Spirometer, << spy ROM uh tuhr, >> is an instrument used to measure the volume of air a person can breathe. Physicians use spirometers to diagnose certain respiratory disorders and to evaluate treatment.
A common type of spirometer consists of an air-filled cylinder, closed at its upper end and open at its lower end. This cylinder floats in the water-filled space between two other cylinders. The air-filled cylinder is connected to the patient’s lungs by a tube with a mouthpiece at one end. When the person exhales, the amount of air in this cylinder increases, and the cylinder floats higher in the water. As the patient inhales, air leaves the cylinder, and it falls. The movements of the air cylinder are recorded on a strip of paper called a spirogram. Electronic spirometers show results on a display screen or paper printout.
A spirometer can measure changes in the volume of air in the lungs. For example, inflammations and tumors reduce the capacity of the lungs. The instrument also measures the speed at which air moves in and out of the lungs. Such diseases as asthma and bronchitis narrow the air passages, reducing the rate of air flow.
