Takeaway Because asthma may worsen gradually, your peak flow measurement may start to decrease hours—and sometimes even days—before you notice any symptoms.

PEFR stands for peak expiratory flow rate. It's a test that measures how fast you can exhale. Learn more about PEFR, why your doctor may suggest this test, how to prepare, what to expect, and ...

A peak flow meter is a simple, small, hand-held tool that can help you maintain control of asthma by providing a measurement of how well air moves out of the lungs. After blowing into the device ...