Fig. 1

Schematic of the system framework and sample collection. We sampled alveolar air from the collecting device with a volatile organic compound filter, capnometer, flow meter, nonrebreathing bag, and a three-way control valve. The capnometer (Masimo, CA, USA) was monitored [49]. Breath samples were stored in a 1-L Tedlar bag (SKC Inc., PA, USA)