Estimating pulse wave velocity using mobile phone sensors

Pulse wave velocity has been recognised as an important physiological phenomenon in the human body, and its measurement can aid in the diagnosis and treatment of chronic diseases. It is the gold standard for arterial stiffness measurements, and it also shares a positive relationship with blood pressure and heart rate. There exist several methods and devices via which it can be measured. However, commercially available devices are more geared towards working health professionals and hospital settings, requiring a significant monetary investment and specialised training to operate correctly. Furthermore, most of these devices are not portable and thus generally not feasible for private home use by the common individual. Given its usefulness as an indicator of certain physiological functions, it is expected that having a more portable, affordable, and simple to use solution would present many benefits to both end users and healthcare professionals alike. This study investigated and developed a working model for a new approach to pulse wave velocity measurement, based on existing methods, but making use of novel equipment. The proposed approach made use of a mobile phone video camera and audio input in conjunction with a Doppler ultrasound probe. The underlying principle is that of a two-point measurement system utilising photoplethysmography and electrocardiogram signals, an existing method commonly found in many studies. Data was collected using the mobile phone sensors and processed and analysed on a computer. A custom program was developed in MATLAB that computed pulse wave velocity given the audio and video signals and a measurement of the distance between the two data acquisition sites. Results were compared to the findings of previous studies in the field, and showed similar trends. As the power of mobile smartphones grows, there exists potential for the work and methods presented here to be fully developed into a standalone mobile application, which would bring forth real benefits of portability and cost-effectiveness to the prospective user base

Photoplethysmography based remote health monitoring system

One of the world's most leading killer diseases is the cardiovascular disease, which accounts for 16.7 million deaths annually. Out of the total population in the world, about 22 million people run the risk of sudden heart failure. However, saving the lives of cardiac patients can be improved by the emergency monitoring so that the initiation of treatment can be taken up within the crucial hour. The acquired signals by pulse oximetry provide significant information about the heart-rate, arterial blood oxygenation, blood pressure and respiratory-rate. Telemedicine provides a great impact in the emergency monitoring of patients located in remote nonclinical environments. A home cardiac telemedicine emergency system based on photoplethysmography has been developed. The acquired signals are processed, transmitted and stored in a local PC. Finally, the data are sent to the remote terminal located at the hospital through internet. The diagnoses are done by specialists from the reading and action can be immediately taken in emergency cases

Bio-Radar Applications for Remote Vital Signs Monitoring

Nowadays, most vital signs monitoring techniques used in a medical context and/or daily life routines require direct contact with skin, which can become uncomfortable or even impractical to be used regularly. Radar technology has been appointed as one of the most promising contactless tools to overcome these hurdles. However, there is a lack of studies that cover a comprehensive assessment of this technology when applied in real-world environments. This dissertation aims to study radar technology for remote vital signs monitoring, more specifically, in respiratory and heartbeat sensing. Two off-the-shelf radars, based on impulse radio ultra-wideband and frequency modu lated continuous wave technology, were customized to be used in a small proof of concept experiment with 10 healthy participants. Each subject was monitored with both radars at three different distances for two distinct conditions: breathing and voluntary apnea. Signals processing algorithms were developed to detect and estimate respiratory and heartbeat parameters, assessed using qualitative and quantitative methods. Concerning respiration, a minimum error of 1.6% was found when radar respiratory peaks signals were directly compared with their reference, whereas a minimum mean absolute error of 0.3 RPM was obtained for the respiration rate. Concerning heartbeats, their expression in radar signals was not as clear as the respiration ones, however a minimum mean absolute error of 1.8 BPM for heartbeat was achieved after applying a novel selective algorithm developed to validate if heart rate value was estimated with reliability. The results proved the potential for radars to be used in respiratory and heartbeat contactless sensing, showing that the employed methods can be already used in some mo tionless situations. Notwithstanding, further work is required to improve the developed algorithms in order to obtain more robust and accurate systems.Atualmente, a maioria das técnicas usadas para a monitorização de sinais vitais em contexto médicos e/ou diário requer contacto direto com a pele, o que poderá tornar-se incómodo ou até mesmo inviável em certas situações. A tecnologia radar tem vindo a ser apontada como uma das mais promissoras ferramentas para medição de sinais vitais à distância e sem contacto. Todavia, são necessários mais estudos que permitam avaliar esta tecnologia quando aplicada a situações mais reais. Esta dissertação tem como objetivo o estudo da tecnologia radar aplicada no contexto de medição remota de sinais vitais, mais concretamente, na medição de atividade respiratória e cardíaca. Dois aparelhos radar, baseados em tecnologia banda ultra larga por rádio de impulso e em tecnologia de onda continua modulada por frequência, foram configurados e usados numa prova de conceito com 10 participantes. Cada sujeito foi monitorizado com cada um dos radar em duas situações distintas: respirando e em apneia voluntária. Algorit mos de processamento de sinal foram desenvolvidos para detetar e estimar parâmetros respiratórios e cardíacos, avaliados através de métodos qualitativos e quantitativos. Em relação à respiração, o menor erro obtido foi de 1,6% quando os sinais de radar respiratórios foram comparados diretamente com os sinais de referência, enquanto que, um erro médio absoluto mínimo de 0,3 RPM foi obtido para a estimação da frequência respiratória via radar. A expressão cardíaca nos sinais radar não se revelou tão evidente como a respiratória, no entanto, um erro médio absoluto mínimo de 1,8 BPM foi obtido para a estimação da frequência cardíaca após a aplicação de um novo algoritmo seletivo, desenvolvido para validar a confiança dos valores obtidos. Os resultados obtidos provaram o potencial do uso de radares na medição de atividade respiratória e cardíaca sem contacto, sendo esta tecnologia viável de ser implementada em situações onde não existe muito movimento. Não obstante, os algoritmos desenvolvidos devem ser aperfeiçoados no futuro de forma a obter sistemas mais robustos e precisos

Assessment of trends in the cardiovascular system from time interval measurements using physiological signals obtained at the limbs

Cardiovascular diseases are an increasing source of concern in modern societies due to their increasing prevalence and high impact on the lives of many people. Monitoring cardiovascular parameters in ambulatory scenarios is an emerging approach that can provide better medical access to patients while decreasing the costs associated to the treatment of these diseases. This work analyzes systems and methods to measure time intervals between the electrocardiogram (ECG), impedance plethysmogram (IPG), and the ballistocardiogram (BCG), which can be obtained at the limbs in ambulatory scenarios using simple and cost-effective systems, to assess cardiovascular intervals of interest, such as the pulse arrival time (PAT), pulse transit time (PTT), or the pre-ejection period (PEP). The first section of this thesis analyzes the impact of the signal acquisition system on the uncertainty in timing measurements in order to establish the design specifications for systems intended for that purpose. The minimal requirements found are not very demanding yet some common signal acquisition systems do not fulfill all of them while other capabilities typically found in signal acquisition systems could be downgraded without worsening the timing uncertainty. This section is also devoted to the design of systems intended for timing measurements in ambulatory scenarios according to the specifications previously established. The systems presented have evolved from the current state-of-the-art and are designed for adequate performance in timing measurements with a minimal number of active components. The second section is focused on the measurement of time intervals from the IPG measured from limb to limb, which is a signal that until now has only been used to monitor heart rate. A model to estimate the contributions to the time events in the measured waveform of the different body segments along the current path from geometrical properties of the large arteries is proposed, and the simulation under blood pressure changes suggests that the signal is sensitive to changes in proximal sites of the current path rather than in distal sites. Experimental results show that the PAT to the hand-to-hand IPG, which is obtained from a novel four-electrode handheld system, is correlated to changes in the PEP whereas the PAT to the foot-to-foot IPG shows good performance in assessing changes in the femoral PAT. Therefore, limb-to-limb IPG measurements significantly increase the number of time intervals of interest that can be measured at the limbs since the signals deliver information from proximal sites complementary to that of other measurements typically performed at distal sites. The next section is devoted to the measurement of time intervals that involve different waves of the BCG obtained in a standing platform and whose origin is still under discussion. From the relative timing of other physiological signals, it is hypothesized that the IJ interval of the BCG is sensitive to variations in the PTT. Experimental results show that the BCG I wave is a better surrogate of the cardiac ejection time than the widely-used J wave, which is also supported by the good correlation found between the IJ interval and the aortic PTT. Finally, the novel time interval from the BCG I wave to the foot of the IPG measured between feet, which can be obtained from the same bathroom scale than the BCG, shows good performance in assessing the aortic PAT. The results presented reinforce the role of the BCG as a tool for ambulatory monitoring since the main time intervals targeted in this thesis can be obtained from the timing of its waves. Even though the methods described were tested in a small group of subjects, the results presented in this work show the feasibility and potential of several time interval measurements between the proposed signals that can be performed in ambulatory scenarios, provided the systems intended for that purpose fulfill some minimal design requirements.Les malalties cardiovasculars són una tema de preocupació creixent en societats modernes, degut a l’augment de la seva prevalença i l'elevat impacte en les vides dels pacients que les sofreixen. La mesura i monitoratge de paràmetres cardiovasculars en entorns ambulatoris és una pràctica emergent que facilita l’accés als serveis mèdics i permet reduir dràsticament els costos associats al tractament d'aquestes malalties. En aquest treball s’analitzen sistemes i mètodes per la mesura d’intervals temporals entre l’electrocardiograma (ECG), el pletismograma d’impedància (IPG) i el balistocardiograma (BCG), que es poden obtenir de les extremitats i en entorns ambulatoris a partir de sistemes de baix cost, per tal d’avaluar intervals cardiovasculars d’interès com el pulse arrival time (PAT), pulse transit time (PTT) o el pre-ejection period (PEP). En la primera secció d'aquesta tesi s’analitza l’impacte del sistema d’adquisició del senyal en la incertesa de mesures temporals, per tal d’establir els requeriments mínims que s’han de complir en entorns ambulatoris. Tot i que els valors obtinguts de l’anàlisi no són especialment exigents, alguns no són assolits en diversos sistemes habitualment utilitzats mentre que altres solen estar sobredimensionats i es podrien degradar sense augmentar la incertesa en mesures temporals. Aquesta secció també inclou el disseny i proposta de sistemes per la mesura d’intervals en entorns ambulatoris d’acord amb les especificacions anteriorment establertes, a partir de l’estat de l’art i amb l’objectiu de garantir un correcte funcionament en entorns ambulatoris amb un nombre mínim d’elements actius per reduir el cost i el consum. La segona secció es centra en la mesura d’intervals temporals a partir de l’IPG mesurat entre extremitats, que fins al moment només s’ha fet servir per mesurar el ritme cardíac. Es proposa un model per estimar la contribució de cada segment arterial per on circula el corrent a la forma d’ona obtinguda a partir de la geometria i propietats físiques de les artèries, i les simulacions suggereixen que la senyal entre extremitats és més sensible a canvis en arteries proximals que en distals. Els resultats experimentals mostren que el PAT al hand-to-hand IPG, obtingut a partir d’un innovador sistema handheld de quatre elèctrodes, està fortament correlacionat amb els canvis de PEP, mentre que el PAT al foot-to-foot IPG està correlat amb els canvis en PAT femoral. Conseqüentment, l’ILG entre extremitats augmenta de manera significativa els intervals d’interès que es poden obtenir en extremitats degut a que proporciona informació complementària a les mesures que habitualment s’hi realitzen. La tercera secció està dedicada a la mesura d’intervals que inclouen les ones del BCG vertical obtingut en plataformes, de les que encara se’n discuteix l’origen. A partir de la posició temporal relativa respecte altres ones fisiològiques, s’hipostatitza que l’interval IJ del BCG es sensible a variacions del PTT. Els resultats experimentals mostren que la ona I del BCG és un millor indicador de l’ejecció cardíaca que el pic J, tot i que aquest és el més utilitzat habitualment, degut a la bona correlació entre l’interval IJ i el PTT aòrtic. Finalment, es presenta un mètode alternatiu per la mesura del PTT aòrtic a partir de l’interval entre el pic I del BCG i el peu del foot-to-foot IPG, que es pot obtenir de la mateixa plataforma que el BCG i incrementa la robustesa de la mesura. Els resultats presentats reforcen el paper del BCG com a en mesures en entorns ambulatoris, ja que els principals intervals objectiu d’aquesta tesi es poden obtenir a partir de les seves ones. Tot i que els mètodes descrits han estat provats en grups petits de subjectes saludables, els resultats mostren la viabilitat i el potencial de diversos intervals temporals entre les senyals proposades que poden ésser realitzats en entorns ambulatoris, sempre que els sistemes emprats compleixin els requisits mínims de disseny.Postprint (published version

Synchronisation of vascular ultrasonic scans with heart activity using ECG signals

Diagnosis, monitoring and curing of various vascular abnormalities can be linked to measurements of wall thicknesses of blood vessels. However, use of echo ultrasonic signals for these measurement is complicated by the low level of reflections from the vessels (1-2% from the incident energy), which results in considerable noise. Since the changes in thickness to be monitored are very small, this requires operation of ultrasonic scanners at high sampling frequencies, much higher than 50–100 MHz sampling frequencies that are used by contemporary ultrasonic scanners. That is because the resolution of the measured thickness is dependent on the time domain resolution of the recorded echoes; the latter is determined by the sampling frequency. An additional issue is the variability in the blood vessel wall thickness depending on the phase of the heart activity. Several studies show that these variations with a cycle time of around one second result in the same changes as building atherosclerosis for one year. The objective of the study was to develop an instrument that would allows recording of ultrasonic A-scans that are synchronised with the heart activity and that would allow improved accuracy of wall thickness measurements. Using an electronics point of view, the objective was met by the simulation, construction, programming and testing of an ECG monitor that triggers ultrasonic scans. The FPGA design of an existing high accuracy ultrasonic A-mode scanner was modified to allow interfacing of this monitor. Ultrasonic scans were taken with different transducers and transducer attachments (“shoes”) using various settings of the scanner. The scans were then analysed using dedicated Matlab programs. Overall, the design proved to be successful – it allowed repeatable records to be obtained at the same stage of heart activity. However, reliable and unambiguous detection of the artery walls (especially the back wall) was achieved only sporadically within the time available for in vivo experiments

Synchronisation of vascular ultrasonic scans with heart activity using ECG signals

Diagnosis, monitoring and curing of various vascular abnormalities can be linked to measurements of wall thicknesses of blood vessels. However, use of echo ultrasonic signals for these measurement is complicated by the low level of reflections from the vessels (1-2% from the incident energy), which results in considerable noise. Since the changes in thickness to be monitored are very small, this requires operation of ultrasonic scanners at high sampling frequencies, much higher than 50–100 MHz sampling frequencies that are used by contemporary ultrasonic scanners. That is because the resolution of the measured thickness is dependent on the time domain resolution of the recorded echoes; the latter is determined by the sampling frequency. An additional issue is the variability in the blood vessel wall thickness depending on the phase of the heart activity. Several studies show that these variations with a cycle time of around one second result in the same changes as building atherosclerosis for one year. The objective of the study was to develop an instrument that would allows recording of ultrasonic A-scans that are synchronised with the heart activity and that would allow improved accuracy of wall thickness measurements. Using an electronics point of view, the objective was met by the simulation, construction, programming and testing of an ECG monitor that triggers ultrasonic scans. The FPGA design of an existing high accuracy ultrasonic A-mode scanner was modified to allow interfacing of this monitor. Ultrasonic scans were taken with different transducers and transducer attachments (“shoes”) using various settings of the scanner. The scans were then analysed using dedicated Matlab programs. Overall, the design proved to be successful – it allowed repeatable records to be obtained at the same stage of heart activity. However, reliable and unambiguous detection of the artery walls (especially the back wall) was achieved only sporadically within the time available for in vivo experiments

Development of a real-time high-resolution 3D ultrasound imaging system

In this work a real-time high-resolution 3D ultrasound imaging system is developed, allowing the 3D acquisition and imaging of high-resolution ultrasound data for biomedical applications. The system uses ultrasound transducers in the ranges of 30 to 100 MHz, and allows full access of the radiofrequency (RF) ultrasound data for the 3D image reconstruction. This work includes the development of two graphical user interfaces in C++ to interact with a high-resolution ultrasound system and to image the high-resolution ultrasound data. In addition, a methodology is described and implemented in the system for 3D ultrasound reconstruction and visualization. The development of these GUIs allows easy 3D high-resolution ultrasound acquisition and imaging to any user with basic knowledge in ultrasound and with only minimal and faster training in the system and the GUIs. This capability opens the system to any researcher or person interested in performing experimentations with high-resolution ultrasound.;The high-resolution 3D ultrasound imaging system is tested to assess atherosclerosis using different mouse models. To assess atherosclerosis, a series of in vitro studies are performed to 3D scan vessels of mouse aortas and carotids vessels with atherosclerosis, as well as mouse hearts with atherosclerosis. The apolipoprotein E-knockout (APOE) and the apolipoprotein E-A1 adenosine receptor double knockout (DKO) mice model with their wild type control (C57) are used. Three-dimensional reconstructions were rendered showing good matches with the samples morphology. In addition, 3D sections of the data are reconstructed showing atherosclerotic plaque in the samples. The 3D ultrasound reconstruction allows for us to analyze a sample from outside and inside by rotating around any angle and cropping non-relevant data, allowing us to observe shape and appearance of the 3D structures. Finally, after reconstructing and analyzing the 3D ultrasound images, a 3D quantitative assessment of atherosclerotic plaque is performed. After analyzing the samples, the plaque lesions of DKO mouse model exhibits smaller areas than those of the APOE mouse model. Additionally, the C57 mouse model is clean of any atherosclerosis. These findings are in agreement with a previous study of our group for these mouse models