A diver complains of aching joints, nausea, and fatigue several hours after a dive. What is the probable cause?

Decompression sickness (DCS). The delayed onset combined with joint pain — the deep ache that gives DCS its colloquial name 'the bends' — nausea, and fatigue is the classic presentation of Type I DCS. Lung overexpansion injuries present within minutes of surfacing, and seasickness does not cause joint pain.

Which lung overexpansion injury is the most serious and why?

Arterial Gas Embolism (AGE) is the most serious. Air bubbles enter the pulmonary veins and travel via the arterial system directly to the brain or coronary arteries. Cerebral AGE causes stroke-like symptoms — sudden confusion, loss of consciousness, or paralysis — typically within seconds of surfacing.

What does the T in the VENTID-C oxygen toxicity mnemonic stand for?

Twitching — not tingling. VENTID-C stands for: Visual disturbances, Ears (tinnitus), Nausea, Twitching, Irritability, Dizziness, Convulsion. Tingling is a common wrong answer and a deliberate distractor in the PADI Instructor Exam.

Why does breathing pure oxygen speed up nitrogen elimination from the body?

When breathing 100% oxygen, the partial pressure of nitrogen in the lungs drops to zero. Tissue nitrogen — at a much higher partial pressure — diffuses rapidly into the blood and out through the lungs along the pressure gradient. This is why surface oxygen is the recommended first aid for suspected DCS.

Two divers surface after a short dive both complaining of headache, nausea, and narrowing vision. What is the likely cause?

Contaminated air — most likely carbon monoxide from a compressor intake positioned near an exhaust. Two divers affected simultaneously after a short dive from the same gas supply is the classic signature. CO binds to haemoglobin with approximately 200 times the affinity of oxygen, starving the brain and eyes of oxygen.

A forceful Valsalva manoeuvre may rupture which structure?

The round window — a thin membrane separating the middle and inner ear. An extremely forceful Valsalva can generate enough pressure to rupture it, causing a perilymph fistula: inner ear fluid leaks into the middle ear, producing sudden severe vertigo, hearing loss, and tinnitus requiring urgent ENT assessment.

Why is hyperventilating before a breath-hold dive dangerous?

Hyperventilation flushes CO2 out of the blood, removing the normal urge to surface. The diver remains submerged while oxygen is consumed, but receives no warning signal. On ascent, the partial pressure of oxygen drops sharply as ambient pressure falls. At a critical threshold the diver loses consciousness without warning — this mechanism kills breath-hold divers annually.

When a diver ruptures their eardrum due to delayed equalisation, which space does water enter?

Water enters the middle ear. The ear canal always contains water when submerged — that is not caused by a ruptured eardrum. The middle ear is normally an airspace and water only enters it if the eardrum is ruptured. The inner ear is not an airspace and water cannot enter it.

PADI Dive Theory Practice Exams — Physiology

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PADI Dive Theory — Physiology Practice Quizzes

Two 16-question quizzes covering the physiology topics tested in the PADI Instructor Exam — based on real IDC exam scenarios from Go Pro Caribbean.

Physiology is one of the five dive theory subjects examined in the PADI Instructor Exam (IE). The questions below are written in the same multiple-choice format used in the real exam, with detailed explanations to help you understand the reasoning — not just memorise the answer.

Work through both quizzes before your IDC. If you get a question wrong, read the explanation carefully: understanding why is what produces consistently high exam scores.

Quiz 1 — 16 questions

Nitrogen narcosis
DCS causes & symptoms
Lung overexpansion injuries
Carbon monoxide poisoning
Dead air space
Gas exchange & respiration
Oxygen toxicity
Silent bubbles

Quiz 2 — 16 questions

Hypercapnia
Contaminated air
Ear barotrauma
Shallow water blackout
CNS oxygen toxicity (VENTID-C)
DCS risk factors
Near drowning
Smoking & diving

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More dive theory practice: Physics • Equipment • Skills & Environment • RDP & eRDPml • All dive theory

Physiology — Quiz 1

Narcosis • DCS • Lung overexpansion • CO poisoning • Dead air space • Oxygen toxicity

Physiology — Quiz 2

Hypercapnia • Contaminated air • Ear barotrauma • DCS • O2 toxicity • Near drowning • Smoking

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