A spirometer measures the flow of breath in and out of the lungs, producing a graphical output that shows airflow and time. The device’s original design was a cylinder suspended in water, but there are now various pressure-sensitive devices available. Spirometry only measures the amount of air that can be pushed in and out of the lungs, not total lung volume. It is important to remember that spirometry is highly dependent on patient cooperation.
A spirometer is a device that is used to measure the flow of breath into and out of the lungs. This device is used in a medical testing procedure known as spirometry, in which a patient breathes in and out of a tube connected to the spirometer so that lung function can be assessed. Many people who are receiving treatment for lung disease have interacted with a spirometer at some point in their lives.
Several methods can be used to construct a spirometer. The goal is to create a device that is highly sensitive to changes in air pressure, so it can measure the subtleties of airflow to and from the lungs. Spirometers produce graphical output, with airflow along one axis and time along another. This allows the doctor to see not only how much air the patient is breathing in and out, but also the length of time it takes. A peak flow value can also be obtained by looking for the highest point on the graph.
The spirometer’s original design was a cylinder suspended in water that could be moved up and down as the patient breathed. As the cylinder moved, it pushed a pen attached to the graph paper, creating a graph that could be read when the test was complete. A variety of other pressure-sensitive devices can be used for spirometry today, although the water-based method is still used in some hospitals.
Working with a spirometer takes some practice. When patients first use the device, they often undergo a test so they know what the experience is like before data is collected. At least three breath cycles on the spirometer are completed to obtain a range of values that can be averaged to reflect the patient’s condition. If the numbers differ significantly, it could be a sign that one or more of the tests were faulty and need to be repeated.
Spirometry is highly dependent on patient cooperation and it is important to remember that it does not measure total lung volume, only the amount of air that can be pushed in and out of the lungs. Someone with severe airflow limitation might have very high lung volume, but this would not be reflected in a spirometry test, as only a limited amount of air might be forced through the airways. Other tests can be used to test lung volume, and a full battery of pulmonary function tests or PFTs can be used to evaluate lung function as a whole.
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