Breathing: Asthma: Peak Flow Meter

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Peak Flow Meter Overview

A peak flow meter is a portable hand-held device that measures how hard a person can exhale. It has a little meter on it that measures the power of each breath. To use a peak flow meter, a person blows out several times in a row to measure the maximum exhale velocity. Once that’s known, it can be helpful in monitoring asthma. It can be helpful to use a peak flow meter with some coaching early on to ensure proper use.


A peak flow meter is typically about the same size or maybe a little bit bigger than an inhaler with a spacer attached. Using a peak flow meter on a daily basis can be very helpful. Seeing small differences in daily measurements is quite normal. The measurements that come from a peak flow meter are in round numbers that are compared to a person’s “best” number that was taken when the air tubes were relaxed. This comparison, stated as a percentage, represents how hard the lungs can work.


Medical professionals typically consider a person to generally be fine if the lungs are operating in the 80% to 100% range. Early in an asthma attack, the peak flow often drops below 80%, and it does so 24 hours before most people even know they’re having an asthma attack. So, if a person don’t use the peak flow measurement everyday, he may not know when that dip happened. Since peak flow measurements can be an early warning sign that an asthma attack is coming, it can allow people to be proactive in how they manage asthma attacks, the activities they choose to participate in and the medications they decide to take.

How to Use a Peak Flow Meter


Doctors can create an asthma action plan their patients to track their peak flow meter measurements. There are many, ways to track it. Classically, this has been done by graphing it so that everyday, a person performs a peak flow measurement and makes a dot on the graph. Now there are many mobile tools and computer-based tools that will do the graphing for the user. It’s important to know when a dip occurs, particularly below 80% of the best measurement. If the best peak flow measurement was 500, a person might see daily measurements bounce around 445, 500, 485, and then one day, all of a sudden, that person could be at 390. That’s below the 80% mark and could be a sign that the air tubes have begun tightening. That can be very helpful because it can give a person up to 24 hours’ notice that he has to be careful. People who suffer from asthma should have a system to track peak flow so that they are ready and know their tubes are tightening up.