Abstract
Cardiovascular diseases are the leading cause of death worldwide. However, their diagnosis is quite late due to the invasive nature of the required tests. Some gases are produced endogenously by the body and rejected through the respiratory system. Measurements in exhaled air are rapid and non-invasive. If it is possible to demonstrate a link between these gases and a particular pathology and quantify them, it is therefore, possible to have access to the body metabolism. To date, only the measurement of nitric oxide (NO) in the exhaled air is recognized and used as a diagnostic value in clinical practices, even though other gases present an established link with different pathologies. One reason for this is the difficulty to standardize the measurement conditions and techniques, as well as the repeatability of the results, which must consider variability factors amongst subjects and within the same subject during different tests. The QEPAS (Quartz Enhanced Photoacoustic Spectroscopy) technique offers an excellent sensitivity and selectivity. The use of tunable lasers with very narrow spectral widths compared to the absorption lines of gases at atmospheric pressure allows the discrimination of a molecule of interest in a complex gas matrix, even at very low concentrations (parts per billion (ppbv)). A sensor has been developed for gases associated with cardiovascular diseases: carbon monoxide, nitric oxide, isoprene and acetone. Combining the sensor with a device used in medical routine has enabled the establishment of a sampling system that takes into account variations related to humidity and exhaled airflow. This has permitted the reconstruction of the complete carbon monoxide expirogram and the measurement of capnography and expiratory flow rates, providing information about the origin of the gases in the airways.