A Capnographic Sensor Using Acoustic Virial Equation for Diagnostic Applications

The concentration of carbon dioxide (CO
₂
) in exhaled breath can provide both noninvasive and continuous information on the metabolic and respiratory functioning of an individual. A capnographic sensor based on the velocity of sound has been proposed to measure the concentration of carbon dioxide in exhaled air using an acoustic virial equation. The extracted capnographic signal is further utilized to diagnose cardiopulmonary disorders such as chronic obstructive pulmonary disease (COPD) and congestive heart failure (CHF). The capnographic signal obtained using the proposed sensor shows a good correlation with the signal from a standard sensor with a squared correlation coefficient of 0.8732. We achieved an accuracy of 91.3, 87.76, and 88.82% for healthy/COPD, healthy/CHF, and COPD/CHF classification cases, respectively. The performance indicates the suitability of the proposed method to be used as a diagnostic device for cardiorespiratory diseases.