Which Peak Flow Meter Do I Have?
During 2004, countries across Europe (including the U.K.) will adopted a new standard for measuring peak expiratory flow (P.E.F.) developed to improve the management of asthma and other respiratory diseases.
The new standard (EN 23747) applies to all peak flow meters sold within the E.U. The traditional scaling for P.E.F. measurement changed from the original Wright (sometimes known as Wright-McKerrow) scale, or the more recent ATS (American Thoracic Society) scaling, to the new ‘EU’ scale, specified in the European Standard EN 23747 .
What are the differences between meters?
There are 3 things to consider: Brand, Scale and Range.
Brand
Most peak flow meters are small, hand-held and light in weight. The original Wright peak flow meter was a large, circular clock-shaped device and was very heavy. Mini-Wright peak flow meters can be recognised from their grey-coloured body and coloured ‘collar’ (usually red), although do beware – there are unauthorised copies of the Mini-Wright available, whose quality and accuracy is not the same as the original.
Other designs of peak flow meter have become available over they years, and they vary in shape and size and colour – look for a description of who made the meter on the device itself. It may be printed on, or moulded into the plastic of the device during manufacture.
Scale
The original Wright meter defined how airflow should be measured in patients in 1959; the Mini-Wright was designed to provide identical readings to the original, heavy Wright meter, and for many years, peak flow was measured only on the ‘Wright’ scale. In the U.K., the Department of Health specified that all meters should read airflow in the same way as an original Wright peak flow meter.
The fact that the Wright scale had been developed from airflow measurements from real patients was of concern to some scientists in the U.S.A., who chose to develop a new scaling for peak flow meters using a series of reproducible ‘waveforms’ (each waveform could be defined by airflow acceleration, duration and deceleration). Thus a new system of testing was proposed, and eventually was adopted by the National Asthma Education Program (N.A.E.P.) and the American Thoracic Society (A.T.S.), becoming known as the ‘ATS’ scale for peak flow meters.
Standards for peak flow meters were also developed in Australia and New Zealand, where additional requirements were made for environmental and life testing, and highlighted the importance of airflow resistance (how much the meter interferes with the movement of air during exhalation).
Investigations by Dr. M. Miller and colleagues has identified certain types of forced exhalation that produce inaccurate readings on both ‘Wright’ and ‘ATS’ scaled meters; the new EN 23747 standard for peak flow meters includes additional airflow ‘waveforms’ to the ATS-method of testing, requirements for life-testing and limits on airflow resistance, all of which should ensure that any instrument compliant with EN 23747 can perform with a high degree of accuracy under all circumstances. Such meters will become known as ‘EU’ scale meters.
Some meters, but not all, will identify which scale the meter uses by printing on the meter itself. Look for ‘Wright’, ‘ATS’ or other words on the meter, and if you are not sure, contact the manufacturer for an explanation.
Range
You can tell which Mini-Wright meter you have by looking at the design with the Standard Range model reading to 800, and the Low Range meter up to 400 (for other brands of meter, the ranges will be similar).
The original Wright peak flow meter was available with a measuring range of 60 to 1000 L/min; subsequently, changes were made to the scale, and a low range version was introduced to increase the accuracy of measurement in children (it was also smaller, less intimidating and lighter to hold).
Similarly, Mini-Wright peak flow meters were originally only available in a ‘standard’ range, and a Low Range version was made available several years later. Research into airflows in the 1990’s allowed the low range design of Mini-Wright to be updated in 1996, resulting in the first low range peak flow meter that gave identical readings to the standard range model (some brands of peak flow meter still give different readings, depending on whether you use the low range or standard range model).
Low range meters are invaluable when monitoring children or the elderly, or those with severe asthma. The smaller size makes the Low Range Mini-Wright easier to handle by children and older patients, and small changes in airflow can be identified more easily on a meter that has been developed only to show the airflows up to 400 L/min. It is also worth considering the negative reaction of patients whose peak flow rarely exceeds 200 l/min, if presented with a meter where their readings are confined to the lowest 25% of the scale.
Which meter do I have?
Standard Range
 | Mini-Wright (Standard Range) ATS scale
|  | White text on a purple background |
 | Mini-Wright White (Standard Range) Wright-McKerrow scale
|  | White text on a black background |
 | Mini-Wright (Standard Range) EU (EN 23747) scale
|  | Blue text on a yellow background |
Low Range
 | Mini-Wright (Low Range) ATS scale |  | White text on a Blue background |
 | Mini-Wright (Low Range) Wright scale |  | White text on a Red background |
 | Mini-Wright (Low Range)EU (EN 23747) scale |  | Blue text on a yellow background |
Is the new EU-scale meter the same as the ATS-scale meter?
No. Whilst the scale may look similar, only meters that display the text ‘EN 23747‘ have been tested to the new standard. The EN 23747 standard includes two important ‘airflow waveforms’ that are not part of the ATS test procedure for peak flow meters. Some ATS-scale meters have already been shown as failing the new EN 23747 standard .
My patient has an old-scale meter, and I have a new EU-scale meter – what do I do?
For conversion of P.E.F. readings from Wright scale to EN 23747 scale, contact us for details and resources, or download our Peak Expiratory Flow Rate Normal Values conversion chart.
