Device for measuring the concentration of gases in exhaled air

A device for measuring gas concentration in exhaled air comprising:

• a first air inlet to introduce the exhaled air of a patient into the device,
• a second air inlet with a filter to introduce filtered ambient air into the device,
• an air suction pump,
• a sensor to measure the gas concentration in the exhaled air,
• a first valve located downstream of the first air inlet and upstream of the sensor, and
• a second valve located downstream of the second air inlet and upstream of the sensor,
• a third valve located downstream of the sensor and upstream of an air outlet,
• a flow meter to measure the air flow exhaled by the patient,
• a humidity stabiliser to stabilise a humidity in the device by drying the air flow exhaled by the patient, and
• a free air exhaust located downstream of the flow meter and upstream of the air suction pump,
• wherein the humidity stabiliser is arranged downstream of the first air inlet and upstream of the flow meter, thereby protecting elements of the device downstream of the first air inlet against moisture condensations,
• wherein the free air exhaust is arranged downstream of the flow meter, the first valve is downstream of the free air exhaust, and the air suction pump is downstream of the first valve, and
• wherein the air suction pump is arranged upstream of the sensor and adapted to maintain a constant air flow rate through the sensor when the patient introduces the exhaled air into the device.