Readings from a peak flow meter can help you to recognize early changes that may be signs of worsening asthma. During an asthma attack, the muscles in the airways tighten and cause the airways to narrow. Reduced readings from the peak flow meter may alert you to the airway narrowing often hours or even days before you have worrisome asthma symptoms such as shortness of breath or chest tightness.

The peak flow meter can also be used to verify that respiratory symptoms are due to bronchospasm. Ask your doctor or allergy specialist for a written asthma action plan that includes the use of a peak flow meter to determine whether you are in the green, yellow, or red zone.