If you’re one of the millions of Americans with asthma, you’ll want to know how to use a peak flow meter. A peak flow meter consists of a plastic tube with a mouthpiece and marker that moves along a numbered scale. It measures how well your lungs can expel air. The force of air, called the peak expiratory flow (PEF), is measured in liters per minute. This simple device can be an integral part of your asthma management plan. Understand the Purpose of a Peak Flow Meter During an asthma attack, muscles in your airways contract, making it harder for your lungs to take in and release air. This process of narrowing typically increases with time. Your airways begin to constrict before you even feel symptoms. A peak flow meter can signal the onset of this narrowing so you can head off an asthma attack. Learn How to Use the Readings To use a peak flow meter, you’ll blow into the mouthpiece, exhaling a hard blast of air as if you were blowing out candles on a birthday cake. Decreases in your PEF reading from your usual measurement can mean your asthma is getting worse even before you have symptoms like wheezing or coughing. Your peak flow meter readings can also help you: Learn how well controlled your asthma is during the day and at night, which is when symptoms are often worse Pinpoint the triggers that make your asthma worse Know when to take your rescue medication and follow other steps on your asthma management plan Decide with your doctor whether your asthma treatment plan is working or whether you need to adjust your medication or add other medications Determine when to seek emergency care If your asthma is severe, you may need to use your peak flow meter several times a day. If your asthma is under control, you may decide to use it only when you feel symptoms. Know When and How to Use a Peak Flow Meter Before using a peak flow meter, make sure the marker is at 0 (liters per minute) on the numbered scale. In one breath, blow as hard as possible and jot down the reading. Repeat the process two more times. The numbers should be close together. Then record the highest of the three readings—this is your “personal best.” It’s the highest PEF you can achieve when your asthma is well controlled. Measure your peak flow rate at about the same time each day. For instance, take readings between 7 a.m. and 9 a.m. and again between 6 p.m. and 8 p.m. and compare them to your personal best. You might want to measure your peak flow rate before and after taking your asthma medicine. Talk with your doctor about when it’s best to use your peak flow meter and what a normal reading is for you. Keep a chart of your peak flow readings and bring the chart with you to your doctor’s appointments. Like a traffic light, peak flow rates fall into three zones—green, yellow and red. Talk with your doctor about what to do if your peak flow reading falls into the yellow or red zone, which indicates your asthma is getting worse or your airways are severely narrowed. Your doctor treats many people just like you who go through ups and downs in managing their asthma. So talk openly about your readings and together you can work out a good action plan.