The Bends: Facts & Myths of Decompression Sickness Part I

The Bends, caissons disease, or decompression sickness can be a mystery to most divers. Every diver learns about decompression on their open water course and learns to plan their dives within No Decompression Limits. However, while everyone has some basic knowledge of decompression, many myths and half-truths are circulating around the diving community. So before you pick up your mask snorkel, BCD, and iPhone underwater housing and head off on your next dive adventure, what are some of the facts and myths around the bends?

A Brief History of The Bends

Decompression sickness or the bends history dates back to well before the invention of scuba diving. It was initially known as caisson disease since those affected were miners working in pressurized caissons. In fact, the first recorded instance of decompression sickness dates back to 1841, when miners working underground in pressurized chambers (caissons) started to develop symptoms.

The term “The Bends” originates from the 1870s when workers building the Brooklyn bridge also developed symptoms of decompression sickness. While at the time, we understood that the issue was caused by “gas in the blood,” little else was known. The term the bends was coined after doctors noticed that those suffering from the condition adopted a similar posture to the then fashionable Grecian Bends posture adopted by many women.

By the early 20th century, our understanding of the effects of inert gas in the body was much more advanced, and in 1908, J.S. Haldane created the first decompression tables after experimenting on goats.

Symptoms of the Bends

One of the biggest problems with diagnosing Decompression Sickness is how varied the symptoms can be. Imagine the saying someone had a “Car Crash. That can range from a minor fender bender when there is a tiny scratch to the paintwork or a minor dent in the bumper. On the other hand, a “Car Crash” can also mean a huge accident where the vehicle is a mass of twisted metal and carbon fiber with multiple fatalities.

The bends are precisely the same. On the one hand, symptoms can be as mild as feeling slightly more fatigued than usual after a dive or even having slightly clouded thinking.

However, on the extreme end, symptoms can include paralysis, cardiac arrest, or even death.

So far, known symptoms of the bends can include fatigue, joint and muscle pain, numbness and tingling, clouded thinking, general and localized weakness, skin rashes, loss of balance and coordination, paralysis, and difficulty breathing, to name a few.

Two Competing Decompression Theory Models.

We know that the bends happen due to bubbles created in the body during and after ascent. The exact reason and mechanism why this happens is not fully understood. Currently, alternative decompression models aim to explain and model the behavior of inert gas in a diver’s body. Each model has its own strengths and weaknesses, and proponents advocate that it is a more “accurate and true” picture of what is happening inside our bodies when we dive.

Dissolved Gas Modelling

Dissolved gas models are the traditional models that date back to Haldane in the early 20th century. These types of models are what you will have been taught about during your open-water course.

In a nutshell, the models assume you have no bubbles in your blood before a dive. As you breathe gas under pressure during a dive, the inert gas dissolves into your tissues and is held in solution. As you start to ascend, your body can slowly eliminate the gas by breathing it out. However, if you create too much of an over-pressurization between the gas pressure in your tissue and the outside pressure, bubbles will start forming within your body.

The classic example used to demonstrate this is a closed bottle of soft drink. After shaking it up, if you open it, lots of gas will suddenly come out of the solution, and it will froth over. That is what happens when you create a large overpressure gradient. On the other hand, if you very slightly crack the top open, you hear a hiss as the gas starts to escape gently without the bottle frothing over. That process is exactly what happens when you have a nice slow ascent, or even some decompression stops, to release the gas from your body without too much of an over-pressurization.

These models aim to control over-pressurization to allow the gas to escape from our tissues safely.

Bubble Models

Bubble models deal with gas in our tissue in a completely different way. The underlying assumption is that all humans have gas seeds in their tissue and that we can tolerate a specific number and size of bubbles within our tissues without any problems.

To put it in layman's terms, these models theorize that as you descend, the gas being absorbed goes into these gas seeds, and as you ascend, it is released as tiny asymptomatic bubbles in the blood. The decompression algorithm then allows the diver to stop where the bubbles can be eliminated through the normal breathing mechanism.

The stops and No Decompression Limits are based on controlling how much gas is in solution and the number and size of the bubbles floating around in the divers' tissues!

No Decompression Limits are not Static.

One of divers' biggest misunderstandings concerns No Decompression Limits NDL. The assumption is that these are set data points based on mathematics; if you stay inside them, you will not suffer from DCS. Sadly, this is not the case, and a vast array of recreational divers have suffered a decompression hit while diving within the limits of a decompression table.

A vast array of factors can influence whether you suffer a hit or not. For instance, if you like working out, even to stay fit for diving. Pumping heavy weights and then going for a dive can result in a hit even if you stay within limits. This is due to all the tears in your muscle fibers not being efficient at off-gassing. Likewise, if you have had major surgery or scarring, you may be more susceptible to DCS because these areas of your body have a less efficient blood flow to remove the inert gas built up during a dive.

Hydration can also be a problem; if you are not properly hydrated, your body's ability to transport and release gas is impaired, meaning you may take a DCS hit even if you dive "within the limits." Along with hydration, your dive profile plays an important role; staying within limits but adopting a saw tooth profile is like shaking up a bottle of fizzy drink and then hoping it does not overflow when you open it!

As a rule, NDLs are a good guideline; however, if you have some predisposing factors, you may want to conder adopting an even more conservative approach to diving and using even more conservative NDL and dive profiles.

Avoid Chasing the Ceiling

Chasing the ceiling is arguably one of the worst habits novice divers with a bit of experience can get into. It generally happens when divers have enough experience to have decent/good air consumption but still lack the training and understanding about decompression.

A typical chasing-the-ceiling dive goes as follows: The diver descends to, say, 30m/99ft. They explore around until they only have a minute or two of NDL left on their computer. They then ascend to, say, 24m/78ft and keep exploring up to when they only have 1 minute or 2 of NDL left on their computer. They then repeat the process at 18m/60ft and 15m/50ft before starting to make their way to the shallows conducting their safety stop and exiting the water.

This is arguably the best way to get yourself bent in recreational diving. When undertaking dives like this, you are trying to fill your body with as much gas as possible while staying within the NDL. Regularly undertaking these kinds of dives will probably mean you will take a DCS hit one day.

If you want to explore deeper and longer, you are better served learning to technical dive, planning, and executing dives properly with more planning, gas management, and more.

Final Thoughts

So far, we have covered some of the basics of the bends. In part 2, we will look at other interesting facts and myths about decompression sickness, including What happens after you have suffered an incident and recovered, and what are the best ways to prevent a decompression hit from occurring in the first place. What happens in a recompression chamber, and how does it treat you?