Ventilation deficit, collapsed lung section
To perform its function, the lungs must be well supplied with blood and well ventilated. This is the only way to ensure an exchange of substances between blood and air, during which the body can breathe in sufficient CO2 and absorb sufficient oxygen. If a part of the lung collapses and is no longer filled with air, it can no longer contribute to breathing. To understand how this can happen, however, it is first important to understand how breathing normally works.
A distinction is made between congenital (fetal, primary) atelectases and those acquired as a result of an unfavourable circumstance (secondary). Congenital atelectasis can result from central nervous dysfunction, malformations or, in premature babies, a surfactant deficiency. Surfactant is a mixture of water, fats and proteins produced by the lungs to reduce the surface tension of the fluid layer in the pulmonary alveoli to such an extent that unfolding is possible at all.
The production of this mixture starts quite late in the lung maturation. Acquired atelectasis can have numerous causes. In the so-called compression atelectasis, the collapsed lung area is squeezed by something and thus prevented from unfolding.
This pressure can be exerted, for example, by a tumour, an accumulation of blood, pus or water in the gap between the lung and the chest wall (pleural gap) or swollen lymph nodes. Injury to the chest wall or lung where air enters the gap between the lung and the chest wall can also cause this air to compress the lung. This form of atelectasis affects an entire lung, is also called relaxation atelectasis or pneumothorax and is a serious clinical picture.
In contraction atelectasis, the lack of ventilation is caused by scarring of the lung at this site, which in turn is the result of a lung disease such as tuberculosis or sarcoidosis. In the case of microatelectasis, for example in a shock situation, the lung tissue at the affected site was insufficiently supplied with blood so that it could not form sufficient surfactant. The surface tension of the fluid in the alveoli (alveolar fluid) then contracts the lung at the site.
Resorption atelectasis occurs when the air in a section of the lung is completely absorbed into the blood. This is conceivable if a patient is ventilated with pure oxygen for more than 3 minutes and then there is almost only oxygen in the alveoli. A subtype of resorption atelectasis is the obstruction atelectasis. This is produced when a branch of the lung (bronchus) is pinched off and the air trapped behind it is absorbed into the blood over time. Such a pinching in turn can be caused by a tumour, swallowing an object or swollen lymph nodes.