To verify or rule out the diagnosis of asthma, a comprehensive lung function test can be carried out. For this procedure, your child sits in a sealed glass cabin, similar to a telephone booth, and breathes through a mouthpiece. By breathing in an out, cabin pressure differences arise that are continuously measured. At the same time, the respiratory flow is measured and recorded in the form of a pressure-volume diagram ("spirometric loop"). Here, the airway resistance and the total lung volume are recorded as well as the air remaining after full exhalation in the lungs, the so-called residual volume.
The body plethysmography provides more detailed and more reliable values than a simple spirometry.