Chapter 44: Physiology of Deep-Sea Diving and Other Hyperbaric Conditions

Written By: Razaullah Khattak (DPT Medical Professional)

Student Source Reference: Guyton and Hall Textbook of Medical Physiology

Chapter: 44

To read more about check out Chapter 27:

 https://mednotesbyrazaullah.blogspot.com/2026/09/chapter-27-urine-formation-by-kidneys.html

Deep-sea diving and underwater

Deep-sea diving and underwater environments subject the human body to hyperbaric conditions. As depth increases, hydrostatic pressure rises rapidly, requiring compressed gases for respiration to maintain pulmonary expansion. Exposure to high alveolar gas pressures induces distinct physiological transformations across systemic circulation, neural signaling, and cellular structures.

Hyperbaric physiology requires analyzing pressure-volume relationships governed by physical gas laws. High partial pressures of nitrogen, oxygen, and carbon dioxide produce specific toxicities, altered gas solubilities, and tissue shifts. Proper decompression protocols, gas selection, and specialized diving systems mitigate fatal physiological complications like gas bubble formation and tissue barotrauma.

Relationship of Pressure to Sea Depth

• Seawater column of 33 feet exerts 1 atmosphere pressure.
• Sea depth of 33 feet equals 2 atmospheres total.
• Depth of 66 feet exerts 3 atmospheres total pressure.
• Every 33 feet adds 1 extra atmosphere of pressure.
• Air weight adds 1 atmosphere above sea level.
• Water weight adds additional pressure proportional to depth.

Effect of Sea Depth on Gas Volume and Boyle's Law

• Gas compresses to smaller volumes as depth increases.
• One liter of air compresses to one-half liter at 33 feet.
• Gas volume compresses to one-eighth liter at 233 feet.
• Gas volume is inversely proportional to surrounding pressure.
• This physical relationship is defined as Boyle's law.
• Pressure expansion can collapse or damage body air chambers.
• Ten liters sea-level volume equals 1 liter at 300 feet.

Nitrogen Narcosis at High Nitrogen Pressures

• Air contains approximately four fifths nitrogen gas.
• High nitrogen pressure produces varying degrees of narcosis.
• Mild narcosis symptoms first appear at 120 feet depth.
• Divers experience joviality and reduced cares at 120 feet.
• Drowsiness occurs between 150 and 200 feet depth.
• Muscle strength wanes between 200 and 250 feet depth.
• Clumsiness impairs required work at 200 to 250 feet.
• Divers become nearly useless beyond 250 feet depth.
• Nitrogen narcosis is called "raptures of the depths".
• Mechanism resembles physical effects of general gas anesthetics.
• Nitrogen dissolves inside fatty neuronal membrane structures.
• Altered membrane ionic conductance reduces neuronal excitability.

Oxygen Toxicity at High Pressures

• Effect of Very High PO2 on Blood Oxygen Transport
• High oxygen partial pressure increases dissolved blood oxygen.
• Dissolved oxygen is minimal below 120 mm Hg PO2.
• High pressures dissolve large amounts in blood water.
• Dissolved oxygen adds to oxygen bound with hemoglobin.

Effect of High Alveolar PO2 on Tissue PO2

• Alveolar PO2 reaches 3000 mm Hg at 4 atmospheres.
• Total oxygen content reaches 29 volumes percent in blood.
• Bound hemoglobin carries 20 volumes percent oxygen.
• Dissolved blood water contains 9 volumes percent oxygen.
• Tissue capillary consumption uses 5 volumes percent oxygen.
• Venous blood retains 24 volumes percent oxygen.
• Delivered tissue PO2 remains extremely high at 1200 mm Hg.
• Normal delivered tissue PO2 measures only 40 mm Hg.
• Critical oxygen levels overwhelm hemoglobin-oxygen buffering mechanisms.
• Buffering failure exposes tissues to excessive oxygen pressure.

Acute Oxygen Poisoning

• High tissue oxygen pressure damages multiple body tissues.
• Four atmospheres oxygen pressure causes brain seizures.
• Seizures occur within 30 to 60 minutes exposure.
• Seizures progress directly to coma and submerged death.
• Early symptoms include nausea, muscle twitching, and dizziness.
• Vision disturbances, irritability, and disorientation occur rapidly.
• Physical exercise accelerates onset of acute oxygen toxicity.

Excessive Intracellular Oxidation and Free Radicals

• Molecular oxygen requires activation to oxidize cellular compounds.
• Active forms of oxygen are called oxidizing free radicals.
• Superoxide and hydrogen peroxide represent major free radicals.
• Normal PO2 forms small amounts of free radicals continuously.
• Peroxidases, catalases, and superoxide dismutase remove radicals.
• Enzymes clear free radicals at normal tissue PO2 levels.
• Alveolar PO2 above 2 atmospheres swamps protective enzymes.
• Excess free radicals oxidize polyunsaturated membrane fatty acids.
• Free radicals oxidize cellular enzymes and destroy metabolism.
• High lipid content makes nervous tissue highly susceptible.
• Acute lethal effects stem primarily from brain dysfunction.

Chronic Oxygen Poisoning and Pulmonary Disability

• One atmosphere oxygen causes no acute nervous system toxicity.
• Twelve hours exposure causes pulmonary airway congestion.
• Exposure causes pulmonary edema, atelectasis, and mucosal damage.
• Alveoli and bronchi suffer direct exposure to high oxygen.
• Internal body tissues remain protected by hemoglobin buffering.

Carbon Dioxide Toxicity at Great Depths

• Normal depth does not increase alveolar carbon dioxide pressure.
• Depth does not alter body carbon dioxide production rate.
• Normal tidal volume exhales produced carbon dioxide smoothly.
• Diving helmets can accumulate carbon dioxide in dead space.
• Rebreathing apparatuses can build up expired carbon dioxide.
• Alveolar PCO2 increases up to 80 mm Hg maximum.
• Respiration increases 8- to 11-fold to compensate.
• PCO2 above 80 mm Hg depresses respiratory center activity.
• Negative metabolic effects cause respiratory compensation to fail.
• High carbon dioxide produces severe respiratory acidosis.
• Patients develop lethargy, narcosis, and surgical anesthesia.

Decompression After High Pressure Exposure

• Breathing compressed air dissolves extra nitrogen in body fluids.
• Blood becomes saturated at high alveolar nitrogen pressure.
• Nitrogen saturates all body tissues over several hours.
• Unmetabolized nitrogen remains dissolved until lung pressure drops.
• Slow respiratory removal process requires multiple hours.

Volume of Nitrogen Dissolved at Different Depths

• Sea level body fluids contain 1 liter dissolved nitrogen.
• Water holds slightly less than half total body nitrogen.
• Fat holds slightly more than half total body nitrogen.
• Nitrogen is five times more soluble in fat than water.
• Body holds 2 liters dissolved nitrogen at 33 feet.
• Body holds 4 liters dissolved nitrogen at 100 feet.
• Body holds 7 liters dissolved nitrogen at 200 feet.
• Body holds 10 liters dissolved nitrogen at 300 feet.
• Water tissues reach nitrogen equilibrium within one hour.
• Fat tissue requires several hours to reach full saturation.
• Fat tissue possesses high storage capacity and low blood supply.
• Brief dives dissolve minimal nitrogen in body tissues.

Decompression Sickness Mechanisms

• Sudden ascent releases dissolved nitrogen into gas bubbles.
• Bubbles form inside cells or extracellular body fluids.
• Decompression sickness is also called bends or caisson disease.
• Deep pressure compresses excess nitrogen in dissolved state.
• Sudden surface pressure drops external force to 760 mm Hg.
• Internal gas pressure exceeds external atmospheric pressure.
• Excess gas escapes solution to form nitrogen bubbles.
• Bubbles plug small blood vessels throughout body tissues.
• Supersaturated states may delay bubble formation for hours.

Symptoms of Decompression Sickness

• Vascular bubble blockages produce tissue ischemia and necrosis.
• Joint and muscle pain occurs in 85 to 90 percent.
• Arm and leg joint pain causes characteristic bends symptoms.
• Nervous system symptoms affect 5 to 10 percent.
• Dizziness occurs in 5 percent of affected divers.
• Paralysis, collapse, and unconsciousness occur in 3 percent.
• Nervous system tissue damage can become permanent.
• Lung capillary microbubbles cause chokes in 2 percent.
• Chokes feature severe dyspnea, pulmonary edema, and death.

Nitrogen Elimination and Decompression Schedules

• Slow ascent allows lungs to excrete dissolved nitrogen.
• Lungs eliminate two thirds nitrogen in 1 hour.
• Lungs eliminate 90 percent nitrogen in 6 hours.
• U.S. Navy decompression tables detail safe ascent schedules.
• Dives to 190 feet for 1 hour require 3 hours decompression.
• Decompression schedule uses progressive decompression stops.
• Divers pause at 50, 40, 30, 20, and 10 feet.

Tank Decompression and Hyperbaric Treatment

• Pressurized tanks decompress professional divers safely on land.
• Tank pressure lowers gradually using standard time schedules.
• Immediate recompression treats active decompression sickness symptoms.
• Recompression places diver at deep pressure levels immediately.
• Subsequent tank decompression takes several times normal duration.

Deep Diving and Gas Mixtures

Saturation Diving Protocols

• Divers live inside pressurized compression tanks for weeks.
• Tank pressure matches deep underwater work environments.
• Body tissues remain fully saturated with breathing gases.
• Returning to matching tank pressure prevents bubble formation.

Helium-Oxygen Breathing Mixtures

• Helium replaces nitrogen in deep diving gas mixtures.
• Helium produces one-fifth the narcotic effect of nitrogen.
• Half as much helium volume dissolves in tissues.
• Dissolved helium diffuses out rapidly during decompression.
• Low helium density reduces airway breathing resistance.
• Compressed nitrogen density causes extreme airway resistance.

Oxygen Concentration Reduction

• Deep dives require reduced breathing oxygen percentages.
• Reduced percentages prevent lethal acute oxygen toxicity.
• One percent oxygen suffices at 700 feet depth.
• Standard 21 percent oxygen delivers 4 atmospheres PO2.
• High oxygen pressure causes seizures within 30 minutes.
• SCUBA (Self-Contained Underwater Breathing Apparatus) Diving
• Open-circuit demand SCUBA dominates modern sports diving.
• System contains compressed air tanks and reducing valves.
• System contains demand inhalation valves and exhalation valves.
• System utilizes tight mask with small dead space.
• Reducing valve lowers tank pressure to ambient water pressure.
• Negative inhalation pressure opens demand valve diaphragm automatically.
• Air flows into mask only during active inhalation.
• Expired air exhausts directly into surrounding seawater.
• Depth severely limits available underwater diving time.
• High air volume flows wash out pulmonary carbon dioxide.
• Compressed air volumes require increased air mass flow.

Special Physiologic Problems in Submarines

Escape from Submerged Submarines

• Escape without apparatus is possible down to 300 feet.
• Helium rebreathers allow escape down to 600 feet.
• Expanding lung gases cause fatal air embolism during ascent.
• Expanding gases rupture delicate pulmonary blood vessels.
• Escaping individuals must exhale continuously during ascent.

Health Hazards in Submarine Environments

• Atomic submarine shielding reduces radiation below cosmic levels.
• Cigarettes liberate poisonous carbon monoxide inside submerged vessels.
• Refrigeration systems can leak toxic Freon gas.
• Hazardous gases require rapid automated air control systems.

Hyperbaric Oxygen Therapy

• High-pressure oxygen exerts powerful cellular oxidizing effects.
• Patients receive hyperbaric oxygen inside large pressure tanks.
• Oxygen is administered at 2 to 3 atmospheres.
• Surrounding chamber contains compressed atmospheric air.
• Oxidizing free radicals mediate therapeutic medical benefits.
• Hyperbaric oxygen effectively treats lethal gas gangrene infections.
• Anaerobic clostridia bacteria stop growing above 70 mm Hg.
• Tissue hyperoxygenation halts anaerobic infection progression completely.
• Therapy treats decompression sickness and arterial gas embolism.
• Therapy treats carbon monoxide poisoning, osteomyelitis, and infarction.n halts anaerobic infection progression completely.
• Therapy treats decompression sickness and arterial gas embolism.
• Therapy treats carbon monoxide poisoning, osteomyelitis, and infarction.

Disclaimer: This content is for educational purposes only and not a substitute for professional medical advice.