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. 2023 May 31;23(11):5233.
doi: 10.3390/s23115233.

Estimating Thoracic Movement with High-Sampling Rate THz Technology

Christoph Hoog Antink  1 , Romina Schulz  2 , Maurice Rohr  1 , Konstantin Wenzel  3 , Lars Liebermeister  3 , Robert Kohlhaas  3 , Sascha Preu  2
Affiliations

Estimating Thoracic Movement with High-Sampling Rate THz Technology

Christoph Hoog Antink et al. Sensors (Basel). .

Abstract

We use a high-sampling rate terahertz (THz) homodyne spectroscopy system to estimate thoracic movement from healthy subjects performing breathing at different frequencies. The THz system provides both the amplitude and phase of the THz wave. From the raw phase information, a motion signal is estimated. An electrocardiogram (ECG) signal is recorded with a polar chest strap to obtain ECG-derived respiration information. While the ECG showed sub-optimal performance for the purpose and only provided usable information for some subjects, the signal derived from the THz system showed good agreement with the measurement protocol. Over all the subjects, a root mean square estimation error of 1.40 BPM is obtained.

Keywords: photonic; respiratory rate; terahertz; unobtrusive sensing.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Processing steps of the THz phase signal. In plot (f), the color map is arbitrarily clipped at −0.3 and 0.6 for better visualization.
Figure 2
Figure 2
Respiratory signal obtained from the THz phase signal. The oscillation of the phases following the study protocol (breath hold for 20 s, 9 breaths per minute for 30 s, 12 breaths per minute for 30 s, 18 breaths per minute for 30 s) is clearly visible, as each respiratory cycle is represented by a triangular excursion.
Figure 3
Figure 3
(Top row) raw ECG signal with upper and lower envelope (dotted red lines). (Bottom row) EDR signal.
Figure 4
Figure 4
Top rows: Synchrosqueezed wavelet transform of the THz signal. Bottom rows: Synchrosqueezed wavelet transform of the EDR signal.
Figure 4
Figure 4
Top rows: Synchrosqueezed wavelet transform of the THz signal. Bottom rows: Synchrosqueezed wavelet transform of the EDR signal.
Figure 5
Figure 5
Respiratory rate as extracted from the THz signal (solid blue line), from EDR (dotted red lines), as well as the time-shifted study protocol (dashed black line).
See this image and copyright information in PMC

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