Exhaled breath condensate (EBC) collection and exhaled nitric oxide measurement
EBC was collected after rinsing the mouth with distilled water using Turbo-Deccs system (Medivac, Parma, Italy). All participants wearing a nose clip were asked to breathe at tidal volume for 8 mins through a mouthpiece connected with a one-way valve, which also served as a saliva trap. Approximately 1 ml of breath condensate was collected and immediately stored at -80℃ for further analysis. Following EBC collection (after 30 minutes of rest), fractional exhaled nitric oxide (FeNO) was measured according to published standards13by using NIOX MINO Airway Inflammation Monitor (Aerocrine, Solna, Sweden) equipped with an electrochemical sensor.