Infrared spectroscopy for exhaled breath diagnosis

Abstract

The World Health Organization has defined cardiovascular diseases as the number one cause of death in the world [1]. The diagnosis of these diseases can be invasive for the patient. With the introduction of new technologies in the medical field, scientists and doctors are working together to find new and less invasive ways to ease medical procedures. For many years, scientists have shed light on several gases present in the exhaled breath: water vapor, nitrogen, oxygen, carbon monoxide (CO)... Some of them are biomarkers and their investigation can lead to the diagnosis of several diseases. We present a Quartz enhanced photoacoustic (QEPAS) [2] sensor based on infrared lasers, dedicated to CO, nitric oxide (NO), and acetone monitoring. CO sensing is performed with a 4.7 um quantum cascade laser. This sensor has proved its sensibility and selectivity with a limit of detection of 20 ppbv in 1s. Therefore, further measurements were also performed in situ in the hospital to confront the sensor to a medical sensor. We have demonstrated the influence of the breath hold, characterized different respiratory compartments and discriminated smokers and non-smokers volunteers [3]. These first measures made on humans have brought out some physiological points that need to be taken in account. The QEPAS signal depends on the resonance frequency (f0) of the quartz tuning fork (QTF). The humidity naturally present in breath causes a shift of f0. Some improvements have been proposed to track f0 and the QTF Q-factor to stabilize the measurement [4].