An investigation of heart rate variability (HRV) and respiratory sinus arrhythmia (RSA) indices using data obtained from Doppler radar cardiopulmonary remote sensing is presented in this paper. High accuracy in extracting the HRV and RSA indices was achieved using a direct-conversion quadrature radar system with linear demodulation method. This method was validated using data obtained from 12 human subjects in seated and supine positions. For supine position measurements, all standard deviation of normal beat-to-beat interval indices from Doppler radar and electrocardiogram reference differed less than 9 ms of each other, while all the root mean square of differences of successive normal beat-to-beat interval indices differed less than 76 ms. The measurements from subjects in seated and supine positions with normal RSA demonstrated that the results from radar correlated well with both respiratory piezoresistor chest belts. Higher level of HRV and RSA was detected in seated position, as expected.Index Terms-Doppler radar, heart rate variability (HRV), remote physiological sensing, respiratory sinus arrhythmia (RSA).

This paper describes the use of Doppler radar to measure respiration rate and air volume. The respiratory volume is measured indirectly via chest wall position. Calibration of displacement to airflow prior to subject measurements and accurate chest wall position information enable mean differences of less than 10 ml; with standard deviation of the difference of 20 ml between radar and reference measurements.

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This paper describes the calibration technique for a non-contact Doppler radar to monitor respiration and tidal volume in human subjects. The detected change in sensor output, reflecting the displacement of lung movement, is found to relate linearly to tidal volume. The DC reconstruction and calibration techniques are used to extract the tidal volume measurement from the radar signal. Comparison of the radar prediction and reference tidal volumes shows the average mean difference (d) to be −38.9 ml in seated subjects and 23.5 ml in supine subjects. Other chest wall displacement measurements from piezo-electric sensors at the upper and lower torso reports worsed: −40.6 ml and −54.8 ml in seated subjects and 246.6 ml and 68.5 ml in supine subjects. The predicted volumes are not significantly affected by either frequency of respiration or variation in subjects. The results in this paper show that Doppler radar could provide a valuable tool for the noncontact and unobtrusive measurement of tidal volume in human subjects.