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What happens during oxygen deprivation? Many of us have had moments in our lives where we experience the strain of holding our breath. Maybe it was trying to hold the longest singing note, playing a wind instrument for too long, choking on food that’s stuck in your throat, or staying underwater the longest. If this were you, you may be familiar with the (concerning) lightheaded and dizzy feeling after holding your breath for too long. That is a very mild state of hypoxia!
Simply defined by Cleveland Clinic (2022), hypoxia occurs when there are ‘low levels of oxygen in your body tissues’. Despite their similar names, Hypoxia is distinct from hypoxemia! While similar, Hypoxemia occurs when one doesn’t have enough oxygen in their blood and can be a cause of hypoxia.
TIP - Breaking Words Down:
‘Hypo’ is a pre-suffix meaning low.
‘Oxia’ is a suffix relating to oxygen.
‘Emia’ is a suffix relating to blood.
There’s a wide range of possible causes for a lack of oxygen, including smoke inhalation, strangulation, drowning, and heart or blood complications. The scientific term for breathing that stops for any reason is called ‘apnea’ (Medline Plus, 2023).
How Does Our Body Use Oxygen?
Let’s cover our bases first. Why do we need oxygen? Inside our lungs, our windpipe attaches to a collection of branch-like structures called bronchi and bronchioles. At the end of bronchioles are tiny little air sacs called alveoli. As we inhale, oxygen travels through the alveolar-capillary barrier to enter the bloodstream, while carbon dioxide leaves the blood and is exhaled. Red blood cells then deliver oxygen around the body for cells to use in aerobic cellular respiration inside the mitochondria to produce energy in the form of ATP. ATP is the body’s energy currency on the cellular level and powers everything from beating hearts to moving muscles and transmitting nerve signals.
Fig 1: (left) a diagram depicting the interior parts (bronchi, bronchiole, and aveoli) of the lungs. Sourced from Shutterstock.
Fig 2: (right) a simple diagram depicting the gas exchange in an alveoli. Sourced from Shutterstock.
When we hold our breath, our lungs are unable to exchange carbon dioxide for oxygen, and oxygen levels in our blood drop while carbon dioxide levels grow. If oxygen levels become too low, our cells are unable to produce enough ATP and die messily through necrosis.
Necrosis is a fancy medical term for unintended cell death.
Fun Fact: Did you know, that our brain usually doesn’t monitor oxygen levels directly? When dissolved in water, carbon dioxide forms carbonic acid, raising the pH level of blood. This change is detected by chemoreceptors, which alert your brain to increase your breathing rate and take deeper breaths. If you’re interested in learning more about how our brain monitors our carbon levels, click here!
The burning sensation you feel.in your lungs when you hold your breath is caused by the accumulation of carbon dioxide, and the subsequent electric impulses your nerves send to your brain, urging you to take a breath
What Happens When Our Brain is Completely Cut Off From Oxygen? - Anoxic Injuries, by the Minute.
Oxygen is a very important gas for humans. On average, a healthy adult takes around 12-20 breaths every minute, 960 every hour, 23,000 every day, and 8,400,000 every year. The mitochondria -the beloved powerhouse of the cell- use oxygen to produce energy, which keeps our muscles moving and cells alive. Needless to say, we really like breathing. So naturally, disastrous things happen when we stop.
What happens when the brain is completely cut off from oxygen? This is known as an anoxic brain injury (eg, cardiac arrest or blocked airways), whereas a hypoxic injury occurs when where oxygen flow is restricted but not fully cut off (eg, shallow breathing).
1-2 minutes: For most people, breath-holding becomes dangerous at the one-and-a-half to two-minute threshold where they fall unconscious. Heart rate speeds up in an attempt to compensate for low oxygen.
2-3 minutes: Brain cells are extremely susceptible to hypoxia, and can start dying only a few minutes after lack of oxygen.
3-5 minutes: There is substantial cell death and the risk of severe and irreversible brain damage grows the longer the apnea continues.
5-10 minutes: death becomes a very likely possibility.
Fig 3: a comparison of anoxic and hypoxic brain injuries, and a brief timeline of the effects of oxygen deprivation on the brain. Sourced from SpinalCord.com. https://www.spinalcord.com/blog/what-happens-to-the-brain-after-a-lack-of-oxygen.
Of course, there is no exact magic number where brain cells start dying. These statistics depend on several personal health factors and are rough guidelines that vary from person to person, just like how people can hold their breath for varying amounts of time.
The longer a casualty is deprived of oxygen, the more severe the damage and the lower rate of recovery. Symptoms also depend on the location of the brain injury. Imagine a car left in a blizzard: the longer you leave the car exposed, the worse the damage it sustains.
How Much Oxygen Does Our Brain Need?
Our brain, liver, and heart use the most oxygen in our body, consuming 20.4%, 18.4%, and 11.6% respectively. Our brain is especially sensitive to oxygen deprivation, and neurons (cells that make up your brain and nervous system) can die far sooner than you would expect. We need consistent breathing and a steady heart rate to keep good oxygen saturation. If one of them fails our oxygen levels drop.
Your brain is the most comfortable when oxygen levels are between 95-100%. This is where you have clear thoughts and make creative interpretations that require ‘connecting the dots’ and drawing evaluations. If you’re high up in the mountains with a thin atmosphere and less oxygen, you’ll notice that you’ll have more difficulty solving problems that require creative thinking, and your motor coordination takes a hit.
You enter the danger zone when your brain's oxygen levels drop below 80%. Brain functions begin to be impaired, you face mild hypoxia, and neurons start dying through necrosis. and A brief dip might leave you dizzy, but prolonged exposure can cause serious brain damage.
As oxygen levels fall even further, we travel further into treacherous territory with severe hypoxia. At the 60-70% oxygen mark, you may experience severe confusion, loss of consciousness, and even seizures.
By the point oxygen levels drop below 60%, brain cells are dying in the masses, and anoxic (complete lack of oxygen flow) brain injuries become very likely.
Diving Response - How Our Body Compensates for Lack of Oxygen in Water
By now, you should have gotten a solid impression of why it’s pretty bad to deprive your body of oxygen and the consequences it can have. But what does your body do when it’s faced with these challenges?
When your face is submerged in cold water or when you hold your breath for extended periods, your body triggers a ‘diving response’ in an attempt to conserve oxygen. Your body prioritizes getting oxygen to the brain by constricting blood vessels in non-essential organs such as arm muscles and increasing your heart rate. While the oxygen levels in your extremities steadily decrease, because your body focuses on delivering blood to your brain your brain receives roughly 4% more oxygen than its baseline after the initial drop. Take a moment to think about that: your body prioritizes your brain to receive more oxygen after you stop breathing.
Sadly, all good things must end; without breathing, oxygen cannot be replenished, and the brain's supply diminishes, eventually causing critical failures. During an investigation conducted at Ghent University in Belgium, by Janne Bouten, Jan Bourgois, and Jan Boone in 2020 (yes, those are their actual names), the average of participants’ brain oxygen levels decreased by 5% by the point holding their breath became too painful to further hold for most volunteers.
If this is interesting to you, check out further details about the diving response here!
While the participants in the experiment stopped holding their breath, it is known that some free divers are capable of holding their breath to the point they fall unconscious. This is incredibly dangerous, especially if it occurs underwater.
FUN FACTS
While it limits your physical ability, it is possible to live with just one lung.
Our body only absorbs 5% of the 21% oxygen available in the air. The rest is exhaled.
Lungs will always retain at least 1 liter of air, regardless of how much we exhale. This means the lungs are the only organ that can float on water.
Budimir Šobat, a Professional breath-hold diver, held his breath underwater for a whopping 24 minutes and 37 seconds.
While the brain can only survive for mere minutes after oxygen deprivation, Skeletal muscles can last for 60 to 90 minutes, and vascular smooth muscles can last for 24 to 72 hours!
Every hour, humans exhale up to 17.5 mL of water.
CONCLUSION
Oxygen is an incredible gas that most of us take for granted; it is crucial for the functions and processes of our entire body, and mere minutes of oxygen deprivation can have disastrous consequences on our physiology. Just today, your lungs have taken thousands of breaths to deliver this vital gas throughout your body
Our lungs work tirelessly, each breath fuels an elaborate biological system designed to sustain us. Even during challenges of rising carbon dioxide levels, the intricate method of the diving reflex helps to maintain homeostasis. The next time you pause, let's take a moment to appreciate the complexity of our body and the work it does to keep us thriving.
Bibliography
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Cleveland Clinic. (2022). Hypoxia: Causes, symptoms, tests, diagnosis & treatment. Cleveland Clinic. [online] Available at: https://my.clevelandclinic.org/health/diseases/23063-hypoxia
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Lung Foundation Australia. (2024). How your lungs work. Lung Foundation Australia. [online] Available at: https://lungfoundation.com.au/lung-health/protecting-your-lungs/how-your-lungs-work/
MedlinePlus. (2016). Cerebral hypoxia. Medlineplus.gov. [online] Available at: https://medlineplus.gov/ency/article/001435.htm?utm_source=chatgpt.com
MedlinePlus. (2023). Breathing - slowed or stopped. Medlineplus.gov. [online] Available at: https://medlineplus.gov/ency/article/003069.htm
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Swiner, N. (2023, April 29). Is It Safe to Hold Your Breath? WebMD. [online] Available at: https://www.webmd.com/a-to-z-guides/is-it-safe-to-hold-your-breath
Zawn Villines. (2016, June 13). What Happens After A Lack of Oxygen to the Brain? Spinalcord.com; SpinalCord. [online] Available at: https://www.spinalcord.com/blog/what-happens-after-a-lack-of-oxygen-to-the-brain
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