What is peak expiratory flow rate (PEFR)?

What is Peak Expiratory Flow Rate (PEFR)?

Peak expiratory flow rate (PEFR) is the maximum flow rate of air achieved during a forceful expiration starting from full lung inflation, measured in liters per second (L/s) or liters per minute (L/min). 1

Definition and Measurement

• PEFR represents the maximal expiratory flow achieved from a maximum forced expiration, starting without hesitation from the point of maximal lung inflation. 1

• When obtained from spirometry flow-volume curve data, PEFR is expressed in L/s, while portable peak flow meters typically display results in L/min. 1

• The measurement reflects the maximum flow at the mouth achieved during an expiration delivered with maximum force starting from the level of maximum lung inflation. 2

Physiological Basis

• PEFR is an effort-dependent parameter that reflects large airway flow and depends on:

  • Lung elastic recoil pressure 3
  • Muscular strength of the patient 3
  • Voluntary effort 3
  • Resistance upstream to the flow-limiting segment 2

• The measurement may be determined by the wave speed flow-limiting mechanism, where high PEF is consistent with low upstream resistance, large cross-sectional area at the choke point, and/or small compliance of the airway wall. 2

Clinical Applications

• PEFR provides a rapid, objective means of diagnosing and monitoring asthma in both office and home settings. 4

• It enables early detection of deteriorating lung function, allowing timely therapeutic intervention and potentially preventing hospital admission. 4

• During acute asthma attacks, PEFR aids in determining whether hospital admission is necessary. 4

• The test is simple, affordable, portable, and widely available for use in clinic or home settings. 5

Important Technical Considerations

• For standardization purposes, forced expiration should be initiated with open glottis immediately after maximal inspiration. 2

• Head position affects measurements: hyperextension may increase PEFR while flexion may decrease it by changing the stiffness of larger airways. 2

• The measurement has no clinical utility superior to FEV₁, FVC, or FEF 25-75% when obtained from maximal expiratory flow-volume loops. 1

• PEFR values vary according to age, gender, height, weight, BMI, ethnicity, and altitude, requiring population-specific reference values. 3