Heart rate detection from an electronic weighing scale

Abstract

We propose a novel technique for beat-to-beat heart rate detection based on the ballistocardiographic (BCG) force signal from a subject standing on a common electronic weighing scale. The detection relies on sensing force variations related to the blood acceleration in the aorta, works even if wearing footwear and does not require any sensors attached to the body because it uses the load cells in the scale. We have devised an approach to estimate the sensitivity and frequency response of three commercial weighing scales to assess their capability to detect the BCG force signal. Static sensitivities ranged from 490 nV V(-1) N(-1) to 1670 nV V(-1) N(-1). The frequency response depended on the subject's mass but it was broad enough for heart rate estimation. We have designed an electronic pulse detection system based on off-the-shelf integrated circuits to sense heart-beat-related force variations of about 0.24 N. The signal-to-noise ratio of the main peaks of the force signal detected was higher than 30 dB. A Bland-Altman plot was used to compare the RR time intervals estimated from the ECG and BCG force signals for 17 volunteers. The error was +/-21 ms, which makes the proposed technique suitable for short-term monitoring of the heart rate.

Towards the standardization of ballistocardiography systems for J-peak timing measurement

“…The effect of phase response was quantified by filtering the reference signals by some simulated filters that have been used or could be used in analog front-ends for BCG acquisition: 1 st order [4,11], 2 nd order Butterworth [10] and 2 nd order Bessel. The timing displacement Δt i of each J peak i on the filtered signals with respect to the reference was measured and, as the effect of phase response is systematic, only E(Δt) was analyzed.…”

“…Nevertheless, this is not the case of the J peak, for which the influence of sources of uncertainty already considered in the detection of the R peak of the ECG, such as the minimal system bandwidth as well as others that can introduce significant systematic and random timing displacements [15] are still to be analyzed. With regard to system bandwidth, some high-pass cutoff frequencies for BCG found in the published work are 0.1 Hz [4,10], 0.2 Hz [5], 0.5 Hz [11] and 1 Hz [6]. Even though the BCG spectrum probably extends to these low frequencies, slow balance-related motion and respiration artifacts dominate in these bands for standing BCG recordings.…”

“…In this context, the ballistocardiogram (BCG), initially understood as the recording of body movements caused by cardiovascular activity [2], has gained a renewed interest [3] because forces related to those movements can be measured from the strain gages in common electronic bathroom scales [4,5,6] or other sensors placed in chairs [7] or beds [8]. Although the BCG can seemingly provide valuable information about the state of the cardiovascular system [2,3,9], until now the signal has been mostly proposed to monitor heart rate [4] and sleep stages [8]. Nevertheless, several recent efforts in this field target the measurement of the delay of the J peak of the BCG acquired from weighing scales with respect to the R peak of the electrocardiogram (ECG), the so-called RJ interval.…”

“…Besides, the effect of low-frequency BCG components on the timing of the J peak may be irrelevant as the peak is a high-frequency feature of the waveform and hence most of its spectrum energy is expected to be on the upper part of the bandwidth. On the other hand, some low-pass cutoff frequencies for BCG used by different research groups are 10 Hz [4,16], 15 Hz [10], 20 Hz [6] and 25 Hz [5,11]. No reasons for selecting any particular cutoff frequency seems to have been published but the power density spectrum of a typical BCG obtained from a bathroom scale with the low-pass filter set at 100 Hz shows that there are significant signal components at least up to 20-25 Hz (Figure 2).…”

Comparación temporal de las ondas características entre el BCG dorsoventral y longitudinal

“…Recientemente se ha registrado el BCG en una variedad de ambientes, para lo cual se han desarrollado sistemas de medida basados en sillas [3], [4], camas [5], básculas de baño [6] y algunos portables en ropa [7].…”