Peak flow

Peak flow, also peak flow or PEF, is a measurement in pneumology that records the maximum rate of expiration in a patient. The value is given in liters of expired air per second or minute. It is measured within the first milliseconds of exhalation, in contrast to one-second capacity.

The relatively simply constructed peak flow meter (there are numerous versions) consists of a short tube with a mouthpiece and an outlet nozzle. Inside the tube is a movable drag connected to a spring and a pointer. The pointer position can be determined on a scale in each case.

Exhaling into the peak flow meter pushes the drag and pointer forward in the tube against the restoring force of the spring. The distance shown depends on the strength of the exhalation. The more forcefully the patient exhales, the greater the spring deflection. As the respiratory flow subsides, the pointer remains at its largest scale value. It does not return to its initial position. Its position can be read on the scale.

The peak flow value therefore indicates the peak flow of the exhaled air. The higher the value, the better the exhalation force of the lungs. If the measured values are recorded over a longer period of time, a recording protocol can be used to assess how the situation of the lungs has developed over a certain period of time. Furthermore, the efficiency of medication can be assessed.

This simplest type of lung function measurement can be carried out at any time by the patient himself, even outside a measuring laboratory. The measurement is easy to perform. Within an asthma training course, the use of a peak flow meter can be learned in detail.