EBI, the impedance network analyzer AD5933. The availability of this EBI spectrometer device opens up new horizons for the integration of the measurement systems to meet the demands of new EBI applications and allowing the development of portable and even wearable measurement systems. This project is focused on the AD5933 impedance network analyzer, and it aims to identify the EBI applications in which, the use of an AD5933 device is suitable. To adapt the AD5933 device for biomedical measurements an Analog Front-End (AFE) has been used to enable the system for 4-electrodes measurements. In order to evaluate the performance of AD5933 with the AFE, experimental measurements on electrical equivalent models have been taken with the AD5933+4E-AFE system and the EBI spectrometer Impedimed SFB7. The obtained impedance spectral data have been used to estimate the values of the equivalent circuit under measurement and the estimated values have been mutually compared in terms of estimation accuracy

Hybrid Nanostructured Textile Bioelectrode for Unobtrusive Health Monitoring

Coronary heart disease, cardiovascular diseases and strokes are the leading causes of mortality in United States of America. Timely point-of-care health diagnostics and therapeutics for person suffering from these diseases can save thousands of lives. However, lack of accessible minimally intrusive health monitoring systems makes timely diagnosis difficult and sometimes impossible. To remedy this problem, a textile based nano-bio-sensor was developed and evaluated in this research. The sensor was made of novel array of vertically standing nanostructures that are conductive nano-fibers projecting from a conductive fabric. These sensor electrodes were tested for the quality of electrical contact that they made with the skin based on the fundamental skin impedance model and electromagnetic theory. The hybrid nanostructured dry electrodes provided large surface area and better contact with skin that improved electrode sensitivity and reduced the effect of changing skin properties, which are the problems usually faced by conventional dry textile electrodes. The dry electrodes can only register strong physiological signals because of high background noise levels, thus limiting the use of existing dry electrodes to heart rate measurement and respiration. Therefore, dry electrode systems cannot be used for recording complete ECG waveform, EEG or measurement of bioimpedance. Because of their improved sensitivity these hybrid nanostructured dry electrodes can be applied to measurement of ECG and bioimpedance with very low baseline noise. These textile based electrodes can be seamlessly integrated into garments of daily use such as vests and bra. In combination with embedded wireless network device that can communicate with smart phone, laptop or GPRS, they can function as wearable wireless health diagnostic systems

Simulation of Impedance Measurements at Human Forearm Within 1 KHz to 2 MHz

This work presents a simulation analysis of the bioimpedance measurements at human forearm. The Ansys® High Frequency Structure Simulator (HFSS) has been used to analyze the electrical response of a section of human forearm with three domains of di-electric behavior- fat, muscle and artery (blood). The impedance values were calculated as the ratio of the output voltage at the electrodes to the applied known current (1mA). A model was developed and was simulated for impedance values obtained within a frequency range of 1 kHz to 2MHz. The measurements were done at three instances of radial artery diameter. The maximum resistance and reactance values were calculated as 445Ω and 178.5Ω, 356Ω and 138Ω, and 368Ω and 144.3Ω for diameters 2.3mm, 2.35mm, and 2.4mm respectively. The set of impedance values obtained followed Cole-plot trend. The results obtained were found to be in excellent agreement with the Cole theory. The set of values obtained at three different diameters reflected the effect of blood flow on impedance values

A Feasibility Study of the Suitability of an AD5933-based Spectrometer for EBI Applications

Projecte final de carrera realitzat en col.laboració amb University of BoräsElectrical Bioimpedance (EBI) measurements have proven their validity in several medical applications like body composition analysis and detection of melanoma among others. The successful application of EBI technology on the field of medicine has lead the way for applications in the field of personal healthcare and body performance in the field of sports. Due to the widespread use of the EBI technology and rising of new EBI applications requiring system portability or even suitable to wear, the manufacturer Analog devices has introduced in the market the first integrated system dedicated to measure EBI, the impedance network analyzer AD5933. The availability of this EBI spectrometer device opens up new horizons for the integration of the measurement systems to meet the demands of new EBI applications and allowing the development of portable and even wearable measurement systems. This project is focused on the AD5933 impedance network analyzer, and it aims to identify the EBI applications in which, the use of an AD5933 device is suitable. To adapt the AD5933 device for biomedical measurements an Analog Front-End (AFE) has been used to enable the system for 4-electrodes measurements. In order to evaluate the performance of AD5933 with the AFE, experimental measurements on electrical equivalent models have been taken with the AD5933+4E-AFE system and the EBI spectrometer Impedimed SFB7. The obtained impedance spectral data have been used to estimate the values of the equivalent circuit under measurement and the estimated values have been mutually compared in terms of estimation accuracy

Development of low Cost Portable Platform for Bioimpedance Based Diagnostics

Analyzing the impedance of biological samples has gained importance in the last decade. Presently all the bioimpedance analyzer available in the market are heavy and costly. In this context, an attempt has been made to develop a portable, low cost bioimpedance analyzer. For this purpose, the portable cartridges for sample analysis were prepared on cupper print circuit board by chemical etching. The developed device was successfully operated in a frequency range of 50 Hz to 20 KHz to measure impedance of various samples such as glucose, NaCl solution, bacterial cell culture and xanthan gum. All the measured samples were shown capacitive dominance. Optimization of electrode spacing and area was done to improve its efficacy in measuring the bioimpedance. Furthermore, the device was also employed for screening of anticancer drugs like cis-platin using HT-29 colon cancer cell line. The device was found operational for analyzing small sample volume (50-200ìl) , moreover portability of this developed device makes it a special among commercially available instruments used for measuring bioimpedance

Wearable impedance plethysmography and electrocardiography sensor

Wearable technology has become increasingly popular in the last few years. This project describes the design and implementation of a wearable impedance plethysmography and electrocardiography sensor. This sensor is developed to be compact and lightweight while having a very extended battery life. This way, it can be easily integrated into other wearable devices or into clothing or shoes. The acquired IPG and ECG data will be transmitted in real-time to a receiving host for further storage and processing by using the Bluetooth Low Energy protocol. By using a so widespread low energy wireless protocol, the data can be received into any compatible device, such as smartphones, laptops or even specialized systems. An android application showing a real-time graphic of the measured signals is also developed for demonstration purposes. To meet the low power consumption requirements of the analog front-end circuitry, multiple techniques were used, such as using low power versions of components such as operational amplifiers and even taking advantage of their limitations to improve circuit performance characteristics. Other techniques such as sensing the correct placement of electrodes or disabling parts of the circuitry when not needed or the signal is not available were also used. A current consumption for the analog frontend in the order of only 100 µA to 200 µA at 3V was achieved while continuously providing both IPG and ECG data. For the digital circuitry, consisting mainly of the nRF51822 System on Chip from Nordic Semiconductor and some peripherals, multiple techniques of power consumption minimization were also used. A current consumption of around 200 µA to 300 µA was achieved, again at 3V, during continuous data processing and transmission. A prototype was implemented on a PCB. Unfortunately, full functionality was not achieved mainly due to some hardware failures and time constraints, however, as multiple innovative solutions were implemented, this work will provide useful information to improve other research projects in this area.Objectius de Desenvolupament Sostenible::3 - Salut i Benesta

Bioimpedanciómetro basado en microcontrolador de 32 bits

En este trabajo se presenta el desarrollo de un bioimpedanciómetro basado en un diseño propio, de implementación simple, tamaño reducido y bajo costo basado en un microcontrolador de 32 bits de arquitectura ARM. Se describe el sistema por completo y se muestran registros de medidas en diversas situaciones. Se presenta también el desarrollo de una aplicación en PC que permite visualizar en tiempo real distintas variables de interés en la medida de bioimpedancia. La validación del sistema implementado constituye un punto de partida sólido para el desarrollo de una segunda versión vestible y con enlace inalámbrico.This work presents the development of a proprietary bioimpedance meter based on an own design, simple to implement, small in size and low cost, based on a 32-bit microcontroller with ARM architecture. The entire system is described, and measurement logs are shown in various situations. The development of a PC application that allows real-time visualization of different variables of interest in bioimpedance measurement is also presented. The validation of the implemented system constitutes a solid starting point for the development of a second version embedded in a wearable system with a wireless link.Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señale

A novel approach to bioelectrical impedance plethysmography for the assessment of arterial and venous circulatory problems in the forearm

Peripheral vascular disease (PVD) and/or peripheral arterial disease (PAD) are sicknesses known to inadequate delivery of either arterial or venous blood towards the extremities. Such sickness may trigger complications owing to the lack of transport of oxygen and nutrients, thus causing hypoxic events that may eventually prompt to ischaemic tissue or even the loss of the compromised limb. One of the most prominent indicators of prosperous health is blood volume and flow. The basic information within these health parameters may show cardiovascular problems or the advance of further complications related to other diseases like diabetes. In clinical setting, there effective methods to measure these parameters like Doppler ultrasound, photoplethysmography or venous occlusion plethysmography. These methods take measurements from either single vessels and/or small volume of tissue. However, it is difficult to establish a relation between the obstruction of arterial and/or venous circulation and the amount of blood received by the tissue. Bioelectrical impedance plethysmography (iPG) measures blood changes by driving a small amount of AC current into the body and after measuring the potential created by fluids flowing through tissue. This technique apart from taking measures within defined volumes of tissue, it is easy to use as only needs four electrodes on the skin. Hence, a bespoken bioelectrical impedance device including hardware and software was built ready to measure changes in blood volume/flow in the upper limbs. The system was assessed in an in-vivo controlled environment with 8 participants. The blood flow towards their left arms was altered by constricting the upper arm with a cuff at three levels: 1) below venous pressure 2) amongst venous and arterial pressure and 3) during total occlusion. Simultaneously, measurements from various instruments like ECG, Doppler ultrasound, laser Doppler flowmetry and PPG were taken and compared to the measurements obtained from the iPG instrument and defining its correlation with the impedimetric signal. The results from the experiments showed that the bioelectrical impedance signal changed in basal and arterial pulses showing specific characteristics for each kind of occlusion. The data indicated that it is possible to differentiate between a venous and arterial occlusion by examining both components of the impedance signal. The impedance during venous occlusion dropped in average 0.658±0.230% from the baseline. On the other hand, during arterial occlusion the base impedance dropped in a higher rate approximately 1.13±04.82%, indicating a differentiator during both type of blood flow disruption. Furthermore, the impedance plethysmography waveform morphology also reshaped during these occlusive periods. The whole waveform during artificial venous obstruction increased in magnitude, the systolic peak rose 31.80%, the dicrotic notch 47.73% and the diastolic point 31.92%, where the value of the latter was higher than the dicrotic notch point. In contrast, in the time of partial arterial occlusion the waveform also increased in size at all these points, but its shape was altered. The impedance magnitude at the diastolic point went below the ones at the dicrotic notch. These fluctuations provided additional further information that it might be possible to differentiate amongst venous and arterial occlusions. By consolidating the data obtained by the iPG device, it is possible to produce an index ratio between the basal impedance and these three reference points which may help to identify early circulatory problems in the arterial and/or venous systems

A NOVEL MULTI-MODAL, WEARABLE SENSING SYSTEM TO AUTOMATICALLY QUANTIFY CHANGES IN EXTRAVASCULAR FLUID LEVELS

The buildup of static edematous fluids (swelling) in the tissue is indicative of a serious medical condition that can lead to long-term tissue damage, reduction in mobility and in some cases loss of limb. This swelling can be due to internal factors such as an immunoresponse to injuries or infections, or external factors such as a leakage of infused intravenous medication to the surrounding tissue (i.e., IV infiltration or extravasation). Detecting and tracking changes in a tissue’s extracellular fluid content is crucial in diagnosing the severity of the injury and/or infection, and thereby preventing irreversible tissue damage. However, current methods for quantifying fluid levels in the extravascular space are either (1) manual and subjective, relying heavily on the medical staff’s expertise, or (2) costly and timely, such as X-rays or magnetic resonance imaging (MRI). In this dissertation, I present non-invasive wearable technologies that utilize localized bioimpedance contextualized by the tissue’s kinematics to robustly quantify changes in the biological tissue’s extracellular fluid content. Towards this goal, several robust and miniaturized systems are designed and implemented by researching different integrated circuits, analog front ends, and novel physiology-driven calibration techniques that together increase the system’s accuracy and reduce its size and power consumption. Next, novel methods and algorithms are developed to allow for unobtrusive real-time detection of changes in extracellular fluid content. The systems, methods and algorithms were validated in human subjects studies, animal models and cadaver models for ankle edema tracking, and in human subjects studies and animal tissue for intravenous infiltration detection.Ph.D