A medical apparatus for determining constituents of expiration volume, using a through-flow sensor for determining constituents of expiration volume, designed as an interchangeable component in order to permit a simple and rapid exchange of the through-flow sensor with its sensor holder without having to dismantle the medical apparatus. The apparatus can thus be used for determining a very wide range of analytes (constituents of the exhalation). Preferred analytes are biomarkers in the breath condensate such as H2O2, leukotrienes, prostaglandins or interferons as indicators for diseased changes in the lung.
