This study evaluates the change in the composition of Volatil Organic Compounds (VOC) in patients treated by monoclonal antibody for severe asthma.

At least one in two patients treated by monoclonal antibody for severe asthma doesn't have satisfying result after 6 months of treatment.

The evaluation of the answer, and even better the answer prediction, are fundamental issues for medico-economic plan as part of these innovative therapeutics.

The interest of the use of VOC as diagnostic or prognostic tool in patients with tumoral thoracic pathology or bronchial or pulmonary vascular diseases has been demonstrated.

VOC analysis will be performed using two different techniques: electronic nose and masse spectrometry. At each visit, in addition to the usual assessment, patients will have two non-invasives collections of exhaled air, one for electronic nose analysis and one for masse spectrometry analysis.

Inclusion Criteria:

• patient aged > 18 years old
• patient with severe asthma who respond to the indication of monoclonal antibody therapy according to SPC and management criteria fixed by Transparency Committee
• signed informed consent
• patient with healthcare insurance

Exclusion Criteria:

• patient not responding to the criteria for the good use of monoclonal antibody in severe asthma
• contraindication to one of monoclonal antibody treatment according to SPC (hypersensitivity to one of compounds)
• patient unable to perform a slow vital capacity
• patient with long-term oxygen therapy , under invasive ventilation
• pregnant women
• patient deprived of liberty by judicial or administrative decision