Abstract
Measures of heart rate variability (HRV) are widely used to assess autonomic nervous system (ANS) function. HRV can be recorded via electrocardiography (ECG), which is both non-invasive and widely available. However, ECG needs three electrodes touching the body of the subjects, which makes them feel nervous and uncomfortable, thus potentially affecting the recording. Contact-free detection of the heartbeat via a microwave sensor constitutes another means of determining the timing of cardiac cycles by continuous monitoring of mechanical contraction of the heart. This technique can measure the heartbeat without any electrodes touching human body and penetrate the clothes at some distances, which in some instances may prove a practical basis for HRV analysis. Comparison of 5-minute recordings demonstrated that there were no significant differences in the temporal, frequency domains and in non-linear dynamic analysis of HRV measures derived from heartbeat and ECG, which suggested this technique may prove a practical alternative to ECG for HRV analysis.
Highlights
Analysis of Heart Rate Variability (HRV) is a powerful tool used to evaluate the regulation of cardiac activity by the autonomic nervous system (ANS)
Four parameters were calculated from time domain R-R intervals (RRIs) and HHI recordings [20] the mean interpulse interval, the standard deviation of the interpulse intervals (SDNN), the square root of the mean squared differences of successive interpulse intervals (RMSSD) and the proportion of differences of successive interpulse interval exceeding 50 ms, known as pNN50; this was derived by the number of interpulse interval exceeding 50 ms dividing by the total number of interpulse intervals
Recent reports suggest that HRV measurement may prove an effective means of detecting early cardiovascular disease [22], as well as for predicting the mode of death in chronic heart failure [4]
Summary
Analysis of Heart Rate Variability (HRV) is a powerful tool used to evaluate the regulation of cardiac activity by the autonomic nervous system (ANS). Contact-free detection of life signatures via a microwave sensor is a new technique, which can penetrate some non-metal media like wood, clothes and remotely sense the respiration and heartbeat signals without any electrodes or sensors touching the body of human subjects [7,8,9,10,11,12]. Applications of this technique were specially used in searching for survivors after earthquakes or snow avalanches due to the good penetration capability of microwaves [13], and some of the published papers [14,15] and patents [16,17] have focused on the detection of movement due to breathing or heartbeat in order to estimate their rate. We show under controlled research conditions that measures of ANS function derived from the ECG system and the microwave sensor are similar by comparing 5minute heartbeat and ECG recordings to compute HRV in time, frequency domains and using nonlinear dynamic indices
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