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ABPM Undersea and Hyperbaric Medicine study materials
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ABPM Undersea and Hyperbaric Medicine practice questions

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Question 1Diving medicine and physiology

A diver descends from the surface to 10 meters of seawater. According to Boyle's law, the volume of gas in the middle-ear space becomes approximately:

  1. one-third of its surface volume
  2. unchanged from its surface volume
  3. one-half of its surface volume Correct answer.
  4. two-thirds of its surface volume

Explanation

At 10 m in seawater the ambient pressure is about 2 ATA, twice the surface pressure. Boyle's law states that at constant temperature gas volume is inversely proportional to absolute pressure, so the volume is halved.

Question 2Diving medicine and physiology

Which barotrauma is the most common in recreational divers?

  1. Pulmonary barotrauma
  2. Sinus barotrauma
  3. Middle-ear barotrauma Correct answer.
  4. Dental barotrauma

Explanation

Middle-ear barotrauma is the most frequently reported diving injury because the Eustachian tube must be actively equalized during descent. Failure to equalize creates a pressure gradient across the tympanic membrane.

Question 3Diving medicine and physiology

Most susceptible divers first notice clinically significant nitrogen narcosis while breathing air at approximately:

  1. 10 m of seawater
  2. 60 m of seawater
  3. 20 m of seawater
  4. 30 m of seawater Correct answer.

Explanation

Nitrogen narcosis usually becomes clinically noticeable around 30 m of seawater, roughly 100 feet, and increases progressively with depth. At 10 to 20 m effects are minimal in most divers, while at 60 m impairment can be marked.

Question 4Diving medicine and physiology

Breathing oxygen at a high partial pressure during a dive most directly predisposes to which acute complication?

  1. CNS seizures Correct answer.
  2. Pneumothorax
  3. Hypothermia
  4. Decompression sickness

Explanation

A high oxygen partial pressure can cause acute central nervous system oxygen toxicity, historically called the Paul Bert effect. This is distinguished from pulmonary oxygen toxicity, which develops more slowly with prolonged exposure.

Question 5Diving medicine and physiology

A diver at 40 m of seawater breathes air containing 21% oxygen. The inspired oxygen partial pressure is approximately:

  1. 0.21 ATA
  2. 1.05 ATA Correct answer.
  3. 0.42 ATA
  4. 5.00 ATA

Explanation

At 40 m of seawater the ambient pressure is about 5 ATA. By Dalton's law, the oxygen partial pressure is 0.21 multiplied by 5 ATA, which equals 1.05 ATA.

Question 6Diving medicine and physiology

A diver surfaces rapidly and within minutes develops confusion and left-sided weakness. Immediate management should include:

  1. 100% oxygen and urgent recompression Correct answer.
  2. NSAIDs, bed rest, and outpatient review
  3. oral fluids and prolonged observation in hospital
  4. return to 10 m on air for in-water recompression

Explanation

Sudden focal neurologic deficits after a rapid ascent suggest arterial gas embolism. Immediate high-flow 100% oxygen and urgent hyperbaric recompression are the priorities, with attention to airway and circulation.

Question 7Diving medicine and physiology

During a breath-hold descent in seawater, which change occurs in the diver's lungs?

  1. Nitrogen is actively washed out of tissues
  2. Lung gas volume falls with increasing pressure Correct answer.
  3. Lung gas volume increases steadily with depth
  4. Carbon dioxide tension falls sharply

Explanation

As depth increases, ambient pressure rises and the gas in the lungs is compressed according to Boyle's law. This reduction in lung volume can lead to lung squeeze if the breath-hold is deep enough.

Question 8Diving medicine and physiology

Which factor most increases the risk of carbon dioxide retention and unconsciousness during a dive?

  1. Wearing a well-fitting full-face mask
  2. Maintaining slow, deep breathing
  3. Breathing a helium-oxygen mixture
  4. Added breathing resistance and dead space Correct answer.

Explanation

Increased breathing resistance and dead space promote hypoventilation and rebreathing of carbon dioxide. Rising carbon dioxide can cause headache, confusion, and loss of consciousness underwater.

Question 9Diving medicine and physiology

A diver breathing air at 30 m for a prolonged period accumulates nitrogen in tissues because:

  1. nitrogen has a lower solubility than oxygen
  2. dissolved gas content is proportional to partial pressure Correct answer.
  3. ambient pressure has no effect on dissolved gas
  4. nitrogen is chemically bound to hemoglobin

Explanation

Henry's law states that the amount of gas dissolved in a liquid at equilibrium is proportional to the partial pressure of that gas. At depth the increased nitrogen partial pressure raises tissue nitrogen content over time.

Question 10Diving medicine and physiology

Which clinical feature most favors decompression sickness rather than arterial gas embolism?

  1. Joint pain worsening over hours Correct answer.
  2. A generalized seizure seconds after ascent
  3. Hemiplegia appearing within one minute of surfacing
  4. Immediate loss of consciousness at the surface

Explanation

Decompression sickness usually develops gradually, often with joint pain, numbness, or fatigue appearing minutes to hours after surfacing. Arterial gas embolism typically produces sudden neurologic symptoms within seconds to minutes.

Question 11Diving medicine and physiology

A patent foramen ovale is relevant to diving because it can:

  1. accelerate nitrogen narcosis
  2. allow venous bubbles to reach arteries Correct answer.
  3. increase the risk of oxygen toxicity
  4. reduce the decompression obligation

Explanation

A patent foramen ovale is a right-to-left shunt that can permit venous gas bubbles to bypass the pulmonary filter and enter the arterial circulation. This creates a risk of paradoxical embolism and embolic injury.

Question 12Diving medicine and physiology

During a dive, switching from air to heliox at constant depth can promote bubble formation because:

  1. nitrogen leaves tissues faster than helium enters
  2. helium enters tissues faster than nitrogen leaves Correct answer.
  3. oxygen partial pressure falls abruptly
  4. helium is much less soluble in blood than nitrogen

Explanation

Isobaric counterdiffusion occurs when two inert gases move in opposite directions at constant ambient pressure. Helium has much higher diffusivity, so it can enter tissues faster than nitrogen leaves, producing transient supersaturation.

Question 13Diving medicine and physiology

Which property of helium makes helium-oxygen mixtures advantageous for deep diving?

  1. High solubility in blood
  2. High density that reduces work of breathing
  3. High narcotic potency
  4. Low density and low narcotic potential Correct answer.

Explanation

Helium has low density, which reduces airway resistance and work of breathing at depth, and it is not narcotic. These properties make heliox useful for deep dives.

Question 14Diving medicine and physiology

In decompression modeling, 'slow tissues' refer to compartments that:

  1. take up oxygen but not nitrogen
  2. saturate and desaturate very rapidly
  3. contain mostly blood rather than fat
  4. exchange inert gas slowly Correct answer.

Explanation

Slow tissue compartments have long inert gas half-times and continue taking up or releasing gas over many hours. They are important in determining decompression requirements after long or repetitive dives.

Question 15Diving medicine and physiology

A diver develops vertigo and hearing loss immediately after a forceful Valsalva maneuver during descent. The most likely diagnosis is:

  1. Inner-ear decompression sickness
  2. Alternobaric vertigo
  3. Inner-ear barotrauma Correct answer.
  4. Middle-ear barotrauma

Explanation

A forceful Valsalva during descent can raise cerebrospinal fluid and perilymph pressure enough to rupture the round or oval window. This causes immediate vertigo, hearing loss, and tinnitus, consistent with inner-ear barotrauma.

Question 16Diving medicine and physiology

Prolonged hyperbaric oxygen exposure at 2.0 to 2.5 ATA most commonly produces which early pulmonary symptom?

  1. Hemoptysis
  2. Pneumothorax
  3. Pulmonary edema
  4. Tracheobronchitis Correct answer.

Explanation

Pulmonary oxygen toxicity, or the Lorraine Smith effect, begins as tracheobronchitis with substernal discomfort, cough, and reduced vital capacity. It results from prolonged exposure to elevated oxygen partial pressures.

Question 17Diving medicine and physiology

A diver ascends from 10 m while breath-holding. The most immediate risk is:

  1. Oxygen toxicity
  2. Alveolar rupture Correct answer.
  3. Carbon dioxide retention
  4. Nitrogen narcosis

Explanation

Gas in the lungs expands during ascent because ambient pressure falls. Breath-holding traps the expanding gas, which can overinflate the lungs and rupture alveoli, causing pneumothorax or arterial gas embolism.

Question 18Diving medicine and physiology

Immersion pulmonary edema in divers is best characterized by:

  1. Sudden hemiparesis
  2. Pain in multiple joints
  3. Immersion-related dyspnea and hypoxemia Correct answer.
  4. Fever and purulent sputum

Explanation

Immersion pulmonary edema presents with dyspnea, cough, and hypoxemia during or shortly after immersion, without aspiration or infection. It is thought to involve increased pulmonary vascular pressures and capillary leak.

Question 19Diving medicine and physiology

A breath-hold diver hyperventilates before a deep dive. This is dangerous mainly because hyperventilation:

  1. greatly increases the body's oxygen stores
  2. causes nitrogen narcosis at shallow depth
  3. raises carbon dioxide and stimulates breathing
  4. blunts the carbon dioxide-driven urge to breathe Correct answer.

Explanation

Hyperventilation lowers carbon dioxide and delays the normal urge to breathe. Oxygen can then fall to a critically low level before the diver feels the need to surface, leading to shallow-water blackout.

Question 20Diving medicine and physiology

Carbon monoxide in compressed breathing air is dangerous mainly because it:

  1. forms carboxyhemoglobin Correct answer.
  2. causes nitrogen narcosis
  3. is odorless and causes oxygen toxicity
  4. increases inert gas loading

Explanation

Carbon monoxide binds hemoglobin with an affinity much greater than oxygen, forming carboxyhemoglobin and reducing oxygen delivery to tissues. Contaminated breathing air can therefore cause headache, confusion, and unconsciousness underwater.

Question 21Diving medicine and physiology

In decompression theory, M-values represent:

  1. the tolerated inert gas pressure limit in a tissue Correct answer.
  2. the depth at which central nervous system oxygen toxicity occurs
  3. the volume of inert gas dissolved in blood at surface pressure
  4. the exponential rate at which a tissue compartment takes up inert gas

Explanation

M-values define the maximum inert gas tension that a tissue compartment can tolerate at a given ambient pressure before decompression is required. They are central to dissolved-gas decompression models and tables.

Question 22Diving medicine and physiology

The classic Haldane decompression model assumes that:

  1. decompression safety depends only on maximum depth
  2. nitrogen is not dissolved in blood at pressure
  3. inert gas uptake is exponential with fixed half-times Correct answer.
  4. bubbles form only within joint spaces and tendons

Explanation

The Haldane model represents the body as parallel tissue compartments, each taking up and releasing inert gas exponentially with a fixed half-time. It assumes dissolved gas kinetics and does not explicitly model bubbles.

Question 23Diving medicine and physiology

Which statement best reflects current understanding of decompression bubble formation?

  1. Micronuclei can lower the supersaturation needed for bubbles Correct answer.
  2. Bubbles form only when supersaturation exceeds 10 ATA
  3. Bubbles require foreign nuclei that never exist in vivo
  4. Bubbles never form in asymptomatic divers

Explanation

Pre-existing gas micronuclei and endothelial surface effects can reduce the supersaturation required for bubble growth. This helps explain why bubbles may form at lower gas tensions than simple dissolved-gas models predict.

Question 24Diving medicine and physiology

Cerebral arterial gas embolism after diving typically produces symptoms:

  1. within seconds to minutes of surfacing Correct answer.
  2. only in the spinal cord
  3. after 6 to 12 hours
  4. only when a patent foramen ovale is present

Explanation

Arterial gas embolism usually occurs when pulmonary barotrauma allows gas to enter the pulmonary veins and reach the systemic circulation. Cerebral symptoms therefore typically appear within seconds to minutes of surfacing.

Question 25Diving medicine and physiology

High-pressure nervous syndrome during deep heliox diving is characterized by:

  1. bradycardia and hypothermia
  2. tremor and myoclonic jerks Correct answer.
  3. hemoptysis and chest pain
  4. joint pain and a pruritic rash

Explanation

High-pressure nervous syndrome appears at great depth and is marked by tremor, myoclonic jerks, nausea, and electroencephalographic changes. It is related to the direct effects of high hydrostatic pressure on the nervous system.

Question 26Diving medicine and physiology

During descent, a diver develops ear pain and muffled hearing. The most likely cause is:

  1. Inner ear barotrauma
  2. Middle ear squeeze Correct answer.
  3. Eighth-nerve decompression sickness
  4. External canal obstruction

Explanation

Descent raises ambient pressure, and the gas space of the middle ear must be equalized; failure to do so creates a pressure gradient that causes pain and muffled hearing. This is middle ear barotrauma, the most common diving ear injury. Inner ear involvement typically causes vertigo and sensorineural hearing loss rather than simple muffled hearing.

Question 27Diving medicine and physiology

At 40 m on air, a diver becomes euphoric and has impaired judgment. This is best explained by:

  1. Increased nitrogen partial pressure Correct answer.
  2. Oxygen toxicity
  3. Hypothermia
  4. Carbon dioxide accumulation

Explanation

Nitrogen narcosis results from the raised partial pressure of nitrogen at depth and produces euphoria, impaired judgment, and slowed reactions. It is reversible on ascent and is not caused by oxygen toxicity or cold alone. Carbon dioxide retention can impair consciousness but usually has a different clinical picture.

Question 28Diving medicine and physiology

In a breathing mixture at depth, the partial pressure of each gas is determined by:

  1. Gas density
  2. Fraction times absolute pressure Correct answer.
  3. Blood solubility
  4. Molecular weight

Explanation

Dalton's law states that the partial pressure of a gas in a mixture equals its fractional concentration multiplied by the total absolute pressure. Density, molecular weight, and solubility affect other properties but not the partial pressure calculation.

Question 29Diving medicine and physiology

The amount of inert gas dissolved in a diver's tissues at equilibrium is proportional to:

  1. Gas diffusivity
  2. Gas density
  3. Diver exertion
  4. Partial pressure of the gas Correct answer.

Explanation

Henry's law states that dissolved gas content at equilibrium is proportional to the partial pressure of that gas above the liquid. Exertion and diffusivity affect the rate of uptake but not the equilibrium content. Density does not determine solubility.

Question 30Diving medicine and physiology

A diver breathing 100% oxygen at 2.8 ATA is at greatest risk of:

  1. Nitrogen narcosis
  2. Carbon monoxide poisoning
  3. Convulsions Correct answer.
  4. Pulmonary fibrosis

Explanation

Acute central nervous system oxygen toxicity can cause seizures at high oxygen partial pressures, and the risk rises with depth and exposure time. Pulmonary fibrosis is a chronic effect of prolonged oxygen exposure. Nitrogen narcosis does not occur with pure oxygen, and carbon monoxide poisoning is unrelated to breathing pure oxygen.

Question 31Diving medicine and physiology

The main purpose of a 3-minute stop at 5 m before surfacing is to:

  1. Allow oxygen to wash out
  2. Reduce inert gas supersaturation Correct answer.
  3. Prevent nitrogen narcosis
  4. Equalize the middle ear

Explanation

A shallow safety stop allows continued inert gas elimination while ambient pressure is still elevated, reducing supersaturation and bubble formation on surfacing. It does not wash out oxygen or prevent narcosis. Middle ear equalization is a descent issue.

Question 32Diving medicine and physiology

The recommended ascent rate for recreational scuba diving is approximately:

  1. 6 m per minute
  2. 9 to 10 m per minute Correct answer.
  3. 3 m per minute
  4. 18 m per minute

Explanation

Recreational training agencies generally recommend an ascent rate no faster than about 9 to 10 m per minute, with a safety stop. Faster rates increase bubble formation, while unnecessarily slow rates are not required for safety.

Question 33Diving medicine and physiology

A diver with spinal decompression sickness has numbness and leg weakness. The most appropriate initial management is:

  1. Oral fluids and observation
  2. NSAIDs and rest
  3. Oxygen and urgent recompression Correct answer.
  4. Deep massage

Explanation

Spinal decompression sickness is a neurological emergency requiring high-flow oxygen, fluid support, and urgent recompression. Delay increases the risk of permanent deficit. Analgesia and rest are supportive only and do not treat the underlying bubbles.

Question 34Diving medicine and physiology

Which factor most increases heat loss in a diver in cold water?

  1. Water's high thermal conductivity Correct answer.
  2. Mask squeeze
  3. Nitrogen narcosis
  4. Raised oxygen partial pressure

Explanation

Water conducts heat far better than air, so immersion rapidly draws heat from the body even in moderately cold water. Oxygen partial pressure, narcosis, and mask squeeze do not directly govern heat loss.

Question 35Diving medicine and physiology

Flying soon after diving increases the risk of decompression sickness because:

  1. Lower cabin oxygen
  2. Dry air causes dehydration
  3. Falling ambient pressure favors bubbles Correct answer.
  4. Vibration increases nitrogen uptake

Explanation

Aircraft cabin altitude lowers ambient pressure, which can turn asymptomatic dissolved nitrogen into bubbles in tissues already loaded from diving. Oxygen concentration, vibration, and dehydration are not the principal mechanism.

Question 36Diving medicine and physiology

Which history most strongly advises against scuba diving because of barotrauma risk?

  1. Well-controlled hypertension
  2. Recurrent pneumothorax Correct answer.
  3. Childhood asthma without symptoms
  4. Allergic rhinitis

Explanation

Recurrent pneumothorax implies lung pathology that may cause air trapping and pulmonary barotrauma during ascent. Asthma can be compatible with diving if well controlled and assessed individually. Rhinitis and hypertension are not absolute contraindications.

Question 37Diving medicine and physiology

In a closed-circuit rebreather, the greatest risk of hypoxia occurs when:

  1. Sensor calibrated in air
  2. Oxygen supply failure Correct answer.
  3. Loop carbon dioxide excess
  4. Helium diluent use

Explanation

If the oxygen supply fails, the loop gas is no longer replenished and the diver can breathe a falling oxygen fraction without warning. Carbon dioxide excess causes hypercapnia, and sensor calibration errors are a separate hazard. Helium diluent alone does not cause hypoxia.

Question 38Diving medicine and physiology

After a rapid ascent with a closed glottis, a diver develops hoarseness and neck crepitus. This indicates:

  1. Oxygen toxicity
  2. Subcutaneous emphysema Correct answer.
  3. Decompression sickness
  4. Mask squeeze

Explanation

Alveolar rupture during ascent can force gas along mediastinal planes and into neck tissues, producing crepitus, hoarseness, and subcutaneous emphysema. This is a form of pulmonary barotrauma. Decompression sickness, oxygen toxicity, and mask squeeze do not produce neck crepitus.

Question 39Diving medicine and physiology

The 'oxygen window' in decompression refers to:

  1. Oxygen consumption lowers tissue inert gas Correct answer.
  2. A visual field defect from hyperoxia
  3. Time between oxygen exposure limits
  4. Interval before recompression begins

Explanation

Metabolism consumes oxygen, so venous and tissue oxygen partial pressures fall below arterial levels; this creates a gradient that helps inert gas leave tissues. The term does not describe exposure limits or a clinical visual defect.

Question 40Diving medicine and physiology

A diver who dives at altitude compared with sea level should:

  1. Breathe pure oxygen
  2. Use sea-level-equivalent depth Correct answer.
  3. Shorten decompression
  4. Ascend more rapidly

Explanation

At altitude the surface pressure is lower, so a given depth corresponds to a greater sea-level-equivalent pressure exposure. Tables and computers must be set to altitude, which effectively increases the decompression obligation. Faster ascent or pure oxygen is not the correct adjustment.

Question 41Diving medicine and physiology

Immersion diuresis in divers is mainly caused by:

  1. Reduced antidiuretic hormone release Correct answer.
  2. Cold-induced diuresis alone
  3. Increased aldosterone secretion
  4. Direct oxygen diuretic effect

Explanation

Immersion shifts blood centrally, increases venous return, and reduces antidiuretic hormone release, producing increased urine output. Cold can contribute but is not the main mechanism, and hyperbaric oxygen does not directly cause diuresis.

Question 42Diving medicine and physiology

Which manifestation is most typical of mild (Type I) decompression sickness?

  1. Bladder dysfunction
  2. Seizures
  3. Joint pain Correct answer.
  4. Hemiplegia

Explanation

Type I decompression sickness typically involves musculoskeletal pain, skin changes, or lymphatic symptoms without neurological involvement. Hemiplegia, bladder dysfunction, and seizures indicate serious neurological Type II disease.

Question 43Diving medicine and physiology

Exhaustion of a rebreather's carbon dioxide absorbent is dangerous because it leads to:

  1. Oxygen toxicity
  2. Hypoxia
  3. Hypercapnia Correct answer.
  4. Nitrogen narcosis

Explanation

The absorbent removes exhaled carbon dioxide; once exhausted, inspired carbon dioxide rises and causes hypercapnia, with headache, dyspnea, confusion, and possible unconsciousness. It does not directly cause hypoxia, narcosis, or oxygen toxicity.

Question 44Diving medicine and physiology

A diver develops severe vertigo, nausea, and hearing loss after a deep dive and rapid ascent. This suggests:

  1. Simple hyperventilation
  2. Middle ear squeeze
  3. Alternobaric vertigo from cold
  4. Inner ear decompression sickness Correct answer.

Explanation

Inner ear decompression sickness can cause acute vertigo, nausea, hearing loss, and nystagmus after a dive with significant inert gas loading. Middle ear squeeze occurs on descent and usually causes pain and muffled hearing. Alternobaric vertigo is brief and related to unequal middle ear pressures.

Question 45Diving medicine and physiology

In decompression illness, intravenous fluids are given mainly to:

  1. Support circulation and reduce hemoconcentration Correct answer.
  2. Raise blood glucose for brain metabolism
  3. Dilute circulating oxygen bubbles
  4. Reduce nausea and vomiting

Explanation

Decompression illness causes endothelial injury and capillary leak, so intravenous crystalloid supports circulation and limits hemoconcentration that worsens bubble-related ischemia. Fluids are not given to raise glucose, dilute oxygen, or primarily treat nausea.

Question 46Diving medicine and physiology

Facial bruising around the eyes after a descent is most likely due to:

  1. Decompression sickness
  2. Mask exhalation failure Correct answer.
  3. Oxygen toxicity
  4. Sinus barotrauma

Explanation

If the diver does not exhale into the mask during descent, the mask space develops a relative vacuum and causes conjunctival and periorbital petechiae or bruising. Sinus barotrauma causes facial pain and epistaxis, and decompression sickness does not produce isolated periorbital bruising.

Question 47Diving medicine and physiology

A diver with insulin-treated diabetes should be advised that:

  1. Glucose is never low under pressure
  2. Hypoglycemia during diving is hazardous Correct answer.
  3. Diving is unrestricted if glucose is normal
  4. Hyperbaric exposure destroys insulin

Explanation

Hypoglycemia can impair consciousness underwater and is difficult to treat, so insulin-treated divers require careful glucose monitoring and dive planning. Diving is not unrestricted, and pressure does not destroy insulin or prevent hypoglycemia.

Question 48Diving medicine and physiology

In decompression schedules, deep stops are intended to:

  1. Avoid middle ear barotrauma
  2. Shorten total ascent time
  3. Reduce oxygen exposure
  4. Limit early bubble growth Correct answer.

Explanation

Deep stops are added at greater depths to slow the early phase of inert gas elimination and limit bubble growth before the diver reaches shallower stops. They do not shorten the ascent or primarily reduce oxygen exposure. Ear barotrauma is unrelated.

Question 49Diving medicine and physiology

Hyperbaric oxygen is used in severe carbon monoxide poisoning mainly to:

  1. Sedate the patient
  2. Treat concomitant decompression sickness
  3. Increase nitrogen elimination
  4. Speed carboxyhemoglobin dissociation Correct answer.

Explanation

Hyperbaric oxygen accelerates the dissociation of carbon monoxide from hemoglobin and improves tissue oxygen delivery, while also reducing delayed neurological injury. It is not a sedative, and nitrogen elimination or decompression sickness is not the main reason in this setting.

Question 50Diving medicine and physiology

A surface interval between repetitive dives is taken to:

  1. Reduce carbon dioxide
  2. Restore body oxygen stores
  3. Rehydrate the diver
  4. Allow inert gas washout Correct answer.

Explanation

During the surface interval, the elevated tissue inert gas tension falls toward equilibrium, reducing the starting load for the next dive and lowering decompression risk. Oxygen restoration and hydration are useful but not the main decompression purpose.