Review of infrared carbon-dioxide sensors and capnogram features for developing asthma-monitoring device

Abstract

Introduction: Asthma is one of the most common heterogeneous respiratory chronic diseases and fourteenth most imperative illness in the world in terms of duration and extent of disability. The existing method for early identification of asthma is based on health care provider’s physical assessment and spirometer or peak flow meter which is manual and unreliable if patients are non-cooperative. Therefore, capnography, which measured the respired carbon dioxide concentration, has been proposed as a patient independent method for the assessment of asthma. Aim: This study aims to critically review, investigate, and compare the specifications of different infrared CO2 sensors and capnogram features to develop an asthma-monitoring device. Materials and Methods: A rigorous and extensive search was carried out on Google scholar, the Web of Science, PubMed, and Scopus and several index terms (CO2 sensor, infrared sensor, CO2 measurement, asthma detection, capnograph, and capnogram) were employed to identify appropriate CO2 sensors, technology, and capnogram features to develop asthma monitoring device. Results: The review revealed that the COMET CO2 sensor is the most suitable and reliable for developing a capnograph device owing to its weight (7 g), output range (0-99 mmHg), warm-up time (2-15 s), and response time (0.028 s). Furthermore, slope and time-frequency components measured from alveolar phase and complete breath cycle respectively are found the most significant features to screen asthma severity level. Further, the effects of pressure and temperature on CO2 values were tested using Proteus software. Finding reveals that the CO2 values changed drastically from 17,835.19 parts per million (ppm) to 86,321.29 ppm as the pressure changed from 16.53 kPa to 81.53 kPa at a constant temperature (25°C). With a change in temperature from 25 to 27°C, the CO2 values were found to change from 16,812.19 ppm to 17,249.13 ppm at a constant pressure (16.53 kPa). Based on the review, a CO2 measurement device using COMET equivalent CO2 sensor was developed. Conclusion: The developed device is capable of the assessment of cardiorespiratory condition instead of asthma severity level due to lack of significant capnogram features, which still remains to be integrated into the device.