A team from ETH Zurich with partners from Spain, Belgium, and the United States investigated pulmonary surfactant and tested how it behaved under normal and deep-breath simulations. Using a bubble-like apparatus filled with surfactant and connected to a syringe, the researchers replicated the physical conditions that unfolded during breathing. The experiment ran on an apparatus, not on lungs, and focused on the physical movement of surfactant during stretching and recompression. Measurements showed that surface tension dropped after deep breaths.
The findings were published in Science Advances.
The team, led by Jan Vermant, found that pulmonary liquid had a multilayer structure: a slightly stiffer surface layer at the air interface and several softer layers beneath. The outermost layer of the thin film hardened over time, and deep breathing helped restore an arrangement in which the top layer was stiffer and the underlying layers were softer.
“This surface stress influences how compliant the lungs are. The more compliant the lungs are, the less resistance there was to expansion and contraction—and the easier it was to breathe,” said Jan Vermant, the study leader, according to a report by CNET. “The fluid wets the entire surface; the lung becomes more deformable—or to put it in technical terms—more compliant,” said Vermant, according to Tagesschau.
The researchers reported that deep inhalations associated with sighing helped reorder the multilayer film of pulmonary surfactant, raised lung compliance, and restored pliability. “Breathing deeply restored the balance and maintained the elasticity of the lungs,” said Maria Novaes-Silva, the first author, according to Gizmodo. “Saturated lipids accumulated, making the interface more densely packed,” said Novaes-Silva, according to Tagesschau. “Sighing compressed the lung fluid, which lowered the surface stress to balance the remaining tension and thus facilitated breathing,” according to a report by Gizmodo.
The findings aligned with clinical observations that breathing became harder with constant shallow breathing. According to the authors, when breaths stayed shallow and the fluid moved little, the layering diminished over time, which could explain progressive stiffness in people who breathed shallowly due to stress, illness, or inactivity.
Pulmonary surfactant sits on the surface of the alveoli, reduces surface tension and stress, and helps prevent collapse, which makes breathing possible. A lack of surfactant in premature infants causes respiratory distress syndrome. In the 1980s, doctors reduced this condition by extracting surfactant from animal lungs and administering it to premature babies.
The authors suggested that the work could guide therapies for adult pulmonary insufficiency. “A promising approach is to identify components that allow us to artificially reconstruct the multilayer structures of pulmonary liquid,” according to a report by Gizmodo.
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