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The Differences Between a Spirometer and a Peak Flow Meter

written by: Vasanth • edited by: Diana Cooper • updated: 1/23/2011

The main difference between a peak flow meter and spirometer is that a peak flow meter measures the rate at which air is expelled from the lungs, while a spirometer measures the total volume of air that is inhaled or exhaled. In terms of cost, a peak flow meter is much cheaper than a spirometer.

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    What Does a Spirometer and Peak Flow Meter Measure?

    A spirometer and peak flow meter are used to test how well the lungs are functioning. Diseases which affect the lungs, such as asthma and chronic obstructive pulmonary disorder, are monitored using these instruments. By examining the results of the tests, one can determine if there is a decline in lung function.

    A spirometer measures the total volume of air that can be exhaled or inhaled. It can also measure the rate at which a certain volume of air is expelled from the lungs. A peak flow meter, on the other hand, only measures the rate at which air is forced out of the lungs. This is known as the peak expiratory flow.

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    Differences in Test Results

    The first time a peak flow meter is used to measure lung function, a baseline is established. Afterward, the results of each test will be compared with the initial baseline and placed into one of three peak flow zones. The green peak flow zone is defined as a peak flow that is 80 to 100% of the initial baseline. This indicates that the lungs are working well and are stable. If the peak flow is between 50 and 80% of the baseline, it indicates that the lungs are not working as well as they should. This is the caution, or yellow peak flow zone. A reading below 50% places the results in the danger, or red peak flow zone. This indicates an emergency that should be treated at a hospital.

    A spirometer produces two measurements: forced vital capacity (FVC) and forced expiratory volume (FEV-1). FVC is the maximum amount of air that is forced out of the lungs after inhaling as deeply as possible. The FEV-1 is the amount of air expelled from the lungs in one second. The value of FEV-1 is divided by the FVC, and the percentage is compared with normal values. Also, a flow-volume graph is produced from the test to see how well the lungs are performing.

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    Size Differences

    Another difference between a peak flow meter and spirometer is their size. A peak flow meter is a small, compact device that fits comfortably in the palm of your hand. It is usually cylindrical in shape. A spirometer is a larger device that is usually square or rectangular. Depending on the model, the mouth piece may be bulkier, and it may contain additional features such as a touchscreen. There are also desktop spirometers that feature a printer.

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    Cost Differences

    The cost difference between a peak flow meter and spirometer is huge. A peak flow meter is generally inexpensive. Quality meters are available for less than $40. Spirometers on the other hand are expensive. They can range between $500 and $2,500 or more.

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    Reference

    1. "Peak Flow Meter." Mayo Foundation for Medical Education and Research. http://www.mayoclinic.com/health/peak-flow-meter/MY01116/DSECTION=results

    2. "Spirometry." Mayo Foundation for Medical Education and Research. http://www.mayoclinic.com/health/spirometry/MY00413/DSECTION=results

    3. "Pulmonary Function Tests." Medline Plus. http://www.nlm.nih.gov/medlineplus/ency/article/003853.htm