More than half of all premature babies born before the 28th week of pregnancy develop respiratory distress syndrome shortly after birth. Their underdeveloped lungs produce insufficient amounts of a crucial fluid that reduces surface tension, leading to the collapse of some alveoli and hindering oxygen intake. This condition, until 40 years ago, often resulted in death. However, a breakthrough in the late 1980s saw pediatricians extract this fluid from animal lungs and inject it into premature infants, significantly improving survival rates.
Jan Vermant, Professor of Soft Materials at ETH Zurich, explains, “This works very well in newborns. The fluid coats the entire surface, making the lungs more deformable or—technically speaking—compliant.” Yet, even in adults, lungs can fail, as evidenced during the coronavirus pandemic when approximately 3,000 people in Switzerland developed acute respiratory distress syndrome. Unfortunately, injecting surface-active fluid from animal lungs into adults does not yield the same results.
The Mechanics of Breathing: More Than Surface Tension
According to Vermant, “It’s not just about reducing surface tension. We believe that mechanical stresses within the fluid also play an important role.” Collaborating with scientists from Spain, Belgium, and the USA, Vermant’s research group used advanced measurement techniques to study how lung fluid behaves under stress. Their findings, published in the journal Science Advances, reveal critical insights into the mechanics of breathing.
In their experiments, the researchers simulated the movements of normal and deep breaths, measuring the surface stress of the fluid in each scenario. “This surface stress influences how compliant the lungs are,” Vermant explains. Enhanced compliance means less resistance to lung expansion and contraction, facilitating easier breathing.
Understanding the Relief of a Deep Sigh
The researchers discovered that surface stress decreases significantly after deep breaths, providing a physical explanation for the relief often felt in the chest after a deep sigh. The lung fluid forms a thin film with several layers, with a slightly stiffer surface layer at the boundary with the air and softer layers underneath. Maria Novaes-Silva, a doctoral student and first author of the study, notes, “This layering returns to equilibrium over time when the fluid remains still or moves only slightly during shallow breathing.”
“A deep breath is needed from time to time to restore this ideal layering,” Novaes-Silva explains. “The pronounced stretching and compression of the pulmonary fluid changes the outer layer’s composition, enriching it with saturated lipids and resulting in a more densely packed interface.”
Clinical Implications and Future Directions
Clinical observations support these findings, as lung compliance is known to change over time, making breathing more difficult with constant shallow breathing. Novaes-Silva concludes, “These similarities indicate that we have captured real properties with our experimental setup.”
The research raises the question of whether these insights can inform treatments for adult lung failure. Vermant suggests that identifying components to artificially reconstruct multilayered structures could be a promising approach. “Therapies involving foam are currently being developed and researched in greater depth by other groups,” he notes.
This development represents a significant step forward in understanding the mechanics of breathing and offers potential new avenues for treating respiratory conditions. As research progresses, the hope is that these insights will lead to more effective therapies for those suffering from lung failure.
Meanwhile, the simple act of taking a deep breath continues to offer a natural, immediate form of relief, underscoring the complex yet elegantly designed nature of human physiology.
