Since 1995 - Non Profit Healthcare Advice

Peak Flow Meter: What Exactly Does it Measure?



My daughter uses her peak flow meter as an objective tool to be able to know if she is not breathing well or not. Sometimes it gives her a good reading when she does not think she is breathing well at all. We have asked many people about this including her pulmonary doctor. He says he does not know why this happens.

One nurse told us it is because it measures the large airways only and does not account for all the many smaller airways. Does this mean that my daughter’s problems are concerning the small airways and the peak flow meter is not designed to be used with them?

Sometimes she gets a bad reading and she is like “That is what I thought” and then she does her rescue inhaler. But on those times where she is like “Why isn’t my breathing good like my reading says it is?”—she does not know whether to take her rescue inhaler or not. It is very disconcerting because she wants that objective “voice” from her peak flow meter. By the way, we used to throw those away thinking something was wrong with the device, but that was not it (just in case you were wondering too). I WOULD LOVE TO KNOW ANSWER TO THIS.

Her asthma started in 5th grade when we noticed she did not recover well from the flu. She takes Adair 100/50 2x a day every day except when she has been sick and then she goes up to 250. It is usually well-controlled. She has tried Singular and breathes even better when she is on it along with Adair, but Singular makes her mood alter towards depression or other times high anxiety. She loves the way it helps her breathing but she cannot take the mood changes. I also would like to know if maybe taking it every other day would be any different.

Thanks for help – it is so hard to come by. Oh yes, my daughter is 21 so it has been a long time dealing with asthma.


In general, a peak flow meter is used to monitor air flow.  The meter is not calibrated like the sprio machines at the doctors office or pulmonary lab so it is not an exact measuring tool.  It is used to monitor trends in airflow only.  The reading is “effort dependent” which means the size of the breath and technique can affect the reading. 

The measurement is best taken in a standing position to obtain maximal expansion of the diaphragm.  Three measurements should be taken and the best of the 3 readings recorded.  If she has an asthma action plan it is generally set up based on symptoms alone or symptoms and peak flow readings.  Follow the plan for determining rescue or other medication use. 

Other conditions such as allergies, sinus disease, uncontrolled acid reflux and vocal cord dysfunction can cause shortness of breath without causing a change in the peak flow readings.  Your daughter may want to discuss any concerns with her provider. 

There have been reports Singulair, Accolate and Zyflo can cause agitation, aggression, anxiousness, dream abnormalities, hallucinations, depression, insomnia irritability, restlessness, tremor, suicidal thinking or suicide. The FDA has requested the manufacturers of each of these medicines include a precaution in their drug labeling.  It is unlikely every other day dosing would eliminate the depression your daughter has experienced on the drug; therefore it is best for your daughter to talk to her doctor about possible alternative medications if her asthma is not fully controlled.  

For more information:

Go to the Asthma health topic.