Signs Of Oxygen Toxicity in Diving: Why Do They Occur?

Oxygen toxicity is a significant risk faced by commercial and technical divers in their daily activities.

When diving with a standard air mixture in recreational diving, oxygen levels are not high enough to cause problems because recreational divers typically do not go very deep or stay underwater for long periods.

However, those who use gas mixtures with higher oxygen content are at greater risk, as the extra oxygen can be dangerous if not used correctly.

In this article, we will not provide a solution to never experience oxygen toxicity symptoms.

Firstly, because the only way to achieve that is through proper training, using common sense, and monitoring the partial pressure of oxygen in the gas mixture you are breathing at the depth you are at, to avoid exceeding the limits. If you exceed them, you will be at risk.

Secondly, because scientists have not fully solved this issue. However, they have made significant progress, and that is what we will share with you. Knowledge always makes scuba divers safer.

In this article, we will explore:

1. How does oxygen toxicity occur?

As discussed in the article “Causes of Hyperoxia in Scuba Diving and How Divers Avoid It” oxygen toxicity occurs when we breathe oxygen at high pressures or for too long.

Signs of oxygen toxicity are associated with using supplemental oxygen or compressed air, such as:

• Oxygen tanks for diving
• Hyperbaric oxygen therapy
• Mechanical ventilators in hospitals

These devices can lead to effects on the body due to excessive oxygen.

Thus, the oxygen from the air is inhaled into the lungs, where it is transferred to the blood, which distributes it throughout the body to ensure that organs and tissues function properly. However, an excess of oxygen can be harmful to tissues. It is important to note that sensitivity to oxygen damage varies between individuals and can change from day to day.

Pulmonary Oxygen Toxicity

When the tissues affected are pulmonary, excess oxygen can cause the alveoli, small air sacs in the lungs, to fill with fluid or collapse, which interferes with lung function and impairs the transfer of oxygen to the blood.

Central Nervous System Oxygen Toxicity

The most severe symptoms occur when oxygen toxicity affects the central nervous system.

2. Signs Of Oxygen Toxicity

2.1. Signs of Pulmonary Oxygen Toxicity

• Itching, burning, and chest pain
• Dry cough
• Chest pain
• Difficulty breathing
• Seizures
• Loss of consciousness

2.2. Symptoms of Oxygen Toxicity in Central Nervous System

• Initial (Prodromal) Symptoms:
  • Tachycardia
  • Tremors
  • Nausea
  • Vomiting
  • Dizziness and vertigo
• Advanced Symptoms:
  • Blurred vision
  • Seizures
  • Irritability and changes in mental state
• Critical Symptoms:
  • Loss of consciousness
  • Difficulty breathing or chest pain
  • Severe seizures

3. Mechanisms Causing Signs of Oxygen Toxicity

What you are about to read is based on the conclusions of Johnny E. Brian, Jr., M.D., Associate Professor in the Department of Anesthesia at the University of Iowa Hospitals and Clinics, gathered in the article Current Thoughts on Mechanisms of Hyperoxic Seizures.

Signs of oxygen toxicity are difficult to prevent, but in recent years, there has been progress in understanding their mechanisms. Here’s what is currently known:

1. Hydrogen Peroxide (H2O2) in the Brain

It is currently believed that free radicals and reactive oxygen species (ROS), such as hydrogen peroxide, are responsible for the symptoms of oxygen toxicity. Here’s how: Molecules are composed of a nucleus with protons, neutrons, and electrons orbiting around it. Electrons are usually paired, but sometimes one is left unpaired.

The “lone” electron seeks a partner and often ends up stealing one from another molecule. This makes the molecule very reactive, destabilizing another molecule and turning it into a radical. This process can trigger chain reactions, particularly affecting lipids in the cell membranes of the brain.

Furthermore, hydrogen peroxide (H2O2), which is toxic, plays a key role in oxygen toxicity signs. You might think, “I don’t have hydrogen peroxide in my brain.” But you do; your cells produce it to defend against excessively reactive free radicals. Typically, the brain controls this with certain enzymes, but excess oxygen can deplete these enzymes.

It is now known that hydrogen peroxide increases significantly in the brain with excess oxygen, by up to 700%. The enzymes cannot keep up, and the brain becomes intoxicated, among other complicated issues.

1. Catecholamines and Stress

Catecholamines are neurotransmitters in the brain, such as epinephrine (adrenaline) and norepinephrine (noradrenaline). These substances help regulate important functions in the body, such as stress and the response to danger.

When catecholamine levels are high, more hydrogen peroxide is produced. Stressors like cold, physical exertion, or dehydration can activate the sympathetic nervous system, increasing catecholamines (like adrenaline). This elevation can increase the risk of oxygen toxicity signs.

Increased CO2 (a problem particularly affecting rebreather divers) also raises stress and activates the sympathetic nervous system, thereby increasing catecholamines.

Medications that elevate catecholamines, such as certain decongestants, can increase the risk of seizures.

4. What Can Help Reduce Central Nervous System Oxygen Toxicity Signs?

Vitamin E:

Some experiments have shown that vitamin E can help delay the onset of oxygen toxicity symptoms. Vitamin E, an antioxidant, acts as a shield for body cells.

Oxygen toxicity symptoms occur because many molecules, like free radicals and hydrogen peroxide, cause a chain reaction that damages cells, especially the lipids in cell membranes. Vitamin E, found in the membrane (the outer layer) of cells, acts as a “guardian” protecting them.

Vitamin E also increases enzyme levels in the brain, which help eliminate hydrogen peroxide.

After reading all this, you might wonder: “What should I do with this information?” The main idea is that signs of oxygen toxicity can be caused by elevated catecholamines. These substances increase with stress, excess CO2 (the gas we exhale), and the use of certain medications like decongestants.

To prevent this while diving:

1. Avoid Stressful Situations: Stress can increase catecholamines, so try to stay calm before and during your dive.
2. Be Cautious with CO2: Equipment malfunctions, such as a poorly functioning regulator, can cause CO2 retention, increasing the risk of seizures. Therefore, keeping your equipment in good condition is crucial.
3. Stay Hydrated and Avoid Decongestants: Dehydration or the use of decongestants can raise the risk of seizures, so it’s best to avoid them.

In summary, stay calm, take care of your equipment, and be mindful of how you feel before diving to reduce the risk of oxygen toxicity symptoms.

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