Plethysmography is measuring the volume or the volume change of organs, limbs or the entire body. The best known application is the measurement of the lung capacity. This is one of the function tests of the respiratory system, in which the elasticity and the airway resistance of the lungs is being examined.
Plethysmography is used to evaluate symptoms of the upper respiratory tract, such as pain or discomfort during breathing, shortness of breath or the feeling of not getting enough air. In people with asthma or bronchitis, plethysmography may help in making the diagnosis and treatment of this disease. In these people, the airway resistance will increase, because the airway becomes partly blocked with mucus and the airway walls are inflamed and swollen.
With the aid of plethysmography is measured how much air a person has in his lungs after maximal inhalation and how much air is left after maximal exhalation. The capability of the elastic lung tissue to shrink during exhalation, is called the lung elasticity. The airway resistance is a determining factor for the ease with which the air can flow through the airway to the lungs.
The patient is sitting in an enclosed space, the size of a phone booth (bodybox). The measurements are done with a spirometer. This is a device that is connected to a tube in rubber or cardboard, in which the patient has to blow. This way, the pulmonary function is measured. The results are graphically shown on a spirogram and can automatically be compared with reference values. The examination takes approximately 20 minutes and has no adverse effects.