Hazards of Deep Sea Diving and Effects of Increased Barometric Pressure

Introduction

Deep-sea diving exposes the body to markedly increased barometric pressure, producing significant physiological challenges. Rapid ascent can precipitate serious decompression disorders; therefore, controlled ascent, recompression therapy, and hyperbaric oxygen are essential for preventing and treating diving-related complications.

Causes and Types of Hazards

• At sea level, atmospheric pressure is approximately 760 millimeters of mercury, equivalent to 1 atmosphere.
• During descent underwater, ambient pressure increases progressively with depth.
• For every 10 meters (33 feet) of seawater descent, ambient pressure rises by approximately 1 atmosphere.
• Therefore, at a depth of about 30 meters (100 feet), the total ambient pressure is nearly 4 atmospheres.
• Divers and workers in pressurized underwater chambers (caissons) are exposed to these elevated pressures.
• In underwater environments, compressed gas mixtures are inhaled to equalize intrapulmonary pressure with the surrounding pressure and permit normal lung expansion.
• According to Henry’s law, increased pressure causes greater quantities of inhaled gases to dissolve in blood and body tissues.
• Excess dissolution of gases and rapid pressure changes can produce several physiological hazards.
• Nitrogen narcosis results from the narcotic effects of nitrogen dissolved in neural tissues at high pressures.
• High-pressure nervous syndrome occurs mainly during exposure to very high pressures, particularly with helium-containing gas mixtures.
• Acute oxygen toxicity develops when high partial pressures of oxygen damage the central nervous system or lungs.
• Dysbarism refers to disorders produced by changes in ambient pressure, including decompression sickness and barotrauma.
• Air embolism may occur when expanding gas enters the circulation during rapid ascent, potentially causing life-threatening vascular obstruction.

Nitrogen Narcosis

• During deep-sea diving, breathing gases are delivered at high ambient pressures.
• Breathing pure oxygen under high pressure can produce central nervous system oxygen toxicity; therefore, oxygen is usually mixed with inert gases.
• Conventional compressed air contains approximately 21 percent oxygen and 79 percent nitrogen.
• At increased pressures, large amounts of nitrogen dissolve in body tissues, especially in lipid-rich neural tissue.
• At depths up to about 30 meters (100 feet), dissolved nitrogen may produce mild euphoria and impaired judgment.
• Symptoms of nitrogen narcosis generally become evident beyond approximately 36 meters (120 feet) and become progressively severe at greater depths.
• Clinical manifestations resemble alcohol intoxication and include impaired reasoning, reduced concentration, altered judgment, and behavioral changes.
• These effects are attributed to the anesthetic action of dissolved nitrogen on neuronal membranes.

High-Pressure Nervous Syndrome

• For very deep dives, mixtures containing helium and oxygen are preferred because helium has markedly lower narcotic potency than nitrogen.
• Helium is less dense than nitrogen, reducing airway resistance and the work of breathing under high-pressure conditions.
• Helium is also less soluble in body fluids, decreasing inert gas accumulation.
• Despite these advantages, exposure to very high pressures while breathing helium-based mixtures may cause high-pressure nervous syndrome.
• This syndrome typically occurs during deep dives at extreme pressures.
• The exact mechanism is not fully understood, but direct effects of pressure and helium on neuronal membranes are believed to contribute.
• Clinical features include tremors, drowsiness, impaired coordination, reduced manual dexterity, and cognitive disturbances.
• Electroencephalographic changes, particularly depression of alpha-wave activity, may also occur.

Acute O2 Toxicity

• During deep-sea diving, breathing gases are supplied under high pressure to maintain adequate lung expansion.
• Carbon dioxide is removed from the breathing mixture because excessive accumulation is potentially life-threatening.
• Breathing 100 percent oxygen at high ambient pressures can produce acute oxygen toxicity.
• The central nervous system is particularly vulnerable to the toxic effects of hyperbaric oxygen.
• Clinical manifestations include nausea, dizziness, irritability, disorientation, visual disturbances, and generalized convulsions.
• Prolonged exposure may also cause pulmonary injury.
• To minimize toxicity, the oxygen concentration in high-pressure breathing mixtures is carefully reduced and regulated.

Dysbarism (Caissons Disease)

• Dysbarism or decompression sickness occurs when individuals exposed to high ambient pressure are rapidly returned to lower pressure.
• It commonly affects deep-sea divers, caisson workers, and individuals exposed to sudden decompression in unpressurized aircraft.
• Ambient pressure increases by approximately 1 atmosphere for every 10 meters of seawater depth.
• Divers breathing compressed air inhale large amounts of nitrogen under high pressure.
• According to Henry’s law, increased pressure causes greater quantities of nitrogen to dissolve in blood and tissues.
• Because nitrogen is highly lipid soluble, it accumulates particularly in adipose tissue and neural structures.
• During gradual ascent, dissolved nitrogen slowly diffuses into the blood and is eliminated through the lungs.
• During rapid ascent, ambient pressure falls abruptly and dissolved nitrogen comes out of solution too quickly.
• This leads to the formation of gas bubbles within tissues and blood vessels.
• These bubbles mechanically obstruct blood flow and directly damage tissues.
• Gas bubbles within muscles and joints produce severe pain, commonly referred to as the bends.
• Symptoms usually develop within 30 minutes after surfacing, although delayed manifestations may occur.
• Involvement of the central nervous system may reduce blood flow to the brain and spinal cord, producing paresthesia, motor weakness, paralysis, and, in severe cases, respiratory failure.
• Pulmonary vascular obstruction by gas bubbles causes dyspnea, chest discomfort, and a sensation of thoracic constriction, known as the chokes.
• Coronary vascular involvement may precipitate myocardial ischemia.
• The severity of decompression sickness depends primarily on the rate and percentage of pressure reduction, rather than the absolute pressure change.
• Gradual, staged decompression minimizes bubble formation and markedly reduces the risk of dysbarism.

Prevention

• Decompression sickness can be prevented by gradual ascent and controlled decompression, allowing dissolved inert gases to be eliminated safely through the lungs.
• Pressure reduction should occur in stages to minimize gas bubble formation.

Treatment

• Symptomatic individuals require immediate recompression therapy in a hyperbaric chamber, followed by slow decompression.
• Hyperbaric oxygen therapy accelerates inert gas elimination and improves tissue oxygenation.
• Although recovery is often complete, persistent neurological deficits may occasionally remain.

Air Embolism

• Air embolism may occur when a diver breathing compressed gas ascends rapidly while holding the breath.
• During ascent, expanding intrapulmonary gas can overdistend and rupture alveoli, allowing air to enter pulmonary blood vessels and the systemic circulation.
• Sudden decompression, such as rupture of a pressurized aircraft cabin at high altitude, can similarly cause rapid gas expansion and air embolism.
• Air embolism may occur even after ascent from relatively shallow depths; therefore, divers should continuously exhale during ascent and should never hold their breath while surfacing.

SCUBA

• SCUBA is a portable breathing system used by underwater divers.
• It consists of high-pressure cylinders, regulators, and valves that permit controlled inhalation and exhalation underwater.
• Deep divers often use helium-oxygen mixtures because helium has lower density and lower narcotic potential than nitrogen.
• These gas mixtures reduce breathing effort and minimize complications associated with deep-sea diving.