The lungs are among the first organs attacked by SARS-CoV-2. Early in the pandemic, it was clear that this virus could cause changes in the lungs apparent on X-Rays. In fact, before RT-PCR assays were developed and widely deployed, many COVID-19 patients were diagnosed based on a specific type of image (ground glass opacities) identified in their lungs with X-Rays.
Most people who die of COVID-19 are thought to die because of respiratory failure (although long term studies may ultimately find other major causes of death in patients with long Covid). SARS-CoV-2 can cause immediate and severe damage to the lungs by a type of pneumonia. Patients can be saved from death using a variety of strategies. Early on, many patients were put on ventilators. Unfortunately, only about 50% of patients would survive this procedure. More recently, other measures have been adopted to reduced the need for ventilation. This has resulted in improved survival rates. Of course, treatment with Paxlovid can prevent the disease from progressing to the stage where ventilators are necessary. For extremely sick patients, Extracorporeal Membrane Oxygenation (ECMO) may be their only hope. This is a type of combination therapy which takes over many of the functions of the lungs and other organs while the patient recovers. It requires expensive machines and a team of trained health care professionals. We need more ECMOs in this country for COVID-19 and future respiratory pandemics.
SARS-CoV-2 can also cause longer term damage through a process called fibrosis. This is a new clinical term: post-COVID-19 pulmonary fibrosis (PCPF) used to describe what can happen to the lungs in people who were infected with SARS-CoV-2. Basically, cells called fibroblasts overproduce themselves in response to factors stimulated by SARS-CoV-2. This overgrowth results in production of substances that can narrow the fine passages needed for the exchange of oxygen and carbon dioxide. This leads to a number of symptoms including shortness of breath and fatigue. Although there are a number of therapies for fibrosis under development, there is no cure at this time.
The diaphragm is the muscle that moves the lungs and is necessary for breathing. The diaphragm is in turn controlled by the phrenic nerve which emerges from the spina cord. There is evidence breathing problems in some patients may be not be due to damage to the lungs per se but rather due to damage to diaphragm and/or phrenic nerve. There are exercise programs that may help recovery from this disorder, but their efficacy is still being studied.
SARS-CoV-2 can cause breathing problems through several, distinct mechanisms. People who are "short of breath" need to know what the exact cause of this non-specific symptom is in order to provide the right therapy for them. Of course, best of all is to try to avoid getting infected in the first place: you know the drill: vaccine, N95 and avoid crowds. These three preventative measures are not going to stop being important any time soon.
References
Bösmüller (2021) The pulmonary pathology of COVID-19. Virchows Archive.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7892326/
Hama Amin (2022) Post COVID-19 pulmonary fibrosis; a meta-analysis study. Ann Med Surg (London).
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8983072/
Marginean et al. (2022) Challenges in the Differential Diagnosis of COVID-19 Pneumonia: A Pictorial Review. Diagnostics (Basel).
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9689132/
Severin (2022) The effects of COVID-19 on respiratory muscle performance: making the case for respiratory muscle testing and training. European Respiratory Review.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9724806/
Shi et al. (2021) Diaphragm Pathology in Critically Ill Patients With COVID-19 and Postmortem Findings From 3 Medical Centers. JAMA Internal Medicine.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7670391/
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