7 research outputs found

    Photoplethysmographic logger with contact force and hydrostatic pressure monitoring

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    Dissertation submitted to the Faculty of Sciences and Technology of the University of Coimbra in partial fulfilment of the requirements for the MSc degree in Biomedical Engineering.Oxygen saturation (SpO2) is a key parameter for assessing a patient condition, mainly in critical care and anaesthesiology. Its fusion with other physiological measurements, such as pulse wave analysis or arterial blood pressure, may lead to new ways of detecting cardiovascular diseases. The current work aims to develop a stand-alone pulse oximeter and a photoplethysmographic (PPG) system with measurements of the contact force and height of the finger relatively to the heart. This module, together with other measurements (e.g. electrocardiogram and pulse wave velocity), will be part of a multichannel platform that will be taken to clinical environment. The project comprises the design of hardware for signal conditioning, as well as the development of firmware to implement in a microcontroller unit (the Arduino™). The latter is used to control the system, acquire data and compute SpO2, heart rate (HR), contact force and height. Currently, the system is able to retrieve a stable PPG waveform and compute the SPO2 in real time through the PPG signal peaks and valleys. Signals acquired in a healthy subject lead to a value of SPO2 = 91.5 ± 1.1%. Moreover, the subject arm and forearm orientation is retrieved by the use of accelerometers and used to compute the offset of the finger relatively to the heart. Contact force between the finger and the probe is also measured.A saturação de oxigénio (SpO2) é um parâmetro indispensável para avaliar a condição de um paciente, principalmente em cuidados intensivos e em anestesiologia. A sua fusão com outras medidas fisiológicas, como a análise da onda de pulso ou a pressão arterial, poderá levar a novas formas de detectar doenças cardiovasculares. O presente trabalho pretende desenvolver um oxímetro de pulso automático e um sistema de fotopletismografia (PPG) com medição da força de contacto e da altura do dedo em relação ao coração. Este módulo, juntamente com outras medidas (e.g. electrocardiograma e velocidade da onda de pulso), fará parte de uma plataforma multicanal que será levada para ambiente clínico. O projecto inclui o design do hardware para condicionamento de sinal, bem como o desenvolvimento do firmware a implementar num microcontrolador (o Arduino™). Este é usado para controlar o sistema, adquirir dados e calcular a SpO2, o ritmo cardíaco (HR), a força de contacto e a altura. Actualmente, o sistema é capaz de adquirir uma onda de PPG estável e de calcular a SpO2 em tempo real através dos picos e vales do sinal de PPG. Sinais adquiridos em sujeitos saudáveis levaram a um valor de SPO2 = 91.5 ± 1.1%. Além disso, a orientação do braço e antebraço do sujeito é estimada através do uso de acelerómetros e usada para calcular o desnível do dedo em relação ao coração. A força de contacto entre o dedo e a ponta de prova é igualmente medida.This work is funded by FEDER, through the Programa Operacional Factores de Competitividade – COMPETE – and by National funds through FCT – Fundação para a Ciência e Tecnologia – in the frame of ―Centro de Instrumentação” – Unidade 217

    Natural shear wave imaging in the human heart: normal values, feasibility and reproducibility

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    Left ventricular myocardial stiffness could offer superior quantification of cardiac systolic and diastolic function when compared to the current diagnostic tools. Shear wave elastography in combination with acoustic radiation force has been widely proposed to non-invasively assess tissue stiffness. Interestingly, shear waves can also result from intrinsic cardiac mechanical events (e.g., closure of valves) without the need for external excitation. However, it remains unknown whether these natural shear waves always occur, how reproducible they can be detected and what the normal range of shear wave propagation speed is. The present study therefore aimed at establishing the feasibility of detecting shear waves created after mitral valve closure (MVC) and aortic valve closure (AVC), the variability of the measurements, and at reporting the normal values of propagation velocity. Hereto, a group of 30 healthy volunteers was scanned with high frame rate imaging (>1000 Hz) using an experimental ultrasound system transmitting a diverging wave sequence. Tissue Doppler velocity and acceleration were used to create septal color M-modes, on which the shear waves were tracked and their velocities measured. Overall the methodology was capable of detecting the transient vibrations that spread throughout the intraventricular septum in response to the closure of the cardiac valves in 92% of the recordings. Reference velocities of 3.2±0.6 m/s at MVC and 3.5±0.6 m/s at AVC were obtained. Moreover, in order to show the diagnostic potential of this approach, 2 patients (one with cardiac amyloidosis and one undergoing a dobutamine stress echocardiography) were scanned with the same protocol and showed markedly higher propagation speeds: the former presented velocities of 6.6 m/s and 5.6 m/s; the latter revealed normal propagation velocities at baseline, and largely increased during the dobutamine infusion (>15 m/s). Both cases showed values consistent with the expected changes in stiffness and cardiac loading conditions.status: accepte

    Velocities of naturally occurring myocardial shear waves increase with age and in cardiac amyloidosis

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    OBJECTIVES: This study sought to evaluate whether velocity of naturally occurring myocardial shear waves (SW) could relate to myocardial stiffness (MS) in vivo. BACKGROUND: Cardiac SW imaging has been proposed as a noninvasive tool to assess MS. SWs occur after mechanical excitation of the myocardium (e.g., mitral valve closure [MVC] and aortic valve closure [AVC]), and their propagation velocity is theoretically related to MS, thus providing an opportunity to assess stiffness at end-diastole (ED) and end-systole. However, given that SW propagation in vivo is complex, it remains unclear whether natural SW velocity effectively relates to MS. METHODS: This study prospectively enrolled 50 healthy volunteers (HV) (43.7 ± 17.1 years of age) and 18 patients with cardiac amyloidosis (CA) (68.0 ± 9.8 years of age). HV were divided into 3 age groups: group I, 20 to 39 years of age (n = 24); group II, 40 to 59 years of age (n = 11); and group III, 60 to 80 years of age (n = 15). Parasternal long-axis views were acquired using an experimental scanner. Tissue (Doppler) acceleration maps were extracted from an anatomical M-mode along the midline of the left ventricular septum. RESULTS: SW propagation velocity was significantly higher in CA patients than in HV after both MVC (3.54 ± 0.93 m/s vs. 6.33 ± 1.63 m/s, respectively; p < 0.001) and AVC (3.75 ± 0.76 m/s vs. 5.63 ± 1.13 m/s, respectively; p < 0.001). Similarly, SW propagation velocity differed significantly among age groups in HV, with a significantly higher value for group III than for group I, both occurring after MVC (p < 0.001) and AVC (p < 0.01). Moreover, SW propagation velocity after MVC was found to be significantly higher in patients with an increasing grade of diastolic dysfunction (p < 0.001). Finally, positive correlation was found between SW velocities after MVC and mitral inflow-to-mitral relaxation velocity ratio (E/E') (r = 0.74; p = 0.002). CONCLUSIONS: End-diastole SW velocities were significantly higher in patients with CA, patients with a higher grade of diastolic dysfunction, and elderly volunteers. These findings thus suggest that the speed of naturally induced SWs may be related to MS.status: accepte
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