What Really Happens Inside Your Body When You Dive: Bubbles, Pressure, and the Truth About Decompression
Paul Lenharr Dec 11, 2025
What Really Happens Inside Your Body When You Dive: Bubbles, Pressure, and the Truth About Decompression
Divers are taught the basics: “don’t come up too fast,” “follow your computer,” “do your safety stop.”
But the why behind these rules lives deep inside your tissues, in the microscopic world of dissolved gases and pressure changes.
Understanding what actually happens in your body when you descend, bottom out, ascend, and surface makes you a smarter, safer diver — and it turns decompression theory from a mystery into a powerful tool.
Let’s pull back the curtain.
Pressure Changes Everything — Starting With Gas Behavior
The moment you descend, the surrounding pressure increases. Boyle’s Law begins quietly reshaping your physiology:
-
Your lung volume decreases
-
Your tissues absorb more nitrogen
-
Your body becomes a high-pressure gas sponge
This isn’t dangerous by itself. It’s simply physics doing its thing. As long as you stay at depth, everything remains dissolved and stable.
The trouble starts when pressure begins to drop.
Your Body Loads and Unloads Gas in Compartments
Instead of treating your body as one big tank, decompression science looks at it as a series of “tissue compartments”:
-
Fast tissues: blood, brain, lungs
-
Medium tissues: muscle
-
Slow tissues: fat, connective tissue
Each category absorbs and releases nitrogen at different rates.
This is why diving isn’t a single formula — it’s a conversation between gas and time.
Your dive computer is constantly estimating how much nitrogen each compartment is storing and how quickly it’s off-gassing. It’s not measuring anything directly — it’s following a model of your physiology.
Where Bubbles Actually Come From
Divers imagine bubbles forming out of nowhere, but that’s not how biology works.
Your body always contains microscopic seed nuclei — tiny pockets of gas at the molecular level. They’re stable and harmless until the pressure drops.
When you ascend:
-
These nuclei can expand
-
Tiny bubbles appear
-
Most are captured and eliminated by your lungs
-
Some get trapped in tissues
-
A few may grow large enough to cause symptoms
Decompression isn’t preventing bubbles entirely — it’s keeping them small and manageable.
This is called bubble control, not bubble elimination.
DCS Isn’t Caused by One Thing — It’s a Perfect Storm
Decompression sickness happens when bubbles become too numerous, too large, or lodge in the wrong place. But here’s the key:
Two divers can do the exact same dive, and one can get bent while the other doesn’t.
Why?
Because DCS is influenced by:
-
Hydration
-
Fatigue
-
Microtrauma
-
BMI
-
Cold stress
-
Heavy exercise before or after the dive
-
Genetics
-
Circulation efficiency
-
Patent foramen ovale (PFO) in the heart
Your table or computer sees none of this.
It treats every diver as the same “standard human.”
This is why conservative habits matter more than numbers.
Decompression Theory Isn’t One Theory — It’s a Family of Models
The diving world uses several major frameworks:
Bühlmann ZHL Models
The backbone of most modern computers. Based on dissolved gas theory — controlling tissue loading in compartments.
Bubble Models (VPM, RGBM)
Focus on controlling bubble formation and expansion rather than just dissolved gas levels.
Gradient Factors
A way to tune Bühlmann by controlling how close your ascent gets to theoretical maximum tissue pressure.
Lower GF = more conservative ascent.
Higher GF = shorter, more aggressive ascent.
These aren’t competing “rules” — they’re different ways to interpret the same physiological reality.
Why Slow Ascents Work Better Than Anything Else
Slow ascents give your body time to:
-
Shrink existing bubbles
-
Off-gas dissolved nitrogen safely
-
Prevent new bubble expansion
-
Maintain stable blood flow
-
Avoid overwhelming your lungs with venous gas
Your lungs are your decompression engine.
Ascend too fast, and you overload the system.
This is why divers who swear by:
-
slow ascents
-
deep stops (controversial but situational)
-
extended safety stops
-
minimizing exertion on ascent
…tend to feel better after diving.
How Your Body Actually Gets Rid of Nitrogen
Your lungs aren’t just for breathing — they function as filtration:
-
Venous blood carries dissolved nitrogen and tiny bubbles to the lungs
-
Nitrogen crosses into alveoli
-
You exhale it
-
Repeat thousands of times
If bubbles sneak past the lungs (like with a PFO), they enter arterial circulation — a fast track to serious DCS.
Your Body Never Reads Your Computer — You Do
Computers don’t know:
-
how hydrated you are
-
if you worked hard at depth
-
if you’re cold
-
if you didn’t sleep well
-
if you have a shunt condition
-
how your individual physiology reacts to pressure
Diving safely is matching your behavior to your biology — not blindly trusting algorithms.
The better you understand what’s happening inside your body, the more intelligently you’ll dive.
The Takeaway
Diving isn’t just about skill — it’s about physiology, physics, and respect for your own biology.
You’re not avoiding nitrogen.
You’re managing it.
You’re not preventing bubbles.
You’re keeping them small.
You’re not following rules — you’re cooperating with your own body.
DCS isn’t random, and decompression isn’t magic.
It’s science, and once you understand it, you never look at your dive computer the same way again.