PEAK FLOW METER

A peak flow meter is a mechanical device in which the patient blows out. The force of

the expiration pushes an indicator. The device

measures air flowing out of the lungs, called peak

expiratory flow rate (PEFR). Peak expiratory flow rate

(PEFR) is the maximum flow rate generated during a

forceful exhalation, starting from full lung inflation.

Peak flow rate primarily reflects large airway flow and

depends on the voluntary effort and muscular strength

of the patient.

Maximal airflow occurs during the effort-dependent portion of the expiratory

maneuver, so low values may be caused by a less than maximal effort rather than by airway

obstruction. Nevertheless, the ease of measuring peak flow rate with an inexpensive small

portable device has made it popular as a means of following the degree of airway obstruction

in patients with asthma and other pulmonary conditions.

A peak flow meter, when used properly, can reveal narrowing of the airways well in advance

of an asthma attack. Used mainly by persons with moderate to severe and persistent asthma,

peak flow meters can help determine:

when to seek emergency medical care.

the effectiveness of a person's asthma management and treatment plan.

when to stop or add medication, as directed by your physician.

what triggers the asthma attack (such as exercise-induced asthma).

Measuring Peak Expiratory Flow

Peak flow meters should be used regularly to check how well the asthma is being controlled.

In addition, the peak flow meter may be a valuable tool during an asthma attack, because it

can help determine how well the short-term, quick-relief asthma medication is working. The

National Heart, Lung, and Blood Institute (NHLBI) recommends measuring lung function

during the following times:

every morning, before taking asthma

medications

during asthma symptoms or an asthma attack

after taking medication for an asthma attack

other times recommended by your physician

During a peak flow measurement the patient needs to sit up straight or stand up.

The patient inspires as deeply as possible, takes the device in his mouth and blows out as

strongly and as fast as he can. It is not necessary to blow out as long as possible, in contrast to

a spirometry test. An expiration of 1 second is sufficient.

The test is repeated at least three times and the best value is withheld.

Peak flow is comared to predicted values or - even better - to the patient's best personal value.

Predicted values are dependant of sex, age, height and ethnicity. Measured peak flow meters

are classified in the peak flow zones.

Peak flow zones are based on the traffic light concept: red means danger, yellow means

caution, and green means safe. Based on your personal best peak flow measurement (the

optimal level of your lung function), your three peak flow zones include:

Green: 80 to 100 percent of your personal best peak flow measurement; asthma is

under control.

Yellow: 50 to 79 percent of your personal best peak flow measurement; asthma is

getting worse; you may need to use quick-relief medications or other medication, as

directed by your physician.

Red: below 50 percent of your personal best peak flow measurement; medical alert,

take quick-relief medication and seek medical help immediately.

The goal of the peak flow zones is to help you recognize when the asthma may start to

become uncontrolled. The goal is to stay within the 80 percent value of your personal best

peak flow measurement. Zones with a smaller range, such as 90 to 100 percent, may be

recommended by some health care providers. Always follow the advice of your doctor

regarding the peak flow rate.

Limitation of Peak Expiratory Flow Measurement

Peak flow measurement is a simple and cheap test, but there are important limitations

to measuring peak expiratory flow.

A peak flow measurement measures per definition only one parameter. The peak flow

is a parameter that can vary significantly and is very effort dependant.

Peak flow measurement historically is used for diagnosis and follow-up of asthma. For this

measurement of peak flow is an acceptable - but limited - method, if different measurements

at different time intervals can be done. Because of the natural varation of the peak expiratory

flow, an isolated measurement has limited value.

Peak flow measurement is often used in diagnosis and follow-up of COPD as well. However,

peak flow measurement is not an adequate means of diagnosis or follow-up for this

pathology. Often in COPD peak flow is only affected in moderate or severe cases. The other

lung function parameters can be so low at this point that the patient is experiencing

respiratory symptoms. COPD is a disease that needs to be detected and treated as early as

possible.

The GOLD guidelines for COPD do not take into account peak expiratory flow for

judging the severity of COPD.

The forced expiratory volume after 1 second (FEV1) and the Tiffeneau index (FEV1/VC%)

are far better parameters to judge COPD severity.

Two obstructive F/V loops are shown. Although the black loop is showing clear signs of obstruction, PEF is normal.The red loop is a GOLD class I COPD patient, but still shows a PEF of approx. 75% of normal value