Wearable bioimpedance for continuous and context-aware clinical monitoring

Abstract

Bioimpedance monitoring provides a non-invasive, safe and affordable opportunity to monitor total body water for a wide range of clinical applications. However, the measurement is susceptible to variations in posture and movement. Existing devices do not account for these variations and are therefore unsuitable to perform continuous measurements to depict trend changes. We developed a wearable bioimpedance monitoring system with embedded real-time posture detection using a distributed accelerometer network. We tested the device on 14 healthy volunteers following a standardized protocol of posture change and evaluated the agreement with a commercial device. The impedance showed a high correlation (r>0.98), a bias of -4.5 Ω, and limits of agreement of -30 and 21 Ω. Context-awareness was achieved with an accuracy of 94.6% by classifying data from two accelerometers placed at the upper and lower leg. The calculated current consumption of the system was as low as 10 mA during continuous measurement operation, suggesting that the system can be used for continuous measurements over multiple days without charging. The proposed motion-aware design will enable the measurement of relevant bioimpedance parameters over long periods and support informed clinical decision making.

Development of a Tetherless Bioimpedance Device That Uses Morphologic Changes to Predict Blood Flow Restrictions Mimicking Peripheral Artery Disease Progression

“…Figure 4 shows the overall characteristics of each node from a circuit perspective. While there are commercially available ICs supporting bioimpedance in the market such as the MAX3000x, or AD594x (Analog Devices, Inc. (Wilmington, MA, USA)) [49][50][51][52][53][54][55], our research took a direct design approach to address issues related to phase differences of local oscillators that may arise and be problematic when simultaneously measuring various points for the future research [56][57][58]. Figure 4a illustrates the circuit and important nodes, while Figure 4b depicts representative images of how the signal changes at those crucial nodes.…”

Critical implementation issues of excitation signals for embedded wearable bioimpedance spectroscopy systems with limited resources

“…Linear signum chirp. The linear signum chirp uses a rectangular pulsewave signal as a signal base, with the same frequency function formula as the linear sine chirp f (t) defined in (2). The term 'signum' comes from a possible interpretation of this signal as a sign of the linear sine chirp [16].…”

“…Bioimpedance spectroscopy is increasingly gaining importance as it provides information about biological tissues and organs as well as whole-body composition in a non-invasive way and without exposure to radiation [1]. In recent years, a pronounced trend toward the integration of bioimpedance spectroscopy in implants and wearable systems has been observed for several emerging medical applications, such as non-invasive clinical monitoring [2], cardiovascular monitoring [3], blood glucose monitoring [4], and urinary bladder filling rate and dysfunction [5].…”