Abstract
Vital parameters are key indicators for the assessment of health. Conventional methods rely on direct contact with the patients’ skin and can hence cause discomfort and reduce autonomy. This article presents a bistatic 24 GHz radar system based on an interferometric six-port architecture and features a precision of 1 µm in distance measurements. Placed at a distance of 40 cm in front of the human chest, it detects vibrations containing respiratory movements, pulse waves and heart sounds. For the extraction of the respiration rate, time-domain approaches like autocorrelation, peaksearch and zero crossing rate are compared to the Fourier transform, while template matching and a hidden semi-Markov model are utilized for the detection of the heart rate from sphygmograms and heart sounds. A medical study with 30 healthy volunteers was conducted to collect 5.5 h of data, where impedance cardiogram and electrocardiogram were used as gold standard for synchronously recording respiration and heart rate, respectively. A low root mean square error for the breathing rate (0.828 BrPM) and a high overall F1 score for heartbeat detection (93.14%) could be achieved using the proposed radar system and signal processing.
Highlights
Automatic recording of vital parameters (VP) as a surrogate for health is part of clinical standard procedures, e.g., heartbeat by electrocardiography (ECG), pulse rate and oxygenation of the blood by pulseoxymetry and blood pressure by intermittent sphygmomanometry
The signal generated by the voltage-controlled oscillator (VCO) has an adjustable output power of maximum 11 dBm [38], which is attenuated by 3 dB due to the losses on the printed circuit board (PCB), connectors and cable
If one compares the root mean square error (RMSE) values of the different methods to determine respiration rate, one can see that on average the deviation using zero crossings (ZCs) is smallest with 0.8 breaths per minute (BrPM), using peak search the largest deviations occur with 2.1 BrPM
Summary
Fabian Michler 1, *,† , Kilin Shi 1,† , Sven Schellenberger 2,† , Tobias Steigleder 3 , Anke Malessa 3 , Laura Hameyer 3 , Nina Neumann 3 , Fabian Lurz 1 , Christoph Ostgathe 3 , Robert Weigel 1 and Alexander Koelpin 2.
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