Extracting respiratory information from seismocardiogram signals acquired on the chest using a miniature accelerometer

Abstract

Seismocardiography (SCG) is a non-invasive measurement of the vibrations of the chest caused by the heartbeat. SCG signals can be measured using a miniature accelerometer attached to the chest, and are thus well-suited for unobtrusive and long-term patient monitoring. Additionally, SCG contains information relating to both cardiovascular and respiratory systems. In this work, algorithms were developed for extracting three respiration-dependent features of the SCG signal: intensity modulation, timing interval changes within each heartbeat, and timing interval changes between successive heartbeats. Simultaneously with a reference respiration belt, SCG signals were measured from 20 healthy subjects and a respiration rate was estimated using each of the three SCG features and the reference signal. The agreement between each of the three accelerometer-derived respiration rate measurements was computed with respect to the respiration rate derived from the reference respiration belt. The respiration rate obtained from the intensity modulation in the SCG signal was found to be in closest agreement with the respiration rate obtained from the reference respiration belt: the bias was found to be 0.06 breaths per minute with a 95% confidence interval of -0.99 to 1.11 breaths per minute. The limits of agreement between the respiration rates estimated using SCG (intensity modulation) and the reference were within the clinically relevant ranges given in existing literature, demonstrating that SCG could be used for both cardiovascular and respiratory monitoring. Furthermore, phases of each of the three SCG parameters were investigated at four instances of a respiration cycle-start inspiration, peak inspiration, start expiration, and peak expiration-and during breath hold (apnea). The phases of the three SCG parameters observed during the respiration cycle were congruent with existing literature and physiologically expected trends.

Toward Continuous, Noninvasive Assessment of Ventricular Function and Hemodynamics: Wearable Ballistocardiography

“…This accelerometer was selected based on its low spot noise (20 μg rms /√Hz at 10 Hz) and total noise (300 μg rms for a bandwidth of 1–10,000 Hz), wide signal bandwidth (0.7–5000 kHz, +/− 1 dB), and its relatively small size (11.4 mm cubed) and low weight (5.4 g). In contrast to micromachined (micro-electromechanical systems, MEMS) accelerometers used in previous studies, the self-noise was several times lower: the LIS344ALH (ST Microelectronics, Geneva, Switzerland) accelerometer used in previous studies [25, 34] represents the lowest noise MEMS accelerometer available, with a self-noise of 350 μg rms for a bandwidth of 1–50 Hz compared to the 60 μg rms for the 356A32 used here. Compared to other instrumentation-grade accelerometers used in previous work, the weight of our accelerometer was 8 x lower, as was the volume: the 4381 (Bruel & Kjaer, Naeurum, Denmark) piezoelectric accelerometer used previously [35, 36] weighs 43 g and is a 20.5 mm diameter x 23.6 mm height cylinder compared to the 5.4 g weight and 11.4 mm cubed dimensions of the sensor used here.…”

A Portable Measurement System for the Superior-Inferior Axis of the Seismocardiogram

“…In fact, comparing the figures 4 and 7, it seems that the trace in the figure 7 displays two main alternative waveforms corresponding to inspiration and exhalation phases. The variation in the SCG signal has been proposed to be due to respiration induced physiological effects in the circulation in earlier studies also [15]. Figure 9, where raw and digitally filtered signals are plotted, backs up the suggestion that the variation isn't probably of due to electrical noise.…”

“…Due to the use of validation procedures, for example, echocardiography (ECHO) the points of mitral valve closure (MC), aortic valve opening (AO), maximum acceleration of blood in the aorta (MA), onset of rapid ejection of blood into the aorta (RE), aortic valve closure (AC), and mitral valve opening (MO) have been detected [11,12]. SCG is normally recorded in the dorso-ventral axis from the sternum [10], but many groups have presented with tri-axial approaches also [13][14][15]. Figure 1 depicts in detail the axes used in SCG research.…”

Theoretical Spectral Analysis of the Ir-Uwb Radar Chest Reflection With Arbitrary Periodic Breathing- And Heart-Induced Displacements

“…However, these models do not address realistic models of typical chest movements. These includes breathing patterns with non-unity inspiration-to-expiration ratio [26], not modelled well with just one or two sinusoids as assumed in [14][15][16], or bursty heartbeat displacement [27,28], not consistent with just one sinusoid as in [16]. In addition, the existing models are derived for an undersampled version of the radar received signal.…”