Measure Peak Flow - Managing Your Asthma: Asthma

Content provided by the Faculty of the Harvard Medical School

Measure peak flow

The best assessment to find out exactly how well your lungs are functioning is to measure your peak flow to find out how fast you can exhale air. When your asthma is well controlled, air flows rapidly through the breathing tubes. When you are having difficulty, the breathing tubes are narrowed and air can be forced only slowly out of the lungs.

You can measure your peak flow quickly and easily, using the same device doctors sometimes use to assess asthma in their offices (see "Peak flow"). First, set the indicator at zero. Then, take a deep breath in, grip the mouthpiece tightly with your lips, and exhale quickly and forcefully. Make a note of how far the indicator moved on the scale. Then set the indicator back to zero and repeat the procedure twice more. The best of your three attempts is your peak flow.

With a peak flow meter, you can compare your breathing to that of a person without asthma. You can also compare your breathing today with your own peak flow measured on a day when you are free of any asthma symptoms (your "personal best" peak flow). By using a peak flow meter and keeping track of results, you can know exactly how your asthma is doing. This is valuable information for you and your physician.

At one time, doctors routinely encouraged patients to check their peak flow every day, but this is no longer a uniform recommendation. For one thing, it places an added burden on already busy lives. For another, it is unclear that daily peak flow recordings will reliably alert you to asthma flare-ups before your symptoms do.

Still, having a peak flow meter at home is useful when it comes to assessing the severity of your asthma symptoms. It's best to keep a peak flow meter at home and think of it like a thermometer. If you are sweaty or chilly and feel feverish, you'll probably find it useful to take your temperature with a thermometer rather than guessing about your temperature. Similarly, if you were to develop persistent coughing and shortness of breath, it would be useful to check your peak flow rather than to guess whether your symptoms are due to asthma and, if so, how severe the flare-up is.

Last updated:	September 27, 2007