ECG measurements: "Our chest strap moistens itself"

Interview with Michel Schmid and Dr. Simon Annaheim, Swiss Federal Laboratories for Materials Science and Technology (German: Eidgenössische Materialprüfungs- und Forschungsanstalt), EMPA


Photo: Michael Schmid (left) and Dr. Simon Annaheim (right)

Michael Schmid (left) and Dr. Simon Annaheim (right); © EMPA

When measuring myocardial activity, it is important for the skin to always stay moist under the electrodes of the ECG. Only then can data be consistently transferred. Athletes have an easier time with this: they are used to sweating. This is a lot harder for older patients.

Scientists at the Swiss Federal Laboratories for Materials Science and Technology, EMPA, have now developed a chest strap ECG-monitor that is self-moistening and thus enables a continuous data transfer. At, Michel Schmid and Dr. Simon Annaheim talk about the many possibilities of this technology.

Mr. Schmid, how exactly does the chest strap work?

Michel Schmid
: Our chest strap offers an alternative to the gold standard of ECG measurements, the gel electrode. This conventional gel electrode cannot be worn over an extended period of time. The electrodes can cause skin irritation after several days and need to subsequently be affixed to another skin area. What’s more, the electrodes need to be connected with cables, which can be annoying. To enable an ECG recording in a continuous fashion with a dry electrode such as the conventional chest strap heart rate monitors, the contact area between skin and electrode needs to be moistened. Otherwise, the signal is disturbed by artifacts.

Our chest strap ECG-monitor is a textile solution and offers improved wearing comfort. It is also self-moistening so that you also obtain great signals for patients without the need for sweat. We developed flexible wetting elements for this, based on membranes that are permeable to water vapor. This wetting element is filled with 30 milliliters of water and continuously releases one to two grams of water vapor. This amount is so small to where the wearer does not notice it. This improves signal transmission. What’s more, we are all used to wearing textile clothing, which is why a textile solution suggests itself for ECG measurements.

Photo: ECG-Monitor

Each chest strap contains two of the specially prepared sensor pads which are connected directly to a data logger; © EMPA

Chest straps that measure heart rates are already being used by athletes…

Simon Annaheim
: Our textile chest strap is based on this technology. Measurements with this type of chest strap are possible with athletes because the electrodes are continuously moistened with their sweat. Thanks to the artificial moisturization, we are now also able to conduct long-term measurements without any special physical exertion. Operating the chest strap is also simple to where the user doesn’t need any help from medical staff.

What materials did you use during the chest strap development?

: We embroidered two electroconductive areas into our chest strap, which make up the electrodes. The electrodes are made of one yarn, a PET fiber of 50-µm diameter, which we layered with a 100-nanometer silver coating using a plasma coating machine. The chest strap also needs to pass the so-called cytotoxicity test for medical applications. This is why we applied an additional thin titanium layer measuring four to seven nanometers on top of the silver coating. When the titanium layer comes in touch with the air, it forms an ultra-thin titanium dioxide layer from which we are able to reduce the silver release. In doing so, the cytotoxicity test requirements are being met and the electrode can be worn on the skin for an extended period of time.

Mr. Annaheim, you oversee the chest strap development from the medical application side. For which exams is the chest strap particularly well suited?

: The chest strap is suited to measure the heart rate as well as heart rate variability. It indicates the variation in time intervals between two heartbeats. A lower variability indicates high strain on the heart and thus an increased risk of heart attack. Our chest strap allows patients to not only measure this variability, but also to conduct further assessments on the sympathetic and parasympathetic activity of the autonomic nervous system in peace. Thanks to the strap’s easy use, this can also be done at home.

Photo: ECG monitor
Grafic: Function diagram
Photo: ECG monitor

What other types of patients could this technology benefit?

: This chest strap is especially beneficial for older patients who move and sweat less. When the physician examines patients, the so-called white coat effect can occur. The patients are nervous and exhibit increased sympathetic nervous system activity. The values measured by the doctor, therefore, do not correspond to the patient’s resting values. If these patients are able to conduct these measurements at home in their usual surroundings, the physician obtains more realistic values to reach a correct diagnosis.

In the future, we want the data collected during the time the device is worn to be directly transmitted to the physician and to already be available during the measurement. In the case of unusual results, the physician is then able to contact the patient directly. This also makes home monitoring or home care possible.

What other application areas are conceivable with the self-moistening electrodes?

: When we integrate additional electrodes into the chest strap – and not just at two places, as is currently the case – we may obtain a more intricate ECG signal to chart additional clinical pictures of the heart such as atrial fibrillation for example.

It is also conceivable to measure cerebral or muscle blood flow with these electrodes. However, we are currently not able to say how well this works in these areas. We also want to try to integrate the technology directly into textiles. We are collaborating with different EMPA departments and several industry partners on the numerous possibilities that are available.

Photo: Michalina Chrzanowska; Copyright: B. Frommann

©B. Frommann

The interview was conducted by Michalina Chrzanowska and translated from German by Elena O'Meara.