FLEISCH TUBE

Typical Number in Hospital: 3

Cost Bands: 2

References: 6,9

This is the transducer used in a pneumotachograph for monitoring the flow of air in and out of the mouth. It consists of a wide bore tube in which there is a mesh or screen which slightly restricts the airflow through it. At each side of the mesh or screen there is a small tube, of two or three millimetres diameter, inserted into the airway, which is connected to a differential pressure transducer. The resistance to flow presented by the screen produces a differential pressure which is proportional to the airflow through the device.

Theoretical problems exist because the inspired and expired volumes and gas mixtures are not the same, so that the pressure drop will not be the same for equal flow in each direction. Also, water vapour in the expired gases may condense on the mesh unless heating is applied, or some other anti-condensation measure is used.

Fleisch tubes are used in equipment for lung function testing and also in connection with artificial lung ventilation systems.