Observations in a small number of autopsied lungs reinforce reports from physicians treating covid-19 patients. Doctors described widespread damage to blood vessels and the presence of blood clots that would not be expected in respiratory disease.
“What’s different about Covid-19 is that the lungs don’t become stiff, injured or destroyed until there is hypoxia,” the medical term for oxygen starvation, said Steven J. Mentzer, professor of surgery at Harvard Medical School and team member. who wrote the report. “For whatever reason, there is a vascular phase” in addition to the damage more commonly associated with viral diseases like the flu, he said.
The research team compared seven lungs of patients who died from covid-19, the coronavirus disease, with the lung tissue of seven patients who died from pneumonia caused by influenza. They also examined 10 lungs donated for transplantation but not used. The lungs, acquired in Europe, were matched by age and sex.
In the large blood vessels of the lungs, the number of blood clots was similar in covid-19 and influenza patients, the researchers wrote. But in Covid-19 patients, they found nine times more micro-clots in the tiny capillaries of small air sacs that allow oxygen to pass into the blood and carbon dioxide to exit. The virus may have damaged the walls of these capillaries and blocked the movement of these gases, the researchers wrote.
They also found inflamed and damaged cells in the lining of the blood vessels in covid-19 patients.
What was most surprising was the evidence that the lungs of people attacked by the SARS-CoV-2 virus have developed new blood vessels.
“The lungs of patients with covid-19 have experienced significant new vessel growth,” a finding that the researchers described as “unexpected.” In an interview, Mentzer hypothesized that the lungs may have attempted to pass more oxygen into hypoxic tissue.
“It may be one of the things that makes people better,” he said.
Researchers looked for genetic and other differences that could help predict who is most susceptible to serious illnesses from the virus, but found none in their small sample. So far in the pandemic, Covid-19 has hit some groups, including the elderly, African Americans and those with underlying illnesses such as diabetes, the most difficult.
“Patients who are doing fairly well have purely respiratory disease, and patients who have problems also have a vascular component,” said Mentzer. But efforts to determine or explain who will belong to each group have been unsuccessful, he said.