Abstract

The infrared spectra of the air exhaled by several groups of volunteers were studied: those suffering from type 1 diabetes, bronchial asthma, and pneumonia. To record infrared spectra, a tunable quantum-cascade laser (QCL) was used. QCL emits in the wavelength range from 5.3 to 12.8 μm in a pulsed mode with a pulse width of 50 ns, a power of up to 150 mW, and a tuning step of 1 cm-1. The laser is optically coupled to an astigmatic gas cell of the Herriot type with an optical path length of 76 m. A difference was found in the intensity of selective lines of biomarker molecules in the spectra of exhaled air of healthy volunteers compared to similar indicators of volunteers suffering from a certain disease. For an example of methods such as the support vector machine (SVM), the k-nearest neighbors (k-NN) and the random forest algorithm (RandomForest), the possibility of classifying volunteers by the infrared spectra of their exhaled air is shown. The use of dimensionality reduction methods (PCA and t-SNE) made it possible to increase the accuracy of disease classification up to 98% in terms of the accuracy metric.

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