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How Does a Spirometer Work?

By Robin Hewitt

Basic Definition

A spirometer measures lung capacity and other breathing conditions. According to the Mayo Clinic, a spirometry test is commonly used in a doctor’s office or hospital as an aid to measure the severity of chronic obstructive pulmonary disease (COPD), asthma and other conditions that affect a patient’s breathing.

Specifics of a Spirometer

The American Lung Association states that when a spirometry test is performed, the patient is requested to breathe into a tube that is attached to the spirometer. The spirometer measures the rate which air in inhaled and exhaled as well as the lung capacity. The typical spirometer measurement is called “forced expiratory volume in one second,” commonly referred to as FEV1, with the expiratory referring to the exhalation. According to the National Heart, Lung and Blood Institute, the spirometer also records the total amount of the exhalation in a measurement called the “forced vital capacity,” or FVC.

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Data Gathered

The spirometer reads the data from the FEV1 and the FVC and compiles it into a graph, which then compares the patient results with average healthy lung capacity data. Upon reading the graph, the physician is able to determine the extent of the patient’s lung damage as a percentile of capacity.

Other Uses

Patients undergoing a stress test may have a spirometer test before and after the exercise period to measure the effect of exercise on the lungs. In this case the spirometer will graph both of the readings on the same chart, enabling the doctor to easily spot any breathing problems (such as asthma) that are induced by physical exertion. Likewise, for certain conditions a doctor will perform one spirometry test and then administer an inhaled medication (called a bronchodilator) to open the lungs before performing another spirometry to measure the effectiveness of the medication in improving airflow.

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