Abstract: A portable pneumotachograph for determining components of the expiration volume, comprising a processor (3), a PEEP valve (4) mounted on the pneumotachograph (1) on the exhaling side, a filter (5) mounted on the pneumotachograph (1) on the inhaling side for removing the portion of the component in the inspiration air to be determined, at least one sensor (7) mounted in or on the pneumotachograph tube (6), wherein in the sensor (7) disposed on the pneumotachograph tube (6), the pneumotachograph tube (6) having an opening (8) on the sensor side, and/or at least one means configured in the pneumotachograph tube (6) for sampling, and further an optical and/or acoustic control device (9) for the expiration flow. This enables a correlation of measurement data of one or more components of the exhaled flow detected with a lung function test, enabling the localization of the seat of the disease.