Managing long-COVID with DLCO

Many of the news stories and epidemiological reports about the COVID-19 pandemic focus on the ever-increasing number of people we’ve lost to the disease. But these tragic stories overshadow a potentially even greater impact on society: The care for those who survive.

It’s not particularly uncommon for someone who has even a relatively brief stay in an intensive care unit to endure long-lasting effects on their lung condition. But as the pandemic has worn on and researchers learn more about the SARS-CoV-2 virus, we continue to encounter more surprises about its effect on the body. One of the most recent surprises is that so-called ‘mild’ cases of COVID-19 may not have the dramatic, severe symptoms of those cases that land people in the hospital, but they may be just as likely to have long-lasting effects on the respiratory system. Cases of ‘long COVID,’ ‘COVID long-haulers,’ and ‘post-COVID syndrome’ are being reported and analyzed, and concerning trends are emerging.

Obviously, the lungs are the most common site for COVID-19 pathophysiologies to appear. The endothelial cells lining the airways are teeming with angiotensin-converting enzyme 2 (ACE-2), which appears to be the prime target for the SARS-CoV-2 virus^*. This allows the virus ready access to the pulmonary vasculature, where it begins to wreak havoc. The lungs of post-COVID patients often show very distinctive changes to that vasculature, with disruptions to the epithelial cell membranes, signs of inflammatory changes, and various other damage^*. These impacts tend to linger, as well. One study in Ireland found that shortness of breath, as well as non-pulmonary symptoms like fatigue, malaise, and ‘brain fog’ were common even two to three months after initial diagnosis^*. In fact, nearly two-thirds of the study cohort reported that they had “not returned to full health”

Similar findings were published by the department of medicine at the University of Washington. This group followed 177 patients with confirmed COVID-19 for between 3 and 9 months, with roughly one-third of them reporting ongoing symptoms during later follow-up^*. In fourteen of those cases, symptoms were still severe enough to affect their activities of daily living; nine of those patients had not even been hospitalized. That means that even relatively ‘mild’ cases of COVID-19 are indeed at risk for physical impairment.

Many of these symptoms, including fatigue and malaise, can still be traced back to SARS-CoV-2’s effect on the pulmonary vasculature. Changes in that vasculature inevitably change the way gases like oxygen and carbon dioxide transfer through the walls of the alveoli and into the bloodstream, and once again those changes can persist. Last year, an Austrian team found significant changes to diffusion capacity (DLCO) and airflow patterns after 100 days in one-fifth of their long-haul cases^*.

These cases may well be the tip of the iceberg. Neither the University of Washington study nor the Irish one used pulmonary function testing in their protocols, and PFT data have been difficult to find. Labs have been under various infection-control restrictions throughout much of the pandemic, resulting in backlogs and chronic delays. Many view the testing itself as risky, suspicious of bioaerosols released during the intense breathing manoeuvres. And PFT staff have been either stretched to their maximum or reassigned to put their valuable respiratory care knowledge to use in other care venues. In some cases, basic office spirometry may be enough to identify restrictive patterns that are frequently associated with the development of the circulatory issues and fibrosis that are thought to be major contributors to post-COVID lung problems, but DLCO has quickly become the gold standard in evaluating these cases. CT scans may also help identify potential problems, but it is sometimes difficult to distinguish between things like early fibrosis and resolving inflammation, and in any case would still require separate care coordination.