Spirometry

Spirometry measures how much air you breathe in and out and how fast you blow it out. This is measured two ways: peak expiratory flow rate (PEFR) and forced expiratory volume in 1 second (FEV1). PEFR refers to the amount of air you can blow out as quickly as possible. FEV1 refers to the amount of air you can blow out in 1 second. Spirometry (meaning the measuring of breath) is the most common of the Pulmonary Function Tests (PFTs), measuringlung function, specifically the measurement of the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. Spirometry is an important tool used for assessing conditions such as asthma, pulmonary fibrosis, cystic fibrosis , and COPD . The spirometry test is performed using a device called a spirometer , which comes in several different varieties.

Procedure

The basic forced volume vital capacity (FVC) test varies slightly depending on the equipment used. Generally, the patient is asked to take the deepest breath they can, and then blow as hard and as long( 6 seconds) as they can into a tube connected to THE SPIROMETER.. This breath is sometimes directly followed by a rapid breath in (inspiration), particularly when assessing possible upper airway obstruction. Sometimes, the test will be preceded by a period of quiet breathing in and out from the sensor (tidal volume), or the rapid breath in (forced inspiratory part) will come before the forced exhalation. Your doctor may have you inhale a medicine that helps open your airways. He or she will want to see whether the medicine changes or improves the test results. During the test, soft nose clips may be used to prevent air escaping through the nose. Filter mouthpieces may be used to prevent the spread of microorganisms.

Limitations of test

The maneuver is highly dependent on patient cooperation and effort, and is normally repeated at least three times to ensure reproducibility. Since results are dependent on patient cooperation, FVC can only be underestimated, never overestimated. FEV1 may sometimes be overestimated in people with some diseases – a softer blow can reduce the spasm or collapse of lung tissue to elevate the measure.

Due to the patient cooperation required, spirometry can only be used on children old enough to comprehend and follow the instructions given (6 years old or more), and only on patients who are able to understand and follow instructions – thus, this test is not suitable for patients who are unconscious, heavily sedated, or have limitations that would interfere with vigorous respiratory efforts. Other types of lung function tests are available for infants and unconscious persons.

Another major limitation is the fact that many intermittent or mild asthmatics have normal spirometry between acute exacerbation, limiting spirometry’s usefulness as a diagnostic. It is more useful as a monitoring tool: a sudden decrease in FEV1 or other spirometric measure in the same patient can signal worsening control, even if the raw value is still normal. Patients are encouraged to record their personal best measures.

 

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