breath gas analysis in patients suffering from depression

According to Smith (Smith, 2011) brain disorders cost Europe almost €800 billion (US$1 trillion) a year - more than cancer, cardiovascular disease and diabetes together.

Major depressive disorders (MDD) can effectively be treated with psychotherapy and/or antidepressants. However, still one third of patients do not respond and would need different treatment options as early as possible (Kennedy and Giacobbe, 2007).
A possible new method for early detection could be breath gas analysis that already was implemented for alcohol tests and recently was found to be clinical applicability e.g. for diabetes detection. Because the lungs act as a gas exchanger between the internal system and external environment, the internal system in disorders like MDD may be assessed through the analysis of exhaled breath especially with respect to stress induced reactions.