Spirometer

A spirometer is a medical device for measuring the on and exhaled air volume, called the tidal volume and the air volume flow and the temporal change. It is used to check in spirometry lung function or the vital capacity. Spirometry is the most commonly performed test in pneumology.

History

In the first spirometers a gas-filled bell was placed on a liquid-filled and sealed piston. The patient was breathing through a tube, the air from the bell on and off, causing the gas volume change inside the bell and it was moved by the pressure differences in exhalation (see Fig red arrow) and inhalation down ( green arrow). These movements could be documented graphically with a suitable recording device such as a kymograph as leveling curve. Through a calibration, such as the use of exactly one liter of air in the bell, the lung volumes and their time course were calculated.

Furthermore, can be achieved by lime the incoming breathing air free from carbon dioxide, reducing the volume of the bell is reduced in proportion to the oxygen consumed the experimental participant. Then can be converted via indirect calorimetry of oxygen consumed in the power dissipated by the body.

Current spirometer

Today, the volume is measured only indirectly. Is integrated over the volume of the measurement of the flow rate in the breathing tube. Standard measurement procedures are now turbine pneumotachograph and ultrasound:

• The advantage of a turbine is the affordable price. Here the volume of the rotation speeds of a turbine in the breathing tube is determined, but the measurement is partly incorrect, since the turbine starts to rotate only when a certain airflow or after the end still nachdreht minimal and very good storage.
• A pneumotachograph determines the flow rate on pressure differences in the breathing tube during the flow of lamellae. He is initially very accurate, loses due to contamination of the slats by the humidity of the air we breathe but of precision. On a regular cleaning or replacement of the blades must be respected.
• With the use of the ultrasonic propagation time difference between two ultrasonic paths are evaluated, one being directed to and from the air flow. This method is most accurate and does not require calibration of the device, because all factors for both test sections are equal and so cancel in the measurement. Obtaining the technique is more expensive than the other methods described generally.