New insights explain the mechanisms behind deep breathing and lung rest

More than half of premature infants born before 28 weeks of gestation develop respiratory distress syndrome shortly after birth. Their lungs are not yet fully developed, so they produce too little of the seemingly magical fluid that lowers the surface tension of their lungs. As a result, some of the alveoli collapse and the lungs cannot receive enough oxygen.

Lungs become more susceptible to deformation

Until 40 years ago, this usually meant death. But in the late 1980s, pediatricians developed a life-saving procedure that involved extracting fluid from an animal's lungs and injecting it into the lungs of a premature baby.

This is very effective for newborns. Because the fluid covers the entire surface, the lungs become more deformable, or in more technical terms, more malleable. ”

Jan Vermant, Professor of Soft Materials, ETH Zurich

However, even adults can have lung failure. Approximately 3,000 people in Switzerland developed acute respiratory distress syndrome during the coronavirus pandemic. However, injecting surfactant from animal lungs into adult lungs has no effect. “This shows that it's not just about lowering surface tension,” Bermant said. “We believe that mechanical stress within the fluid also plays an important role.”

His research group, in collaboration with scientists in Spain, Belgium, and the United States, used advanced measurement techniques to investigate exactly how lung fluid behaves when it is stretched and recompressed in the laboratory. The fluids in our bodies undergo similar movements as our lungs expand during inhalation and contract again during exhalation. The researchers have just published their findings in a journal. Science progresses.  

Chest relief explanation

In the experiment, the researchers simulated the movements of normal breathing, especially deep breathing, and measured the surface stress of the fluid in each case. “This surface stress affects the flexibility of the lung,” explains Vermant. The more flexible your lungs are, the less resistance they have to expand and contract, making it easier to breathe.

With the help of a measuring device, researchers found that surface stress decreases significantly after deep breathing. Apparently, there's a physical explanation for the feeling of relief in your chest that often occurs after taking a deep sigh. The explanation begins with understanding that the thin membrane formed by lung fluid on the surface of the lungs is actually made up of several layers.

“Directly at the interface with the air, there is a slightly harder surface layer. Beneath that, there are several layers that are supposed to be softer than the surface layers,” explains María Novaes Silva, a PhD student in Fermant's research group and lead author of the study. As she demonstrated in experiments, this layered structure returns to equilibrium over time if the body fluids do not move at all or move only slightly during shallow breathing.

Reconstruction of multilayer structure

To regain this ideal layering, you need to take a deep breath every now and then. Based on their analysis, the researchers found that the composition of the outer layer changes due to significant stretching and compression of lung fluid. “It is rich in saturated lipids, which results in a more densely packed interface,” Novaes-Silva says. Vermant added: “This is a state outside the boundaries of thermodynamic equilibrium and can only be maintained by mechanical work.”

Additionally, in clinical practice, it is known that lung compliance gradually changes over time, making breathing increasingly difficult as shallow breathing continues. Therefore, laboratory measurements are likely to reflect clinical observations. Novaes-Silva concludes, “These similarities indicate that we captured real properties in our setting.”

Can the new insights obtained by materials scientists also be used to draw appropriate conclusions and insights into lung failure in adults? “A promising approach is to identify components that can artificially reconstruct multilayer structures,” the researchers say in a technical article. In our conversation, Bermant points out treatments using forms that are currently being developed and studied more deeply by other groups.