Ballistocardiography: Cardiac monitoring of astronauts

It is an exciting time for space exploration: Will there be more space stations, lunar outposts, or Mars missions in the future? No matter where they are in space, lack of gravity causes astronauts to lose muscle mass during their missions. Even the fittest among them lose heart muscle. An experiment on the International Space Station (ISS) plans to detect whether sensors show heart changes.

In this MEDICA-tradefair.com interview, Prof. Ulf Kulau talks about ballistocardiography and explains how it can deliver insights into the cardiovascular health of astronauts.

Prof. Kulau, why do you plan to monitor the vital signs of astronaut Matthias Maurer onboard the ISS?

Prof. Ulf Kulau: We are studying the ballistocardiography (BCG) technique, which means we measure the motions of the human body generated by the heartbeat. We built a system that enables us to measure the smallest vibrations at low noise. The microgravity environment found aboard the International Space Station (ISS) has no gravitational acceleration as an external factor. This enables us to measure the actual acceleration caused by the heartbeat as a reference.

Our findings will deliver insights into future uses considering that astronauts will spend prolonged time in space as they embark on future missions to the moon and Mars. This will make their returns to earth far more challenging, which is why we need a good and accurate health monitoring system in the future for early problem detection, since absence of gravity changes the physiology of the heart.

Does this also facilitate medical applications on Earth?

Kulau: BCG could complement an electrocardiogram (ECG), for example. An ECG is a common, robust, and efficient method, while the BCG technique could produce a representation of the physiology of the heart. For the latter, we need the space measurements for reference and the option of deducting the influence of gravitational acceleration. We can do this via signal processing.

What kinds of sensors do you use?

Kulau: We use simple acceleration sensors and measure in a low frequency range. Most available sensors – including those used in the medical realm - measure in higher frequency. We measure acceleration at the low milli-G level, so the signal-to-noise ratio is high. We solve this problem by conducting signal processing directly on the sensors. This enables us to register even small accelerations.

How long will the experiment take?

Kulau: The first experiments with Matthias Maurer are planned at the beginning or in the middle of January. We will take measurements every two weeks until April. Fortunately, the Italian astronaut Samantha Cristoforetti has also agreed to assist us, which means we will have a test subject starting in April. The sensors are expected to be sent back to Earth in October, at which point we will check the hardware for radiation effects, for example. Data evaluation will also begin in October.

How could these findings be used in future applications?

Kulau: It is essential that we first use the method to make evaluations. Time passed in zero gravity accelerates the aging process, causing a reduction of heart muscle. That's what makes this technique so great: It enables you to see physiological changes in a relatively short period of time, and we must assess how this is reflected in the signals themselves. In subsequent experiments, we can use these findings to look for characteristics that are relevant for cardiologists. For now, we are working extensively with raw data, but the next step would be to conduct automated signal processing on the sensors to read these types of markers.