Ramon Casanella

Ballistocardiography and Seismocardiography: A Review of Recent Advances

In the past decade, there has been a resurgence in the field of unobtrusive cardiomechanical assessment, through advancing methods for measuring and interpreting ballistocardiogram (BCG) and seismocardiogram (SCG) signals. Novel instrumentation solutions have enabled BCG and SCG measurement outside of clinical settings, in the home, in the field, and even in microgravity. Customized signal processing algorithms have led to reduced measurement noise, clinically relevant feature extraction, and signal modeling. Finally, human subjects physiology studies have been conducted using these novel instruments and signal processing tools with promising results. This paper reviews the recent advances in these areas of modern BCG and SCG research.

A Fast and Easy-to-Use ECG Acquisition and Heart Rate Monitoring System Using a Wireless Steering Wheel

This work presents a novel easy-to-use system intended for the fast and noninvasive monitoring of the Lead I electrocardiogram (ECG) signal by using a wireless steering wheel. The system uses a dual ground electrode configuration connected to a low-power analog front-end to reduce 50/60 Hz interference and it is able to show a stable ECG signal with good enough quality for monitoring purposes in less than 5 s. A novel heart rate detection algorithm based on the continuous wavelet transform has been implemented, which is specially designed to be robust against the most common sources of noise and interference present when acquiring the ECG in the hands, i.e., electromyographic (EMG) noise and baseline wandering. The algorithm shows acceptable performance even under non-ordinary high levels of EMG noise and yields a positive predictivity value of 100.00% and a sensitivity of 99.75% when tested in normal use with subjects of different age, gender, and physical condition.

Oil-Water Interface Level Sensor Based on an Electrode Array

A novel liquid interface level sensor is presented that is able to determine the position of the interface between a conductive and an insulating liquid. The sensor consists of an array of equally spaced electrodes, two of which are used to inject a current into the conductive liquid and the remaining electrodes are used to measure the drop in voltage across the conductive medium. An inverse problem algorithm of the Levenberg-Marquardt type is used to adjust a theoretical model of the system to the experimental data. This procedure allows us to determine the position of the interface between two liquid layers with a resolution and accuracy better than the electrode spacing without using any previous calibration procedure. Measurements performed with a prototype electrode array with 5 cm interelectrode spacing, achieved a 1 cm accuracy and 0.3 cm resolution in determining the oil-water interface position in a cylindrical tank

Pulse arrival time estimation from the impedance plethysmogram obtained with a handheld device

This paper describes a novel method to estimate pulse arrival time (PAT) from the electrocardiogram (ECG) and the impedance plethysmogram (TPG) obtained by using a compact and easy-to-use handheld device with only four electrodes. A proof-of-concept has been carried out where PAT values obtained with the proposed device have been compared to PAT values measured between the ECG and the photoplethysmogram (PPG) during three experiments of paced respiration to induce controlled PAT changes. The results show that both methods yield equivalent PAT values in within ± 7 ms (95 % confidence interval), which is less than typical deviations reported for common PAT measurements.

Heart and respiratory rate detection on a bathroom scale based on the ballistocardiogram and the continuous wavelet transform

Ballistocardiography is a non-invasive technique that yields information about the cardiovascular system that is not available in other external signals such as the electrocardiogram (ECG). In the last years, several research groups have obtained the ballistocardiogram (BCG) by using instrumentation methods simpler than those available in the 1950s and that did not progress because of their complexity as compared to ultrasound and other noninvasive techniques that are in common use nowadays. We describe a novel method for real-time robust heart- (HR) and respiratory- (RR) rate detection from a subject that stands on a common electronic bathroom scale. BCG signals from the scale are wirelessly sent to a PC where algorithms based on the continuous wavelet transform (CWT) extract the HR and the RR. HR results are compared to those obtained from the ECG. To better assess the RR results, subjects have been asked to synchronize their breathing rate to an on-screen bar-graph set at a constant rate of breaths per minute. This method to obtain the heart and respiratory rates is simple, compact, non-invasive and passive, and can be applied to any person able to stand on an electronic weighing scale, even if wearing shoes.

Differential synchronous demodulator for modulating sensors and impedance measurements

This paper describes a novel differential synchronous demodulator intended for signal conditioning in modulating sensors and impedance measurements. The circuit proposed merges the demodulating and low-pass filtering stages in a single integrator stage and yields, for differential measurements, the performance quality inherent to coherent demodulation, with the added advantages of compactness and low cost. We analyse the theoretical limits of the relevant performance parameters, such as the common mode rejection ratio (CMRR), signal-to-noise ratio (SNR), linearity and quadrature rejection. Our experimental results validate the theoretical predictions. In the range from 1 kHz to 50 kHz, the CMRR, which does not depend on matching integrating capacitors, exceeds 65 dB for unity differential gain, and the SNR exceeds 90 dB.

Continuous liquid level measurement using a linear electrode array

This paper describes a novel continuous liquid level measurement technique based on a linear electrode array, which is vertically immersed in the liquid to inject an electric current into it and measure the voltage profile at different depths. We develop models that describe the relationship between voltage and liquid level for several vessel geometries of practical interest. Then, an inverse problem iterative algorithm is used to calculate the liquid level from the set of voltage measurements. The level accuracy values are far smaller than the interelectrode spacing and no calibration procedure is required. We describe a prototype measurement system to measure the water level in a 100 cm deep rectangular tank with a level accuracy of 3 mm when the electrodes are 5 cm apart.

Synchronous Demodulator for Autonomous Sensors

A novel differential synchronous demodulator is presented that uses the on-off switching characteristic of the power supply in autonomous systems as control signal for demodulation. The proposed circuit, which uses a single op amp and SPDT switch, can be useful in sensors networks or distributed data acquisition systems involving ac sensors or impedance measurements. A prototype demodulator yields a nonlinearity of 0.8% FSR and CMRR = 47 dB at 15 kHz for unity gain. The feasibility of the circuit when supplied by a piezoelectric energy converter is also verified.

Multi-signal bathroom scale to assess long-term trends in cardiovascular parameters

This paper describes the circuits and signal processing techniques that convert an electronic bathroom scale intended for bioimpedance analysis (BIA) into a compact system to acquire the electrocardiogram (ECG), the ballistocardiogram (BCG), and the impedance plethysmogram (IPG) using only plantar measurements. The signal processing methods proposed rely on the higher quality of the IPG as compared to the ECG and BCG and they enhance the signal-to-noise ratio (SNR) of these two signals, which otherwise could be too poor in non-controlled environments. The system is suitable for long-term periodic monitoring of cardiovascular function.

Can driven-right-leg circuits increase interference in ECG amplifiers?

The Driven-Right-Leg (DRL) circuit has been used for about 50 years to reduce interference due to common-mode voltage in biopotential amplifiers in scenarios that range from fixed equipment supplied from power lines to battery-supplied ambulatory monitors, and for systems that use gelled, dry, textile, and capacitive electrodes. However, power-line interference models predict that for isolation amplifiers, currently mandated by safety standards, power-line interference can often couple mostly in differential mode rather than in common mode. In this work we analyze the effect of the DRL circuit in different ECG leads to elucidate its actual effect on power-line interference reduction. It turns out that that the DRL circuit, which effectively reduces common-mode interference, affects differential-mode interference in an unpredictable way and can increase interference.