Noninvasive respiratory monitoring system based on the piezoceramic transducer’s pyroelectric effect

Abstract

This paper presents a simple alternative method and system for noninvasive respiratory airflow monitoring. The proposed system uses a piezoceramic transducer to measure respiratory airflow. When a piezoceramic transducer is impacted by respiratory airflow, there is a piezoelectric and a pyroelectric response to pressure and thermal airflow fluctuations. In this study, the selected transducer's response output is dominated by the pyroelectricity factor. Therefore, the piezoelectric effect is not significant and can be ignored in this study. Using the transducer's pyroelectricity to measure thermal flow variations, a subject's respiratory rate and respiratory air volumetric flow rate can be monitored. The proposed system was evaluated for accuracy and response time using quiet and postphysical exertion breathing modes. Using the pneumotach system as a benchmark, the proposed system's respiratory rate measurement accuracy for the two breathing modes is approximately 98.78%. In addition, the proposed system's output voltage is highly correlated with the respiratory volumetric flow rate measured by the selected pneumotach (r2=0.9783). The average correlation coefficient between the pneumotach system's output waveform and the proposed system is approximately 0.9389. Moreover, the proposed system and the selected pneumotach have almost the same rapid response time to respiratory airflow. When compared to a temperature measurement thermistor system, the thermistor on average is approximately 25.3 ms slower than the proposed system. Furthermore, compared to the selected screen-type pneumotach system, the proposed system simplifies the respiration monitoring requirements. Instead of sensing the pressure drop across a mesh screen, like the screen-type pneumotach, it measures respiration at one point within the respiratory airflow. The proposed system benefits from simplified processing circuits and a mesh-free design. The advantages of this new respiratory airflow measurement method are fast response time, high accuracy, low cost, and ease of implementation.