Peak flow meter records peak flow or peak expiratory flow rate (PEFR), the fastest rate at which air can move through the airways during a forced expiration starting with fully inflated lungs. PEFR correlates well with FEV1, which a spirometer measures. PEFR is typically used for asthma diagnosis by comparing a patient’s PEFR with his/her normal personal best PEFR or his/her predicted PEFR value. A PEFR reading lower than normal may be a warning sign of asthma, as described in the Peak Flow Zone system below.
The Peak Flow Zone System
Peak flow (PEFR) numbers are divided into zones that are set up like a traffic light. This helps you to know what to do when your peak flow number changes. For example:
Green Zone (80 to 100 percent of your personal best number) signals that asthma is under control. No asthma symptoms are present, and you may take your medication as usual.
Yellow Zone (50 to 80 percent of your personal best number) signals that asthma has begun to deteriorate. You may be having an episode of asthma that requires an increase in your medication. Consult your doctor.
Red Zone (below 50 percent of your personal best number) signals that an attack of asthma may be coming. You must take an inhaled beta2-agonist right away and call your doctor immediately if your peak flow number does not return to the Yellow or Green Zone and stay in that zone.
PEFR readings provide an objective measurement of the state of your asthma. Recording PEFR twice a day regularly for 2-3 weeks is important for establishing a diagnosis. The pattern of PEFR obtained during this period may help you (your physician) in identifying environmental asthma triggers and guiding decisions for therapy. If you cannot, for example, achieve 80% of your personal best/predicted PEFR for 2-3 weeks even after taking a bronchodilator, you may need to start a course of corticosteroid tablets to get your PEFR back to normal levels.
A PEFR lower than personal best/predicted may indicate either airway narrowing, as in asthma, or a loss of lung volume as in other lung diseases. However, asthma is confirmed if:
- Reversibility test is positive.
- PEFR variability in a day is more than 20%.
- There is 15% or greater decrease in PEFR after running or other exercise.
Common related terms
Normal peak flow (PEFR)
There are two kinds of normal peak flow (PEFR) readings you might come across: predicted peak flow and personal best peak flow. Normal peak flow value may vary among people.
Predicted Peak Flow
Predicted peak flow is estimated and not measured. Your predicted peak flow is based on the peak flow of someone who is the same age, height, sex and ethnic origin, and who does not have asthma. The problem with this system of measurements is that you can fall quite a long way above or below your predicted peak flow value and still be normal. This is why personal best peak flow is usually preferred over predicted peak flow.
Personal Best Peak Flow
Personal best peak flow is measured by recording PEFR 3-4 times a day for several asymptomatic days. Your personal best peak flow (PEFR) number is the highest peak flow (PEFR) number you can achieve over a 2-week period when your asthma is under good control. Good control is when you feel good and do not have any asthma symptoms.
In reversibility test, increase in peak flow (PEFR) after administration of bronchodilator medicine is recorded and compared with the normal peak flow. An increase of over 20% is diagnostic of bronchial asthma. This is another useful application of peak flow meter.
PEFR variability is the difference between the highest and the lowest PEFR values recorded in one day. It expressed in terms of the percentage of the lowest PEFR value. PEFR normally varies slightly in a day. The lowest PEFR is usually observed in the early morning and the highest in the afternoon. A PEFR variability of over 20% is diagnostic of bronchial asthma. A high PEFR variability indicates an increase in asthma severity.
Contains your detailed asthma action plan with information on,
- PEFR readings
- Suspected triggers
- Emergency contacts and protocols