A peak flow meter (PFM) is a portable, handheld device designed to measure how quickly air can be forced out of the lungs after a full inhalation. This measurement is called the Peak Expiratory Flow Rate (PEFR), expressed in liters per minute (L/min). The device’s primary function is to provide an objective, numerical measure of lung function, specifically how open the airways are. Regular use helps people with conditions like asthma to monitor changes in their air passages, often detecting airway narrowing before obvious symptoms occur.
The Step-by-Step Measurement Process
Taking an accurate peak flow reading relies on performing the technique consistently every time. Before starting, move the sliding marker on the device to the lowest number on the scale, typically zero. Standing up straight is recommended, as consistency in position is most important.
Begin by taking the deepest breath possible, filling the lungs completely with air. Hold this breath briefly while placing the meter’s mouthpiece into the mouth, ensuring the lips seal tightly around it and the tongue is kept clear of the opening.
Next, blow the air out of the lungs as hard and as fast as possible in one single, forceful exhale. This should be a quick, hard blast of air, not a slow exhalation. The force of the breath moves the marker up the numbered scale, and the number where it stops should be noted.
The entire procedure must be repeated two more times, resetting the marker to zero before each attempt. Record the three readings, but only the highest number is considered the final measurement for that session, as it reflects the best effort.
Establishing Your Personal Best and Monitoring Routine
The numerical readings from the peak flow meter are most meaningful when compared to an individual’s “Personal Best” (PB). The PB is the highest peak flow reading achieved over two to three weeks when the condition is under good control. This value serves as the baseline against which all future daily measurements are judged.
To establish this baseline, readings should be taken twice a day, typically morning and evening, for the entire period. Measure the peak flow before using any quick-relief inhalers to obtain a true reading of the current airway function. Once the PB is determined, update it periodically or whenever a new meter is used.
For ongoing monitoring, a consistent routine is necessary to track daily variations and recognize early changes. Readings are usually taken every morning upon waking and again in the late afternoon or evening, maintaining the same time window each day. The recorded peak flow number, along with any symptoms experienced, should be logged to create a comprehensive record.
Understanding the Peak Flow Zone System
The interpretation of the daily peak flow number uses a simple, color-coded traffic light system based on the Personal Best (PB). This system translates the measured volume into actionable steps outlined in a patient’s action plan, with zones calculated as a percentage of the individual PB.
Green Zone
The Green Zone represents 80% to 100% of the PB, signaling that the airways are open and the condition is well-controlled. A reading in this range indicates that the regular maintenance treatment plan should be continued as directed. No immediate changes to medication are necessary.
Yellow Zone
The Yellow Zone spans 50% to 80% of the PB, serving as a caution signal that airway narrowing is beginning. This range suggests the condition is worsening, even if symptoms are mild or not yet present. Readings in this zone require specific action, such as adding quick-relief medication or contacting a healthcare provider, according to the personal action plan.
Red Zone
The Red Zone is defined as any measurement falling below 50% of the PB, signaling a medical alert requiring immediate attention. Emergency medication should be taken right away. If the number does not quickly return to the Yellow or Green zones after treatment, urgent medical care or emergency services must be sought.