Do you want to learn more about breathing and airflow?

We understand that helpful information can be hard to find.

This post provides illustrations and information for breathing and airflow including background, anatomy, and illustrations.

An Ear, Nose and Throat surgeon wrote this blog post.

Endoscopy of the upper airway in a woman. Note the endoscope is placed into the nose and the airway can be seen. The voice box (vocal cords) is shown on the screen of the endoscope. The illustration shows the airway (larynx, trachea and lungs). CamachoMD.com
Endoscopy of the upper airway in a woman. Note the endoscope is placed into the nose and the airway can be seen. The voice box (vocal cords) is shown on the screen of the endoscope. The illustration shows the airway (larynx, trachea and lungs).

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Summary for Breathing and Airflow:

Air travels into the human body through the upper and lower airway so that gas (oxygen and carbon dioxide can be exchanged).

The airflow pathway during breathing is as follows: the diaphragm contracts, the lungs expand, air flows from either the nose or mouth into the upper airway, into the pharynx, around and behind the epiglottis, between the right and left arytenoids and aryepiglottic folds, through the vocal cords (glottis), through the trachea down to the carina, down the left and right primary bronchi, along each primary bronchi, secondary bronchi, tertiary bronchi, through the bronchioles and then to the alveoli which is where gas (oxygen and carbon dioxide) is then exchanged.

Have you ever wondered why we need to breathe and how oxygen and carbon dioxide travel through our bodies?

It is an interesting process in which air and gas enters the nose or the mouth and is exchanged at the alveoli in the lungs and then travels out again via the nose or mouth.

The goal of the blog post is to educate you on why we need to breathe, how air flows between upper airway (nose and mouth) and the lower airway (lungs and alveoli) and why obstructive sleep apnea doesn’t allow for proper airflow.

After reading this blog post you will better understand why proper airflow through your body matters.

This blog post provides illustrations that show the upper and lower airways, demonstrating how the air travels through the structures.

Remember, that the information provided herein is for educational purposes only, and if you have seen a healthcare provider, then they are the ones who can provide the best information for your specific situation.

Why do humans and other animals need to breathe?

Gas exchange is critical for the human body because our organs, tissues, and cells need oxygen in order for a critical process called aerobic respiration to take place.

Aerobic respiration is a process in which the body is able to use oxygen that is inhaled and nutrients that are consumed such as proteins, carbohydrates, and fats as a fuel source (to create energy).

Therefore, we need two things in order to have proper levels of oxygen in the body.

First, we need to have proper levels of oxygen available in the atmosphere so that we can breathe it in.

Second, we need to have an efficient system to get oxygen into our bodies.

The air in our atmosphere (by volume) is approximately 21% oxygen, 0.04% carbon dioxide, 78% nitrogen and 0.93% argon.[1]

Interestingly, when the body takes in and uses the oxygen at the cellular level, a byproduct of the reaction is carbon dioxide.  Carbon dioxide builds up in the body and needs to be eliminated and the lungs (and alveoli) help to eliminate it.

The illustration shows the upper airway (to include the throat (pharynx), voice box (larynx) and windpipe (trachea). CamachoMD.com
The illustration shows the upper airway (to include the throat (pharynx), voice box (larynx) and windpipe (trachea).

How do oxygen and carbon dioxide travel in our blood?

When oxygen and carbon dioxide travel in our bloodstream, they bind with hemoglobin found in red blood cells.


Oxygen and carbon dioxide (bound with hemoglobin) reach the lungs and the alveoli.

Carbon dioxide and oxygen are then exchanged at the alveoli and is then transported out of the body via the airway; eventually traveling out through the nose or mouth.

What is the path that air takes from the nose down to the lungs (alveoli)?

Our bodies need to take in air in order to use the oxygen for our cells, tissues, organs and body systems.

Because our body needs to take in the oxygen, there is a system set up to get the air into our bodies.

The first event that triggers airflow is that the diaphragm contracts.

When the diaphragm contracts, the lungs become larger.

As the lungs become larger, they provide negative pressure which then pulls air from the environment into the body.

When the air is being sucked into the airway, the air travels through the nose or mouth and then travels downward.

The nose has a higher resistance to airflow, but the nose better humidifies the air.

Air then travels from the nose or mouth down toward the pharynx (back of the throat). The pharynx behind the nose is the nasopharynx and the pharynx behind the tongue is the oropharynx.

Upper airway that is open with normal breathing. Note that the oxygen goes into the airway and the carbon dioxide leaves the airway. CamachoMD.com
Upper airway that is open with normal breathing. Note that the oxygen goes into the airway and the carbon dioxide leaves the airway.

The air then travels down the hypopharynx (area of the throat from the hyoid bone to the entrance to the vocal cords).

Air flows behind the epiglottis (tissue that is behind the tongue) and then goes between the right and left parts of the supraglottis (the tissue just above the vocal cords) known as the arytenoids and the aryepiglottic folds.

Air then travels between the true vocal folds and the false vocal folds and then goes into the subglottis at the level of the cricoid cartilage (a complete ring of cartilage).

In children the cricoid cartilage is the narrower than the trachea, but not in adults.

The trachea (windpipe) is the middle part of the airway that allows air to travel between the vocal cords (voice box) and the lungs.

The front part of the trachea has cartilage rings, while the back part of the trachea has no rings and is soft (the esophagus sits against the back part of the trachea).

The air then travels down the trachea.

At the end of the trachea, there is a branching point (the carina) where the air goes into the primary bronchi (right and left) that branches further (secondary and tertiary bronchi).

Air then travels to the bronchioles and gas is exchanged at the level of the alveoli.

The alveoli are small sacs with surrounding capillaries with very thin walls that allow for the exchange of oxygen and carbon dioxide.

The oxygen travels in red blood cells and is carried to organs, tissues, and cells throughout the body.  Aerobic respiration then takes place and carbon dioxide is a byproduct.

The illustration shows the upper airway (to include the throat (pharynx), voice box (larynx) and windpipe (trachea); and the lower airway (right lung in this illustration). CamachoMD.com
The illustration shows the upper airway (to include the throat (pharynx), voice box (larynx) and windpipe (trachea); and the lower airway (right lung in this illustration).

Carbon dioxide binds to hemoglobin, travels in the red blood cells back to the alveoli and is exchanged there and is exhaled via the airway structures (traveling from the lungs back to the upper airway and eventually to the nose or mouth).

What is the summary of how the air travels in the body?

  • The diaphragm contracts,
  • The lungs expand,
  • Air flows from either the nose or mouth into the upper airway,
  • Air flows into the pharynx,
  • Air flows around and behind the epiglottis,
  • Air flows between the right and left arytenoids and aryepiglottic folds,
  • Air travels through the vocal cords (glottis),
  • Air flows through the trachea down to the carina,
  • The air then travels down the left and right primary bronchi,
  • Air travels along each primary bronchi, into the secondary, then tertiary bronchi,
  • Once the air reaches the bronchioles, the alveoli are encountered and gas (oxygen and carbon dioxide) is then exchanged.

How does obstructive sleep apnea prevent proper airflow during sleep?

Obstructive sleep apnea (OSA) is a common disorder in humans.

OSA occurs when there is a partial or complete blockage of airflow during sleep that lasts at least 10 seconds.[2]

During an obstructive sleep apnea event, the patients can have a decrease in their body’s oxygen level and/or an increase in their body’s carbon dioxide level.

Upper airway obstruction at the level of the soft palate. Note that since the airflow is blocked, the oxygen cannot get into the airway and carbon dioxide cannot leave. The light blue arrow points to the obstructed palate. CamachoMD.com
Upper airway obstruction at the level of the soft palate. Note that since the airflow is blocked, the oxygen cannot get into the airway and carbon dioxide cannot leave. The light blue arrow points to the obstructed palate.

Patients with OSA can have problems, especially patients with severe OSA.

For symptomatic patients, they can present with snoring, sleepiness, tiredness, fatigue, irritability, headaches, neurocognitive dysfunction, lightheadedness, high blood pressure, atrial fibrillation, enlargement of the heart and other signs and symptoms.[2] 

These changes and oxygen and carbon dioxide levels can be monitored during a sleep study with sensors. The entire night is then recorded and the obstructive events are noted and the oxygen and carbon dioxide levels are tagged.

Upper airway obstruction at the level of the tongue. The obstruction makes it so that oxygen cannot get into the airway and carbon dioxide cannot leave. The light blue arrow points to the obstructed tongue. CamachoMD.com
Upper airway obstruction at the level of the tongue. The obstruction makes it so that oxygen cannot get into the airway and carbon dioxide cannot leave. The light blue arrow points to the obstructed tongue.

If the obstruction reduces the airflow by 90% or more for at least 10 seconds with or without any change in oxygen level then this is known as an apnea.[3]

If the obstruction reduces airflow by 30-50% and decreases the oxygen level in the body by 3-4% or more, for 10 seconds, then the event is known as a hypopnea.[3]

Although there are many potential sites of blockage in patients who have obstructive sleep apnea with the most common sites being the soft palate, the tonsils, the back of the tongue, the entire pharynx itself, the epiglottis, and the supraglottis.

If a patient has obstructive sleep apnea then the airflow below the level of the obstruction can become impaired and the hemoglobin in red blood cells will not be able to exchange oxygen and carbon dioxide at the upper level of the alveoli.

This lack of proper airflow during apneas or hypopneas can cause the body’s oxygen saturation can decrease and carbon dioxide in the body can increase.

If the obstructions occur at least 5 times per hour, then the patient is diagnosed with mild obstructive sleep apnea. If there are 15 to 30 obstructions per hour, then the patient is diagnosed with moderate obstructive sleep apnea.

If the patient has 30 or more obstructions per hour, then the patient is diagnosed with severe obstructive sleep apnea.

Upper airway obstruction at the level of the soft palate and the tongue. Note that since the airflow is blocked, the oxygen cannot get into the airway and carbon dioxide cannot leave. The light blue arrow points to the obstructed palate and the obstructed tongue. CamachoMD.com
Upper airway obstruction at the level of the soft palate and the tongue. Note that since the airflow is blocked, the oxygen cannot get into the airway and carbon dioxide cannot leave. The light blue arrow points to the obstructed palate and the obstructed tongue.

In order to eliminate obstructive sleep apnea, adult patients are often treated with continuous positive airway pressure therapy (CPAP) or an oral appliance (a dental device that moves the lower jaw forward).[4]

Patients who fail medical management may undergo surgery.[4]

In adults who have large tonsils, a tonsillectomy may be first-line therapy.[2] 

In children, a tonsillectomy with adenoidectomy is typically the first-line surgery.[5]

With proper treatment, if the obstructive events are eliminated, the oxygen saturations and carbon dioxide saturations can normalize, and the patient’s symptoms will typically improve.

Government Disclaimer: The views expressed in this website are those of the author(s) and do not reflect the official policy or position of the Department of the Army, Department of Defense, or the US Government.

References:

1.            Cox, A.N., Allen’s Astrophysical Quantities (Fourth ed.). AIP Press, 2000: p. pp. 258–259.

2.            AASM, e.a., American Academy of Sleep Medicine. International classification of sleep disorders, 3rd ed. (ICSD-3). American Academy of Sleep Medicine. Darien, IL., 2014.

3.            Berry, R.B., et al., The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications, Version 2.0.2. 2013, Darien, Illinois, USA: American Academy of Sleep Medicine.

4.            Camacho, M., et al., Thirty-five alternatives to positive airway pressure therapy for obstructive sleep apnea: an overview of meta-analyses. Expert Rev Respir Med, 2018. 12(11): p. 919-929.

5.            Brietzke, S.E. and D. Gallagher, The effectiveness of tonsillectomy and adenoidectomy in the treatment of pediatric obstructive sleep apnea/hypopnea syndrome: a meta-analysis. Otolaryngol Head Neck Surg, 2006. 134(6): p. 979-84.