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PHYSIOLOGICAL ADAPTATIONS TO FREEDIVING IN MARINE MAMMALS
Alexandru RUSSU
Freedive Dahab, AIDA Instructor Course, September 2009
introduction
- The dolphin is often recognised as a symbol of Freediving (e.g. Apnea Academy logo)
- Swimming techniques and materials (e.g. the monofin) are inspired from what we tend to see as a model – the marine mammals, the perfect freedivers.
Together with the fascination for the marine mammals comes also some common questions:Why are they diving better than us? Do they have the same physiological limitations?Do they use different diving techniques?
more O2 in the muscles Retia mirabilia
higher blood volume Splenic O2 stores
Aortic bulb aerobic system more O2 in the blood more red cells more O2 in the brain more globins
1. More energetic resources
more glycogen anaerobic system Lactic acid delayed 2. Better adaptation to
pressureO2 repartition Flexible chest walls
cartilaginous rings sphincter muscles variable body density
3. Better dive response
bradicardia metabolic inhibition
selective ischemia 4. Better breath hold
controlno contractions
5. Better O2 recovery
More oxygen stored in the muscles:
Terrestrial mammals: 1g mioglobin / 100g muscle
Marine mammals: 3-7g mioglobin / 100g muscles
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Higher blood volume
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Retia Mirabilia
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Splenic O2 stores
The seals & sea lions spleen is 4.5% of their body weight and 3 times heavier than terrestrial mammals of same size
For the Weddell seal, the spleen gives 60 % increase in haemoglobin concentration in the first 10 min of the dive.
For humans, the increase in haemoglobin is around 3%
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The Aortic bulb
The aortic bulb the bulb has a capacity for storage of the stroke work of more than two normal heart beats and a volume of more than three times normal stroke volume.
functions through energy and volume storage actions and through uncoupling actions to maintain arterial pressures and stroke volume at near predive levels during a dive
It is common to all pinnipeds but the size of the bulb is bigger for the deep diving species
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More red cells/haemoglobin
Humans have 20ml/kg
Shallow diving mammals (including humans):
14-17g haemoglobin / 100 ml blood
Deep diving mammals 21-25g haemoglobin / 100 ml blood
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Higher concentration of globins
Some species have evolved the capacity to protect their brains from conditions of low oxygen.
They are protected by elevated levels of complex oxygen-carrying proteins--called globins--, in the cerebral cortex.
Weddell seals, animals that dive and hunt under the Antarctic sea ice hold their breath for as long as 90 minutes, and remain active and mentally alert the whole time.
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More glycogen stored in the muscles
“the heart of harp seals has enlarged stores of glycogen” which means that cardiac tissues have a bigger anaerobic capacity
Annalisa Berta
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Delayed effects of the Lactic Acid
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The lactic acid is blocked by the vasoconstriction
Allocation of O2 stores away from lungs
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Flexible chest walls
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The chest can squeeze to let the lungs virtually airless
Cartilaginous rings reinforcing the airways
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Shallow diving mammals have partially calcified rings prohibiting deep diving.
Deep diving mammals have low calcification of trachea rings which can bent without breaking at depth.
Sphincter muscles in the smaller airways
Marine mammals have very muscular bronchioles able to close the air passages
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Control of body floatability (density)
The dugong uses the earlier mentioned sphincter muscles of the bronchioles to compress the density of air in the lungs and change floatability without expelling air or using flippers.
Spermaceti is an organ regulating the corporal density of the sperm whale, with similar benefits as the BCD of a scuba diver
The spermaceti weights a few tones and is positioned in the head of the animal – ideal positioning for a “variable weight” dive
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The collapsible airway system is probably the most important adaptation to pressure and it’s main advantage is the fact that it allows to avoid the N2 build-up and the related problems (DCS & narcoses).
Bradicardia
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Heart rate of marine mammals can go bellow 5% of predive period vs. 70% for humans
The heart rate at the start of the dive is correlated with the duration of the dive they prepare for a dive of a certain time (if they go for a longer dive they start with a lower heart rate).
Metabolic inhibition with reduction in temperature
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They adjust swimming speeds and metabolic rates to sustain all dives aerobically
Selective ischemia
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peripheral vasoconstriction, like for humans
No diaphragmatic contractions
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The inspiratory reflex in marine mammals is diminished, allowing them to remain under water until the total exhaustion of available oxygen
Measurements on exhaled gases after deep diving showed values of :- 10% CO2 (man would black-out at 6%) - and less than 2% O2.
Further evidence is provided by the analysis of intratissualires diatoms.No diatom has ever been found in the bodies of marine mammals found dead in fishing nets, suggesting that they die not drowned, but suffocated
More effective recovery
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marine mammals remove almost 90% of the O2 available in each breath in comparison with humans which are only able to remove 20% .
Diving behaviour
Empty lungsThe Phocids exhale at the initiation of the dive - they have a collapsible airway system
Full lungsOtariids inhale before the dive and their airway system does not completely collapse
Exhale on descent
Throughout its descent, the seal let escape from his rib cage, the air pushed by the pressure.
Exhale on ascent
Antarctic fur seals dive with full lungs and exhale on the last part of the ascent
Worm-up
Beaked whales are feeding close to 2000m deep and it looks like even they need to prepare for such a dive.Beaked whales have been observed doing a succession of shallow dives (without eating behaviour, 90 min) and just after going for the deep dives (with eating behaviour )
Deco. Stops
The four digits feeding depths of the sperm whales are exposing them DCS and they naturally follow a decompression protocol: slow ascent and "deco stop" before surfacing
Conclusion
• From a physiological perspective, the specific adaptations of the cardio-vascular & respiratory system makes the marine mammals better freedivers than humans
• however, this is not necessarily the most relevant perspective for humans.
• Diving for cultural reasons instead of physical necessities makes us more sensitive to the cultural perspective and here the better freediver may be the one who enjoys it more and makes the most out of it to enhance his life experience