KIN 424 Module 7: Diving Medicine/ Hyperbaric lecture

What are some examples of hyperbaric exposures?

SCUBA diving, rebreathers, umbilical/surface supply diving, hyperbaric chamber exposure, and breath-hold/free diving.

What is SCUBA diving?

Open-circuit diving in which expired gases are released as bubbles.

What is a rebreather?

A closed-circuit apparatus that recycles breathing gases so no bubbles are exhausted.

Who commonly uses surface supply or umbilical diving systems?

Military and commercial divers.

What is breath-hold or free diving?

Diving on a single breath

What is Boyle’s law?

At a constant temperature, the pressure of a gas is inversely proportional to its volume.

Why is Boyle’s law important in diving?

Because gas volume changes as pressure changes during descent and ascent.

What happens to gas volume during descent in diving?

Gas volume decreases as pressure increases.

What happens to gas volume during ascent in diving?

Gas volume increases as pressure decreases

What is shallow water blackout?

Loss of consciousness near the surface during breath-hold diving, often related to critically low oxygen

What are “squeezes” in diving?

Barotrauma injuries caused by pressure differences between body spaces and the environment

What is mask squeeze?

Barotrauma caused by buildup of relative negative pressure in the mask during descent

How do you relieve mask squeeze?

By exhaling a small amount of air through the nose into the mask

What can mask squeeze cause?

Facial barotrauma and subconjunctival hemorrhage.

What is ear squeeze?

A pressure difference between the middle ear and outer ear that stretches the tympanic membrane

What symptoms can ear squeeze cause?

Fullness and pain in the ear

What is one maneuver divers use to equalize ear pressure?

The Valsalva maneuver

What is sinus squeeze?

Barotrauma caused by poor communication between a sinus and the nose, leading to pressure trapping

What can sinus squeeze cause?

Congestion, edema, bleeding, and pain.

What is suit squeeze?

Barotrauma caused when trapped gas in a dry suit compresses during descent and the suit pinches the body

What is dental squeeze?

Pressure-related pain caused by a trapped air space between a tooth and filling that does not communicate with the mouth.

What is pulmonary barotrauma?

Lung injury caused by pressure changes, especially gas expansion during ascent.

What are 4 manifestations of pulmonary barotrauma?

Mediastinal emphysema

subcutaneous emphysema

pneumothorax

arterial gas embolism.

What is a pneumothorax?

Loss of negative pressure in the pleural space due to air entering that space, causing lung collapse.

What is pneumomediastinum?

Air in the mediastinum caused by barotrauma.

What is arterial gas embolism (AGE)?

Air entering the arterial circulation after pulmonary barotrauma and traveling through the bloodstream.

Why is AGE (air embolism) so dangerous?

It can immediately obstruct blood flow to vital organs such as the brain and heart.

What percentage of divers with AGE may have complete recovery? What percentage may die?

About 50% recover

5% die

Why are AGE symptoms so variable?

Because symptoms depend on which tissues or organs the air bubbles affect

What 4 cerebral symptoms can AGE cause?

Numbness

weakness

altered level of consciousness

poor cognition.

What cardiac consequences can AGE cause?

Cardiac arrest or myocardial infarction.

What general neurologic description fits AGE well?

Stroke-like symptoms.

What are 5 key prehospital treatments for AGE?

Emergency evacuation

oxygen

positioning

treating near-drowning if needed

fluids if possible.

What hospital treatment is used for AGE?

Recompression in a hyperbaric chamber with 100% oxygen

What is recompression therapy?

Treatment using increased pressure, usually with 100% oxygen, to shrink and re-dissolve gas bubbles

How does recompression help AGE or DCS?

It resolubilizes bubbles and improves oxygen delivery

What is decompression sickness (DCS)?

Illness caused by formation of inert gas bubbles, usually nitrogen, in the bloodstream or tissues during ascent or depressurization

What gas law is especially important in decompression sickness (DCS)?

Henry’s law

What is Henry’s law?

The amount of gas dissolved in a liquid is directly related to the pressure of that gas.

Why is Henry’s law important in diving?

Because higher pressure at depth causes more inert gas to dissolve, and ascent can allow it to come out of solution as bubbles

When does DCS occur?

Upon ascent or depressurization.

What are musculoskeletal symptoms of DCS?

Joint pain, tingling, numbness, and swelling.

What is the main physical sign of musculoskeletal DCS?

Tenderness and pain with joint motion.

What are neurological symptoms of DCS?

Back pain

abdominal pain

weakness

paralysis

urinary retention

incontinence.

What brain symptoms can occur with DCS?

Visual loss, headache, and confusion.

What signs may be seen in cerebral DCS?

Disorientation and abnormal visual field testing.

What are 2 cutaneous DCS symptoms/signs?

Pruritis (uncomfy itching sensation)

mottled skin (patchy web-like discolouration, usually red or blue)

What are “chokes” in decompression sickness?

A form of DCS causing dyspnoea, cough, and chest pain with signs such as cyanosis, tachycardia, and tachypnoea.

What is decompression shock?

A severe form of DCS with weakness, sweating, unconsciousness, hypotension, tachycardia, pallor, and decreased urination.

What are key prehospital treatments for DCS?

Emergent evacuation

oxygen

near-drowning treatment if needed

fluids if possible.

What is the definitive hospital treatment for DCS?

Hyperbaric recompression with oxygen

What is decompression illness (DCI)?

The broader term that includes both decompression sickness and arterial gas embolism

What is the difference between DCI and DCS?

DCI includes both DCS and AGE, while DCS refers specifically to inert gas bubble illness from decompression

How is decompression sickness prevented?

By using dive tables or dive computers and following safe dive profiles

What 3 dive profile factors are considered in DCS prevention?

Depth

bottom time

surface time.

What are 6 risk factors for DCS?

Exceeding depth-time limits

rapid ascent

dehydration

residual deficits from previous DCS

lung disease

intracardiac septal defects.

Why is rapid ascent dangerous in diving?

It promotes bubble formation and barotrauma.

Why is dehydration a risk factor for DCS?

It may worsen bubble-related effects and impair physiological compensation.

What is immersion pulmonary edema (IPE or SIPE)?

Pulmonary edema that occurs in otherwise healthy divers or swimmers during immersion.

What does SIPE stand for?

Swimming-induced pulmonary edema.

What 6 symptoms can occur with IPE/SIPE?

Cough

dyspnoea

haemoptysis

hypoxemia

loss of consciousness

death.

What happens physiologically during immersion that contributes to IPE?

Blood shifts to the core which increases pulmonary artery pressure

What 3 factors increase risk of IPE/SIPE?

Heavy exertion

cold water

previous history.

True or false: IPE only occurs in cold water

False

In what activities can IPE/SIPE occur?

SCUBA diving, free diving, endurance swimming, and similar immersion sports.

Who appears to be at higher risk of IPE among divers?

Older divers.

What is one possible pathophysiologic mechanism of IPE?

High pulmonary pressures and fluid movement into the alveoli during immersion and exertion

What 3 treatments are used for IPE/SIPE?

Emergent evacuation

oxygen

treatment of any near-drowning complications.

How can asthma increase diving risk?

Gas trapping from obstructed airways can expand during ascent and cause barotrauma.

When should an asthmatic person not dive?

If they have had an exacerbation in the past 48 hours or symptoms triggered by cold or exercise

What is a spontaneous pneumothorax?

A pneumothorax that occurs without trauma, often due to lung blebs or bullae.

Why is spontaneous pneumothorax a major issue for divers?

A pneumothorax at depth can become an emergency and may progress to tension pneumothorax

Who commonly gets spontaneous pneumothorax?

Tall, slender males.

What is the recurrence rate of spontaneous pneumothorax?

About 50%.

Why is spontaneous pneumothorax usually a contraindication to future diving?

Because recurrence underwater could be catastrophic.

Why should divers never hold their breath?

Because gas expands during ascent and can cause pulmonary barotrauma and AGE.

Why should divers avoid flying soon after diving?

Reduced cabin pressure can precipitate decompression sickness

How long should someone generally wait to fly after a single non-decompression dive?

At least 12 hours.

What are the 5 key prevention strategies for decompression illness and related conditions?

Follow dive tables

avoid rapid ascents

make decompression stops

never hold your breath

avoid flying soon after diving

What symptoms did the triathlete with probable IPE have?

Dyspnoea, cough, chest tightness, and poor performance after water running and floating starts.