Understanding Shortness of Breath

What Causes Trouble Breathing?

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To figure out why you're feeling short of breath, you have to understand what makes you crave breathing in the first place. You might think it's a lack of oxygen, but in most cases, it's something else entirely. There are two parts to breathing—ventilation and respiration—and interrupting either one can lead to shortness of breath.

Following are the four ways we become short of breath and the medical conditions that might lead to each one.

First Cause of Shortness of Breath: Body Demands More Air

Creating a demand for more air than you're currently getting makes you feel short of breath. These are the most common causes of increased demand, either because you need to get rid of carbon dioxide or because your body needs more oxygen:

When the body simply needs more air because of increased demand, there isn't too much we can do other than fix the demand (stop exercising, treat the shock or the heart attack). Supplemental oxygen is one way to do it, but there is evidence that adding more oxygen to the bloodstream than is natural—when airflow isn't the problem—may do more harm than good. Indeed, some studies showed heart attack patients doing worse rather than better when they got supplemental oxygen.

It's not always the demand for air that's causing the problem.

Sometimes it's the supply.

Second Cause of Shortness of Breath: Too Little Airflow

Most of the time, when folks think of having difficulty breathing, they think of problems getting air into the lungs. Anything that restricts airflow deep into the lungs—all the way into the small sacs (alveoli)—gets in the way of moving oxygen into the bloodstream and moving carbon dioxide out of the bloodstream.

Certain diseases can cause restricted airflow, and these either cause constriction of the airways from swelling or inflammation, or congestion from fluid or mucus:

Illnesses aren't the only causes of restricted airflow. Moving air in and out of the lungs is a mechanical process, so injuring the structures of the lungs and airways could also restrict the amount of air that makes it through. Most of the injuries that can cause restricted airflow are injuries to the chest, head or neck:

There are other mechanical causes that aren't always thought of as injuries:

  • choking
  • drowning
  • collapsed lung (pneumothorax), which can be caused by a hard thump on the chest, a penetration wound or may even happen spontaneously as part of a weakened lung from a disease like COPD

For the last two types of causes, some patients might not actually feel short of breath. Instead, they might simply experience weakness or confusion. Because in these cases, the body doesn't always realize it's having any trouble at all.

Third Cause of Shortness of Breath: Trouble Transporting Oxygen in the Bloodstream

Some things can prevent the bloodstream from adequately carrying oxygen from the lungs to the cells of the body. There are two problems that happen fairly often:

Final Cause of Shortness of Breath: Lack of Oxygen in the Air

Sometimes, there's just nothing you can do to make things better. At high altitudes, the air is too thin to contain an adequate supply of oxygen for the body's needs.

In a confined space with limited air, eventually the amount of oxygen and carbon dioxide in the air will match exactly with what the body is exhaling and the body won't be able to absorb oxygen or get rid of carbon dioxide.


Henry, Mark C., and Edward R. Stapleton. EMT Prehospital Care. 3rd Ed. 2004. Mosby/Jems

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