Feasibility Analysis and Implementation of Head-Mounted Electrical Impedance Respiratory Monitoring

Abstract

The respiratory rate is one of the crucial indicators for monitoring human physiological health. The purpose of this paper was to introduce a head-mounted respiratory monitoring solution based on electrical impedance sensing. Firstly, we constructed a finite element model to analyze the feasibility of using head impedance for respiratory sensing based on the physiological changes in the pharynx. After that, we developed a circuit module that could be integrated into a head-mounted respiratory monitoring device using a bioelectrical impedance sensor. Furthermore, we combined adaptive filtering and respiratory tracking algorithms to develop an app for a mobile phone. Finally, we conducted controlled experiments to verify the effectiveness of this electrical impedance sensing system for extracting respiratory rate. We found that the respiration rates measured by the head-mounted electrical impedance respiratory monitoring system were not significantly different from those of commercial respiratory monitoring devices by a paired t-test (p > 0.05). The results showed that the respiratory rates of all subjects were within the 95% confidence interval. Therefore, the head-mounted respiratory monitoring scheme proposed in this paper was able to accurately measure respiratory rate, indicating the feasibility of this solution. In addition, this respiratory monitoring scheme helps to achieve real-time continuous respiratory monitoring, which can provide new insights for personalized health monitoring.

Keywords: bioelectrical impedance; health monitoring; respiratory monitoring; wearable devices.

Figure 1

Head-mounted respiratory monitoring scheme.

Figure 2

Construction of finite element model. (a) Anatomical structure of the head. (b) Schematic diagram of electrode adhesion in subjects. (c) Equivalent breathing simulation model of the head. (d) Head cross-sectional current density mode distribution.

Figure 3

Relationship between pharyngeal volume and head impedance during respiration.

Figure 4

Schematic diagram of the electrical impedance sensing system for respiratory monitoring.

Figure 5

Display of electronic devices and software flow chart: (a) The physical diagram of the electronic device; (b) The flow chart of the embedded software.

Figure 6

Impedance data of the head and their time–frequency distribution. (a) Subject one’s head impedance amplitude changes during breathing. (b) Head impedance time–frequency diagram during breathing in subject one.

Figure 7

Respiratory waveform after adaptive filtering and its time–frequency plot. (a) Adaptive filtering and noise reduction to extract respiratory waveform based on subject one’s head impedance data. (b) Time–frequency plot of the extracted respiratory waveform based on subject one’s head impedance data with adaptive filtering and noise reduction.

Figure 8

Comparison of respiratory waveforms measured by the two devices.

Figure 9

Bland–Altman distribution of respiration rates measured by the two device.