Alveolar breath of the volunteers is collected using an "offline" method that effectively separates the endogenous from the exogenous breath volatile biomarkers and excludes the nasal entrainment. Two bags of 750 ml of breath samples per volunteer are collected in inert Mylar bags (Eco Medics, Duerten, Switzerland). Vapor sampling was performed by extended breath sampling into the collection apparatus for 15-20 minutes, with several stops during this process. The first three minutes of breath sampling are discarded due to the possible contamination of the upper respiratory air. The subsequent deep air is retained for testing purposes. The samples are collected with a tube that was introduced in the volunteer's mouth and connected to the collection bag. All participants provide a signed informed consent to this study, which is performed following the approval and according to the guidelines of the Helsinki Committee of Carmel Medical Center and Technion's committee for supervision of experiments in humans.