You may have heard of a peak flow meter if you have Asthma and wonder is it really worth it. How do you use it? What good is it really? Well it turns out that it's often hard to tell how strong your breathing is at any given moment. There are so many other things going on in your life - if you're tired, if you're feeling happy, if you're feeling down. And you may think you know how tight your airways are, but often people don't. I'm Dr. Alan Greene and I want to explain to you how powerful it can be to have real numbers telling you how well you're breathing. If you've got accurate numbers and you keep them day after day, you can use that to adjust your medicines. That means you can use the lowest amount of medicine possible to feel the best possible.So here's how they work. Usually there's a mouthpiece. You just screw into one end so you can keep it clean. And there's a little gauge here that reads the numbers and you move it all the way down to 0. Then just seal your mouth around the mouthpiece and blow hard, as hard as you can once. (Blow sound) Made it almost to the end. Scored pretty well. Then what you do is write down that number. Pull it back to the beginning and do it a total of 3 times. Whatever the highest number is, that's how well you're breathing right now. Then you can compare it that your asthma action plan. That number will either fall in the green zone, or the yellow zone, or the red zone. And it will help you know exactly what to do to best control your asthma with the minimal amount of medications. Really, really worth it.Reviewed ByReview Date: 09/18/2011David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.