An electronic nose distinguishes the exhaled breath condensates of alpha-1-antitrypsin deficiency patients and healthy controls

Background: Exhaled respiratory air contains countless volatile organic compounds (VOCs). The composition of those VOCs varies dependent of different pulmonary diseases. With the customizable electronic nose Cyranose 320 (C-320) it is possible to detect VOCs and distinguish between different VOC patterns. It was the aim of this study to analyze and distinguish the VOCs in exhaled breath condensate (EBC) of patients with α₁-antitrypsin deficiency (AATD) and healthy controls (HC).

Materials and methods: The EBC was collected from ten HCs and ten AATD patients with the RTube by ten minutes of tidal breathing. 250µl of EBC were heated up to 37°C and argon gas was passed though with a constant flow of 350 ^ml/_min for two minutes. Subsequently, the samples were measured by holding the snout of the C-320 above the surface of the samples and drawing gas for ten seconds. Ten samples of ambient lab air were taken as loading controls. A principal component analysis (PCA) (to reduce the dimensionality) and a linear discriminant analysis (LDA) (to separate the different groups) were performed on the data.

Results: The analyses showed that AATD patients, HCs and lab air are clearly separable. The predictive positive value (PPV) was calculated with a 100-fold-cross-validation using ten percent of the training data as test data (see table 1).

Table 1: Mahalanobis distances (and PPVs) between the groups

	HC	lab air
AATD	2.166 (94.5%)	2.355 (100.0%)
HC		2.305 (100.0%)

Conclusion: Using the C-320, we could distinguish between EBCs from AATD patients and HCs. This approach also shows EBC contains enough VOCs to separate two different patient groups. An advantage of using the EBC is the lower contamination risk by not measuring for example infectious patients directly with the C-320 and easiness to sample and store EBC.