Our Physician's 

COVID-19 and the Lungs

June 30, 2020 5 min read

Diagram of a human heart

Dr. Sandra El Hajj -MSc, N-MD, DHSc

The SARS-CoV2 can infect both the upper or lower respiratory tract. When hands, contaminated with droplets containing the virus, come in contact with your eyes, nose, or mouth, the virus can be introduced into the body. This offers the virus a passage to the mucous membranes towards the throat. From the throat, the virus makes its way down into the air sacs (alveoli) found in the lungs giving it full access to the lower respiratory tract, which involves the lungs.

Lungs and their functions

Lungs are organs in the chest that are in charge of exchanging oxygen and carbon dioxide. This exchange occurs between the air we breathe and our blood. Our body contains cells that are continuously in need of a new supply of oxygen to function properly and produce energy. When oxygen is lacking, cells cannot function well and damages occur at a cellular level.

Air enters our body through the nose and mouth. It goes into the windpipe (trachea) and keeps traveling into the lungs through two bronchi. Every lung is made of different lobes; the left lung has two lobes, the right one has three. Once in the bronchi, air keeps traveling into smaller tubes called the bronchioles reaching small air sacs called the alveoli. This branching of pipes may look like a tree branches pattern.

Infographic of the human respiratory system

Part of the respiratory system is the blood circulation that fosters the exchange of oxygen and carbon dioxide. When you inhale, you are bringing in oxygen from the outside air into your lungs. When you exhale, you are passively forcing air out of the lungs through your mouth.

COVID-19 and your lungs

The COVID-19 virus uses its spiked proteins to interact with ACE2 receptors found in the respiratory tract. ACE2 receptors are proteins that are found on the surface of specific cells. They are enzymes that form small proteins from large ones by cutting them. The large proteins are the angiotensinogens. In healthy individuals, the small proteins resulting from angiotensions help keep our blood pressure stable. Since lungs have more ACE2 receptors specifically expressed on alveolar epithelial cells, as compared to the rest of the respiratory tract, this makes it a virus that is more likely to affect your lungs.

COVID-19 utilizes the cell as machinery for self-replication and multiplication. Once replications and multiplications are successful, the virus eventually destroys the cell, allowing itself to move out and infect other neighboring healthy cells. This causes more cellular damage to the body. Coughing, sneezing, high fever and increased mucus production are defenses of the body to get rid of the virus. They are commonly manifested as symptoms of the infection. About 80 percent of people who have COVID-19 get mild to moderate signs such as cough or a sore throat.

COVID-19 and pneumonia

Some people may end up developingpneumonia, a lung infection in which the alveoli are inflamed. It is when the air sacs on one of both lungs get inflamed and get filled with pus. That’s when an infected person starts coughing pus and phlegm, develops a fever and starts experiencing chills and difficulty breathing. It is a condition that can be life-threatening. Its impact is accentuated in people older than 65 years and those with a weak immune system. Children are also heavily affected by this inflammatory illness.

Being very different from seasonal flu, COVID-19 has a much higher mortality and infectivity rate. This novel virus is infectious even during its pre-symptomatic phase, meaning that people can start spreading the virus even before symptoms start showing. The reason behind this fast spread can be the result of the virus’s ability to bind tightly to our cells, increasing its chances to introduce its RNA. A small German study indicated the importance of COVID’s survival is accentuated in its replication in the nose at its earliest exposure(1).

About 13.8 percent of COVID-19-infected individuals do develop severe disease. Among them, 75 percent develop bilateral pneumonia. This is when parts of the lungs collapse, making it difficult for the lungs to open the alveoli for proper respiratory function. Following the insertion of the virus to the alveoli, the immune system reacts by producing white blood cells that rush to the site of infection. At the same time, blood vessels surrounding the dysfunctional air sacs become leaky due to the increase in inflammatory chemicals from the white blood cells. This fluid creates another pressure on the alveoli (from the outside) causing a collapse. The result is difficulty breathing and breathlessness. Acquiring supportive intravenous fluids and oxygen via mask can help the infected individual recover from this complication.


Although many COVID-19 positive individuals do not show signs or only manifest mild symptoms, some develop severe respiratory illnesses requiring them to be admitted in intensive care units. This is especially the case of those who ended up developing acute respiratory distress syndrome (ARDS).

ARDS is a type of respiratory failure characterized by a rapid onset of widespread inflammation in the lungs causing shortness of breath, rapid breathing, and bluish skin coloration due to lack of oxygen. Patients who are suffering from ARDS have damage done to the walls of the air sacs (alveolar damage) in their lungs. In healthy lungs, oxygen within these air sacs (alveolus) travels through to small blood vessels (capillaries). These tiny vessels, in turn, deliver the oxygen to your red blood cells.

Infographic displaying gas exchange

SARS-CoV2 damages both the wall and lining cells of the alveolus, as well as the capillaries. The resulting debris that accumulates because of this process causes damage to the lining walls of the alveolus. The damage to capillaries also causes them to leak plasma proteins, which adds to the wall’s thickness. Eventually, the wall of the alveolus gets thicker, causing a more difficult oxygen transfer. The lack of oxygen leads to shortness of breath, difficulty in breathing, bluing of the skin and possibly death.

Researchers from China have linked COVID-19 to acute respiratory distress syndrome (ARDS). Their study examined existing risk factors for 191 confirmed coronavirus patients who died while being treated in two hospitals in Wuhan, China. They found that 50 of the 54 patients, who died, have developed ARDS while only nine out of the 137 survivors had ARDS. The conclusion made was that COVID-19 has a significant contribution to deaths among infected patients(2).

Doctors monitor COVID-19 patients for possible ARDS by looking into four main things such as:

  • The progress of symptoms that started within one week
  • The development of new or worsening symptoms
  • Possible shortness of breath that isn’t explained by heart failure or fluid overload
  • Low oxygen levels in the blood (severe hypoxia)

Finally, they also monitor whether both lungs appear white and opaque (versus black) on chest X-rays (called bilateral lung opacities on chest imaging).

In summary

Coronaviruses are viral infections affecting the respiratory tract. They are referred to as respiratory illnesses. While some may not show any symptoms, many start developing a fever, cough and shortness of breath up to 14 days post-infection. More than 6.2 million cases have been reported as of the writing of this, along with over 380,000 deaths worldwide. The world has witnessed many similar infections, namely the SARS and the MERS that invaded the world in 2003 and 2013.

While the first attack of the virus occurs at the pulmonary levels, studies have shown that it could progress and end up damaging many other organs like the heart, liver and brain. COVID-19 is a controversial severe infection that needs more research and studies to properly understand its physiology.