Dive Physiology Basics
Physiology is really just physics applied to your body. Once you see how pressure affects your air spaces, your gases and your temperature, the exam questions start answering themselves.
Air spaces and equalizing
Your body has air spaces — ears, sinuses, and the mask on your face. As you descend, rising pressure squeezes them (Boyle's Law again), and if you don't add pressure to balance them you get a painful 'squeeze', or barotrauma. The fix is to equalize early and often, and gently, from the moment you start down. If your ears won't clear or you're congested, don't force it — end the descent.
Breathing under pressure
The air you breathe gets denser with depth, so you use gas faster the deeper you go — a tank lasts far less time at 30 metres than at 10. That's why monitoring your gas is a constant habit, and why steady, relaxed breathing (never holding your breath, never rapid 'skip breathing') matters for both safety and air consumption.
Nitrogen and your tissues
Under pressure your body absorbs extra nitrogen into its tissues, and it releases that nitrogen slowly as you ascend and rest on the surface. This single fact underpins dive tables, no-decompression limits, safety stops and decompression sickness — it's the reason you plan and pace your dives at all.
Staying warm
Water draws heat from your body far faster than air — even 'warm' water will cool you over a dive. Getting cold dulls your judgment, raises your gas consumption, and is thought to increase decompression risk, which is why appropriate exposure protection is a safety item, not just a comfort one.
On the exam
Physiology questions reward understanding the 'why':
- Know how and why you equalize, and what barotrauma is.
- Explain why you use air faster at depth.
- Connect nitrogen absorption to dive planning and decompression sickness.
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Frequently asked questions
Why do my ears hurt when I descend?
Rising pressure squeezes the air space in your middle ear. If you don't equalize — adding air to balance the pressure — the squeeze becomes painful and can cause barotrauma. Equalize gently and often from the start of your descent, and never force it.
Why do I use air faster at depth?
The air you breathe is denser under pressure, so each breath contains more gas. At 30 metres you're breathing roughly four times as much gas per breath as at the surface, so a tank lasts far less time.
Why do divers get cold so quickly?
Water conducts heat away from the body far faster than air, so you lose warmth much more quickly underwater — even in comfortable-feeling water. Getting cold affects judgment and gas use, which is why exposure protection matters.
What is barotrauma?
Injury caused by a pressure difference in one of the body's air spaces — most often the ears or sinuses — usually when a diver descends without equalizing. Equalizing early, often and gently prevents it.