Olivier Chételat

Combination of body sensor networks and on-body signal processing algorithms: the practical case of MyHeart project

Smart clothes increase the efficiency of long-term non-invasive monitoring systems by facilitating the placement of sensors and increasing the number of measurement locations. Since the sensors are either garment-integrated or embedded in an unobtrusive way in the garment, the impact on the subjects comfort is minimized. However, the main challenge of smart clothing lies in the enhancement of signal quality and the management of the huge data volume resulting from the variable contact with the skin, movement artifacts, non-accurate location of sensors and the large number of acquired signals. This paper exposes the strategies and solutions adopted in the European 1ST project MyHeart to address these problems, from the definition of the body sensor network to the description of two embedded signal processing techniques performing on-body ECG enhancement and motion activity classification

Force and Torque Analytical Models of a Reaction Sphere Actuator Based on Spherical Harmonic Rotation and Decomposition

This paper presents an analytical model for the force and torque developed by a reaction sphere actuator for satellite attitude control. The reaction sphere is an innovative momentum exchange device consisting of a magnetic bearings spherical rotor that can be electronically accelerated in any direction making all the three axes of stabilized spacecrafts controllable by a unique device. The spherical actuator is composed of an 8-pole permanent magnet spherical rotor and of a 20-coil stator. Force and torque analytical models are derived by solving the Laplace equation and applying the Lorentz force law. The novelty consists in exploiting powerful properties of spherical harmonic functions under rotation to derive closed-form linear expressions of forces and torques for all possible orientations of the rotor. Specifically, the orientation of the rotor is parametrized using seven decomposition coefficients that can be determined noniteratively and in a linear fashion by measuring the radial component of the magnetic flux density from at least seven different locations. Therefore, force and torque models for all possible orientations of the rotor are expressed in closed form as linear combination of mutually orthogonal force and torque characteristic matrices, which are computed offline. The proposed analytical models are experimentally validated using a developed laboratory prototype.

Parametric estimation of pulse arrival time: a robust approach to pulse wave velocity

Pulse wave velocity (PWV) is a surrogate of arterial stiffness and represents a non-invasive marker of cardiovascular risk. The non-invasive measurement of PWV requires tracking the arrival time of pressure pulses recorded in vivo, commonly referred to as pulse arrival time (PAT). In the state of the art, PAT is estimated by identifying a characteristic point of the pressure pulse waveform. This paper demonstrates that for ambulatory scenarios, where signal-to-noise ratios are below 10 dB, the performance in terms of repeatability of PAT measurements through characteristic points identification degrades drastically. Hence, we introduce a novel family of PAT estimators based on the parametric modeling of the anacrotic phase of a pressure pulse. In particular, we propose a parametric PAT estimator (TANH) that depicts high correlation with the Complior(R) characteristic point D1 (CC = 0.99), increases noise robustness and reduces by a five-fold factor the number of heartbeats required to obtain reliable PAT measurements.

Chest Pulse-Wave Velocity: A Novel Approach to Assess Arterial Stiffness

Pulse-wave velocity (PWV) is considered as the gold-standard method to assess arterial stiffness, an independent predictor of cardiovascular morbidity and mortality. Current available devices that measure PWV need to be operated by skilled medical staff, thus, reducing the potential use of PWV in the ambulatory setting. In this paper, we present a new technique allowing continuous, unsupervised measurements of pulse transit times (PTT) in central arteries by means of a chest sensor. This technique relies on measuring the propagation time of pressure pulses from their genesis in the left ventricle to their later arrival at the cutaneous vasculature on the sternum. Combined thoracic impedance cardiography and phonocardiography are used to detect the opening of the aortic valve, from which a pre-ejection period (PEP) value is estimated. Multichannel reflective photoplethysmography at the sternum is used to detect the distal pulse-arrival time (PAT). A PTT value is then calculated as PTT = PAT - PEP. After optimizing the parameters of the chest PTT calculation algorithm on a nine-subject cohort, a prospective validation study involving 31 normo- and hypertensive subjects was performed. 1/chest PTT correlated very well with the COMPLIOR carotid to femoral PWV (r = 0.88, <; 10-9). Finally, an empirical method to map chest PTT values onto chest PWV values is explored.

SpO2 Sensor Embedded in a Finger Ring: design and implementation

A novel concept of Oxygen Saturation (SpO2) sensor embedded in a finger ring is presented in this paper. Due to the mechanical conception of the probe, the sensor fits any finger topology and assures a constant force applied to the phalanx. Ambient light artifacts are rejected at the analog electronics level. Finally, an innovative distribution of light sources and detectors and a dedicated signal processing procedure resolve the anatomical heterogeneity of different phalanx topologies, compensate low perfusion indexes due to the phalanx anatomy and estimates equivalent pulse oximetry SpO2 indexes. First in-vivo validation results of the novel sensor are discussed at the end of the paper

WELCOME — Innovative integrated care platform using wearable sensing and smart cloud computing for COPD patients with Comorbidities

We propose WELCOME, an innovative integrated care platform using wearable sensors and smart cloud computing for Chronic Obstructive Pulmonary Disease (COPD) patients with co-morbidities. WELCOME aims to bring about a change in the reactive nature of the management of chronic diseases and its comorbidities, in particular through the development of a patient centred and proactive approach to COPD management. The aim of WELCOME is to support healthcare services to give early detection of complications (potentially reducing hospitalisations) and the prevention and mitigation of comorbidities (Heart Failure, Diabetes, Anxiety and Depression). The system incorporates patient hub, where it interacts with the patient via a light vest including a large number of non-invasive chest sensors for monitoring various relevant parameters. In addition, interactive applications to monitor and manage diabetes, anxiety and lifestyle issues will be provided to the patient. Informal carers will also be supported in dealing with their patients. On the other hand, welcome smart cloud platform is the heart of the proposed system where all the medical records and the monitoring data are managed and processed via the decision support system. Healthcare professionals will be able to securely access the WELCOME applications to monitor and manage the patients conditions and respond to alerts on personalized level.

Cooperative dry-electrode sensors for multi-lead biopotential and bioimpedance monitoring.

Cooperative sensors is a novel measurement architecture that allows the acquiring of biopotential signals on patients in a comfortable and easy-to-integrate manner. The novel sensors are defined as cooperative in the sense that at least two of them work in concert to measure a target physiological signal, such as a multi-lead electrocardiogram or a thoracic bioimpedance.This paper starts by analysing the state-of-the-art methods to simultaneously measure biopotential and bioimpedance signals, and justifies why currently (1) passive electrodes require the use of shielded or double-shielded cables, and (2) active electrodes require the use of multi-wired cabled technologies, when aiming at high quality physiological measurements.In order to overcome the limitations of the state-of-the-art, a new method for biopotential and bioimpedance measurement using the cooperative sensor is then presented. The novel architecture allows the acquisition of the aforementioned biosignals without the need of shielded or multi-wire cables by splitting the electronics into separate electronic sensors comprising each of two electrodes, one for voltage measurement and one for current injection. The sensors are directly in contact with the skin and connected together by only one unshielded wire. This new configuration requires one power supply per sensor and all sensors need to be synchronized together to allow them to work in concert.After presenting the working principle of the cooperative sensor architecture, this paper reports first experimental results on the use of the technology when applied to measuring multi-lead ECG signals on patients. Measurements performed on a healthy patient demonstrate the feasibility of using this novel cooperative sensor architecture to measure biopotential signals and compliance with common mode rejection specification accordingly to international standard (IEC 60601-2-47) has also been assessed.By reducing the need of using complex wiring setups, and by eliminating the presence of central recording devices (cooperative sensors directly sense and store the measured biosignals on the site), the depicted novel technology is a candidate to a novel generation of highly-integrated, comfortable and reliable technologies that measure physiological signals in real-life scenarios.

Wearable PWV technologies to measure Blood Pressure: eliminating brachial cuffs

The clinical demand for technologies to monitor Blood Pressure (BP) in ambulatory scenarios with minimal use of inflation cuffs is strong: new generation of BP monitors are expected to be not only accurate, but also non-occlusive. In this paper we review recent advances on the use of the so-called Pulse Wave Velocity (PWV) technologies to estimate BP in a beat-by-beat basis. After introducing the working principle and underlying methodological limitations, two implementation examples are provided. Pilot studies have demonstrated that novel PWV-based BP monitors depict accuracy scores falling within the limits of the British Hypertensive Society (BHS) Grade A standard. The reported techniques pave the way towards ambulatory-compliant, continuous and non-occlusive BP monitoring devices, where the use of inflation cuffs is drastically reduced.

An open-loop control strategy of a reaction sphere for satellite attitude control

This paper presents an open-loop strategy for the control of the orientation of a reaction sphere actuator. The reaction sphere is a magnetic bearing spherical motor composed of an 8-pole permanent magnet spherical rotor and a 20-pole stator. The control law is based on a rotating magnetic field obtained from a sequence of desired rotor orientations. Hence, the reaction sphere can be accelerated about any desired axis. Force and torque inverse models are developed and employed to derive the control scheme. The proposed method is successfully employed to drive a reaction sphere laboratory prototype up to 480 rpm.

Continuous multi-parameter health monitoring system

A concept for continuous multi-parameter health monitoring system is presented. The system can measure and process physiological signals of high medical value, but difficult to measure in an unobtrusive and comfortable ambulatory way. Blood pressure, SpO2, core body temperature, activity, as well as multi-lead ECG and respiration with dry electrodes are addressed. There are only four interfaces with the body, and they are located at the chest. The European Space Agency has mandated CSEM to develop a prototype of its concept for a long-term survey at the Concordia Base Station in the Antarctica, in order to prepare future long-term manned missions. The delivery of the fully functional ready-touse prototype is for mid 2007. This paper outlines the general concept and presents some first experimental results for the SpO2 probe place at the manubrium sterni (upper sternum).