Elsevier

Journal of Veterinary Behavior

Volume 17, January–February 2017, Pages 19-23
Journal of Veterinary Behavior

Equine Research
Validation of smart textile electrodes for electrocardiogram monitoring in free-moving horses

https://doi.org/10.1016/j.jveb.2016.10.001Get rights and content

Abstract

This article focuses on the validation of smart textile electrodes used to acquire electrocardiogram (ECG) signals in horses in a comfortable and robust manner. The performance of smart textile electrodes is compared with standard Ag/AgCl electrodes in terms of the percentage of motion artifacts (MAs, the noise that results from the movement of electrodes against the skin) and signal quality. Seven healthy Standardbred mares were equipped with 2 identical electronic systems for the simultaneous collection of ECGs. One system was equipped with smart textile electrodes, whereas the second was equipped with standard Ag/AgCl electrodes. Each horse was then monitored individually in a stall for 1 hour, without any movement constraints. The ECGs were visually examined by an expert who blindly labeled the ECG segments that had been corrupted by MAs. Finally, the percentage of MAs (MA%) was computed as the number of samples of the corrupted segments over the whole length of the signal. The total MA% was found to be lower for the smart textiles than for the Ag/AgCl electrodes. Consistent results were also obtained by investigating MAs over time. These results suggest that smart textile electrodes are more reliable when recording artifact-free ECGs in horses at rest. Thus, improving the acquisition of important physiological information related to the activity of the autonomic nervous system, such as heart rate variability, could help to provide reliable information on the mood and state of arousal of horses.

Introduction

In the last decade, several bioengineering solutions have been adopted to collect physiological parameters, aimed at improving human health and welfare. Wearable systems have met the growing demand for comfort, reliability, and robustness against signal noise (artifacts). Electrodes based on textile substrates have recently been identified as one of the most effective solutions. Although textile materials are not electrical conductors, smart textiles have been developed by combining conductive yarn (based on stainless steel fibers) with elastane, which is attached to the fabric during manufacturing (Lymberis and Paradiso, 2008). This technology has led to a smart textile, which combines the lightness and total noninvasiveness of a simple textile material with the characteristics of an electrical conductor, which is essential for acquiring biomedical parameters. In addition, this technology is easily integrated with miniaturized electronic devices. Wearable systems have thus overcome several issues related to continuous everyday monitoring in humans.

Smart textiles have also been hypothesized for use in several fields of equine sciences (McGreevy et al., 2014). For example, high electrocardiogram (ECG) signal quality has enabled important physiological information to be obtained during daily activities, through the analysis of physiological signals (Pacelli et al., 2006) such as heart rate variability to estimate the activity of the autonomic nervous system (Lanata et al., 2015a), and it has also been recognized as useful in horses (Lanata et al., 2015b).

Given their electrical and structural characteristics, textile electrodes are therefore suitable for use in horses where lightness and simplicity play an important role in preventing arousal and undesired reactions during scientific research and clinical monitoring (Lanata et al., 2015b). Such reactions should be prevented during ECG recordings in horses because they lead to a massive increase in motion artifacts (MAs).

Regarding horses, the ambulatory ECG at rest has a high diagnostic value for both continuous and occasional dysrhythmias and often requires monitoring in the stall (Verheyen et al., 2010). A high-quality ECG recording is therefore crucial in everyday clinical practice and is also important in sports medicine and exercise physiology. For example, problems related to MAs in equine ECGs are more important during exercise, when a good-quality ECG can provide information on poor performance and training (Reef et al., 2014). Notwithstanding the technical strategies (e.g., glue, adhesive bandages) and the reliability achieved by portable Holter devices (Verheyen et al., 2010), ECG-related MAs are a critical issue in resting and exercise horses (Reef et al., 2014, Young and van Loon, 2013).

ECG traces are often corrupted by MAs, which is the noise that results from the movement of electrodes against the skin. MAs are generated by the modification of the charge distribution at the interface between the skin and the electrode due to the skin stretch deformation (Webster, 1984). The skin can be seen as an electric current generator because it produces a potential difference between the inner and outer layers of the skin. Its stretching produces a temporary change in the half-cell potential which modifies the potentials involved and subsequently the recorded signal. This produces large-amplitude signals in the ECG waves (MAs) which may be misinterpreted by clinicians or automated systems, thus resulting in an alteration of the heart rate variability parameters. Many studies have attempted to reduce the effect of MAs by modifying the support and material involved (Tam and Webster, 1977) or by developing algorithms (Lanata et al., 2015b, Martini et al., 2010). For an overview of the signal–noise issues in human ECG, see Webster (2009).

Such problems become highly significant in animals in which body movement cannot be easily controlled. In fact, restraining horses while monitoring their cardiac activity is strongly discouraged because it leads to stress stimuli that increase the sympathetic contribution in heart control, with misleading ECGs even in rest conditions (Vitale et al., 2013). In terms of new biotechnologies, smart textile electrodes could provide a more comfortable and innovative solution for monitoring cardiac activity in horses under various conditions, thus helping to provide a better-quality ECG trace. We hypothesize that smart textile electrodes could be easily applied to horses and could lead to more reliable ECG recordings compared to commercial Ag/AgCl electrodes. The present work thus compares the ECG traces collected simultaneously from textile and Ag/AgCl electrodes in horses left free to move.

Section snippets

Animals and housing conditions

Seven healthy Standardbred mares (mean age, 8.4 ± 1.3 years) were enrolled in the study. They were housed in a paddock (75 × 75 m2) and were provided with ad libitum access to hay and water. The horses had been used as recipients in the embryo transfer program at the Department of Veterinary Sciences (University of Pisa, Italy), where this study was performed. The mares were in a healthy condition, and none of them was pregnant when the protocol was carried out.

Experimental protocol

Each horse was equipped with 2

Results

A statistical comparison of the MA% obtained by visual examination (Figure 4) revealed that the smart textile electrodes (median = 35.00, median absolute deviation = 2.63) reported a significantly lower percentage of MAs (Wilcoxon matched-pair signed-rank test, N = 7, W = 28, P = 0.0156) compared to the standard electrodes (median = 51.49, median absolute deviation = 3.60). The Friedman test also revealed that the smart textile electrodes showed a statistically significant (χ2 = 55.4, df = 1, P

Discussion

A visual inspection carried out by an expert in the field, blinded to the treatment condition of the horses, confirmed that the smart textile electrode solution outperformed the standard solution. The statistical analysis showed that the ECG signals acquired with the textile electrodes consistently had a lower percentage of corrupted ECGs over time. In fact, both MA% and the evaluation of the distribution of MAs over time highlighted the better performance of the textile electrodes.

Conclusions

The results of the analysis of the differences between standard Ag/AgCl and smart textile electrodes highlighted the higher robustness of the smart textile electrodes related to MAs. Such properties are crucial in the study of equine behavior and welfare but also in veterinary practice. A wearable system that can monitor heart activity (and parameters related to the autonomic nervous system) could also provide a new opportunity for research in horse–human interactions (Baragli et al., 2009) and

Acknowledgments

The authors thank Prof. Claudio Sighieri and Dr. Micaela Sgorbini for the horses and stable facilities. No institutional, private, and corporate financial support has been received for this research.

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