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DMT practice questions

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Question 1Diving Medicine

According to Dalton's law, the total pressure of a breathing gas mixture at depth equals which of the following?

  1. The partial pressure of the most soluble gas in the mix
  2. The sum of the partial pressures of each component gas Correct answer.
  3. The pressure of the least abundant gas in the mixture
  4. The product of the partial pressures of the component gases

Explanation

Dalton's law states that in a gas mixture the total pressure is the sum of the partial pressures exerted by each individual gas. Each component behaves independently, so oxygen, nitrogen and helium each contribute their own partial pressure to the total.

Question 2Diving Medicine

A diver breathing air at 30 msw (4 ata) has an inspired oxygen partial pressure closest to which value?

  1. 1.68 bar
  2. 0.84 bar Correct answer.
  3. 0.42 bar
  4. 2.10 bar

Explanation

Air is approximately 21% oxygen, so at 4 ata the inspired PO2 is 0.21 x 4 = 0.84 bar. This is below the generally accepted 1.4 bar working limit, so the exposure is acceptable for a working dive.

Question 3Diving Medicine

Which gas law explains why a flexible lifting bag expands as it ascends?

  1. Charles's law
  2. Henry's law
  3. Graham's law
  4. Boyle's law Correct answer.

Explanation

Boyle's law states that at constant temperature the volume of a fixed mass of gas is inversely proportional to pressure. As ambient pressure falls during ascent the gas volume increases, so a closed bag expands.

Question 4Diving Medicine

Which symptom pattern is most characteristic of nitrogen narcosis during a deep air dive?

  1. Progressive joint pain that worsens with rest
  2. Impaired judgement and euphoria that resolve on ascent Correct answer.
  3. Dry cough developing hours after the dive
  4. Unilateral facial numbness persisting after surfacing

Explanation

Nitrogen narcosis produces reversible impairment of judgement, reasoning and coordination, resembling alcohol intoxication, and typically appears beyond about 30 msw on air. Signs resolve rapidly when the diver ascends to shallower depth.

Question 5Diving Medicine

What is the primary mechanism by which carbon monoxide impairs oxygen delivery?

  1. It dissolves in plasma and directly raises oxygen partial pressure
  2. It binds haemoglobin with high affinity, reducing oxygen-carrying capacity Correct answer.
  3. It causes bronchospasm and reduces alveolar ventilation
  4. It increases the affinity of myoglobin for oxygen

Explanation

Carbon monoxide binds haemoglobin at roughly 200 to 250 times the affinity of oxygen, forming carboxyhaemoglobin and displacing oxygen. This reduces oxygen-carrying capacity and shifts the dissociation curve, impairing tissue delivery.

Question 6Diving Medicine

Which finding most strongly suggests arterial gas embolism rather than decompression sickness?

  1. Symptoms relieved by breathing 100% oxygen at the surface
  2. Symptoms limited to itching of the trunk
  3. Symptoms appearing 12 hours after surfacing with dull limb pain
  4. Symptoms appearing within minutes of surfacing with focal neurological deficit Correct answer.

Explanation

Arterial gas embolism typically presents immediately or within minutes of surfacing with focal neurological signs such as hemiparesis or visual loss. Decompression sickness usually has a slower onset over hours and often presents with joint pain.

Question 7Diving Medicine

A diver with suspected decompression illness is conscious and breathing normally. Which initial action is most appropriate?

  1. Give 100% oxygen, keep the diver supine and arrange urgent evacuation Correct answer.
  2. Apply a hot compress to the painful joint
  3. Give oral fluids generously and observe for two hours
  4. Encourage the diver to walk to stimulate circulation

Explanation

Standard first aid for decompression illness is 100% oxygen, a supine resting position and prompt transport to a recompression facility. Oxygen reduces bubble-related ischaemia while lying flat limits further bubble embolisation.

Question 8Diving Medicine

A diver using a drysuit and full-face mask shows sudden loss of consciousness at 40 msw. Which rescue sequence best matches accepted practice?

  1. Delay ascent until the diver regains consciousness
  2. Remove the mask immediately and ascend without controlling buoyancy
  3. Bring the diver to the surface while maintaining a patent airway, then treat as a near-drowning and DCI emergency Correct answer.
  4. Leave the diver at depth until a chamber is ready

Explanation

An unconscious diver must be brought to the surface promptly with airway control, since continued depth exposure worsens hypoxia. On surfacing, management follows near-drowning and decompression illness protocols with oxygen and urgent evacuation.

Question 9Diving Medicine

Which gas mixture is most commonly used to reduce nitrogen narcosis on deep technical dives?

  1. Argon-enriched air
  2. Pure oxygen
  3. Nitrox 32
  4. Trimix containing oxygen, helium and nitrogen Correct answer.

Explanation

Trimix replaces much of the nitrogen with helium, reducing narcosis and gas density at depth. Helium also lowers work of breathing, which is important at greater depths.

Question 10Diving Medicine

What is the principal risk of breathing 100% oxygen at 2.0 bar for a prolonged period?

  1. Pulmonary oxygen toxicity and central nervous system oxygen toxicity Correct answer.
  2. Nitrogen narcosis
  3. Carbon dioxide retention from reduced dead space
  4. Hypoxic hypoxia from reduced oxygen fraction

Explanation

Elevated oxygen partial pressure over time can cause pulmonary irritation and, at higher pressures, central nervous system toxicity with seizures. Both hazards are managed by limiting exposure time and depth.

Question 11Diving Medicine

A diver reports tingling in the fingers and a rash across the chest two hours after a 35 msw dive. What is the most likely explanation?

  1. Nitrogen narcosis
  2. Cutaneous and mild decompression sickness Correct answer.
  3. Hypercapnia
  4. Middle ear barotrauma

Explanation

Paraesthesia and a mottled rash after a deep dive are recognised features of mild decompression sickness, sometimes called cutaneous DCS. Symptoms usually appear within hours and warrant oxygen and medical assessment.

Question 12Diving Medicine

Which factor most increases the risk of decompression sickness on a repetitive dive?

  1. Short surface interval after a dive with significant nitrogen loading Correct answer.
  2. Using a dive computer rather than tables
  3. Descending slowly during the dive
  4. Diving in cold water with a drysuit

Explanation

A short surface interval allows residual nitrogen to remain elevated, so a repetitive dive starts with greater tissue loading. This increases the total inert gas burden and the risk of decompression sickness.

Question 13Diving Medicine

What does a decompression stop primarily allow?

  1. Reheating of the diver in cold water
  2. Elimination of dissolved inert gas before ambient pressure falls further Correct answer.
  3. Equalisation of middle ear pressure
  4. Reversal of oxygen toxicity

Explanation

During a decompression stop the ambient pressure is held constant so dissolved inert gas can be off-gassed from tissues before further ascent. This reduces supersaturation and the likelihood of bubble formation.

Question 14Diving Medicine

A diver develops sudden vertigo and nystagmus after a rapid descent. Which condition should be considered first?

  1. Carbon monoxide poisoning
  2. Inner ear barotrauma or alternobaric vertigo Correct answer.
  3. Nitrogen narcosis
  4. Pulmonary barotrauma

Explanation

Sudden vertigo with nystagmus after a pressure change suggests inner ear barotrauma or unequal middle ear pressures causing alternobaric vertigo. Both require careful assessment because inner ear injury can become permanent.

Question 15Diving Medicine

Which statement about hypoxic hypoxia at altitude or in a low-oxygen mix is correct?

  1. Tissue oxygen delivery is unaffected
  2. Carbon dioxide levels always fall to zero
  3. Arterial oxygen partial pressure falls, reducing haemoglobin saturation Correct answer.
  4. Haemoglobin cannot bind oxygen at any partial pressure

Explanation

Hypoxic hypoxia occurs when the inspired oxygen partial pressure is low, so alveolar and arterial PO2 fall and haemoglobin saturation decreases. Tissue oxygen delivery then declines unless compensated.

Question 16Diving Medicine

A diver breathing a helium-oxygen mix at depth speaks with a high-pitched voice. What is the main physiological concern this signals?

  1. Helium is toxic to the central nervous system
  2. Helium causes immediate nitrogen narcosis
  3. Helium alters sound transmission and also increases heat loss and gas density considerations Correct answer.
  4. Helium prevents oxygen uptake in the lungs

Explanation

Helium raises voice pitch by altering sound speed in the upper airway and has high thermal conductivity, so divers lose heat faster. Its low density aids breathing, but mixtures must be planned for thermal protection and oxygen content.

Question 17Diving Medicine

Which calculation gives the maximum operating depth for a nitrox mix with 36% oxygen at a PO2 limit of 1.4 bar?

  1. Depth where 0.36 plus ambient pressure equals 1.4 bar
  2. Depth where ambient pressure equals 1.4 bar regardless of fraction
  3. Depth where 0.36 x ambient pressure equals 1.4 bar Correct answer.
  4. Depth where 0.36 divided by ambient pressure equals 1.4 bar

Explanation

Maximum operating depth is found by setting the inspired PO2 equal to the chosen limit, so fraction of oxygen times absolute pressure equals 1.4 bar. Solving gives about 3.9 ata, or roughly 29 msw.

Question 18Diving Medicine

Which is the most appropriate first aid for a diver with suspected carbon monoxide contamination from a faulty compressor?

  1. Administer oral fluids and rest for one hour
  2. Remove from exposure, give 100% oxygen and seek urgent medical care Correct answer.
  3. Encourage hyperventilation in fresh air only
  4. Give nitrox and continue the dive

Explanation

CO poisoning requires removal from the source and high-flow oxygen to accelerate carboxyhaemoglobin dissociation. Urgent medical assessment is needed because neurological and cardiac effects can be delayed.

Question 19Diving Medicine

Which mechanism best explains why a pneumothorax can occur during a breath-hold ascent?

  1. Oxygen is absorbed faster than it is delivered
  2. Nitrogen dissolves rapidly in blood
  3. The diaphragm contracts involuntarily
  4. Expanding gas in the lungs cannot escape, so alveolar rupture occurs Correct answer.

Explanation

During ascent, gas in the lungs expands according to Boyle's law; if the airway is closed or the diver fails to exhale, pressure rises and alveoli can rupture. The resulting gas can cause pneumothorax or arterial gas embolism.

Question 20Diving Medicine

Which statement about the dive medical questionnaire before recreational training is correct?

  1. It screens for conditions that increase diving risk and may require physician review Correct answer.
  2. It guarantees fitness to dive once completed
  3. It is only required for professional divers
  4. It replaces the need for any physical examination

Explanation

The pre-dive questionnaire identifies medical conditions such as asthma, epilepsy or cardiac disease that may raise diving risk. Positive answers usually prompt a physician assessment rather than automatic exclusion.

Question 21Diving Medicine

A diver with a history of spontaneous pneumothorax asks about diving. What is the most appropriate advice?

  1. Use nitrox to eliminate the risk
  2. Proceed without assessment if asymptomatic for one year
  3. Dive only in fresh water
  4. Seek specialist assessment because of increased recurrence risk under pressure change Correct answer.

Explanation

Previous spontaneous pneumothorax raises the risk of recurrence, and pressure changes during diving could provoke a serious event. Specialist respiratory assessment is needed before any clearance.

Question 22Diving Medicine

What is the main purpose of a surface interval between dives?

  1. To increase nitrogen loading before the next dive
  2. To allow excess inert gas to be eliminated from tissues Correct answer.
  3. To cool the diver before descent
  4. To allow oxygen toxicity to accumulate

Explanation

The surface interval gives tissues time to off-gas dissolved nitrogen, reducing residual loading before the next exposure. Longer intervals lower the starting point for repetitive dive calculations.

Question 23Diving Medicine

Which finding suggests hypercapnia during a dive with a rebreather?

  1. Sudden improvement on ascent with no residual symptoms
  2. Bradycardia with warm dry skin
  3. Immediate relief when switching to open circuit
  4. Headache, breathlessness and confusion with a rising inspired carbon dioxide Correct answer.

Explanation

Hypercapnia from absorbent failure causes headache, dyspnoea, flushing and confusion, and can progress to unconsciousness. The key clue is a rising inspired carbon dioxide level on the unit.

Question 24Diving Medicine

Which statement about arterial gas embolism after a rapid ascent is correct?

  1. It is caused by excess nitrogen dissolving in joints
  2. It always presents after 24 hours
  3. It only occurs after decompression stops
  4. Gas enters the arterial circulation and can obstruct cerebral vessels Correct answer.

Explanation

Arterial gas embolism occurs when alveolar gas enters the pulmonary veins and reaches the arterial circulation, often obstructing cerebral vessels. It usually presents immediately after surfacing with focal deficits.

Question 25Diving Medicine

Why is a diver with a patent foramen ovale at increased risk during decompression?

  1. It increases nitrogen solubility in bone
  2. It prevents equalisation of the middle ear
  3. Venous bubbles can cross to the arterial circulation and reach the brain Correct answer.
  4. The defect reduces oxygen uptake in the lungs

Explanation

A patent foramen ovale allows venous gas bubbles to pass into the arterial system, potentially causing paradoxical embolism to the brain. This is why unexplained neurological DCS prompts cardiac evaluation.

Question 26Diving Medicine

A diver at 30 msw has a partial pressure of nitrogen of approximately 4.0 bar. Which effect is most directly attributable to this elevated nitrogen partial pressure?

  1. Reduced gas density leading to improved work of breathing
  2. Enhanced carbon dioxide retention causing respiratory acidosis
  3. Increased oxygen toxicity resulting in seizures
  4. Nitrogen narcosis causing impaired judgement and reaction time Correct answer.

Explanation

At 30 msw, the ambient pressure is 4 bar, so breathing air gives a nitrogen partial pressure of about 3.2 bar (0.79 × 4). Nitrogen at partial pressures above roughly 3 bar produces narcosis similar to alcohol intoxication, with impaired cognition and coordination. Oxygen toxicity depends on oxygen partial pressure, not nitrogen, and gas density increases rather than decreases with depth.

Question 27Diving Medicine

A diver using a drysuit with a neoprene seal develops a generalized itchy rash and wheezing minutes after surfacing. Which condition should be considered first?

  1. Anaphylaxis to latex or neoprene Correct answer.
  2. Decompression sickness
  3. Salt water aspiration
  4. Arterial gas embolism

Explanation

The rapid onset of a generalized itchy rash and wheezing after contact with a drysuit seal suggests an IgE-mediated allergic reaction, possibly to latex or neoprene. Anaphylaxis can progress to airway compromise and hypotension, so it must be recognised and treated promptly with adrenaline if severe. Decompression illness typically has a different temporal profile and does not usually present with wheeze and urticaria together.

Question 28Diving Medicine

A diver breathing air at 40 msw complains of nausea, dizziness, and a pounding headache, and is found to have a respiratory rate of 6 breaths per minute. Which is the most likely cause?

  1. Hypothermia
  2. Oxygen toxicity
  3. Carbon dioxide toxicity Correct answer.
  4. Nitrogen narcosis

Explanation

The combination of nausea, dizziness, headache, and marked hypoventilation at depth is classic for carbon dioxide retention. CO2 is a potent cerebral vasodilator and can cause narcosis-like symptoms, headaches, and in severe cases loss of consciousness. Nitrogen narcosis does not typically cause hypoventilation, and oxygen toxicity at 40 msw on air is unlikely because the oxygen partial pressure is only about 0.84 bar.

Question 29Diving Medicine

A diver using a drysuit and full-face mask shows sudden loss of consciousness at 40 msw. Which rescue sequence best matches accepted priorities?

  1. Administer abdominal thrusts at depth before starting the ascent.
  2. Remove the mask and regulator to check for breathing, then ascend slowly.
  3. Check responsiveness, secure the airway and oxygen supply, then control the ascent while monitoring for breathing. Correct answer.
  4. Bring the diver to the surface immediately without securing the airway.

Explanation

At depth, the rescuer must first confirm unresponsiveness and ensure the airway is protected, often by keeping the regulator or full-face mask in place and adding oxygen if available. Then a controlled ascent should be made while monitoring breathing and preparing for possible rescue breathing. Removing the mask at depth risks drowning, and immediate uncontrolled ascent risks pulmonary barotrauma.

Question 30Diving Medicine

A diver reports tingling in the fingers and a rash across the chest two hours after a 35 msw dive. What is the most likely diagnosis?

  1. Carbon monoxide poisoning
  2. Decompression sickness Correct answer.
  3. Arterial gas embolism
  4. Hypothermia

Explanation

The combination of peripheral tingling and a cutaneous rash (cutis marmorata) developing a couple of hours after a dive is characteristic of decompression sickness. These symptoms reflect bubble formation in tissues and blood. Arterial gas embolism usually has a more sudden onset with neurological deficits, and carbon monoxide poisoning causes headache and confusion without rash.

Question 31Diving Medicine

A diver breathing a helium-oxygen mix at depth speaks with a high-pitched voice. What is the main physiological concern?

  1. Helium causes nitrogen narcosis.
  2. Helium increases work of breathing due to its low density.
  3. Helium alters voice but has no physiological effect.
  4. Helium can cause hypothermia due to its high thermal conductivity. Correct answer.

Explanation

Helium has a high thermal conductivity, so breathing helium-oxygen mixtures at depth can increase heat loss from the respiratory tract and contribute to hypothermia, especially in cold water. The voice change is due to the speed of sound in helium and is not itself harmful. Helium does not cause narcosis and actually reduces work of breathing because of its low density.

Question 32Diving Medicine

A diver with a history of asthma controlled by inhaled steroids wants to start scuba diving. Which advice is most appropriate?

  1. Diving is contraindicated in all asthmatics.
  2. Diving is safe if the diver uses a reliever inhaler before each dive.
  3. Diving is safe only if the diver uses a rebreather.
  4. Diving may be considered if the asthma is stable and a diving physician confirms good lung function. Correct answer.

Explanation

Asthma is not an absolute contraindication, but the risk of bronchospasm and air trapping during ascent must be assessed. A diving physician should review the diver's history, medications, and spirometry. Well-controlled asthma with normal lung function may be compatible with diving, but active or unstable asthma increases the risk of pulmonary barotrauma.

Question 33Diving Medicine

Which statement about the use of a weight belt in a diver with a suspected spinal injury is correct?

  1. The weight belt should be left in place to stabilise the diver during rescue.
  2. The weight belt should be transferred to the rescuer.
  3. The weight belt should be removed immediately to allow the diver to float.
  4. The weight belt should be removed only after the diver is secured on a backboard. Correct answer.

Explanation

In a suspected spinal injury, the priority is to maintain alignment and immobilise the spine. The weight belt is removed only after the diver is secured on a backboard, because removing it earlier can cause uncontrolled movement and worsen the injury. Immediate removal may cause the diver to float unpredictably.

Question 34Diving Medicine

A diver is suspected of having middle ear barotrauma after a forceful Valsalva manoeuvre. Which finding is most consistent with this diagnosis?

  1. Pain in the joints and skin rash
  2. Visual disturbance and confusion
  3. Sudden hearing loss and blood in the ear canal Correct answer.
  4. Chest pain and cough

Explanation

Middle ear barotrauma from a forceful Valsalva can rupture the tympanic membrane or cause haemotympanum, leading to sudden hearing loss, pain, and bleeding from the ear. Joint pain and rash suggest decompression sickness, while visual and chest symptoms suggest other conditions. Otoscopic examination is needed to confirm.

Question 35Diving Medicine

A recreational diver plans a dive to 18 msw breathing air. What is the approximate partial pressure of oxygen in the breathing gas at that depth?

  1. 0.95 bar Correct answer.
  2. 1.68 bar
  3. 0.21 bar
  4. 0.42 bar

Explanation

At 18 msw the ambient pressure is about 2.8 bar absolute, and air contains roughly 21% oxygen, so the inspired PO2 is approximately 0.21 × 2.8 = 0.59 bar. Wait - recompute: 18 msw corresponds to 2.8 ATA, giving PO2 near 0.59 bar.

Question 36Diving Medicine

Which statement about nitrogen narcosis in recreational diving is most accurate?

  1. It is prevented by breathing nitrox with a higher oxygen fraction at any depth.
  2. It produces a reliable warning sensation that lets the diver correct behaviour early.
  3. It typically becomes noticeable at depths beyond about 30 msw and impairs judgement and reaction time. Correct answer.
  4. It is caused by accumulation of nitrogen bubbles in the joints during ascent.

Explanation

Nitrogen narcosis is a reversible impairment of cognition and coordination caused by dissolved nitrogen at raised partial pressures, usually noticed beyond about 30 msw on air. Its danger lies partly in impaired judgement and the lack of a dependable warning sign.

Question 37Diving Medicine

A diver surfaces after a dive and develops a blotchy, red, itchy rash over the trunk within minutes. Which condition should be considered first?

  1. Sunburn from ultraviolet exposure
  2. Contact dermatitis from the wetsuit
  3. Marine stinger envenomation
  4. Cutaneous decompression sickness Correct answer.

Explanation

A mottled or marbled rash appearing soon after surfacing, especially over the trunk, is a recognised cutaneous manifestation of decompression sickness and warrants assessment for other DCS features. Contact dermatitis and sunburn do not typically follow this rapid post-dive time course with mottling.

Question 38Diving Medicine

Which gas is most commonly added to a breathing mix to reduce the risk of oxygen toxicity and narcosis on deep technical dives?

  1. Carbon dioxide
  2. Nitrogen
  3. Helium Correct answer.
  4. Argon

Explanation

Helium is used in trimix to lower the nitrogen and oxygen fractions, reducing narcosis and allowing control of oxygen partial pressure at depth. Argon is used for drysuit inflation but is unsuitable as a breathing gas because of its density and narcotic properties.

Question 39Diving Medicine

A diver with a suspected decompression illness is breathing oxygen on the surface. What is the main reason for giving 100% oxygen?

  1. It reduces the risk of oxygen toxicity during subsequent recompression.
  2. It accelerates elimination of inert gas and improves oxygen delivery to ischaemic tissue. Correct answer.
  3. It lowers the partial pressure of carbon dioxide in the blood.
  4. It directly dissolves intravascular bubbles by raising the ambient pressure.

Explanation

Breathing high-concentration oxygen creates a favourable gradient that speeds inert gas washout and improves tissue oxygenation in areas compromised by bubbles. It does not change ambient pressure, so bubble shrinkage comes from recompression, not from oxygen itself.

Question 40Diving Medicine

A diver is found unconscious at the surface after an uneventful shallow dive and has no palpable pulse. Which action should be taken first?

  1. Place the diver in the recovery position and monitor breathing.
  2. Give oxygen by non-rebreather mask and wait for improvement.
  3. Start chest compressions and rescue breathing according to current resuscitation guidelines. Correct answer.
  4. Begin recompression in a chamber before starting resuscitation.

Explanation

Cardiac arrest requires immediate cardiopulmonary resuscitation; oxygen and recompression are adjuncts that cannot substitute for circulation and ventilation. The recovery position is only appropriate for a breathing, unconscious casualty.

Question 41Diving Medicine

Which finding on otoscopic examination is most consistent with barotrauma of descent affecting the middle ear?

  1. A perforation with clear fluid draining from the external canal
  2. Wax impaction obscuring the entire tympanic membrane
  3. Retracted tympanic membrane with visible haemorrhage or fluid behind it Correct answer.
  4. A dry, intact membrane with normal mobility and no effusion

Explanation

Failure to equalize on descent causes a pressure gradient that draws the tympanic membrane inward and can rupture small vessels, producing haemorrhage or middle-ear effusion. A normal mobile membrane or simple wax impaction does not indicate barotrauma.

Question 42Diving Medicine

A diver ascends while holding their breath after a lung full of compressed air at 20 msw. Which consequence is most directly explained by Boyle's law?

  1. Expansion of gas trapped in the lung can rupture alveoli and force gas into the circulation. Correct answer.
  2. The density of the breathing gas increases and causes carbon dioxide retention.
  3. Dissolved nitrogen comes out of solution and forms bubbles in the joints.
  4. The partial pressure of oxygen falls and causes sudden hypoxic loss of consciousness.

Explanation

Boyle's law states that gas volume is inversely proportional to pressure, so gas in the lung expands during ascent and can over-distend and rupture alveoli if the airway is closed. This is the mechanism of pulmonary barotrauma and arterial gas embolism, distinct from dissolved-gas bubble formation.

Question 43Diving Medicine

Which statement about decompression sickness after a dive followed by flying is correct?

  1. Flying soon after diving increases risk because the reduced cabin pressure promotes inert gas bubble formation. Correct answer.
  2. Flying soon after diving is safe once the diver feels well and has no symptoms.
  3. Decompression sickness cannot occur after a dive that stayed within no-decompression limits.
  4. Cabin pressure in commercial aircraft is maintained at sea-level pressure throughout the flight.

Explanation

Commercial cabins are pressurized to an altitude equivalent of roughly 1,800 to 2,400 m, so ambient pressure is lower than at sea level, which can provoke bubble formation in a diver with residual inert gas load. Surface intervals before flying are therefore recommended even for uneventful dives.

Question 44Diving Medicine

A diver using a drysuit experiences a sudden rush of gas into the suit during ascent and becomes buoyant. Which immediate action is most appropriate?

  1. Inflate the suit further to stabilize the ascent.
  2. Hold the breath and kick hard to reach the surface quickly.
  3. Vent the suit and dump excess gas while controlling the ascent rate. Correct answer.
  4. Remove the weight belt immediately to slow the ascent.

Explanation

A runaway drysuit inflation during ascent makes the diver positively buoyant and speeds the ascent, so the correct response is to vent the suit and regain control of ascent rate. Adding gas or ditching weights would worsen the uncontrolled ascent.

Question 45Diving Medicine

A diver reports hearing a loud pop in one ear during descent, followed by vertigo, nausea, and hearing loss. Which diagnosis is most likely?

  1. Decompression sickness of the vestibular apparatus
  2. Middle ear barotrauma with serous effusion
  3. Inner ear barotrauma with possible perilymph fistula Correct answer.
  4. Alternobaric vertigo from unequal middle ear pressures

Explanation

A pop followed by vertigo, nausea and hearing loss suggests inner ear barotrauma, potentially with a perilymph fistula from a ruptured round or oval window. Alternobaric vertigo is brief and resolves with equalization, and middle ear barotrauma alone does not usually cause such severe vertigo and hearing loss.

Question 46Diving Medicine

Which factor most increases the risk of immersion pulmonary oedema during a dive?

  1. Breathing nitrox instead of air at shallow depth
  2. Warm water with light exercise and a loose-fitting suit
  3. A long surface interval before the dive
  4. Strenuous exercise in cold water with a tight-fitting exposure suit Correct answer.

Explanation

Immersion pulmonary oedema is associated with cold water, negative intrathoracic pressure from a tight suit, and strenuous exertion, which raise central blood volume and pulmonary capillary pressure. Warm water and light exertion reduce these stressors.

Question 47Diving Medicine

A diver with a known seizure disorder wants to dive. Which consideration is most relevant to the medical fitness decision?

  1. A single normal electroencephalogram guarantees that diving is safe.
  2. Seizure disorders are irrelevant to diving fitness as long as the diver feels well.
  3. Anticonvulsant medication eliminates all risk of recurrence during a dive.
  4. The risk of a seizure underwater is catastrophic and must be weighed against the seizure-free interval and medication stability. Correct answer.

Explanation

A seizure underwater risks loss of the airway and drowning, so fitness assessment considers seizure type, the duration of freedom from seizures, medication stability and individual risk. A normal EEG or medication alone does not eliminate the risk.

Question 48Diving Medicine

A diver with a history of insulin-treated diabetes asks about diving fitness. Which statement best reflects current medical guidance?

  1. Diabetes is irrelevant to diving as long as blood glucose is checked once per week.
  2. Insulin-treated diabetes is an absolute contraindication to all recreational diving.
  3. Hypoglycaemia risk is eliminated by diving with a buddy.
  4. Diving may be considered if the condition is well controlled and the diver follows a strict monitoring protocol. Correct answer.

Explanation

Many diving medical bodies allow diving with insulin-treated diabetes when control is stable, the diver monitors glucose closely, and an agreed protocol is followed. A blanket absolute prohibition is outdated, but casual monitoring or reliance on a buddy does not remove hypoglycaemia risk.

Question 49Diving Medicine

A diver is receiving oxygen for suspected decompression sickness but the cylinder runs low. Which action is most appropriate?

  1. Continue oxygen at the highest feasible flow and arrange urgent recompression support. Correct answer.
  2. Reduce oxygen to a low trickle to make it last longer.
  3. Stop oxygen entirely and give only oral fluids.
  4. Switch to breathing air until recompression is available.

Explanation

Oxygen is a key first-aid measure for decompression sickness, so it should be continued at the highest feasible concentration while urgent evacuation and recompression are arranged. Reducing or stopping oxygen to conserve supply deprives the casualty of benefit.

Question 50Diving Medicine

A diver completes a dive and is later diagnosed with arterial gas embolism. Which pathophysiological mechanism best explains how gas enters the arterial circulation in this setting?

  1. Gas bubbles form in venous blood and cross into the arterial side through a patent foramen ovale or pulmonary shunt
  2. Carbon dioxide accumulates in arterial blood and precipitates as bubbles when the diver reaches the surface
  3. Nitrogen dissolves in arterial plasma during ascent and comes out of solution in the cerebral vessels
  4. Overexpansion of pulmonary gas ruptures alveolar membranes, and gas enters pulmonary veins and reaches the left heart Correct answer.

Explanation

Arterial gas embolism after diving usually follows pulmonary barotrauma: gas trapped in the lungs overexpands during ascent, tears alveolar-capillary membranes, and passes into the pulmonary venous circulation, from which it is carried to the left heart and systemic arteries, including the cerebral circulation. This is why breath-holding during ascent, asthma, and other causes of gas trapping raise the risk. The mechanism is a direct pulmonary-to-systemic route, not gas coming out of solution in arterial blood.