How to keep the lungs safe from pressure changes while diving

• Diving is generally safe, although injury or illness can occur due to the drastic change of environment, the use of unsuitable equipment, potentially dangerous wildlife and, most importantly, the changes in pressure.
• Health checks for diving are classified into 2 types: ‘fit to dive,’ which is suitable for both first-time divers and experienced divers who want to check if their body is ready for diving, and ‘return to dive,’ which is suitable for divers who have previously experienced illness or problems from diving and want to dive again. Both types must be performed by a medical specialist.
• One of the main issues to be cautious about after diving is boarding an airplane because of the changes in pressure it involves. At least 12 hours should pass after diving before boarding a plane, or 24 hours for those who have taken part in multiple dives over several days.
• Diving is generally considered a safe activity, but accidents can occur due to human factors, such as breaking rules or acting against advice, improper use of equipment, and poor health. Reducing these human risk factors can decrease the chance of accidents, which is why it is important to undergo a health check before diving.

Diving can be classified into 2 main types according to its purpose:

• Recreational diving: this involves diving to a depth not exceeding 40 meters for relaxation and to admire the beauty of the underwater world, including coral reefs and various sea creatures, and has recently gained popularity among Thai people.
• Professional diving: this refers to military diving for missions or commercial diving for tasks like laying gas pipes or underwater cables, cutting trees in reservoirs, and exploring archaeological sites, and cultural diving by local communities for catching aquatic animals.
• Even though diving is generally safe, the drastic change of environment, the use of unsuitable equipment, the potentially dangerous wildlife and, most importantly, the change in atmospheric pressure can all lead to injury or illness. Therefore, diving-related illnesses often refer to those caused by changes in pressure, such as:
• Barotrauma: a condition that occurs due to changes in pressure affecting various organs, causing the expansion or contraction of air in body cavities, resulting in symptoms such as ear pain, headaches, breathing difficulties, and impaired vision.
• Decompression sickness: also known as "the bends," this occurs due to the formation of gas bubbles in the blood or tissues, often caused by diving and ascending too quickly in reduced atmospheric pressure. Its symptoms can affect many parts of the body.
• Cerebral arterial gas embolism: this refers to the tearing of lung tissue that leads to the presence of air bubbles in the bloodstream, often occurring during or after surfacing from a dive.

Robert Boyle, an Irish scientist, outlined Boyle's Law in 1662, which states that changes to volume are inverse to changes in pressure, meaning that if the pressure increases, the volume decreases. For example, the lungs of a human have a capacity of about 6 liters at the surface level, so when diving to a depth of 10 meters, 20 meters, and 30 meters, the volume of air will be reduced to 3 liters, 2 liters, and 1.5 liters, respectively. Conversely, if a balloon with a volume of 3 liters of air is brought up from a depth of 30 meters to the surface, the volume of air will expand to 12 liters, or 4 times its original size.

This law is beneficial in terms of explaining the injuries and illnesses that can be caused by changes in atmospheric pressure.

Barotrauma
The pressures that act upon divers are composed of two parts: atmospheric pressure and hydrostatic pressure (the weight of the water above the diver). At sea level, the atmospheric pressure is equivalent to one layer of air from the surface to the edge of space. However, for every 10 meters a diver descends, the pressure increases by 1 atmosphere (1 atmosphere of atmospheric pressure plus 1 atmosphere of hydrostatic pressure).

Therefore, the pressure on the surface of the water at 1 atmosphere, when diving to a depth of 10 meters, becomes 2 atmospheres. At 20 meters it becomes 3 atmospheres. The increased pressure will decrease the volume of gas in the lungs. For example, if the lungs have a capacity of 6 liters at the surface, at a depth of 10 meters, the volume will decrease to 3 liters because the pressure changes from 1 atmosphere to 2 atmospheres. If the depth is further increased to 20 meters, where the pressure is 3 atmospheres, the lung capacity will become 2 liters. Conversely, when ascending from a depth of 30 meters, the pressure decreases from 4 atmospheres to 1 atmosphere of hydrostatic pressure, and the volume of air in the lungs will expand up to 4 times, or 12 liters, causing injuries due to the pressure change, also known as barotrauma.

The compression and expansion of gas can cause injuries to the middle ear, or in parts of the body with air pockets, such as the lungs and sinuses, teeth (in people with dental fillings or crowns), eyes, and the digestive system. Additionally, there can be injuries caused by other types of pressure, such as mask squeeze, which can result in bruising on the face due to changes in pressure.

Middle ear barotrauma
Ear barotrauma, also known as ear squeeze, is a condition caused by pressure changes in the middle ear. The middle ear is like a room with only one door, which is connected to the throat by the eustachian tube. If the pressure increases, the volume of air changes, and the eardrum moves. Normally, the pressure in the air is 1 atmosphere, and the volume of the middle ear is the same. However, when diving 10 meters, the pressure doubles, causing the middle ear to become smaller. This pulls the eardrum inward, causing ear pain. When diving deeper, the pressure increases, and the volume of the middle ear becomes smaller again, which may cause bleeding in the middle ear or rupture of the eardrum.

Pulmonary barotraumas
The lungs are the largest pockets of air in the body, with a combined capacity of around 6 liters. Pulmonary barotraumas can be classified into two main forms:

• Diving on a single breath of air reduces the volume of air in the lungs. This can cause swelling of the mucosal tissue (mucosal edema), bloating of the blood vessels (vascular engorgement), and even lung hemorrhage, resulting in lung squeeze injury.
• Scuba divers may hold their breath while ascending, which can cause air in the lungs to expand beyond their capacity, and if the excess air cannot escape the lungs it can lead to lung overexpansion syndrome and alveolar rupture. In addition, gas bubbles can escape into the bloodstream and circulatory system, causing a gas embolism. Should these bubbles spread throughout the body and obstruct blood flow to an organ, it can cause that organ to malfunction, such as in the case of restricted blood flow to the brain, leading to stroke, paralysis, or loss of consciousness.

Decompression sickness
There is also a rule known as Henry's Law, written by the English chemist William Henry, which states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid.

The basics of decompression sickness, or "the bends," come from the physics principle that gasses can dissolve in liquids. When pressure increases, gas dissolves more readily in a liquid. This is similar to how carbon dioxide dissolves in water under pressure in a soda bottle, subsequently bursting out when the bottle is opened.

The air we breathe is composed of 21% oxygen and 79% nitrogen. When diving, the increased pressure causes nitrogen to dissolve more readily in the body, and when ascending too quickly, the excess nitrogen can form bubbles in tissue and blood, causing decompression sickness or "the bends." Symptoms include joint pain or, in severe cases, paralysis or stroke. Additionally, the gas bubbles can stimulate blood clotting and inflammation throughout the body.

• Remove the patient from the water or dangerous area as quickly as possible.
• Evaluate their condition and provide basic life-saving treatment while maintaining a suitable position, such as lying flat or lying on the left side to prevent gas bubbles from entering the heart.
• Patients who are injured from diving should receive 100% oxygen before being transferred to a medical facility for further treatment.
• Keep the patient warm.
• In the case of urinary retention, it may be necessary to perform catheterization.
• Send the patient urgently to receive treatment in the nearest hyperbaric chamber for high-pressure air treatment.
• Avoid air transfers of patients where possible. If necessary, a plane with adjustable air pressure should be utilized, while for helicopters, the flight’s maximum altitude should not exceed 1,000 feet, as higher altitudes increase the severity of the condition.

Hyperbaric oxygen therapy is a treatment that involves administering 100% oxygen under high pressure of more than 1 atmosphere inside a hyperbaric chamber. This is done to increase the amount of oxygen delivered to the body beyond what can be achieved through normal breathing.

The main principle of the hyperbaric chamber is to increase the amount of oxygen in tissue and to quickly flush nitrogen from the body. This reduces the amount of gas bubbles in the blood and eventually eliminates them altogether, with the following results:

• Reduces the size of gas bubbles that accumulate in the body, such as from air embolisms in the blood vessels, helping oxygen deficient tissue to recover.
• Improves the efficiency of gas dissolution back into the bloodstream, as well as improving excretion through respiration.
• Effective in treating conditions like decompression sickness, which is caused by gas bubbles in organs and tissue, by reducing the size of the gas bubbles.

• Fill out the required information or questionnaire.
• Consult a specialist who is experienced in conducting health assessments for divers to assess the body's basic condition and determine if additional tests are necessary.
• Conduct a physical examination; measure weight, height, BMI, and blood pressure; and perform other basic health checks, such as ear and throat examinations, and a general fitness assessment.
• Perform certain laboratory tests, including CBC, EKG, chest X-ray, pulmonary function test, audiogram test, and others as necessary.
• Once all tests are complete, the doctor will explain the results and provide appropriate guidance, particularly in cases where a pre-existing condition may affect diving.

Kamonsak Tangchai, M.D. is a diving medicine and hyperbaric specialist. A medical degree graduate from the Faculty of Medicine, Siriraj Hospital, Mahidol University, the doctor was awarded the title of "Hero Diver" for his involvement in the rescue of the Wild Boar soccer team trapped in Tham Luang Cave, Mae Sai District, Chiang Rai Province. He was one of the behind-the-scenes team members who helped locate and rescue the 13 young soccer players and their coach who were stranded inside the cave. In addition, Kamolsak Tangchai, M.D., has certifications in the fields of underwater medicine and high-altitude medicine.