Lung Clearance Index (LCI) will be performed in healthy volunteers with a multiple breath nitrogen washout device.

Multiple breath washout is a pulmonary function test that does not require patients' cooperation. It studies the number of lung volumes (turn-over) to clear a gaz such as nitrogen form the lungs. LCI 2,5 is most frequently reported outcome measure. It corresponds to the sum of the total expired lung volumes needed to decrease the initial gaz concretion to its 1/40th, divided by functional residual capacity.

LCI can be measured in infant, preschoolers and thereafter. In order to obtain reproducible tests, three acceptable maneuvers are needed.