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Undersea Medicine. Michael Jacobs MD MPH Undersea Medical Officer Occupational/Preventive Medicine Physician Naval Hospital Great Lakes michael.jacobs@nhgl.med.navy.mil. Learning Objectives. Understand the scope of undersea medicine practice Understand basic principles of diving physiology

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Undersea Medicine

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Undersea medicine l.jpg

Undersea Medicine

Michael Jacobs MD MPH

Undersea Medical Officer

Occupational/Preventive Medicine Physician

Naval Hospital Great Lakes


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Learning Objectives

  • Understand the scope of undersea medicine practice

  • Understand basic principles of diving physiology

  • Recognize symptoms and signs of decompression illness

  • Understand principles of treatment for decompression illness

  • Identify medical contraindications for diving

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What is Undersea Medicine?

  • Also known as “Diving Medicine”

  • Field of medicine that deals with the effects of the undersea environment on health

    • Prevention and treatment of diving-related injuries/illnesses

    • Pre-employment/Pre-placement examinations

    • Fitness-for-diving evaluations

    • NOT management of chronic medical conditions

  • “Undersea and Hyperbaric Medicine” – board certification offered by the American Board of Preventive Medicine

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Examples of Diving-Related Injuries/Illnesses

  • Decompression Sickness (“The Bends”)

  • Arterial Gas Embolism

  • Sinus/Aural barotrauma

  • Pneumothorax

  • Nitrogen Narcosis

  • Drowning/Near Drowning

  • Hypothermia

  • Bites/Envenomations

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Who sees a “diving doctor”?

  • Recreational divers

  • Professional/Commercial divers

    • Dive instructors/Dive Masters

    • Military/Police/Technical divers

    • Inshore professionals – Oceanographers, Marine biologists, Engineers, Salvors

    • Offshore professionals – Saturation welders, Mixed-gas construction teams

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Diving Physics

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  • Pressure – force applied per unit area

    • Atmosphere (atm): pressure exerted on all bodies/structures by earth’s atmosphere

    • Sea Level = 1 atm = 14.7 psi (lb/in2)

  • Pressure under water

    • Every 33 ft of depth (sea water) = 1 atm or 14.7 psi

    • Example: Diver at depth of 66 ft

      • 1 atm (sea level) + 2 atm (water depth) = 3 atm

      • Diver at 66ft is under 3 atm pressure

P = Pressure

D = Depth

fsw = Feet of sea water

P (atm) = D (fsw) + 1

33 fsw

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  • Object in liquid floats or sinks depending on density of object relative to liquid

    • Your pet rock will sink in water

    • Your rubber ducky will float

  • State of “neutral buoyancy” – object neither floats nor sinks

  • Divers use various methods to maintain neutral buoyancy throughout a dive

    • If it feels like you are sinking – negatively buoyant

    • If it feels like you are floating up - positively buoyant

    • Both cause extra effort and potential injuries

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Gas Laws

  • Boyle’s Law: P1V1 = P2V2

    A rubber balloon with a volume of 1 cf at the surface is submerged to a depth of 33 fsw. What is the volume of the balloon now?

    P1V1 = P2V2P1 = atmospheric press.

    1 atm x 1 cf = 2 atm x V2V1 = volume at P1

    0.5 cf = V2P2 = press at 33 fsw

    V2 = volume at 33 fsw

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Sea Level1 atmVol=1

33 fsw2 atmVol=1/2

66 fsw3 atmVol=1/3

99 fsw4 atmVol=1/4




As a diver descends, atmospheric pressure increases and the volume of compressible tissues/gases decreases (e.g. gas bubbles, lung tissue)

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Dalton’s Law

  • Ptotal = pPa + pPb + pPc + . . . pPn

    (P = pressure, pP = partial pressure)

  • pPa = PtotalFa

    (F = % gas by volume)

  • What is the partial pressure of oxygen when breathing air at sea level? At 99 fsw?

    pPO2 = 1 atm (0.21) = 0.21 atm

    pPO2 = 4 atm (0.21) = 0.84 atm

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Henry’s Law

  • The amount of gas that will dissolve in a liquid is almost directly proportional to the partial pressure of that gas








High pPN2





As a diver descends, inspired gases are more soluble in blood

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Gas Diffusion

  • The difference between the partial pressure of a gas inside a liquid and its outside partial pressure will cause the gas to diffuse in or out of the liquid and will also control the rate of diffusion

    Example: At 66 fsw, pPN2 = 3 atm * 0.79 = 2.4 atm

    BloodDiffusion DirectionTissue

    pPN2 = 2.4 atmpPN2 = 0 atm

As a diver descends, inspired gases diffuse into tissues; as a diver ascends, gases diffuse out of tissues and into the blood

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Diving Gases

  • Most recreational divers use compressed air:

    • 79.1% Nitrogen

    • 20.9% Oxygen

    • 0.033% Carbon Dioxide

    • Various inert and trace gases

  • Other options include:

    • Nitrox (Nitrogen/Oxygen) – reduces nitrogen narcosis

    • Heliox (Helium/Oxygen) – reduces DCS

    • Trimix (Nitrogen/Helium/Oxygen)

    • 100% Oxygen – eliminates DCS (special ops use with scrubber system to eliminate bubbles)

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Diving Gases

  • Nitrogen

    • colorless, odorless, tasteless, inert

    • under pressure

      • soluble in body tissues

      • Anesthetic/intoxicant on CNS

        • “Nitrogen Narcosis”: (50 ft = 1 martini)

  • Oxygen

    • Colorless, odorless, tasteless

    • Too little (low Partial Press.) = hypoxia

    • Too much (high Partial Press.) = CNS toxicity (seizures)

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Diving Gases

  • Carbon Dioxide

    • Principal stimulant for respiration

    • Slight elevations cause headache, dizziness

    • High concentrations cause unconsciousness, death

  • Carbon Monoxide

    • Product of incomplete combustion

    • Toxic, asphyxiant

  • Helium

    • Inert and nontoxic

    • Often used as a nitrogen substitute for deep-diving divers to prevent nitrogen narcosis

    • Associated with High Pressure Nervous Syndrome (HPNS)

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In 1900, a Royal Navy diver descended to 150 fsw in 40 minutes, spent 40 minutes at depth searching for a torpedo, and ascended to the surface in 20 minutes with no apparent difficulty. Ten minutes later he complained of abdominal pain and fainted. His breathing was labored, he was cyanotic, and he died after seven minutes. An autopsy the next day revealed the organs to be healthy, but gas was present in the liver, spleen, heart, cardiac veins, venous system, subcutaneous fat, and cerebral veins and ventricles. By present U.S. Navy Standard Air Decompression Tables, this diver should have had 174 minutes of decompression time before reaching the surface.

Diagnosis: Decompression Sickness (DCS)

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  • DCS recognized in divers and compressed air workers since late 1800s

  • Prevailing guideline was to ascend slowly

    • Standards ranged from 1.5 ft/min to 5 ft/min

    • DCS still occurred but less frequently

  • Bert*: DCS associated with nitrogen bubbles

  • Haldane: Shorter/shallower dives associated with less frequent/less severe DCS

*Bert P. Barometric pressure. Researches in experimental physiology. Bethesda, MD. Undersea Medical Society, 1878.

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Decompression Theory

  • Body tissues absorbs nitrogen at depth

    • Each tissue type absorbs nitrogen at different rate

  • Slow, staged ascent (“decompression”) releases nitrogen harmlessly and is exhaled

    • Stages determined by time/depth of each dive

  • Ascent without adequate decompression causes nitrogen bubble formation

    • Clinical manifestations = “Decompression Sickness”

    • Origin of bubbles is controversial

    • Form in extra vascular spaces, such as skin and joints (including spine)

    • Reach venous circulation through lymphatics

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Decompression Illness (DCI)

  • Decompression Sickness (DCS)

    • Typically presents minutes to hours after dive

      • 95% within 6 hours

    • Nitrogen bubble formation from inadequate decompression

    • Onsite treatment: ABCs, Oxygen

    • Definitive treatment: Recompression

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Type I DCS

  • Musculoskeletal pain (Limb bends)

    • Most common manifestation of DCS

      • Dull pain, not well localized; no change with movement

      • Knees, elbows, or shoulders most commonly involved

  • Cutaneous DCS (Skin bends)

    • Pruritis and erythema of trunk

    • Cutis marmorata (mottling appearance of skin)

  • Treatment: Recompression

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  • Risk of permanent disability or death

  • Pulmonary DCS (“Chokes”)

    • Venous gas emboli clog pulmonary arterial circulation

    • Rare; occurs with rapid ascent from deep dive

    • Substernal discomfort, cough; worse with deep inspiration

    • May lead to right-sided heart failure and cardiovascular collapse

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Type II DCS (con’t)

  • Neurologic DCS

    • Predilection for spinal cord

    • Recreational divers doing short, deep dives

    • Syndrome – over minutes to hours after ascent

      • Tingling in trunk

      • Progressive numbness and paresthesias

      • Ascending motor weakness

      • Bowel/bladder incontinence

      • Severe cases may present with LOC/paraplegia

      • Cerebral Sx: memory impairment, aphasias, visual disturbances, personality changes

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Type II DCS (con’t)

  • Vestibular DCS (“Staggers”)

    • Sudden onset of dizziness, nausea, vomiting, nystagmus, +/- hearing loss and tinnitus

    • Not common in recreational divers

    • Confused with middle ear barotrauma

  • Treatment of Type II DCS:

    • Rapid recompression with hyperbaric oxygen

    • Supportive care: Fluids, pressors

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You and your dive buddy are out on the Great Barrier Reef. Your dive buddy is a novice diver on his first “real” diving trip. Your first dive is planned to a depth of 60 fsw for 45 minutes. Thirty-five minutes into your dive, your dive buddy points frantically toward a beautiful nine foot reef shark. After observing the shark for a few moments, you turn back to see your dive buddy swimming quickly for the surface. By the time you reach him on the surface, he is unconscious. The boat crew brings him on board and finds him unresponsive with a weak pulse. A review of your diving profile reveals that the dive was well within the decompression limits for a 60 ft dive. All other divers on the boat had no complications from their dives. What is the most likely diagnosis?

Diagnosis: Arterial Gas Embolism

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Arterial Gas Embolism (AGE)

  • 2nd only to drowning as most common cause of death in recreational divers

  • More common in novice divers

  • Pathophyisiology

    • Usually secondary to pulmonary barotrauma (PBT)

      • Lung overinflation from diving activities

        • Breath holding, bronchospasm, intrinsic abnormality

      • Excessive pressure disrupts lung parenchyma and allows gas into interstitium

        • Gas can cause mediastinal/subcutaneous emphysema, pneumothorax, or it can enter arterial circulation

    • Extraalveolar gas enters left side of heart and can embolize (to cerebral/coronary vessels, etc.)

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AGE (con’t)

  • Presents immediately or within minutes of ascent

  • Group 1 (5%)

    • Apnea, unconsciousness, cardiac arrest

    • AGE to coronary/cerebral circulation

  • Group 2 (95%)

    • Varying systemic neurologic signs but vital signs preserved

    • Typical: LOC/stupor/confusion, hemiparesis, seizures, vertigo, or headache

  • Treatment: Rapid recompression

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Evaluation of DCIs

  • Obtain accurate history

    • Dive profile (depth, time, previous dives), rate of ascent, time of onset of symptoms

  • Physical Exam

    • Vital signs, evidence of pulmonary barotrauma (PTX), thorough neurologic exam

  • Diagnostic tests – may not be time

  • Differential Diagnosis

    • Pain, rash, dyspnea, or neurologic changes after a dive should be assumed to be a diving-related illness

    • Consider other dx for symptoms >6 hours after dive

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DCI Treatment

  • Emergency treatment – ABCs first priority

  • Oxygen administration (100%)

    • enhances washout of inert gas (Nitrogen)

    • May resolve Sx or improve outcome

  • Definitive treatment – Recompression

    • Reduce bubble size

    • Promote bubble resolution

    • Delays lead to inflammatory changes, cell death, and poorer recovery

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Recompression Chamber

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  • Increased ambient pressure shrinks bubbles

    • Can often reduce symptoms

    • Controlled decompression allows dissipation of bubbles

  • Breathing gases

    • Air: Acceptable, but leads to additional nitrogen uptake and potential for additional DCS

    • Oxygen: Enhances diffusion of nitrogen out of tissues (“Oxygen window”)

      • Oxygenates ischemic tissue

      • Reduces cerebral edema

      • Probably inhibits endothelial leukocyte accumulation

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Treatment Tables

  • Designed to allow 100% oxygen breathing at highest practical ambient pressure

    • Oxygen toxicity occurs above 3 atm

      • Typical treatments max depth = 60 ft (2.8 atm)

    • Minimize nitrogen absorption

  • Type of treatment depends on type/severity of DCI

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U.S. Navy Dive Table 5*

*U.S. Navy Diving Manual Revision 4, March 2001

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Example: Treatment Table 5

  • Used for Type 1 DCS (pain only)

  • All symptoms must resolve within 10 minutes of reaching 60 ft in chamber

  • Other cases treated with similar tables, but longer duration

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Effectiveness of Recompression for DCS

  • Workman1

    • Military divers: 110 of 114 cases (96.3%) completely resolved

    • Civilians divers: 70% resolution

  • Diver’s Alert Network (DAN) – 19942

    • Recreational divers: 56% resolution

      • 30-90 days later: residual Sx in 33% pain-only DCS; 46% in mild neurologic DCS; 75% in severe neurologic DCS

  • Workman RD, Aerospace Medicine 1968.

  • DAN, 1996.

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Other injuries and illnesses are much more common during a typical dive

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1) Descent

Aural/Sinus barotrauma


2) On bottom

Nitrogen Narcosis


3) Ascent

Aural/Sinus barotrauma

CO poisoning




4) After surfacing


AGE (within 10 min)

PTX (within 10 min)


Potential problems during a dive

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Medical Evaluation of Divers

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Contraindications to Diving(Recreational Divers)

  • Relate to pressure changes and need to be completely comfortable in surroundings (underwater, heavy gear, away from land/medical treatment)

  • Absolute (typically):

    • Neuro: Severe brain damage (e.g. following head injury), seizure disorders, illnesses causing significant neurological deficits (stroke)

    • Endocrine: Diabetes with end-organ disease or symptomatic hyper/hypoglycemia

    • Gastrointestinal: Achalasia, symptomatic hernias, gastric-outlet syndrome, SBO

    • Pulmonary: Uncontrolled asthma, COPD, spontaneous PTX

    • Cardiac: Unstable angina, Septal defects

    • Medications: Decision usually relates to underlying condition

  • Relative contraindications are numerous and may require thorough evaluation/discussion with specialist

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Commercial Divers

  • Initial/periodic exams usually required

    • Very thorough evaluation (neurologic, pulmonary)

    • Functional testing may be required (Exercise Treadmill Test, Pulmonary Function Test)

  • Contraindications similar but much more strict than for recreational divers

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Related topics

  • Other diving-related disorders

    • Nitrogen narcosis, High pressure nervous syndrome, gas toxicity, hypothermia, marine animal injuries

  • Mixed gas diving (Nitrox, Trimix, 100% oxygen)

  • Hyperbaric Oxygen Therapy (HBOT)

    • Non diving injuries/illnesses

      • Poor wound healing

      • CO poisoning

      • Necrotizing fasciitis

      • Radiation necrosis

    • Benefit derives from increased oxygen delivery to tissues

    • Area of active research

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  • Bove AA. Bove and Davis’ Diving Medicine, 4th edition. WB Saunders, Philadelphia, 2004.

  • Navy Diving Manual, 4th edition. 2001. (www.vnh.org/DivingManual/DMTOC.html)

  • www.dive.noaa.gov (NOAA)

  • www.scubamed.com (Underwater Medicine Associates)

  • www.diversalertnetwork.org (DAN)

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