Peak Flow Measurement

Peak flow (English : peak expiratory flow, PEF; synonyms: PEF value; peak expiratory flow; maximum expiratory flow rate) is the airflow, or more precisely the maximum respiratory flow rate, during forced vigorous expiration (expiration).The PEF value is determined during spirometry and can be read from the flow-volume diagram. Another measurement method-which can also be performed by the patient-is measurement with a peak flow meter (see below).

Indications (areas of application)

Among other things, peak flow measurement is an important tool for distinguishing asthma disease from chronic obstructive pulmonary disease (COPD) and for monitoring the progression of bronchial asthma.

The procedure

The measurement is performed using a peak flow meter.The value is expressed in l/sec or l/min and compared with normal values. The result is then expressed as a percentage of the normal value. Normal values for peak flow depend on sex, age, and body size and thus vary from individual to individual. Instructions for the patient on how to perform the test: After a deep inhalation, hold your breath for a short moment. In the meantime, bring the device, which is equipped with a mouth tube, horizontally to your mouth. The mouthpipe is firmly enclosed by your lips so that no air can escape. You must then exhale into the mouthpiece as quickly and as forcefully as you can. In the second step, the doctor will administer a bronchodilator (brochodilator) spray (ß-2 mimetic: e.g. -400 μg salbutamol) if your peak flow is below the normal range. If this is the case, the peak flow also changes significantly to the positive – the value increases – and there is most likely an asthma disease.If the previously reduced peak flow remains reduced after the attempt of bronchodilation (airway expansion), this speaks more for a chronic obstructive pulmonary disease (COPD).The peak flow meter can also be used to monitor the progress at home. To do this, three measurements are usually taken several times a day before taking medication, with the highest reading being noted. In order to monitor whether the medication is working well, a measurement will also be taken again after taking the medication, if the doctor recommends this.It is recommended that you keep a diary and check the values regularly. In this way, you and your doctor can see exactly whether the airways are clear and whether the medication is sufficiently effective and is being taken regularly. At the same time, an impending asthma attack can be detected and sometimes prevented by taking medication in time. PEF value and therapeutic consequences

PEF Assessment Therapy
80-100% of PBW Complaint-free patient Continue current therapy
60-80% of PBW Increasing discomfort:

  • Wheezing
  • Chest tightness
  • Cough
  • Shortness of breath
  • Waking up at night with asthma symptoms
  • Decreased ability to perform daytime activities
 Immediate initiation or intensification of therapy (after consultation with the physician).
<60% of PBW Absolute emergency!One or more warning signs may occur:

  • Increasingly difficult to breathe
  • Not being able to sleep or do daytime activities because of breathing difficulties
 Immediate medical consultation

PBW (= personal best):

  • Best peak flow value after approximately 14 days of measurement.
  • Under optimal drug therapy
  • In a stable phase of the disease

Further note

  • The PEF value in the morning should not vary by more than 10% compared to the value measured the evening before: If this so-called PEF variability is > 20%, this indicates inadequate therapy for bronchial asthma.