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Informative capsule dedicated to plethysmography for the detection of residual volume in CF, with Josep Lluís Valera, from Son Espases University Hospital.
Differences between plethysmography and spirometry
Plethysmography is the test that allows us to know the residual volume of a person’s lungs. Josep Lluís Valera, a nurse at the Son Espases University Hospital, explains that it is a complementary test, just like spirometry, which is used to measure the volume of air in a forced expiration.
Residual lung volume
The residual volume is the amount of air remaining in the lung after forced expiration. This remaining air is necessary so that the lung does not collapse, but only if it is not in excessive quantity.
A person with a high residual volume will have less space in his or her lungs to perform normal breathing, noting, in this case, how the person performs short inspirations and expirations at a faster rate.
When the plethysmography result indicates that there is a high residual volume, it is necessary to find out why in order to know what treatment to apply.
When is plethysmography necessary?
This test is performed in a first assessment of a person and when a reduction in forced expiratory capacity is detected with spirometry.
In this case we must know if this person cannot exhale an amount of air within normal parameters because he/she does not have that air due to an obstruction for any reason or if he/she has that air and cannot expel it (air trapping).
This last case usually occurs in obstructive disease patterns, such as Cystic Fibrosis, which, due to dynamic compression of the bronchus, the air is trapped and cannot be expelled. At that moment, the operative capacity of the lung is reduced by the high residual volume and the breathing rate accelerates.