Smart Multi-Frequency Bioelectrical Impedance Spectrometer for BIA and BIVA Applications

Abstract

Bioelectrical impedance analysis (BIA) is a noninvasive and commonly used method for the assessment of body composition including body water. We designed a small, portable and wireless multi-frequency impedance spectrometer based on the 12 bit impedance network analyzer AD5933 and a precision wide-band constant current source for tetrapolar whole body impedance measurements. The impedance spectrometer communicates via Bluetooth with mobile devices (smart phone or tablet computer) that provide user interface for patient management and data visualization. The export of patient measurement results into a clinical research database facilitates the aggregation of bioelectrical impedance analysis and biolectrical impedance vector analysis (BIVA) data across multiple subjects and/or studies. The performance of the spectrometer was evaluated using a passive tissue equivalent circuit model as well as a comparison of body composition changes assessed with bioelectrical impedance and dual-energy X-ray absorptiometry (DXA) in healthy volunteers. Our results show an absolute error of 1% for resistance and 5% for reactance measurements in the frequency range of 3kHz to 150kHz. A linear regression of BIA and DXA fat mass estimations showed a strong correlation (r2=0.985) between measures with a maximum absolute error of 6.5%. The simplicity of BIA measurements, a cost effective design and the simple visual representation of impedance data enables patients to compare and determine body composition during the time course of a specific treatment plan in a clinical or home environment.

A Portable Sensor for Skin Bioimpedance Measurements

“…While bioimpedance is an attractive method for continuously assessing tissue properties, commercial impedance analyzers are expensive and too large for remote monitoring or large scale clinical deployment. Many researchers have turned to cheaper alternatives such as designing analog front ends (AFE) for the AD5933, an impedance analyzer on an integrated circuit (IC) from Analog Devices [10][11][12][13][14][15]. Many of these circuits change the output of the AD5933 IC into a constant current source and measure tissue impedance using a four-electrode configuration with two current sourcing electrodes and two voltage sensing electrodes.…”

Fundamentals, Recent Advances, and Future Challenges in Bioimpedance Devices for Healthcare Applications

“…The injected current can be monitored to avoid exceeding the established limits [44], but the most common method is the injection of a fixed amplitude current [108]. Although multiple current source topologies have been employed for the VCSS, most are based on the improved Howland current pump [102,106], implemented by discrete designs based on operational amplifiers (OPAM).…”

“…As the impedance of the electrode-medium interface is in series with the bioimpedance to be measured, important errors may arise. To solve this problem, the four-electrode configuration (tetrapolar) is usually employed [107,108]. In this scheme, the current is injected by the external electrodes (distal electrodes) and the voltage is measured in the internal electrodes (proximal electrodes) (see Figure 9) by means of an instrumentation amplifier.…”

“…Some commercial chips have also been developed to perform bioimpedance measurements. AD5933 impedance network analyzer of Analog Devices performs impedance measurements between two terminals within the frequency range of 1 kHz to 100 kHz [22,95,108]. For this, it uses a 12-bit ADC and a processing based on FFT.…”

Simultaneous Recording of ICG and ECG Using Z-RPI Device with Minimum Number of Electrodes

“…Development of personalized health (p-health) solutions and advances in smart textiles and textile manufacturing has allowed new developments of wearable measurement systems targeting fitness and even home-care but often they have been limited to biopotential recordings [19,20]. Recent advances in microelectronics have produced system-on-chip (SoC) solutions for biopotential and bioimpedance measurements, and most of them have been successfully tested in several EBI applications [21][22][23][24][25]. Thus, we can confirm that their availability and accessibility have indeed fostered research and development activities targeting p-health monitoring applications based on different embedded electronic wearable measurement systems and patch technology [23,[26][27][28].…”