A man lay on his back on the floor of a hotel pool in Croatia, perfectly still, for nearly half an hour.
Nobody touched him.
He was not holding an oxygen tank.
He was holding his breath.
Official judges stood at the edge of the pool, and a crowd stood behind them.
What was happening inside his chest during those 29 minutes is the real story here.
What actually lets a body go nearly half an hour without a breath
The freediver, Vitomir Maričić, breathed pure oxygen for about ten minutes before he ever went under, a technique called denitrogenation. The process flushes nitrogen out of the blood and packs the body with oxygen instead. Ordinary air is only about 21 percent oxygen, so starting with the lungs and blood flooded with pure oxygen leaves a far larger reserve to draw on once breathing stops.
Once he was submerged, an older piece of machinery took over as well. In the mammalian dive reflex, the heart slows, which lowers oxygen consumption, blood vessels in the extremities constrict and channel oxygen rich blood to vital organs, and the spleen contracts.
That last step is the strange one. The spleen is a fist sized organ beside the stomach that filters old cells and supports the immune system, but it also holds a reservoir of oxygen carrying red blood cells. When it squeezes down it delivers what one researcher called an “oxygen boost,” estimated at up to a 9 percent increase in oxygen, prolonging dive time.
A pool in Opatija stood in for the open sea
The attempt took place in a pool only about 10 feet deep in the town of Opatija on Croatia’s Adriatic coast. His near half hour feat unfolded at the Bristol Hotel in front of five official judges and some 100 spectators, with the diver lying on his back at the bottom, hands behind his head.
So the whole thing came down to stillness. Lying motionless kept his muscles from burning oxygen they did not have to spend, while his mind worked to override an urge that fires long before oxygen actually runs short.
That detail matters more than it sounds. The urge to breathe is driven by rising carbon dioxide rather than falling oxygen. Pre-breathing oxygen raises body oxygen stores and blunts the normal panic signal from carbon dioxide sensing chemoreceptors, delaying the urge to breathe and pushing the body deeper into its reserves.
How the final number compares to everything before it
When he finally surfaced, the official time was 29 minutes 3.07 seconds. The previous mark, 24 minutes 37 seconds, belonged to fellow Croatian Budimir Šobat, and the new time surpassed it by more than four minutes.
Maričić did not describe it as a steady grind. “After the 20-minute mark, everything became easier, at least mentally,” he said after surfacing, but he explained that the experience had “got worse and worse physically, especially for my diaphragm, because of the contractions. But mentally I knew I wasn’t going to give up.”
Most of us can hold our breath for between 30 and 90 seconds. Researchers writing about the record put his hold at roughly 60 times longer than most people manage. On ordinary air, without any oxygen assistance, the competitive static apnea world record is 11 minutes 35 seconds.
Why a seal under Antarctic ice shares part of his trick
Weddell seals are the extreme case. They have been recorded diving to nearly 2,000 feet, with a maximum logged duration of 82 minutes. Researchers studying them estimated that about 5 gallons of red blood cells were sequestered at rest and released during diving.
The same squeeze has been measured in human divers who work for a living. In Korean ama, women making repeated dives to about 20 feet, calculated spleen volume fell by about 20 percent and hemoglobin concentration rose by about 10 percent. Three Japanese men who did not routinely dive showed no change in spleen size at all.
The organ can also simply be bigger. Among the Bajau of Southeast Asia, median spleen size runs 50 percent larger than in their land dwelling Saluan neighbors, and the enlargement shows up in non-diving Bajau too. That ruled out a simple training response of the kind a cold water swimmer builds through repeated exposure.
What the record still cannot tell us
How much the spleen contributes is still debated. One analysis estimated that splenic contraction would extend a hooded seal’s aerobic dive limit by only about 105 seconds, and a review of the human diving response concluded that more research is needed before its role in oxygen conservation can be settled, though the hypothesis seems reasonable.
The oxygen is the bigger lever, and also the dangerous one. Breathing pure oxygen can cause oxygen toxicity, which can be fatal, and should not be attempted by anyone who is not a competitive freediver under close medical supervision.
Still, the underlying reflex belongs to everyone. The same spleen squeeze and heart rate drop that helped a Croatian man stay under for 29 minutes also fire, in a far smaller way, in anyone who plunges into cold water and holds their breath. It is a reminder that the ocean’s oldest tricks are still wired into bodies that mostly live on land.
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