Scientists have discovered that smoking changes human lungs in a way that may make breathing physically harder over time. A new study found that lung tissue from smokers becomes stiffer and less flexible, behaving more like scarred lungs affected by fibrosis.
The research was conducted at the University of California, Riverside and published in the Journal of the Royal Society Interface.
The lungs are made mostly of soft tissue called parenchyma. This tissue acts like a flexible sponge that stretches and relaxes with every breath. In healthy lungs, the tissue expands easily, helping oxygen move into the body and carbon dioxide move out.
Smoking damages many parts of the respiratory system, but researchers wanted to understand exactly how it changes the physical mechanics of human lung tissue itself.
To answer this question, the scientists obtained human lungs donated either for transplantation or for scientific research. They cut small pieces of lung tissue and tested how the tissue behaved when stretched.
Unlike many earlier studies that stretched tissue in only one direction or relied heavily on animals such as mice, the researchers designed experiments that stretched the lung samples across multiple directions at the same time. This better copied how lungs naturally expand during breathing.
The differences between smokers and nonsmokers were very clear.
Tissue from smokers resisted stretching much more strongly, meaning the lungs had become stiffer and less elastic. Researchers said the tissue behaved similarly to lungs affected by fibrosis, a disease in which scar tissue builds up and makes breathing increasingly difficult.
When lungs lose flexibility, the body must work harder to breathe. Over time, this can reduce oxygen delivery and increase strain on the respiratory system.
Lead researcher Mona Eskandari explained that understanding the true mechanics of human lung tissue is important because lungs do not stretch evenly in real life.
The study also showed that even healthy lungs are not mechanically identical throughout the organ.
Researchers found that tissue from the upper lung regions was generally stiffer than tissue from lower lung areas.
The researchers suspect gravity may play a role. Since humans spend most of their lives standing or sitting upright, different parts of the lungs experience different physical forces over many years.
This discovery may help explain why certain lung injuries develop unevenly.
For example, patients on ventilators sometimes experience lung damage when certain regions of the lungs become overstretched. The study suggests some areas of the lungs may naturally tolerate stress less effectively than others.
The scientists also measured how much energy the lungs lose during repeated stretching cycles.
Human lung tissue lost more energy than researchers usually observe in mice. This finding may help explain why animal studies do not always accurately predict how human lungs behave.
This issue has become increasingly important because researchers are developing advanced computer simulations known as “digital twin” lungs. These computer models aim to predict breathing patterns, disease progression, and responses to treatments.
If those simulations rely mostly on animal data, they may fail to accurately reflect human lung mechanics.
The research team also observed early evidence suggesting that lungs may stiffen naturally with age, although more studies are needed before firm conclusions can be made.
One limitation of the study is that obtaining healthy donated human lungs for detailed testing is extremely difficult. Because of this, the number of available samples was limited.
Still, researchers say the study provides one of the most detailed analyses ever performed on human lung parenchyma.
The findings may eventually improve medical technologies such as ventilators, surgical planning tools, and computer models used to study lung diseases.
The work was carried out through Eskandari’s biomechanics Experimental and Computational Health laboratory, known as the bMECH laboratory, which focuses on understanding the mechanical behavior of biological tissues.
Overall, the study gives scientists a clearer picture of how smoking physically alters the lungs. One important strength is that the research used real human lung tissue rather than depending mainly on animal models. The findings may help future doctors and engineers create more accurate tools for treating lung disease.
However, additional research with larger numbers of lung samples will still be needed to fully understand how smoking, aging, and lung diseases affect lung mechanics over time.
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Source: University of California, Riverside.
