The spirometer is an instrument used in medicine to measure the volume of air inhaled and exhaled. The device is considered an essential tool in the detection of chronic obstructive pulmonary disease, which includes emphysema and chronic bronchitis. Chronic obstructive pulmonary disease was the fourth most common cause of death in the United States in 1993. In addition, spirometers are typically used to track the breathing capability of individuals with respiratory ailments such as asthma. Spirometers are also used to estimate limits of activity for people with respiratory problems.
The spirometer measures the capacity of the lungs to exhale and inhale air, and the amount of air left remaining in the lungs after voluntary exhalation. This knowledge enables physicians to gauge the strength and limitations of the respiratory system.
The earliest spirometers were water seal spirometers, first described by British physician John Hutchinson (1811-1861) in 1846 and still used in a refined form today. The devices were first distributed widely in the 1940s. Water seal spirometers measure the amount of water displaced in a sealed container when a patient exhales. The patient breathes into a hose, which is connected to a water-filled container. Inside the container is a lightweight plastic object, often called a bell, which rises as water is displaced during the patient's exhalation. A pen hooked up to the bell documents the exhalation and inhalation on a rotating chart carrier. The chart produced is called a spirogram.
Automated-flow spirometers, another type of spirometer, do not measure the complete volume of exhaled air. Instead, they measure the rate of the air flow and the time it takes to exhale, then compute the total volume. To accomplish this, the spirometer converts the flow of air into an electrical signal. Results are recorded as flow-volume curves or as spirograms.
Spirometers are used on patients of any age with a defect which limits or obstructs breathing. In addition, experts suggest that they also be used to detect respiratory problems in all cigarette smokers over the age of 40 and in workers exposed to industrial hazards such as coal dust or asbestos. Exposure to these substances increases the risk of respiratory illness.