The Digital Medicine department at Bielefeld University was on board as a medical project partner. The focus of the TUHH-led experiment, titled ARTIFACTS, was to study how motion artifacts in ballistocardiography (BCG) and seismocardiography (SCG) signals are influenced by gravity-dependent sensor movements.
Research Background
(BCG) and Seismocardiography (SCG) are non-invasive methods for measuring oscillating recoil movements of the whole body or the chest, respectively, caused - among others - by ballistic forces generated by the heart’s mechanical actions and blood flow. The accelerations of these movements can be derived from digital 3D-acceleration sensors (accelerometers) on the body surface and analyzed to retrieve the heartrate and physiological information on the blood flow and valvular actions. Despite numerous research, there is still a fundamental uncertainty in characterizing the SCG/BCG signals, making interpretation extremely difficult. The sensors roll, pitch and yaw due to the movements generated by the heart and blood flow which are transmitted to the body surface as well as due to earth’s gravity.
As a result, some of the acceleration data in the BCG/SCG signal is not due to acceleration of the heart, but to movements of the sensor itself (the so-called intrinsic rotation of the sensors), which are not of interest if conclusions are to be drawn about the heart. This is referred to as BCG-/SCG-like acceleration artifacts on the axes. As a consequence of these sensor movements, constructive or destructive interference with the actual BCG/SCG signal can occur which can lead to deformation and, thus, misinterpretations of the signal.
Objectives of the ARTIFACTS Study
The ARTIFACTS experiment aimed to differentiate between actual heart-induced signals and artifact-induced signals under controlled gravitational conditions. By using parabolic flight maneuvers, the research team was able to collect data during phases of microgravity (0g), normal gravity (1g), and hypergravity (1.8g). This allowed for a controlled environment to study how gravitational forces affect sensor behavior.
Technical Approach
the DLR funded projects SArES and AuRelia, the Smart Sensors Group is developing an SCG sensor system that offers high measurement accuracy and is also qualified for use in space missions. In the SpacePatch project, this sensor, which weighs 6g and measures approx. 2cm, is to be used in upcoming missions. For the ARTIFACTS experiment, in addition to these sensors, specially developed reference hardware was also developed for the highly accurate and synchronous measurement and recording of cardiovascular reference data. The experiment was controlled via a laptop, and software for fault-tolerant data recording and direct labeling of prominent points during flight was also developed by the Smart Sensors Group. Technologically, the very low accelerations are recorded using the differential sensing method with a significantly higher SNR than conventional sensors. The method was also developed and integrated by the Smart Sensors Group.
Expected Outcomes and Applications
The data analysis focuses on mapping and compensating for artifacts that result from sensor orientation and movement. This will improve signal quality in SCG/BCG and support the development of more accurate wearable devices. TUHH’s work is particularly relevant for space applications (e.g., in the DLR SpacePatch project), but also for terrestrial use cases such as outpatient monitoring and telemedicine.
In the long term, the methods developed in ARTIFACTS will contribute to the design of more robust, lightweight, and low-power biosignal processing systems that can function reliably even under challenging environmental conditions. The Smart Sensors Group will continue this researchin the frame of the recently started DFG funded project KORVEKSiS (54215145)
