Percussion of the thorax is a maneuver used by physicians to assess part of the integrity of lungs: their emptiness. As the lungs should be filled with air enough to be ventilated and proceed with the local gas exchange.
Lungs are like a huge sponge with a big difference from the typical ones: their dividing walls are full of blood and their spaces are full of air. The amount of air inside lungs is a big one: around 5 liters. Imagine 5 bottles of 1 liter each one inside the thorax and containing only air.
Just touching with two fingers
When percussion is performed hitting the tip of one middle finger on dorsal side of last joint in the other middle finger there is no special sound but some dullness. However, if the second finger is put over the thorax (not in the cardiac area) the sound is like the one on an empty box, similar to a drum, or the body of a guitar.
Some lung divisions
Lungs are composed by lobules (like having more than 2 sponges together). The right lung has 3 sponges together and the left has 2 and small one to give some space to the heart. The right has a big almost pyramidal that goes from the base of the thorax toward the whole back. Over its front there are the two other lobules: one bottom and other top. Here it was described right lung’s lobules: lower, middle, and upper.
For the purpose of this explanation, let’s avoid the left lung description.
Sonority vs dullness
The percussion of the thorax is normally sonorous (resonant). However, it’s not like an empty stomach but with some muffling (due to local blood circulation).
Some variety may be heard according to individuals. The resonance may be softer in an obese person than in the skinny. The expert will find normal sonority in each normal patient.
Changes in the back of right side of the thorax implies changes in the right lower lobe. In the front but bottom, percussion explores middle lobe while in the top front, it talks about upper right lobe.
Obvious changes of percussion in COPD
In COPD, the trapped air tend to increase the sonority of the thorax. It also happens in the symptomatic asthmatic as well as in other different circumstances. However, percussion of thorax is made with the purpose of looking for dullness like in pneumonia (when areas of the lung are filled with pus), pleural effusion (when the space between lung and rib cage is filled with more liquid that necessary to allow the breathing movement).
Granularities of COPD percussion
When a COPD patient has more emphysema than chronic bronchitis, the sonority by percussion is increased. It is also increased when the emphysema has led to creation of big bubbles called bullae. Its localized pattern may lead to clues about the severity of emphysema in precise areas.
A fact on percussion of the thorax
Percussion is a very helpful maneuver during physical exam of symptomatic respiratory patients. It completes the auscultation when it is abnormal. Not all patients will be explored with percussion but some of them may require this type of assessment when it’s necessary to confirm the excess presence of air, or a condition associated with dullness.
Don’t expect your general practitioner to do percussion in a routine manner. It’s just a confirmatory maneuver.