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

Contact

alex.russu79@gmail.com