Originally believed to be an upper respiratory virus, it was no surprise when people infected with the SARS-CoV-2 virus experienced respiratory symptoms, such as shortness of breath. Typically, after a viral respiratory infection resolves, these symptoms gradually improve. However, many people continue to experience shortness of breath as a Long COVID, or post-acute sequelae of COVID-19 (PASC), symptom. While we can expect to see lingering shortness of breath after severe COVID cases requiring hospitalization, those with mild cases still report continual or newly-developed shortness of breath. But what is causing this symptom to continue or develop long after acute infection? Did the SARS-CoV-2 virus damage the lungs or is something else behind these symptoms?
Lung Damage and Shortness of Breath
We know that acute COVID can lead to lung damage. This damage can include severe inflammation of the lung tissue and scarring, or fibrosis. In some cases, this can cause interstitial lung disease (ILD). When this damage occurs, it is easily seen in routine testing and shortness of breath is easily understandable. But what happens if routine tests come back normal? Does that mean your lungs are clear and the cause is something else? In fact, researchers have found that routine lung function tests may not be enough to reveal lung damage from COVID. Using hyperpolarized xenon MRI (XeMRI) scans, researchers find lung abnormalities that were not detectable with traditional CT scans. The damage they discovered is limiting oxygen from getting into the bloodstream. This oxygen reduction may cause breathing abnormalities, such as shortness of breath.
Cardiac Damage and Breathlessness
In addition to infecting the respiratory system, the SARS-CoV-2 virus can also contribute to heart damage. The three conditions most seen with Long COVID are myocarditis (inflammation of the heart muscle), pericarditis (inflammation of the outer heart lining), and heart arrhythmias, such as tachycardia (high heart rate) or bradycardia (slow heart rate). In fact, early studies showed that as many as 78% of recovered COVID patients showed heart abnormalities 2-3 months after recovery. This damage to the heart can contribute to symptoms such as shortness of breath because it affects how well and how quickly oxygenated blood travels around the body.
If you are experiencing increasing shortness of breath, along with chest pain, ankle swelling, heart arrhythmias, lightheadedness, or dizziness that is new, the American Heart Association recommends you see a physician immediately.
Endothelial Dysfunction and Microclots
Research shows that the SARS-CoV-2 virus also targets the endothelium in blood vessels throughout the body. The endothelium is the thin membrane that lines the inside of blood vessels. Endothelial cells release enzymes that work to regulate vascular relaxation and contraction, blood clotting, immune function, and platelet adhesion. When the SARS-CoV-2 virus damages the endothelium, oxygen transportation through the blood is affected. This occurs due to inappropriate relaxation/contraction of blood vessels, as well as the increased presence of micro blood clots due to inappropriate clotting. Symptoms of endothelial dysfunction can include chest pain that gets worse with activity and/or stress and shortness of breath.
Many people with Long COVID describe a worsening of symptoms after exercise or the inability to exercise without increased symptoms. Additional studies show that vascular endothelial dysfunction may contribute to exercise intolerance, as well as play a role in post-exertional malaise experienced by those with ME/CFS, a common Long COVID comorbidity.