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

Remotely Powered Two-Wire Cooperative Sensors for Biopotential Imaging Wearables

Biopotential imaging (e.g., ECGi, EEGi, EMGi) processes multiple potential signals, each requiring an electrode applied to the body's skin. Conventional approaches based on individual wiring of each electrode are not suitable for wearable systems. Cooperative sensors solve the wiring problem since they consist of active (dry) electrodes connected by a two-wire parallel bus that can be implemented, for example, as a textile spacer with both sides made conductive. As a result, the cumbersome wiring of the classical star arrangement is replaced by a seamless solution. Previous work has shown that potential reference, current return, synchronization, and data transfer functions can all be implemented on a two-wire parallel bus while keeping the noise of the measured biopotentials within the limits specified by medical standards. We present the addition of the power supply function to the two-wire bus. Two approaches are discussed. One of them has been implemented with commercially available components and the other with an ASIC. Initial experimental results show that both approaches are feasible, but the ASIC approach better addresses medical safety concerns and offers other advantages, such as lower power consumption, more sensors on the two-wire bus, and smaller size.

Evaluation of a Wearable System for Fetal ECG Monitoring Using Cooperative Sensors

Fetal electrocardiography (fECG) has gotten widespread interest in the last years as technology for fetal monitoring. Compared to cardiotocography (CTG), the current state of the art, it can be designed in smaller formfactor and is thus suited for long-term and unsupervised monitoring. In the present study we evaluated a wearable system which is based on CSEM's cooperative sensors, a versatile technology that allows for the measurement of multiple biosignals and an easy integration into a garment or patch. The system was tested on 25 patients with singleton pregnancies and an age of gestation ≥ 37 weeks. To reject unreliable fetal heart rate (fHR) estimations, the signal processing algorithm provides a signal quality index. In 12 out of 21 patients available for analysis, a good performance of fHR estimations was obtained with a mean absolute error < 5 bpm and an acceptance rate >70%. However, the remaining 9 patients showed low acceptance rates and high errors. Besides investigating the source of these high errors, future work includes the investigating improved signal processing algorithms, different body positions and the use of dry electrodes. Clinical Relevance - The aim of this work is to develop a wearable system that can be offered in hospitals as an alternative to cardiotocography, or as a home monitoring tool for at risk fetuses, in the era of evolving telemedicine.

Spatial Ventilation Inhomogeneity Determined by Electrical Impedance Tomography in Patients With Chronic Obstructive Lung Disease

The aim of this study was to examine whether electrical impedance tomography (EIT) could determine the presence of ventilation inhomogeneity in patients with chronic obstructive lung disease (COPD) from measurements carried out not only during conventional forced full expiration maneuvers but also from forced inspiration maneuvers and quiet tidal breathing and whether the inhomogeneity levels were comparable among the phases and higher than in healthy subjects. EIT data were acquired in 52 patients with exacerbated COPD (11 women, 41 men, 68 ± 11 years) and 14 healthy subjects (6 women, 8 men, 38 ± 8 years). Regional lung function parameters of forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), forced inspiratory vital capacity (FIVC), forced inspiratory volume in 1 s (FIV₁), and tidal volume (V _T ) were determined in 912 image pixels. The spatial inhomogeneity of the pixel parameters was characterized by the coefficients of variation (CV) and the global inhomogeneity (GI) index. CV and GI values of pixel FVC, FEV₁, FIVC, FIV₁, and V_T were significantly higher in patients than in healthy subjects (p ≤ 0.0001). The ventilation distribution was affected by the analyzed lung function parameter in patients (CV: p = 0.0024, GI: p = 0.006) but not in healthy subjects. Receiver operating characteristic curves showed that CV and GI discriminated patients from healthy subjects with an area under the curve (AUC) of 0.835 and 0.852 (FVC), 0.845 and 0.867 (FEV₁), 0.903 and 0.903 (FIVC), 0.891 and 0.882 (FIV₁), and 0.821 and 0.843 (V_T), respectively. These findings confirm the ability of EIT to identify increased ventilation inhomogeneity in patients with COPD.

Intraoperative real-time stress in degenerative lumbar spine surgery: simultaneous analysis of electroencephalography signals and heart rate variability: a pilot study

BACKGROUND CONTEXT

Interest in intraoperative stress has increased due to its potentially detrimental impact on surgical performance and burnout among spine surgeons.

PURPOSE

The purpose of this study was to analyze intraoperative stress in real time in terms of electroencephalography signals and heart rate variability using a wearable device during spine surgery.

STUDY DESIGN

Prospective observational study.

PATIENT SAMPLE

Five orthopedic spine surgeons with experience ranging from 1 to 30 years were included.

OUTCOME MEASURES

The outcome measures included stress levels among the spine surgeons and differences in stress parameters between novice and expert surgeons and between assistants and operators.

METHODS

From June 2018 to November 2018, 179 consecutive records of intraoperative stress measures, including intraoperative electroencephalography signals and heart rate variability, comprising beats per minute (BPM) and low frequency/high frequency ratio, for the orthopedic spine surgeons were prospectively gathered, compared, and analyzed.

RESULTS

Among all measures, sensory-motor rhythm (SMR) waves, gamma waves, and BPM differed significantly during surgery (analysis of variance; p=.040, .013, .002, respectively). Surgery duration and intraoperative bleeding were positively correlated with stress parameters, including gamma waves and tension. For operators, surgeon experience was negatively correlated with concentration, tension, and SMR, gamma, M-beta, and H-beta waves (Pearson correlation, p<.05). However, for assistants, surgeon experience was positively correlated with concentration, tension, BPM, and SMR, M-beta, H-beta, and gamma waves. Bleeding amounts were correlated positively with gamma waves and tension for both operators and assistants (Pearson correlation, p<.05). Stress among operators was higher than that among assistants in terms of low frequency/high frequency ratio.

CONCLUSIONS

Operators and surgeons with low experience exhibited higher stress levels during surgery, which should be addressed when scheduling elective surgery to ensure optimal conditions among spine surgeons.

Two-Wire Bus Combining Full Duplex Body-Sensor Network and Multilead Biopotential Measurements

Classical approaches to make high-quality measurements of biopotential signals require the use of shielded or multiwire cables connecting the electrodes to a central unit in a star arrangement. As a consequence, increasing the number of leads increases cabling and connector complexity, which is not only limiting the patient comfort but is also anticipated as the main limiting factor to future miniaturization and cost reduction of tomorrow's wearables. We have recently introduced a novel sensing architecture that significantly reduces the cabling complexity by eliminating shielded or multiwire cables and by allowing simple connectors, thanks to a bus arrangement. In this architecture, electrodes are replaced by so-called cooperative sensors that require synchronous operation for systems larger than two sensors. This paper presents a novel full duplex body-sensor network based on a simple two-wire bus that combines biopotential measurements, synchronization, and gathering of data in a single cooperative sensor with a throughput up to 2 Mb/s. When compared to others, the suggested approach is advantageous as it keeps the cabling complexity at its minimum and does not require every sensor to be equipped with wireless communication capabilities. First experimental measurements demonstrated the reliability of the approach for a wearable 12-lead electrocardiogram monitoring system tested in real-life scenario.

Electromagnetic disturbances rejection with single skin contact in the context of ECG measurements with cooperative sensors

Classical approaches to make high-quality measurements of biopotential signals require the use of shielded or multi-wire cables connecting the electrodes to a central unit in a star arrangement. Consequently, increasing the number of leads increases cabling and connector complexity which is not only limiting patient comfort but also anticipated as the main limiting factor for future miniaturization and cost reduction of tomorrow's wearables. We have recently introduced a novel sensing architecture that significantly reduces cabling complexity by eliminating shielded or multi-wire cables as well as by allowing simple connectors thanks to a bus arrangement. In this architecture, electrodes are replaced by so-called cooperative sensors. However, in this design, one of the cooperative sensors needs to be equipped with two contacts with the skin for proper common mode rejection, thus making its miniaturization problematic. This paper presents a novel common mode rejection principle which overcomes this limitation. When compared to others, the suggested approach is advantageous as it keeps the cabling complexity to its minimum. First measurements demonstrated in a real-life scenario the feasibility of this common mode rejection principle for a wearable 12-lead electrocardiogram monitoring system.

Clinical validation of LTMS-S: A wearable system for vital signs monitoring

LTMS-S is a new wearable system for the monitoring of several physiological signals--including a two-lead electrocardiogram (ECG)--and parameters, such as the heart rate, the breathing rate, the peripheral oxygen saturation (SpO2), the core body temperature (CBT), and the physical activity. All signals are measured using only three sensors embedded within a vest. The sensors are standalone with their own rechargeable battery, memory, wireless communication and with an autonomy exceeding 24 hours. This paper presents the results of the clinical validation of the LTMS-S system.

Synchronization and communication of cooperative sensors

Cooperative sensors are an emerging technology consisting of autonomous sensor units working in concert to measure physiological signals requiring distant sensing points, such as biopotential (e.g., ECG) or bioimpedance (e.g., EIT). Their advantage with respect to the state-of-the-art technology is that they do not require shielded and even insulated cables to measure best quality biopotential or bioimpedance signals. Moreover, as all sensors are simply connected to a single electrical connection (which can be for instance a conductive vest) there is no connecting limitation to the miniaturization of the system or to its extension to large numbers of sensors. This results in an increase of wearability and comfort, as well as in a decrease of costs and integration challenges. However, cooperative sensors must communicate to be synchronized and to centralize the data. This paper presents possible communication strategies and focuses on the implementation of one of them that is particularly well suited for biopotential and bioimpedance measurements.