- A recent study, which appears in the journal Radiology, examined the effect of long COVID on the lungs and found potential long-term effects on lung function.
- The researchers found evidence of small airway disease on chest scans in people who had persistent symptoms after SARS-COV-2 infection, regardless of infection severity.
- Longer-term follow-up is necessary to determine the lasting clinical consequences of the findings.
People with COVID-19 often experience various symptoms depending on the severity of their illness. Symptoms appear 2–14 days after exposure to the SARS-CoV-2 virus and last 1–4 weeks on average.
It has been difficult to estimate the prevalence of long-term symptoms following SARS-CoV-2 infection, partly because diagnostic criteria remain unclear.
However, last year, the Office for National Statistics published data suggesting that long-term symptoms occur in 7–18% of people who experienced symptomatic COVID-19.
These long-term effects after COVID-19 are known as long COVID or post-acute sequelae of COVID-19 (PASC).
PASC can range from mild to debilitating, with new symptoms arising or evolving long after the initial infection.
Dr. Brett M. Elicker, M.D., a clinical professor in the Department of Radiology and Biomedical Imaging at the University of California, San Francisco, discusses radiology findings in an editorial that accompanies the recent research.
Dr. Elicker explains that the long-term effects of viral pneumonia depend on the direct injury that the virus causes and the body’s immune reaction to the virus. Damage to the lungs occurs in two patterns:
- Constrictive bronchiolitis, or small airway disease: Inflammation within the bronchioles — the small airways — and surrounding areas results in airway narrowing due to scarring or fibrosis.
- Diffuse alveolar damage (DAD): Fibrosis to the alveoli — tiny balloon-shaped structures at the end of the bronchioles that exchange gas in the lungs — which may improve over time, but often some scarring remains.
He was responding to a study that used CT scans to image the lungs of people with persistent symptoms following confirmed SARS-CoV-2 infection. The scans showed air trapping, which indicates small airway disease.
Air trapping refers to pockets of air that become trapped in the lung after breathing out. In other words, they prevent the individual from exhaling completely. Air trapping is common in conditions such as asthma and chronic obstructive pulmonary diseases.
CT scans of people who have experienced COVID-19 also indicate ground glass opacity (GGO), suggesting DAD.
Small airway damage
Researchers from the University of Iowa recently conducted a study to understand the long-term effects of COVID-19 on lung function. They published their findings in the journal Radiology.
The study enrolled 100 adults with a confirmed SARS-CoV-2 infection who remained symptomatic for more than 30 days following the diagnosis, with a control group of 106 healthy participants.
In all, 67% of participants with PASC had not needed hospitalization for COVID-19 — the authors refer to these participants as ambulatory. Additionally, 17% required hospitalization, and 16% needed intensive care during the initial infection.
The most common persistent PASC symptoms were:
- shortness of breath (73%)
- fatigue (56%)
- cough (34%)
Alongside a chest CT scan, the researchers performed several pulmonary function tests to measure how well the lungs worked. These tests included:
- Forced vital capacity (FVC): The total volume of air a person exhales during maximal exhalation.
- Forced expiratory volume in 1 second (FEV1): The volume of air an individual exhales after a maximal inhalation in 1 second.
- FEV1/FVC: The proportion of FVC a person exhales in 1 second.
- Total lung capacity (TLC): The volume of air in the lungs at maximal inflation.
- Residual volume (RV): The volume of air in the lungs after exhaling maximally.
- Diffusing capacity of the lung for carbon monoxide (DLCO): This indicates how efficiently oxygen gets into the blood from the air.
The study found that participants in the hospitalized and ICU groups had significantly lower FVC, FEV1, TLC, and DLCO than those in the ambulatory group. The ambulatory group’s FVC, FEV1, and RV were similar to the healthy control group.
Participants received a chest CT scan within a median of 75 days from diagnosis.
The average percentage of the total lung that air trapping affected was significantly higher in the ambulatory (25.4%), hospitalized (34.6%), and ICU (27.3%) than the healthy controls (7.2%).
Also, the average percentage of the total lung with GGO was significantly higher in the hospitalized (13.2%) and ICU groups (28.7%) than the ambulatory group (3.7%), but higher in the ambulatory group than the healthy controls (0.06%).
Dr. Alejandro P. Comellas, M.D., senior author and professor of internal medicine in the Division of Pulmonary and Critical Care Medicine and the Carver College of Medicine, University of Iowa, Iowa City, spoke with Medical News Today.
He stated that the strengths of the trial were its design and inclusion of only nonvaccinated participants, which reduced confounding effects.
However, it was a small single-center trial that involved only the initial SARS-CoV-2 variant, limiting the generalizability of results to subsequent variants.
Dr. Comellas stated, “The results provide evidence, quantitatively and qualitatively, of airway damage many months after the initial SARS CoV-2 infection, including patients who were initially treated in the ambulatory setting.”
“Despite expected pulmonary functions tests in the ambulatory patients,” Dr. Comellas continued, “30% of their lungs had evidence of small airway disease.” As he explained, for some of the participants, this was more than 6 months after the initial infection.
In the companion editorial, Dr. Elicker elaborates:
“This paper suggests that airway obstruction and post-organizational pneumonia [or] DAD fibrosis contribute to persistent symptoms after [SARS-CoV-2] infection with the contribution of airways disease higher in the outpatients, and the contribution of OP [or] DAD greater in the patients admitted to ICU.”
“Longer-term studies assessing the clinical and imaging manifestations 1–2 years after the initial infection are needed to fully ascertain the permanent manifestations of post-COVID fibrosis.”
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