Sistema Vestible para la Detección Simultánea y No Invasiva del ECG y el Flujo Sanguíneo / Wearable System for Simultaneous and Noninvasive Detection of ECG and Blood Flow

Resumen Se desarrolló un sistema vestible para la detección simultánea y no invasiva de dos señales provenientes de la actividad cardiaca: el ECG y el flujo sanguíneo. Se utilizaron dos electrodos secos para detectar la derivación I del ECG. La detección del flujo sanguíneo se realizó de forma no invasiva mediante un sensor magnetorresistivo tipo Túnel (TMR) basándose en la firma magnética de la sangre sobre un campo magnético constante proveniente de un imán permanente. Los electrodos, el sensor TMR y el imán se montaron en un brazalete tipo pulsera para la comodidad del usuario. La instrumentación desarrollada para detectar el ECG y el flujo sanguíneo se diseñó en base a una configuración diferencial con una relación de rechazo en modo común superior a 87 dB a 60 Hz y con una tensión de ruido de tal forma que las señales cardiacas presentaron una relación señal a ruido superior a 41 dB, siempre y cuando el sujeto no se mueva durante la medida. La calidad de las señales fue suficiente como para extraer información de dichas señales mediante algoritmos sencillos de implementar. El sistema propuesto es una alternativa a los sistemas vestibles presentados hasta ahora, del cual es posible valorar la salud cardiovascular del sujeto en ambientes no hospitalarios.

Abstract A wearable system was developed for the simultaneous and non-invasive detection of two signals from cardiac activity: the ECG and blood flow. Two dry electrodes were used to detect the lead I of the ECG. The detection of blood flow was performed non-invasively using a tunnel-magnetoresistance (TMR) sensor based on the magnetic signature of the blood over a constant magnetic field from a permanent magnet. The electrodes, the TMR sensor and the magnet were mounted on a wristband-type bracelet for the user comfort. The instrumentation developed to detect the ECG and blood flow was designed based on a differential configuration with a common-mode rejection ratio higher than 87 dB at 60 Hz and with a noise voltage in such a way that the cardiac signals presented a signal-to-noise ratio greater than 41 dB, as long as the subject stays still during the measurement. The quality of the signals was enough to extract information from these signals by means of simple to implement algorithms. The proposed system is an alternative to the wearable systems presented so far, from which it is possible to assess the cardiovascular health of the subject in non-hospital environments.

Desarrollo de un Sistema con Potencial Aplicación de Fototerapia para Ictericia Neonatal / Design of a System with a Potential Application to Neonatal Jaundice Phototherapy

RESUMEN En este proyecto se diseñó y construyó un prototipo con potencial aplicación a un sistema de fototerapia para ictericia neonatal utilizando por primera vez LEDs de 10 W de alta potencia. Se describe la metodología aplicada para el diseño de los diferentes circuitos electrónicos que se utilizaron para la alimentación de la corriente de excitación de los LEDs, se describe el método de control de corriente mediante el uso de la modulación por ancho de pulsos, Pulse Width Modulation (PWM, por sus siglas en inglés), generados por el circuito integrado 555. Se diseñó la placa de circuito impreso mediante la ayuda del simulador Orcad Layout. Se utilizaron dos LEDs de alta potencia de 10 W para el propósito de conservar la intensidad requerida para el tratamiento, minimizando el espacio utilizado por la cantidad de LEDs utilizados en los equipos convencionales. Entre las limitaciones que se presentaron en esta investigación fue el uso de la plataforma Arduino, ya que se tienen varias oportunidades de mejora para darle el mejor uso al microcontrolador, y de esta manera digitalizar el sistema de una forma más completa, reduciendo la circuitería de control. El prototipo presentado cumple con los requerimientos necesarios para un sistema de fototerapia.

ABSTRACT This project consisted in the design and construction of a prototype with potential application to a phototherapy system for neonatal jaundice using for the first-time high power 10 W LEDs. The methodology for the design of different electronic circuits which were used for feeding the drive current of the LEDs, the current control method described using pulse width modulation (PWM) generated by the known 555 integrated circuit is described. The printed circuit board was designed with the help of the Orcad Layout simulator. Two high-power 10 W LEDs were used for maintaining the intensity required for the treatment, minimizing the space used by the number of LEDs used in the conventional equipment. Among the limitations presented in this research was the use of the Arduino platform, due to several improve that can be used to improve and increase the use of this microcontroller, and in this way to digitize the system, reducing the circuitry of control. The prototype presented meets the requirements for a phototherapy system according to the different references used.

Respiratory Rate Detection by a Time-Based Measurement System / Detección de frecuencia respiratoria mediante un sistema de medida basado en el tiempo

Abstract: This paper proposes a system that converts a time-modulated signal from a resistive sensor into a digital signal with the goal to estimate the respiratory rate of a subject. To detect breathing, a known method based on a nasal thermistor, which detects temperature changes near the nostrils, is used. In this work, the thermistor mounted in a Wheatstone bridge, forms a RC circuit which is connected directly to a microcontroller, without using any analog circuit or analog-digital converter. Thus, whenever the subject breathes, it causes a fractional change in resistance x (∆R/R 0) on the thermistor, and this produces a time-modulated signal that is directly digitized with the microcontroller. Measurements were made on 23 volunteers, obtaining changes of x > 0.01. The temperature resolution was 0.2 °C, and the time response was 0.8 s, mainly limited by the thermistor properties; these features were enough to obtain a well-defined waveform of the breathing, from which was easy to estimate the respiratory rate by a compact, low cost and low power consumption system. Unlike interface circuits based on voltage or current amplitude, with this kind of interface, the self-heating of the sensor is avoided since the thermistor does not require any voltage or bias current.

Resumen: Este trabajo propone un sistema que convierte una señal modulada en tiempo, proveniente de un sensor resistivo, en una señal digital con el fin de estimar la frecuencia respiratoria de un sujeto. Para detectar la respiración se utilizó el método basado en un termistor nasal, el cual detecta los cambios de temperatura cerca de las fosas nasales. En este trabajo, el termistor, montado en un puente de Wheatstone, forma un circuito RC que se conecta directamente a un microcontrolador, sin necesidad de usar ningún circuito analógico, ni conversor analógico-digital. Así, cada vez que el sujeto respire, provoca un cambio fraccional de resistencia x (∆R/R 0) en el termistor, y esto produce una señal modulada en tiempo que se digitaliza directamente con el microcontrolador. Se hicieron medidas en 23 voluntarios, obteniendo cambios de x > 0.01. Se obtuvo una resolución en temperatura de 0.2 °C y un tiempo de respuesta de 0.8 s, limitado principalmente por las propiedades del termistor utilizado. Estas características demostraron ser suficientes para obtener una forma de onda de la respiración bien definida, de la cual es sencillo estimar la frecuencia respiratoria mediante un sistema compacto, de bajo costo y bajo consumo de energía. A diferencia de los circuitos de interfaz basado en la amplitud de tensión o corriente, con este tipo de interfaz se evita el autocalentamiento del sensor, ya que el termistor no requiere ningún voltaje o corriente de polarización.

Heart rate detection from an electronic weighing scale.

We propose a novel technique for beat-to-beat heart rate detection based on the ballistocardiographic (BCG) force signal from a subject standing on a common electronic weighing scale. The detection relies on sensing force variations related to the blood acceleration in the aorta, works even if wearing footwear and does not require any sensors attached to the body because it uses the load cells in the scale. We have devised an approach to estimate the sensitivity and frequency response of three commercial weighing scales to assess their capability to detect the BCG force signal. Static sensitivities ranged from 490 nV V(-1) N(-1) to 1670 nV V(-1) N(-1). The frequency response depended on the subject's mass but it was broad enough for heart rate estimation. We have designed an electronic pulse detection system based on off-the-shelf integrated circuits to sense heart-beat-related force variations of about 0.24 N. The signal-to-noise ratio of the main peaks of the force signal detected was higher than 30 dB. A Bland-Altman plot was used to compare the RR time intervals estimated from the ECG and BCG force signals for 17 volunteers. The error was +/-21 ms, which makes the proposed technique suitable for short-term monitoring of the heart rate.

Heart rate detection from an electronic weighing scale.

We propose a novel technique for heart rate detection on a subject that stands on a common electronic weighing scale. The detection relies on sensing force variations related to the blood acceleration in the aorta, works even if wearing footwear, and does not require any sensors attached to the body. We have applied our method to three different weighing scales, and estimated whether their sensitivity and frequency response suited heart rate detection. Scale sensitivities were from 490 nV/V/N to 1670 nV/V/N, all had an underdamped transient response and their dynamic gain error was below 19% at 10 Hz, which are acceptable values for heart rate estimation. We also designed a pulse detection system based on off-the-shelf integrated circuits, whose gain was about 70x10(3) and able to sense force variations about 240 mN. The signal-to-noise ratio (SNR) of the main peaks of the pulse signal detected was higher than 48 dB, which is large enough to estimate the heart rate by simple signal processing methods. To validate the method, the ECG and the force signal were simultaneously recorded on 12 volunteers. The maximal error obtained from heart rates determined from these two signals was +/-0.6 beats/minute.

Heart rate detection from plantar bioimpedance measurements.

The heart rate is a basic health indicator, useful in both clinical measurements and home health care. Current home care systems often require the attachment of electrodes or other sensors to the body, which can be cumbersome to the patient. Moreover, some measurements are sensitive to movement artifacts, are not user-friendly and require a specialized supervision. In this paper, a novel technique for heart rate measurement for a standing subject is proposed, which is based on plantar bioimpedance measurements, such as those performed by some bathroom weighting scales for body composition analysis. Because of the low level of heart-related impedance variations, the measurement system has a gain of 1400. We have implemented a fully differential AC amplifier with a common-mode rejection ratio (CMRR) of 105 dB at 10 kHz. Coherent demodulation based on synchronous sampling yields a signal-to-noise ratio (SNR) of 55 dB. The system has a sensitivity of 1.9 V/Omega. The technique has been demonstrated on 18 volunteers, whose bioimpedance signal and ECG were simultaneously measured to validate the results. The average cross-correlation coefficient between the heart rates determined from these two signals was 0.998 (std. dev. 0.001).

Gestión del conocimiento: una visión integradora del aprendizaje organizacional

Presenta como argumento la necesidad de concebir una gestión del conocimiento vinculada al aprendizaje organizacional como medio para asegurar la correcta asimilación de conocimientos claves indispensables para la agregación de valor y la construcción de ventajas competitivas sólidas.

A lower prevalence of atopy symptoms in children with type 1 diabetes mellitus.

BACKGROUND: The Th1/Th 2 concept is a model to understand the pathophysiology of certain diseases. Atopic diseases (asthma, eczema and hayfever) are characterized by a chronic inflammatory reaction that is dominated by Th 2 cells, and type 1 diabetes mellitus (DM) is Th1 cell dominated. Because it is known that Th1 and Th 2 cells reciprocally counteract each other, it can be speculated that the prevalence of Th 2-mediated disease is lower in patients with Th1-mediated disease. OBJECTIVE: To compare the prevalence of atopic diseases between children with DM and age-matched controls. METHODS: Parents of children with DM were requested by Dutch paediatricians to complete the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire on the prevalence of atopic diseases. A control group was derived from a Dutch cross-sectional survey (the ISAAC2 study). RESULTS: We received 555 completed questionnaires, which is estimated to be 25% of the total number of Dutch children with DM. The control group consisted of 777 children. After age-matching, the questionnaires of 188 DM patients were used. Symptoms of asthma, hayfever and eczema were reported less in the group of children with DM compared with the control group (wheeze last year, OR 0.796, 95% CI 0.408-1.554; hayfever symptoms last year, OR 0.642, 95% CI 0.369-1.118; eczema symptoms last year, OR 0.693, 95% CI 0.430-1.115). CONCLUSION: The lower prevalence of astma, hayfever and eczema symptoms in DM patients compared with age-matched controls, although not statistically significant, is consistent with the Th1/Th 2 concept.