Live Peak Flow Meter testing (Asthma) at NPTI Florida. A peak flow meter is a handheld device that measures how well air moves out of your lungs. During an asthma episode, your airways often narrow. A peak flow meter can measure this narrowing hours, even days, before you have any asthma symptoms. In fact, it’s so sensitive to changes in your airways that it can alert you to breathing issues even better than a doctor can when listening to your lungs with a stethoscope. By taking your asthma medi