Wearable and Noninvasive Device for Integral Congestive Heart Failure Management in the IoMT Paradigm

Abstract

Noninvasive remote monitoring of hemodynamic variables is essential in optimizing treatment opportunities and predicting rehospitalization in patients with congestive heart failure. The objective of this study is to develop a wearable bioimpedance-based device, which can provide continuous measurement of cardiac output and stroke volume, as well as other physiological parameters for a greater prognosis and prevention of congestive heart failure. The bioimpedance system, which is based on a robust and cost-effective measuring principle, was implemented in a CMOS application specific integrated circuit, and operates as the analog front-end of the device, which has been provided with a radio-frequency section for wireless communication. The operating parameters of the proposed wearable device are remotely configured through a graphical user interface to measure the magnitude and the phase of complex impedances over a bandwidth of 1 kHz to 1 MHz. As a result of this study, a cardiac activity monitor was implemented, and its accuracy was evaluated in 33 patients with different heart diseases, ages, and genders. The proposed device was compared with a well-established technique such as Doppler echocardiography, and the results showed that the two instruments are clinically equivalent.

Keywords: CMOS integrated circuits; bioimpedance; cardiac output assessment; congestive heart failure.

Figure 1

(a) Simplified equivalent circuit (2R1C) of a single cell in the extracellular medium; (b) four-electrode bioimpedance measurement technique.

Figure 2

Standard ICG four-electrode measurement setup.

Figure 3

System overview of the developed bioimpedance device for continuous hemodynamic assessment and physiological parameters related to breath behavior, pulmonary edema, and muscle quality.

Figure 4

Simplified block diagram of a polar demodulator architecture.

Figure 5

Simplified block diagram of the proposed analog front-end.

Figure 6

(a) XOR logic gate used in the phase measuring circuit; (b) its transistor-level implementation, and (c) the DC component V_p of the pulse train v_p.

Figure 7

Experimental characterization of the CMOS AFE: (a) Measured vs. ideal values of test impedance magnitude, (b) phase. Diamonds: experimental data; dashed line: fitting.

Figure 8

Statistical analysis of the measured impedance magnitude error in 10 test-chip prototypes: (a) Magnitude error (%) at 12 different resistor values; (b) MAE for the impedance measurement at TI range.

Figure 9

Cole–Cole plot in the impedance plane for the 2R1C circuit (R_e = 681 Ω; R_i = 909 Ω; C_m/2 = 3.3 nF), measured by the bioimpedance sensor (red diamonds); ideal, i.e., obtained by the impedance expression using R and C values measured by the LCR meter (blue squares); and mathematical, i.e., obtained by the impedance expression using nominal R and C values (thin blue solid line).

Figure 10

(a) Electrode placement for TI measurements in a healthy volunteer; (b) screen capture of the graphical user interface for SV and CO measurements.

Figure 11

Pattern of Z and dZ/dt waveforms recorded by the proposed bioimpedance device.

Figure 12

Thoracic impedance signals (Z and dZ/dt) during cardiac output monitoring test.

Figure 13

Passing–Bablok plot of correlation of SV measured with the proposed bioimpedance device and a Doppler echocardiograph [R² = 0.8308]. The plot shows the observations with the regression line (solid blue line), the confidence interval for the regression line (dashed lines) and identity line (x = y, dotted red line).