Why divers are taught never hold your breath.

By John Hauxwell, Red Sea Tribe

“Never hold your breath, except at the same depth.

Don’t hold it for too long, or everything goes wrong!”

All diving students are told, from the beginning of their training to never hold their breath. I have heard the statement extended to ” Never hold your breath, except at the same depth”, which whilst correct (from a physics perspective) doesn’t account for gas build-ups in your system due to lowering your respiratory rate. This is addressed by the next line “Don’t hold it for too long or everything goes wrong”.

Passionate scuba educator & sidemount tech wreck fanatic Andy Davis said “We undergo training to program intuitive and instinctive responses, and they should encourage the correct behavior under pressure (physical and cognitive). So teaching the ‘never hold your breath’ mantra instils in students, from day one, the correct behavior for when divers find themselves in difficult circumstances.”

So why shouldn’t we hold our breath? 

1. Risk of DCI

Pressure is everything in scuba diving; the deeper you descend, the more the pressure increases. If you think of your lungs when you take a deep breath above water and then descend five meters, the pressure on your lungs increases and so the volume of your lungs decreases. Even though you haven’t breathed out any of the air, you took in on the surface your lungs could take on more air as the volume of the gas in your lungs has decreased This is known as Boyles law, commonly expressed as 

p1v1=p2v2

The air we breathe at depth is at pressure (in a full tank at the start of the dive 200 bar – give or take effects for changes in tank pressure with temperature (Gay-Lussac’s law). As long as you keep breathing the air in your lungs can escape. If you hold your breath and the pressure surrounding you decreases, (i.e., you ascend) the air in your lungs will expand. 

When the air cannot escape in a natural way, the pressure in the lungs increases and a DCI results.

Overexpansion of the lung can lead to serious injuries. Examples of these are:

Arterial Gas Embolism (AGE):When a person suffers from AGE, air diffuses into the blood (Henrys Law) and makes its way up the minuscule capillaries of the brain, forming an air bubble and consequently blocking the blood carrying vessels. This obstructs the flow of blood in the body and oxygen supply is cut off to vital body tissues. The consequences can be as deadly as paralysis, brain damage, heart stroke, and death. AGE is the most dangerous effect of a lung overexpansion injury and is potentially fatal. AGE affects the body at a more rapid rate than any of the other manifestation of lung overexpansion injury.

Mediastinal Emphysema (ME): ME is a condition in which air is trapped in the cavities that surround the delicate heart muscles. This air, in turn, places pressure on the heart muscles, which in turn stop functioning properly; as a result, blood supply to the body becomes erratic. This condition is not as severe as AGE, but extreme Mediastinal Emphysema can lead to heart failure.

Pneumothorax: In this condition, the air is collected at the outer side of the lungs causing the lungs to cave in upon themselves. The victim may end up with partial or completely collapsed lungs. Since pneumothorax involves injury to lungs, it causes acute pain in the chest which may be accompanied by coughing up blood. Pneumothorax worsens as a diver ascends because the pressure on the damaged lung increases with the ascent

Subcutaneous Emphysema: Probably the least damaging of all common lung overexpansion injuries, Subcutaneous Emphysema is a condition in which air pockets are formed near the collarbone and the neck. With Subcutaneous Emphysema, there is irritation and squishiness in the skin, which may even crack if it is touched.

1. CO2 Build up –  Hypercapnia is excess carbon dioxide (CO2) build-up in your body.

The condition, also described as carbon dioxide retention, can cause effects such as headaches, dizziness, and fatigue, as well as serious complications such as seizures or loss of consciousness. Common symptoms of hypercapnia, if they do occur, include fatigue, an inability to concentrate or think clearly, headaches, flushing, dizziness, dyspnea (shortness of breath), tachypnea (rapid breathing) and increased blood pressure. 

In serious episodes this can lead to paranoia, depression, and confusion, muscle twitches, seizures, palpitations (a feeling that you are having a rapid heart rate), panic, or a feeling of impending doom, dilation (widening) of superficial veins in the skin and papilledema (swelling of the optic nerve).

Any of the symptoms occurring during a dive should be enough to abort the dive immediately and seek medical advice as hypercapnia can lead to respiratory failure and coma if left untreated.

1. So how should we breathe underwater?

We should breathe normally in a regular slow and deep fashion, using as much of our lungs as possible When

mastered, diaphragm initiated breathing will not only help you optimize the gas exchange in your lungs but also breathe more efficiently under demanding diving conditions. So simply put: long, deep even breaths. Breathing in this way also helps you to relax and thus improves your gas consumption.

There are various techniques that could help:

1. Box breathing – A slow inhalation over 3-4 seconds, hold for 3-4 seconds, exhale over 3-4 seconds, and then hold for 3-4 seconds before the next inhalation. Timing this with a frog kick pattern (inhale on opening the legs and exhale on closing them) makes for maximum efficiency as the ribcage expands as you push your legs apart.
2. The Reilly Emergency Breathing Technique (R-EBT) – A slow inhalation followed by an exhalation controlled with the diver making a humming sound as the breath is released. We use this in Controlled Emergency Swimming Ascent and Buoyant Emergency Ascent, and it can be easily modified for use whilst diving. Some people hum as they work, why shouldn’t divers?
3. Straw breathing – A slow inhalation followed by an exhalation controlled by pursing the lips to mimic breathing through a straw. Many dive instructors get students to breathe through a straw to get used to this idea. Using a long slow controlled exhale is similar to the R-EBT is a good idea but pursing of the lips is almost impossible with a regulator in place, so a long slow exhale is recommended. Some instructors actually get their students to breathe through a straw to get used to the feeling of breathing with a regulator!
4. Skip breathing – A normal inhalation held for several seconds, followed by an additional inhalation before exhalation is NOT recommended as this can easily lead to over inflation with a smaller change in depth.

So, don’t hold your breath, breathe regularly in a slow controlled cycle. Don’t skip breath and don’t put yourself at risk, and of course, NEVER hold your breath when ascending or descending! For further information on diving techniques and theory please contact us 

Further Reading

http://www.emdocs.net/twenty-thousand-leagues-under-the-ed-common-diving-emergencies/
https://www.nuemblog.com/blog/scuba
https://en.wikipedia.org/wiki/Decompression_sickness