An apparatus for the decomposition of a gaseous agent in exhaled air from patients, comprising a gas flow line along which there is a) an inlet arrangement, b) a decomposition unit with a chamber for decomposition of the agent, and c) an outlet arrangement. The characteristic feature is the presence of a gas regulating arrangement comprising a) a gradually adjustable function, e.g. a blower, for adjusting the flow through the chamber, and b) an optional by-pass valve function permitting adjustment of the gas pressure upstream of the adjustable function. An apparatus of the same kind as in the first sentence of the previous paragraph in which the chamber is combined with a regenerative heat exchanger preferably equipped with a puff filter. Methods are also claimed.
