Pierre-Yves Gumery

Modelling Biological Gel Contraction by Cells: Mechanocellular Formulation and Cell Traction Force Quantification

Traction forces developed by most cell types play a significant role in the spatial organisation of biological tissues. However, due to the complexity of cell-extracellular matrix interactions, these forces are quantitatively difficult to estimate without explicitly considering cell properties and extracellular mechanical matrix responses. Recent experimental devices elaborated for measuring cell traction on extracellular matrix use cell deposits on a piece of gel placed between one fixed and one moving holder. We formulate here a mathematical model describing the dynamic behaviour of the cell-gel medium in such devices. This model is based on a mechanical force balance quantification of the gel visco-elastic response to the traction forces exerted by the diffusing cells. Thus, we theoretically analyzed and simulated the displacement of the free moving boundary of the system under various conditions for cells and gel concentrations. This modelis then used as the theoretical basis of an experimental device where endothelial cells are seeded on a rectangular biogel of fibrin cast between two floating holders, one fixed and the other linked to a force sensor. From a comparison of displacement of the gel moving boundary simulated by the model and the experimental data recorded from the moving holder displacement, the magnitude of the traction forces exerted by the endothelial cell on the fibrin gel was estimated for different experimental situations. Different analytical expressions for the cell traction term are proposed and the corresponding force quantifications are compared to the traction force measurements reported for various kind of cells with the use of similar or different experimental devices.

iBalance-ABF: A Smartphone-Based Audio-Biofeedback Balance System

This paper proposes an implementation of a Kalman filter, using inertial sensors of a smartphone, to estimate 3-D angulation of the trunk. The developed system monitors the trunk angular evolution during bipedal stance and helps the user to improve balance through a configurable and integrated auditory-biofeedback (ABF) loop. A proof-of-concept study was performed to assess the effectiveness of this so-called iBalance-ABF-smartphone-based audio-biofeedback system-in improving balance during bipedal standing. Results showed that young healthy individuals were able to efficiently use ABF on sagittal trunk tilt to improve their balance in the medial-lateral direction. These findings suggest that the iBalance-ABF system as a telerehabilitation system could represent a suitable solution for ambient assisted living technologies.

A model of mechanical interactions between heart and lungs

To study the mechanical interactions between heart, lungs and thorax, we propose a mathematical model combining a ventilatory neuromuscular model and a model of the cardiovascular system, as described by Smith et al. (Smith, Chase, Nokes, Shaw & Wake 2004 Med. Eng. Phys.26, 131–139. (doi:10.1016/j.medengphy.2003.10.001)). The respiratory model has been adapted from Thibault et al. (Thibault, Heyer, Benchetrit & Baconnier 2002 Acta Biotheor. 50, 269–279. (doi:10.1023/A:1022616701863)); using a Liénard oscillator, it allows the activity of the respiratory centres, the respiratory muscles and rib cage internal mechanics to be simulated. The minimal haemodynamic system model of Smith includes the heart, as well as the pulmonary and systemic circulation systems. These two modules interact mechanically by means of the pleural pressure, calculated in the mechanical respiratory system, and the intrathoracic blood volume, calculated in the cardiovascular model. The simulation by the proposed model provides results, first, close to experimental data, second, in agreement with the literature results and, finally, highlighting the presence of mechanical cardiorespiratory interactions.

Cardiogenic oscillations extraction in inductive plethysmography: Ensemble empirical mode decomposition

The purpose of this study is to investigate the potential of the ensemble empirical mode decomposition (EEMD) to extract cardiogenic oscillations from inductive plethysmography signals in order to measure cardiac stroke volume. First, a simple cardio-respiratory model is used to simulate cardiac, respiratory, and cardio-respiratory signals. Second, application of empirical mode decomposition (EMD) to simulated cardio-respiratory signals demonstrates that the mode mixing phenomenon affects the extraction performance and hence also the cardiac stroke volume measurement. Stroke volume is measured as the amplitude of extracted cardiogenic oscillations, and it is compared to the stroke volume of simulated cardiac activity. Finally, we show that the EEMD leads to mode mixing removal.

A multi-modal approach using a non-parametric model to extract fetal ECG

This study presents a non-parametric method to extract and separate maternal and fetal electrocardiogram (ECG) from an abdominal channel. The proposed method relies on the use of two additional reference signals related to the maternal and to the fetal ECGs. The fetal and maternal ECG contributions which exist in the abdominal channel are modeled from their respective references using a Gaussian process. Both of these signals are modeled considering a thoracic ECG reference, and an abdominal PCG reference, respectively for maternal ECG and fetal ECG. This general method provides a good behavior to extract fetal ECG as stated by the numerical experiments and shows that it can make use of 1-bit reference signals, which can be easier to record and more efficient to process.

A Wearable Technology Revisited for Cardio-Respiratory Functional Exploration: Stroke Volume Estimation from Respiratory Inductive Plethysmography

The objective of the present study is to extract new information from complex signals generated by Respiratory Inductive Plethysmography (RIP). This indirect cardio-respiratory (CR) measure is a well-known wearable solution. The authors applied time-scale analysis to estimate cardiac activity from thoracic volume variations, witnesses of CR interactions. Calibrated RIP signals gathered from 4 healthy volunteers in resting conditions are processed by Ensemble Empirical Mode Decomposition to extract cardiac volume signals and estimate stroke volumes. Averaged values of these stroke volumes (SVRIP) are compared with averaged values of stroke volumes determined simultaneously by electrical impedance cardiography (SVICG). There is a satisfactory correlation between SVRIP and SVICG (r=0.76, p

Modeling quasi-periodic signals by a non-parametric model: Application on fetal ECG extraction

Quasi-periodic signals can be modeled by their second order statistics as Gaussian process. This work presents a non-parametric method to model such signals. ECG, as a quasi-periodic signal, can also be modeled by such method which can help to extract the fetal ECG from the maternal ECG signal, using a single source abdominal channel. The prior information on the signal shape, and on the maternal and fetal RR interval, helps to better estimate the parameters while applying the Bayesian principles. The values of the parameters of the method, among which the R-peak instants, are accurately estimated using the Metropolis-Hastings algorithm. This estimation provides very precise values for the R-peaks, so that they can be located even between the existing time samples.

Rectus Abdominis ElectroMyoGraphy and MechanoMyoGraphy comparison for the detection of cough

We recently developed a novel active implant for the treatment of severe stress urinary incontinence. This innovative medical device has been developed with the main purpose of reducing the mean urethral occlusive pressure of the current prosthesis. This goal is achieved by detecting circumstances implying either high or low intra-abdominal pressures by a single 3-axis accelerometer. In fact, posture and activity of the patient are monitored in real time. We investigated in this study the possibility of detecting cough events (one of the main causes of urine loss in incontinent patient) by MechanoMyoGraphy (MMG) of the Rectus Abdominis (RA) using the same accelerometer. We compared MMG signal detection characteristics (burst onset times and RMS values) to the method of reference, the ElectroMyoGraphy (EMG). It is shown that detection of cough effort by MMG presents lower performances, mostly in terms of cough anticipation, than EMG detection. However, MMG still remains a good option for an implantable system comparing to implantable EMG disadvantages.

Array processing technique for the acquisition of surface EMG signals

The estimation and detection of surface EMG signals provides us with more detailed information on the functional state of a muscle, when measurement applied with smaller pickup areas. In fact the signal to noise ratio (SNR) of the observed EMG activity is proportional to the area of the pickup electrodes, and depends on the type of the muscle. The activity of small muscles is more difficult to sensed with small electrodes, that is why large surface electrodes are used, and in this case more physiological information lost. The estimation and detection of these signals can aid in the diagnosis of many pathological conditions after extracting some physiological parameters (e.g. median frequency). The relevance of these parameters estimated from the surface EMG signals, depends largely on the SNR. Our method is to use an array of small surface electrodes to capture the surface EMG activity. Two processing techniques based on the orthogonal projection principle were employed to enhance the SNR, one of them can be applied in real time processing.

Single cell volume measurement using a computer controlled patch-clamp electrode displacement

Using a hydraulic micromanipulator, the authors have developed a new instrument to pilot precisely the displacement of a patch-electrode via a PC. The aim of this instrument is to measure the changes of the height of a single cell in culture using the same equipment as for the patch-clamp technique.