A spirometer is an apparatus for measuring the volume of air inspired and expired by the lungs. A spirometer measures ventilation, the movement of air into and out of the lungs. The spirogram will identify two different types of abnormal ventilation patterns, obstructive and restrictive.
A spirometer is the main piece of equipment used for basic Pulmonary Function Tests (PFTs). Lung diseases such as asthma, bronchitis, and emphysema may be ruled out from the tests. In addition, a spirometer often is used for finding the cause of shortness of breath, assessing the effect of contaminants on lung function, the effect of medication, and evaluating progress for disease treatment.
The earliest attempt to measure lung volume can be dated back to the period A.D. 129–200. Claudius Galen, a Roman physician and philosopher, did a volumetric experiment on human ventilation. He had a child breathe in and out of a bladder and found that the volume did not change. The experiment proved inconclusive.
1681, Borelli tried to measure the volume of air inspired in one breath. He assembled a cylindrical tube partially filled with water, with an open water source entering the bottom of the cylinder. He occluded his nostrils, inhaled through an outlet at the top of the cylinder and measured the volume of air displaced by water. Nowadays, this technique is very important in determining parameters of lung volume.
Whole-body plethysmograph: This type of spirometer provides a more accurate measurement of lung volume components compared to other conventional spirometers. The person is enclosed in a small space when the measurement is taken.
Fully electronic spirometer: Electronic spirometers have been developed that compute airflow rates in a channel without the need for fine meshes or moving parts. They operate by measuring the speed of the airflow with techniques such as ultrasonic transducers, or by measuring pressure difference in the channel. These spirometers have greater accuracy by eliminating the momentum and resistance errors associated with moving parts such as windmills or flow valves for flow measurement. They also allow improved hygiene by allowing fully disposable air flow channels.
Incentive spirometer: This spirometer is specially designed to encourage improvement of one's lung function.
Peak flow meter: This device is useful for measuring how well a person's lungs expel air.
Windmill-type spirometer: This type of spirometer is used especially for measuring forced vital capacity without using water; it has broad measurements ranging from 1000 ml to 7000 ml. It is more portable and lighter than traditional water-tank type spirometers. This spirometer should be held horizontally while taking measurements because of the presence of a rotating disc.