, the devastating disorder that floods the lungs with fluid and has ushered countless millions to death after infection with pneumonia, sepsis, and COVID-19.
Two centuries after the lung damage caused by the disorder was first described in medicine, it’s now clear that ARDS is an autoimmune condition spurred by the body’s overactive defenses. There’s interest in disrupting “crosstalk” between cells, and rise of a new form of genetic analysis is allowing researchers to test their hypotheses more effectively than ever before. And, perhaps most importantly, recent findings reveal how stem cells in the epithelial lining of the lungs get stalled in an intermediate stage before regenerating into new cells. Reversing this process could trigger repair and recovery.
There’s still a ways to go before clinical trials can test therapies to turn things around at the epithelial level, acknowledged University of Michigan, Ann Arbor, professor of internal medicine Rachel L. Zemans, MD, in an interview. Still, “it’s a pretty exciting time,” said Dr Zemans, who manages a lab that explores how the lung epithelium responds to injury.
A lung disorder’s deep roots in human history
A British doctor first described the traits of ARDS in 1821, although this form of pulmonary edema had been described in “ancient writings,” according to a 2005 report by Gordon Bernard, MD, of Vanderbilt University Medical Center, Nashville, Tennessee. Sometimes called “double pneumonia,” ARDS was almost always fatal until the last few decades of the 20th century. “The advent of well-equipped ICUs, well-trained staff, and the availability of reliable positive pressure ventilators has allowed patients to be kept alive much longer and thus have the opportunity to heal the pulmonary injury and survive,” Dr Bernard wrote.
According to the Mayo Clinic, there are many causes of ARDS. Sepsis is the most common, and others include severe pneumonia, head/chest injuries, massive blood transfusions, pancreatitis, burns, and inhalation of harmful substances. Since 2020, ARDS has been a hallmark of COVID-19.
In an interview, University of Washington, Seattle, emeritus professor of medicine Thomas R. Martin MD, explained that ARDS occurs when the epithelium barrier in the lungs breaks down. Unlike the permeable endothelial barrier, the alveolar epithelium is “like a brick wall or a big dam, keeping red cells and plasma out of the airspace.”
In cases of pulmonary edema due to heart failure, fluid can back up into the lungs, said Dr Martin, who studies ARDS. However, pumps in the epithelium can clear that excess fluid pretty quickly because the epithelium remains in a normal state, he said. “Given enough time and enough medical support, people with heart failure and pulmonary edema can get better without lung injury.”
In ARDS, however, “the epithelium is damaged. Cells die in the alveolar wall, the scaffolding is exposed, and the fluid in the alveoli cannot be cleared out. You’ve got a disaster on your hands because all of the fluid and red blood cells and inflammatory products in the blood are going right into the airspace. The patient gets extremely short of breath because their oxygen level falls.”