A novel autonomic activation measurement method for stress monitoring: non-contact measurement of heart rate variability using a compact microwave radar

Abstract

We developed a novel method for non-contact monitoring of stress-induced autonomic activation through the back of a chair, using a compact 24 GHz microwave radar (8 x 5 x 3 cm), without large-scale equipment and placing a heavy burden on the monitored individual. Following a silent period of 120 s, audio stimuli using a composite tone of 2,120 and 2,130 Hz sine-waves at 95 dB were conducted for 120 s. From dorsal, LF/HF of HRV reflecting sympatho-vagal balance was determined by microwave radar with the maximum entropy method using eight volunteers (mean age 23 +/- 1 years). Mean LF/HF measured by non-contact and contact (using electrocardiography for reference) methods during audio stimuli increased 34 and 37%, respectively, as compared with those of the silent period. Maximum cross-correlations between contact and non-contact measurements averaged 0.73 +/- 0.10. Our method appears to be promising for future monitoring of stress-induced autonomic activation of operators and may reduce stress-induced accidents.

An approach to a non-contact vital sign monitoring using dual-frequency microwave radars for elderly care

“…We have previously reported a non-contact method that uses a ceiling-attached microwave radar to monitor the respiratory rates of subjects in bed through thick bedding [9] and attached it to the back of a chair to monitor changes of autonomic activation [10]. Microwave radar has the following characteristics: 1) it can detect movement of a remote object without having to make contact; and 2) microwaves can be transmitted through most solid substances except metal or water.…”

Remote Sensing for Medical and Health Care Applications

“…To determine stress levels when driving or operating equipment, a 24 GHz compact microwave radar was used to perform remote measurements of the heart rate variability (HRV) under autonomic activation induced by a stressful sound and foods (Suzuki et al, 2008. Changes in the ANS (sympathovagal balance) can be monitored by measuring the HRV.…”

“…1. Prototype chair equipped with a non-contact microwave radar system to monitor mental stress in workers (Suzuki et al, 2008). In both non-contact and contact (ECG) measurements, the LF of a subject (reflecting sympathetic activation) exhibits a peak during audio stimulation.…”

An Approach to Remote Monitoring of Heart Rate Variability (HRV) Using Microwave Radar during a Calculation Task

“…The diffusion angle (q d ) of the microwave radar antenna is about 40°, the antenna gain is 10 dBi, and the electrical field intensity is 0.7 mW/cm 2 . This antenna has approximately the same specifications as that used in our previous research (Suzuki et al, 2008a;.…”

“…We have already tried to monitor changes in HRV that are induced by stressful audio stimuli using a noncontact measurement system with a 24 GHz compact microwave radar, which can easily be attached to the rear surface of the back of a chair (Suzuki et al, 2008a). The aim of this study was to develop a prototype of the same type of system for cardiac monitoring, using microwave radar without making contact with the body and without removing clothing-namely, a complete noncontact, remote monitoring system.…”