Peak flow meter

A peak flow meter is a small, hand-held device used to manage asthma by monitoring airflow through the bronchi and thus the degree of obstruction in the airways.

Function

The peak flow meter measures the patient's maximum ability to exhale, or peak expiratory flow rate (PEFR or PEF). Peak flow readings are higher when patients are well, and lower when the airways are constricted. From changes in recorded values, patients and doctors may determine lung functionality, severity of asthma symptoms, and treatment options.

The measurement of peak expiratory flow was pioneered by Dr. Martin Wright, who produced the first meter specifically designed to measure this index of lung function. Since the original design of instrument was introduced in the late 1950s, and the subsequent development of a more portable, lower cost version (the 'Mini-Wright' peak flow meter), other designs and copies have become available across the world.

Measurement of PEFR requires training to correctly use a meter and the normal expected value depends on a patient's sex, age and height. It is classically reduced in obstructive lung disorders such as asthma.

Due to the wide range of ‘normal' values and high degree of variability, peak flow is not the recommended test to identify asthma. However, it can be useful in some circumstances.

A small proportion of people with asthma may benefit from regular peak flow monitoring. When monitoring is recommended, it is usually done in addition to reviewing asthma symptoms and frequency of reliever medication use.( [National Asthma Council of Australia]

When peak flow is being monitored regularly, the results may be recorded on a peak flow chart.

It is important to use the same peak flow meter every time.

Peak flow monitoring is not recommended for children under 12 years

Scales

There are a number of non-equivalent scales used in the measurement of Peak Flow. cite journal | author = Martin R. Miller | year = 2004 | month = June | title = Peak expiratory flow meter scale changes: implications for patients and health professionals | journal = The Airways Journal | volume = 2 | issue = 2 | pages = 80 | url = http://www.airwaysextra.com/AJJune2004-Miller-published.pdf | format = PDF | accessdate = 2006-06-06]

Graphs or tables are available of predicted normal values based on a person's gender, age and height. It should be noted that there is a wide natural variation in results from healthy test subjects.
* "Wright" scale cite journal | author=Nunn A, Gregg I | title=New regression equations for predicting peak expiratory flow in adults | journal=BMJ | volume=298 | issue=6680 | pages=1068–70 | year=1989 | pmid=2497892 - Predicted peak expiratory flow in normal adults using Wright-scale] cite journal | author = Godfrey S, Kamburoff PL, Naim JL | year = 1970 | title = Spirometry, lung volumes and airway resistance in normal children ages 5 to 18 | journal = Br J Dis Chest | volume = 64 | pages = 15–24 | doi = 10.1016/S0007-0971(70)80045-6 - Predicted peak expiratory flow in normal children using Wright-scale]
* "EN 13826" or EU scale cite web | author =Clement Clarke International | year=2004 | url=http://www.peakflow.com/top_nav/normal_values/index.html | title =Predictive Normal Values (Nomogram, EU scale) | publisher =Clement Clarke International | accessdate =2006-06-06 - Downloadable PDF charts for adults and children using EU scale]
* "A.T.S." (American Thoracic Society) scale

In 2004 the UK switched from the original Wright scale to the newer, more accurate European scale. Limited information on converting between the scales exists. cite web | author=Clement Clarke International | year = 2004 | url=http://www.mortonmedical.co.uk/PEFscale.exe | title =Mini-Wright Peak Flow Meter - Wright to EU (EN13826) converter | format =EXE macromedia flash | publisher =Clement Clarke International | accessdate =2006-06-06]

Measurement

The best of three readings is used as the recorded value of the Peak Expiratory Flow Rate. It may be plotted out on graph paper charts together with a record of symptoms or using peak flow charting software. [cite website| title=Peak flow charting software| url=http://www.my-peak-flow.com/peak-flow-info.html] This allows patients to self-monitor and pass information back to their doctor or nurse. cite journal | author = Scottish Intercollegiate Guidelines Network & The British Thoracic Society | year = 2003 | title = British Guideline on the Management of Asthma - Annex 8: Personal Asthma Action Plan | journal = Thorax | volume = 58 | pages = Suppl I | url = http://www.enterpriseportal2.co.uk/filestore/bts/annex8asthma05.pdf | format = PDF | accessdate=2006-06-06 - for recording chart of PEFR readings]

Peak flow readings are often classified into 3 zones of measurement according to the American Lung Association [cite website| title=How can I determine a normal peak flow rate for me?| author=American Lung Association| url=http://www.lungusa.org/site/pp.asp?c=dvLUK9O0E&b=22586] ; green, yellow, and red. The color system is based on the colors of street traffic lights. Doctors and health practitioners can develop an asthma management plan based on the green-yellow-red zones.

The Green Zone means 80 to 100 percent of the usual or normal peak flow readings are clear. A peak flow reading in the green zone indicates that the asthma is under good control.

The Yellow Zone means 50 to 80 percent of the usual or normal peak flow readings indicate caution. It may mean respiratory airways are narrowing and additional medication may be required.

The Red Zone means less than 50 percent of the usual or normal peak flow readings indicate a medical emergency. Severe airway narrowing may be occurring and immediate action needs to be taken. This would usually involve contacting a doctor or hospital.

See also

* Spirometry
* Metered dose inhaler
* Asthma inhalers
* Salbutamol
* COPD
* DOG

References