by As pulmonologists and critical care physicians who treat patients with lung disease, we have heard many of our patients recovering from COVID-19 tell us this even months after their initial diagnosis. Although they may have survived the most life-threatening phase of their illness, they are still not back to their pre-COVID-19 baseline, struggling with activities ranging from vigorous exercise to doing laundry.
These lingering effects, called prolonged COVID-19, have affected up to 1 in 5 American adults diagnosed with COVID-19. Long-term COVID includes a wide range of symptoms including brain fog, fatigue, cough and shortness of breath. These symptoms can result from damage or dysfunction of multiple organ systems, and understanding the causes of long-term COVID is a special research focus of the Biden-Harris administration.
Not all respiratory problems are related to the lungs, but in many cases the lungs are affected. Examining the basic functions of the lungs and how they can be affected by the disease can help clarify what’s on the horizon for some patients after a COVID-19 infection.
Normal lung function
The main function of the lungs is to bring oxygen-rich air into the body and expel carbon dioxide. When air flows into the lungs, it comes into close proximity to the blood, where oxygen diffuses into the body and carbon dioxide diffuses out.
This process, as simple as it sounds, requires an excellent coordination of air flow or ventilation and blood flow or perfusion. There are over 20 sections in your airway, starting with the main trachea, or trachea, to the small balloons at the end of the airway, called alveoli, that are in close contact with your blood vessels.
By the time an oxygen molecule reaches the end of the airway, there are about 300 million of these tiny alveoli it could end up in, with a total surface area of more than 1,000 square feet (100 square meters) where gas exchange takes place.
The matching of ventilation and perfusion rates is critical to basic lung function, and damage anywhere along the airway can lead to difficulty breathing in a variety of ways.
Obstruction – reduced airflow
One form of lung disease is the blockage of air flow in and out of the body.
Two common causes of such lesions are chronic obstructive pulmonary disease and asthma. In these diseases, the airways narrow either because of damage from smoking, as is common in COPD, or because of allergic inflammation, as is common in asthma. In both cases, patients have difficulty blowing air out of their lungs.
Researchers have observed ongoing airflow obstruction in some patients who have recovered from COVID-19. This condition is usually treated with inhalers that deliver medication that opens the airways. Such treatments may also be helpful during recovery from COVID-19.
Restriction – reduced lung volume
Another form of lung disease is referred to as restriction or difficulty expanding the lungs. The restriction reduces the volume of the lungs and subsequently the amount of air they can take in. The restriction often results from the formation of scar tissue, also called fibrosis, in the lungs due to injury.
Fibrosis thickens the walls of the alveoli, which makes gas exchange with the blood more difficult. This type of scarring can occur in chronic lung conditions, such as idiopathic pulmonary fibrosis, or as a result of severe lung damage in a condition called acute respiratory distress syndrome, or ARDS.
ARDS can be caused by injuries that originate in the lungs, such as pneumonia, or serious disease in other organs, such as pancreatitis. About 25% of patients recovering from ARDS develop restrictive lung disease.
The researchers also found that patients who have recovered from COVID-19, especially those who had severe disease, may later develop restrictive lung disease. Patients with COVID-19 who require a ventilator may also have recovery rates similar to those who require a ventilator for other conditions. The long-term recovery of lung function in these patients is still unknown. Drugs that treat fibrotic lung disease following COVID-19 are currently undergoing clinical trials.
Perfusion disorder – reduced blood flow
Finally, even when airflow and lung volume are unaffected, the lungs cannot complete their function if blood flow to the alveoli, where gas exchange occurs, is reduced.
COVID-19 is associated with an increased risk for blood clots. If blood clots travel to the lungs, they can cause a life-threatening pulmonary embolism that restricts blood flow to the lungs.
In the long term, blood clots can also cause chronic problems with blood flow to the lungs, a condition called chronic thromboembolic pulmonary hypertension, or CTEPH. Only 0.5% to 3% of patients who develop pulmonary embolism for reasons other than COVID-19 develop this chronic problem. However, there is evidence that severe COVID-19 infections can damage blood vessels in the lung and impair blood flow during recovery.
What’s next?
The lungs can function less optimally in these three general ways, and COVID-19 can lead to all of them. Researchers and clinicians are still looking for ways to better treat the long-term lung damage seen in long-term COVID.
For clinicians, close monitoring of patients who have recovered from COVID-19, particularly those with persistent symptoms, may lead to faster diagnoses of long-term COVID-19. Severe cases of COVID-19 are associated with higher rates of long-term COVID-19. Other risk factors for developing long-lasting COVID include preexisting Type 2 diabetes, presence of virus particles in the blood after initial infection, and certain types of abnormal immune function.
For researchers, the long COVID-19 is an opportunity to study the underlying mechanisms of how different types of lung-related conditions develop that result from COVID-19 infection. Unraveling these mechanisms will allow researchers to develop targeted therapies to speed recovery and get more patients feeling and breathing like their pre-pandemic selves once again.
In the meantime, everyone can stay up-to-date on recommended vaccinations and use preventative measures such as good hand hygiene and a mask when appropriate.
Jeffrey M. Sturek, Assistant Professor of Medicine, University of Virginia and Alexandra Kadl, Assistant Professor of Medicine and Pharmacology, University of Virginia
This article is republished from The Conversation under a Creative Commons license. Read the original article.
