RGI 5 Notes
Hyperbaric Therapy and Gas Toxicity Notes
Learning Outcomes
RGI.04.06: Discuss implications and consequences of Boyle’s law in diving.
RGI.04.07: Describe other scuba-related injuries such as mediastinal emphysema, cerebral embolism, and venous gas embolism.
RGI.04.08: Describe the circumstances leading to shallow-water blackout in breath-hold diving.
RGI.05.01: Describe the basic principles of hyperbaric therapy.
RGI.05.02: List conditions that can be treated with hyperbaric therapy.
RGI.05.03: Discuss the causes of altitude sickness.
RGI.05.04: Differentiate between high-altitude pulmonary edema (HAPE) and high-altitude cerebral edema (HACE).
RGI.05.05: Explain the therapeutic use of Gamow bags.
Boyle's Law in Diving
Definition: For an enclosed volume of gas at constant temperature, the pressure and volume are inversely proportional (PV = constant).
Application in Diving: Boyle's law impacts divers during descent and ascent due to changes in pressure affecting air spaces in the body (e.g., lungs, ears, sinuses).
Consequences: Increased external pressure during descent compresses volumes of gas, leading to potential injuries if equalization isn’t performed properly.
Effects during descent: Squeeze on ears; can lead to perforated eardrum if pressure isn’t equalized using the Valsalva maneuver.
Sinus squeeze may occur with upper respiratory tract infections (URTIs).
Pressure Equalization Techniques
Valsalva Maneuver: Technique used to equalize pressure in the ears by opening the Eustachian tube, allowing high-pressure air to enter the middle ear.
Mask Squeeze: Occurs if the pressure in a scuba mask is not equalized; divers can allow air into the mask by exhaling through the nose.
Diving Injuries from Pressure Changes
Controlled Ascent: Holding one’s breath during an uncontrolled ascent can cause over-expansion of the lungs, leading to serious injuries such as:
Arterial Gas Embolism (AGE): Gas bubbles block blood flow, causing ischemic damage.
Pneumothorax: Air leaks into the pleural space, potentially caused by ruptured alveoli.
Bullous Emphysema: Mechanical deformation of alveoli due to pressure changes; may not involve rupture.
Mediastinal Emphysema: Air leaks into the mediastinum from alveolar ruptures.
Shallow Water Blackout
Occurrence: Common among breath-hold divers when diving without sufficient preparation.
Causes: Hyperventilation before the dive lowers carbon dioxide levels, making divers less aware of the need to breathe. A drop in oxygen below 0.1 atm during ascent can lead to loss of consciousness.
Psychological Factors: Many victims of shallow-water blackout exhibit competitive psychological profiles, leading to risky diving behavior.
Hyperbaric Therapy (HBOT)
Definition: Use of elevated gas/air pressure to treat various medical conditions.
Treatable Conditions Include:
Radiation Tissue Damage: Soft tissue and osteoradionecrosis.
Clostridial Myonecrosis (Gas Gangrene): Anaerobic infection.
Compromised Skin Grafts and Flaps
Crush Injury and Compartment Syndrome
Infections and Osteomyelitis
Acute Carbon Monoxide Poisoning
Cerebral Arterial Gas Embolism
Cyanide Poisoning
Decompression Sickness
Gamow Bag for Altitude Sickness
Function: A portable hyperbaric chamber used to treat altitude sickness, especially HAPE and HACE.
Additional Information
Incident Example: In 2009, a diver sustained severe burns while diving the wreck of the Lusitania, due to the auto-ignition of heat packs used in a dry-suit under high pressure, leading to injury. The U.S. Navy has since changed their guidelines regarding undergarments for divers to prevent such incidents.
Detailed Answers to Learning Outcomes
RGI.04.06: Discuss implications and consequences of Boyle’s law in diving.
Boyle's law states that for a given amount of gas at a constant temperature, the pressure and volume are inversely related (PV = constant). In diving, this principle affects air spaces within the body, such as the lungs, ears, and sinuses.
During descent, external pressure increases, causing the volume of gas in these spaces to decrease. Divers must equalize the pressure to avoid injuries such as ear squeeze, which can result in perforated eardrums if not managed through techniques like the Valsalva maneuver. Failing to equalize can lead to serious complications associated with pressure changes, including sinus squeeze during respiratory infections.
RGI.04.07: Describe other scuba-related injuries such as mediastinal emphysema, cerebral embolism, and venous gas embolism.
Arterial Gas Embolism (AGE): This occurs when gas bubbles enter the bloodstream and block vascular flow, resulting in ischemic damage to tissues. Commonly caused by holding one’s breath during an uncontrolled ascent.
Pneumothorax: Air gets trapped in the pleural space, often due to ruptured alveoli, leading to lung collapse.
Bullous Emphysema: Gas-filled blebs form in the lungs due to pressure changes; it may not involve rupture but affects lung mechanics.
Mediastinal Emphysema: Air leaks into the mediastinal space from ruptured alveoli, potentially damaging surrounding structures.
Cerebral Embolism: Similar to AGE, but the embolism occurs in the brain, which can lead to stroke-like symptoms and neurological deficits.
RGI.04.08: Describe the circumstances leading to shallow-water blackout in breath-hold diving.
Shallow-water blackout is commonly experienced by divers who hyperventilate prior to diving, lowering their carbon dioxide levels. This can diminish the urge to breathe, leading divers to ignore the body's signals. As the dive progresses, oxygen levels decrease, and if they drop below 0.1 atm during ascent, the diver may lose consciousness unexpectedly. Psychological factors, particularly among competitive divers, play a role in risky behaviors that increase the likelihood of this incident.
RGI.05.01: Describe the basic principles of hyperbaric therapy.
Hyperbaric therapy (HBOT) involves the administration of oxygen at pressures higher than atmospheric levels. This approach helps enhance oxygen delivery to tissues, which can promote healing in various medical conditions, improve infections, and decrease bubbles in decompression sickness.
RGI.05.02: List conditions that can be treated with hyperbaric therapy.
Radiation Tissue Damage
Clostridial Myonecrosis (Gas Gangrene)
Compromised Skin Grafts and Flaps
Crush Injury and Compartment Syndrome
Infections and Osteomyelitis
Acute Carbon Monoxide Poisoning
Cerebral Arterial Gas Embolism
Cyanide Poisoning
Decompression Sickness
RGI.05.03: Discuss the causes of altitude sickness.
Altitude sickness, or acute mountain sickness (AMS), occurs due to rapid ascent to high altitudes where the oxygen levels are lower than what the body is accustomed to. The body struggles to acclimatize quickly enough, leading to symptoms such as headaches, nausea, dizziness, and in severe cases, high-altitude pulmonary edema (HAPE) or high-altitude cerebral edema (HACE).
RGI.05.04: Differentiate between high-altitude pulmonary edema (HAPE) and high-altitude cerebral edema (HACE).
HAPE occurs when fluid accumulates in the lungs due to changes in atmospheric pressure and decreased oxygen levels, resulting in breathing difficulties, coughing, and a risk of respiratory failure.
HACE, on the other hand, involves swelling of the brain, leading to neurological symptoms such as confusion, lack of coordination, and in severe cases, coma. Both conditions are life-threatening if not treated promptly and require immediate descent and medical intervention.
RGI.05.05: Explain the therapeutic use of Gamow bags.
Gamow bags are portable hyperbaric chambers used to treat altitude sickness, particularly in cases of HAPE and HACE. By simulating increased atmospheric pressure, these bags facilitate the absorption of oxygen, helping to alleviate symptoms and improve oxygenation until professional medical assistance can be obtained.