The human body works in complex ways—sometimes, certain motions are so small that it’s easy to miss how they might cause discomfort in the body. In this way, the surface tissues in our lungs actually “resist” the expansion and contraction of the lungs when we inhale or exhale.
Normally, fluids inside the lungs help reduce this tension, but a new study suggests that the fluids themselves may also be subjected to similar motions that could get in the way of smooth breathing. That said, the scientific solution to this fluid mix-up is extremely simple: take a deep breath, and let out a long sigh. The experiment that arrived at this conclusion, published recently in Science Advances, focused solely on the physical movement of lung fluid when stretched and recompressed in the laboratory.
Specifically, the thin film that lung fluid forms to smooth out the breathing process actually consists of several layers. Taking deep breaths from time to time helps to “restore this ideal layering,” the researchers explained in a statement.
That allows the fluid to coat “the entire surface, making the lungs more deformable or—with a more technical word—compliant,” added Jan Vermant, study senior author and a material scientist at ETH Zurich in Switzerland, in the release.
Lung compliance
The researchers sought to characterize the “mechanical stresses within the fluid,” or the interactions between the multiple layers of lung fluid film during breathing. These stresses influence “how compliant the lungs are,” Vermant explained.
For their experiment, the researchers built a bubble-like apparatus filled with lung surfactant, connecting it to a syringe for replicating physical conditions that unfold in the lungs during breathing. Surprisingly, they found that deep breaths reorder the multilayer film in a way that raises the compliance of the lungs, according to the paper.
“Directly at the boundary with the air, there is a slightly stiffer surface layer,” explained Maria Novaes-Silva, the study’s first author and a doctoral student at ETH Zurich, in the statement. “Underneath, there are several layers that should be softer than the surface layer.”
Sigh the pain away
Sighing compresses the lung fluid, which “lowers the surface stress to balance the remaining tension and thus facilitates breathing,” the paper noted. This mechanical process is consistent with clinical observations that have suggested consistently taking short breaths could cause difficulty in breathing, the authors added.
Given the new findings, therapeutic treatments for lung failure may need to be revised. For instance, developing material to artificially mimic or aid the multilayered structure of lung fluids may more effectively treat adult patients having trouble breathing. As a shorter-term alternative, the findings illustrate—in scientific terms—the “feeling of relief experienced in the chest that often occurs after a deep sigh,” the researchers said.
Of course, the experiment was performed on an apparatus, not actual lungs. In real life, clearly, patient lungs are prone to stimuli from more things than shallow breathing. Still, the researchers argue that the lab experiments strongly indicate “we have captured real properties with our experimental setup,” according to Novaes-Silva. In any case, further investigations should illuminate whether the findings will lead to tangible guidance for real-life patients.
That said, we now have a scientific account for why sighing feels so good. So it wouldn’t hurt to stop a couple times each day to breathe in and let out a long sigh for science—and for your health.
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