Physiology · Temperature, exercise and metabolism
Diving, decompression and hyperbaric oxygen !
- Mechanism
- For completeness
Underwater, pressure rises fast; gases are squeezed and dissolve more in blood, and on the way up they can form bubbles.
Updated 2026-11-01
Also called: Decompression sickness, Barotrauma
See it in 3D: Pleura · Right upper lobe · Left upper lobe · Eardrum
What it is
Every 10 m of seawater adds ≈1 atmosphere. By Boyle's law air spaces shrink on descent and expand on ascent (barotrauma); by Henry's law more nitrogen dissolves in tissues. If a diver rises too fast, nitrogen comes out of solution as bubbles (decompression sickness). The same physics underlies hyperbaric oxygen. In Colombia recreational diving is common in San Andrés, Santa Marta and on the Pacific coast.
How it works, step by step
- On descent, ambient pressure compresses the air in ears, sinuses and lungs; pressures must be equalized.
- Alveolar N₂ partial pressure rises and nitrogen slowly dissolves into tissues, especially fat.
- On ascent pressure falls; if it falls faster than the lungs can clear N₂, bubbles form.
- Bubbles block vessels and activate platelets and endothelium: joint pain, spinal cord injury, breathlessness.
- Chamber recompression redissolves the bubbles and 100% O₂ speeds N₂ washout.
Oxygen–hemoglobin dissociation curve
P50 17.2 mmHgArterial blood 59 %Mixed venous blood 54 %O₂ given up to the tissues 5 %
With 40% HbCO those sites no longer carry O₂ (the plateau falls) and the rest release it less well (left shift): that is why the harm is greater than in an anaemia of the same size. A standard pulse oximeter may still read normal.
Left shift (P50 17.2 mmHg): Hb holds O₂ more tightly and gives up less in the tissues.
- Current curve
- Normal curve (pH 7.40 · 37 °C)
- Arterial blood (PO₂ 100)
- Mixed venous blood (PO₂ 40)
- O₂ given up to the tissues
Diving problems and their physical law
| Problem | Physics | Picture |
|---|---|---|
| Ear and sinus barotrauma | Boyle (descent) | Pain, ruptured eardrum |
| Pulmonary barotrauma | Boyle (ascent) | Pneumothorax, arterial gas embolism |
| Decompression sickness | Henry (N₂) | Joint pain («bends»), spinal cord injury, «chokes» |
| Nitrogen narcosis | High N₂ partial pressure | Euphoria, impaired judgement |
| Oxygen toxicity | High O₂ partial pressure | Seizures, lung injury |
Clinical notes
- Flying soon after diving lowers ambient pressure and can trigger decompression sickness: a waiting period is advised.
- CO poisoning: hyperbaric oxygen speeds CO elimination and may reduce neurological sequelae.
- A patent foramen ovale lets venous bubbles cross into the arterial circulation.
Test yourself
Think of the answer, then tap the question to see it.
Why can a diver who rises from 10 m holding their breath get a pneumothorax?
Pressure falls from 2 to 1 atm and, by Boyle's law, lung air tries to double in volume; with no escape through the glottis the alveoli rupture.
Why does a fast ascent cause decompression sickness when a slow one does not?
On a slow ascent dissolved N₂ returns to blood and leaves through the lungs; if pressure drops fast, tissues are supersaturated and N₂ forms bubbles.
How does a hyperbaric chamber help in carbon monoxide poisoning?
A very high PO₂ competes with CO for hemoglobin and shortens carboxyhemoglobin's half-life; it also raises O₂ dissolved in plasma.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
Related conditions
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 22.3 The Process of Breathing (OpenStax (Rice University), 2022); 22.5 Transport of Gases (OpenStax (Rice University), 2022); Carbon Monoxide Poisoning: MedlinePlus (MedlinePlus, US National Library of Medicine, 2026); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 45). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.