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Coping with Altitude and Depth

Yuxiang Wang

Chap 11.4, 11.6, 12.3, 15.4, 16.4

OT Chap. 9.4, 9.6, 9.10, 10.3, 13.4,14.4

I. Coping with altitude (air-breather)

II. Coping with deep sea (diving air-breather)

I. Coping with Altitude

• O2 and Hypobaric hypoxia?

• Hypocapnia-respiratory alkalosis

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Challenges at high altitude

• Lower temperature (-0.6oC/100m) - hypothermia

• Lower atmospheric pressure– Exponential decrease air pressure (50% per 5500m)

– dehydration

• Reduced Po2

– Not a big issue to aquatic and tracheal animals

– Big problem for lung-breathing vertebrates

Physiological Responses (non-birds)

1) Hyperventilation – maintain alveolar Po2

– Conflicts with acid-base balance2) Induce inorganic phosphates and 2,3-DPG in RBC to

reduce Hb-O affinity – unload O2 @ peripheral sitesreduce Hb O affinity unload O2 @ peripheral sites3) Extra Hb and RBC in blood to increase O2 carrying

capacity*4) Bohr Shift – left @ respiratory sites , higher affinity5) increase functional lung volume*

6) Increase capillary density – reduce diffusion distance*

7) Reduce muscle fibers diameter*

*long term structural

How do birds and insects cope with altitude?altitude?- Whooper swan 9,000m

- Ruppell griffon 12,000m

- Spider 7,300m Mount Makalu

How do birds and insects cope with altitude?

• Whooper swan 9,000m

• Ruppell griffon 12,000m

• Spider 7 300m Mount Makalu• Spider 7,300m Mount Makalu

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How do birds fly high?

• More hypoxia tolerant

• Can fly over height 0 to 9,000m in 1 day (bar-headed geese cover 1000 miles)(bar headed geese cover 1000 miles)

• Flight requires more than 15x more energy

• Need to maintain O2 supply!

Migratory route of the bar-headed Geese

• Breed in Tibet-Qinghai Plateau (3000-4000m), Mongolia Gobi Desert

Migratory route of the bar-headed Geese

• Annual migrations flying over the Himalayan mountain range.

• Flocks have been sighted above Mtsighted above Mt. Everest (8848m)

• Winter in India

How do birds stay in sane in thin air?

Respiratory system

• Crosscurrent gas-blood flow arrangement and hyperventilation to increase gas exchange efficiency

• Extra thin gas-blood exchange barrier to overcome perfusion limit

• Greater PaO2 under same Po2 in inspired air –greater blood O2 content

• Low temp in inspired air – increase O2 diffusion

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O2 transport system

• High Hb oxygen affinity (P50 =27mmHg) -> increase O2 carrying capacity– Hb Alpha chain Pro -> Ala– Hb Beta chain Leu -> Ser

• Low Pco2 and high pH -> left Bohr shift• Lower Tb in hypoxic birds -> left Bohr shift• Without hypocarpnia induced

vasoconstriction

Cardiovascular system

• Larger heart and stroke volume

• Great cardiac output scope (5-7x)

• Less redistribution of blood to critical tissue• Less redistribution of blood to critical tissue (brain and heart) under severe exercise because a higher O2 content can be maintained in high altitude birds

Cerebral circulation

• In mammals, – cerebral blood vasodilation is caused by hypoxia– Hypocapnia causes cerebral vasoconstriction– Inhale CO2 can increase blood flow to brain and

alleviate mountain sickness (CA inhibitor does the (same)

• In birds,– Hypocapnia does not alter cerebral blood flow– Hypercapnia significantly increase cerebral blood flow– Severe hypocapnic hypoxia does not affect cerebral

circulation– Arterial blood from retes in the eyes has higher Po2 to

enhance O2 in brain

Individual tissues

• High capillary density in muscle and brain

• High MT density and aerobic enzymes activity in performance muscleactivity in performance muscle

• High Mb O2 affinity and concentration

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Myoglobin

• Birds have very low myoglobin P50 values.– Eg. Melanotrochilus fuscus…

2.5 mmHg

– Human ~5 mmHg

M l bi i d t• Myoglobin is very good at holding onto oxygen.

• Cardiac musculature in birds has higher concentrations of myoglobin,

Human adaptations to high altitudes

• Tibetans (4,200m)

• Andean (3,900m)

• Ethiopian (3,530)

Different Adaptive Mechanisms?

• Increase RBC count in blood?l i d– Present only in Andean

• Higher hemoglobin concentrations?

• Change in carbonic anhydrase activity?

• Different hemoglobin P50 values?

• Nitric Oxide?

Tibetan Andean

Beall et al, 2006

• At 4000m, Andean has 21% higher Hb than Tibetan and Ethiopian• Tibetans need stronger stimuli to boost Hb (5000m)

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Andean

Ethiopean

• O2 Sat% indicate hypoxia stress• Tibetans show clear altitude dose-response• Ethiopians show no sign of stress

Tibetan Andeans: high Hb, high Hct, high Arterial O2, low O2 Sat%

Tibetans: Low O2 Sat %, low arterial O2

Ethiopians: NO EFFECTS!

High O2 sat% phenotype has greater infant survival rate suggest that natural selection is favor high Sat% allele at this major gene locus

Nitric oxide• Tibetans and Andean populations have higher pulmonary nitric oxide

concentrations, but not in Ethiopian.

18.6 p.p.b. 9.5 p.p.b. 7.4 p.p.b.

Nature 414, 411-412 (22 November 2001)

Tibetans and Viagra - the missing link?November 23, 2001 Posted: 4:04 AM EST (0904 GMT)

• Could the blockbusting anti-impotency drug Viagra and high altitude living Tibetans possibly have anything in common?– Scientists think the link being nitric oxide. – Recent research shows that the same chemical

that increases blood flow in Tibetan's lungs allowing them to breathe at high altitudes, also gives lift to a flagging penis.

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Nitric oxide as an adaptive mechanism

• Endogenous nitrates (NO) are produced by blood vessels.

• Relax smooth muscle -vasodilation

• Nitroglycerin relieves Angina pectoris.

• Giving low altitude individuals NO, increases their O2 content

during hypoxiaduring hypoxia.

• NO dilates pulmonary blood vessels, increases pulmonary blood

flow.

• NO facilitates oxygenation of hemoglobin.

II. Coping with Deep Sea (pressure)

Fish– Relatively straightforward in stable ocean environment,

no direct depth effect except in the anaerobic zone.– Respiratory pigments can be affected by pressure and

low temperature in the species living in this zonelow temperature in the species living in this zone.– Left-shift of O2 dissociation curve, high O2 extraction

efficiency (~50%)– Hb can be temperature insensitive in some species

(tuna)– Organic phosphate and lactic acid are used to modify

the pigment O2-affinity.

Diving Tetrapods and birds

• Physiological Challenges– Hypoxia, store sufficient O2 to support

metabolism.– Hydrostatic pressure on air-filled cavities (1

atmospheric pressure/10m)– The bends and air bubbles due to changing

pressure (decompression) – N2

– Low temperature– Free-radicals formed during repeat diving

Champion divers

• Seals, max 1600m

• Emperor penguins, 50-550m,2-10min, max 22min22min

• Weddell seals, 50-600m, 10-20min, max 82min

• Elephant seals, 200-800m, 20-30min

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A Hallmark of diving animals

• Substantial elevation of muscle myoglobins concentration

• Two diving strategies– Seals, rely on aerobic metabolism (< Aerobic

Diving Limit, ADL)

– Birds, rely on anaerobic metabolism (>ADL)

Physiological responses to diving

• Apnoea – regulate respiratory muscles• Increase O2 storage – RBS, Hb, Mb, • Hypoperfusion to visceral organsHypoperfusion to visceral organs• Hypometabolism, lower Tb• Increase anaerobic metabolism and

withhold lactate in ICF till finishing the dive

• Bradycardia and reduce cardiac output

• Neuronal and hormonal control of cardiac and spleen action (via catecholamine.)

• Smaller lung (some deep diving mammals) in comparison to upper airways to reduce bubble formation and “the bends”

• Decrease Tb to reduce metabolic rate• Decrease Tb to reduce metabolic rate

critical

Fig. 11.44 OT Fig. 9.44

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Comparison of O2 storage between seal and human

Schmidt-Nielsen

Mb O2 capacity

Schmidt-Nielsen

• Bradycardia and hypoperfusion are ancestral characteristics

• Spleen RBC and blood volume adjustmentsSpleen, RBC and blood volume adjustments are diver-specific.

Effects of pressure

• Mechanical distortion and compression of tissues

• High gas tension in lung results in increased gas absorption into tissues

• Dissolved gas tension is higher than ambient pressure during ascent – gas bubble in blood and tissue

• High pressure nerve syndrome

• What is diving bents?

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Lung is a liability for deep divers

• Reduce lung volume or allow it to collapse to reduce N2 absorption (challenge to re-inflate –surfactant)

• Reinforcement of upper airway to prevent collapse• Reinforcement of upper airway to prevent collapse• Shorten airway to allow quick air

exhalation/inhalation during resurfacing• How do animal divers perform quick ascent

without the “bends”? – frequent short-shallow dives after long-deep dive- decompression

Diving Challenges

Pressure

Oxygen/Nitrogen

L. Martin, 1997

temperature

Depth, volume and density, Boyle’s law

Depth (msw)

Pressure (atm)

Air vol in a balloon (l)

Density Relative size

( )

0 1 12 1x

10 2 6 2x

20 3 4 3x

30 4 3 4x

40 5 2.4 5x

Four types of diving (human)

a) Breath-hold diving ("breath-hold")

b) Diving in a heavy-walled vessel ("vessel")

c) Diving with compressed air or other gasc) Diving with compressed air or other gas supplied from the surface ("surface air")

d) Diving with compressed air or other gas in a container carried by the diver ("scuba")

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Human diving technology evolved mirroring our understanding of diving

physiology of Animal• Human use external air carrying device to

expand diving range and extend time underwater

• Decompression chamber allow human divers to perform deeper dive without decompression sickness

Scuba is an acronym for 'self-contained underwater breathing apparatus‘ - SCUBA

• compressed air tank • 1st stage regulator. • 2nd stage demand regulator and mouthpiece,• a face mask • an extra second stage regulator and mouthpiece,

carried by the diver in case of emergencycarried by the diver in case of emergency • two submersible gauges,

• accurate depth • air remains in the tank

• an inflatable vest (buoyancy compensator, BC)• a weight belt and weights• fins to facilitate self-propulsion in the water. • a wet suit or other type of body protection

Compressed gas to increase oxygen storage during diving

L. Martin, 1997

Major events in diving history marks our

understanding of diving physiology

• New technology– Nitrox (32% O2 balance N2)

– Heliox, helium to replace N2, avoid narcosisHeliox, helium to replace N2, avoid narcosis

– Trimix

• O2 under high pressure can be toxic

• Pure O2 treatment for bubble disease

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Ana (Pearl) Diver of Japan and South Korea

• A practice with >1,500yr history

• Funado (assisted)20 40 meters 30sec/dive 30 dives/hr– 20-40 meters, 30sec/dive, 30 dives/hr

• Cachido (un-assisted) – 3-5meter, 25-30sec/dive, 60 dives/hr

Go Snorkeling Why do elephants have long nostril trunk?

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Elephants

• Aquatic ancestral (Manatee’s cousin)

• “ …whenever they have to traverse the water they lift the nostril trunk above thewater, they lift the nostril trunk above the the water surface and breath through it”

– in De Partibus Animalium, Aristotle, 4th century B.C.E.

• Elephants are champion snorkellers!

How could elephants snorkel beyond2 meters depth?

• Physiological consequences:– 2m water = 150mmHg (20kPa) above atmospheric

pressure– Alveolar pressure remains at atmospheric level (open toAlveolar pressure remains at atmospheric level (open to

air)– Systemic vascular pressure increase to 150mmHg to

maintain tissue perfusion– Pressure in thoracic cavity remain low– Negative pressure between lung and the rest of body –

blood vessels in the pleura is at risk of tearing – Boyle’s law P1xV1 = P2 xV2.

Water Surface

Elephants

<30cm 100mmHgHuman snorkeling

~7x

Elephants

(West, 2001) Pa + hydraulic pressure

-150mmHg

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Elephant’s solution

• Structure - function:– Dense connective tissue to replace pleura tissue to

obliterate cavity – preventing rapture of blood vessel

– Separated parietal and visceral pleura with connectiveSeparated parietal and visceral pleura with connective tissue to allow sliding movement – lubricating

– Thickening of pleura is primary evolutionary change to protect microvessels (2mm, 4x thicker), the addition layer of connective tissue is secondary response

– Thickening of diaphragm (3mm) to 10x of other’s

Sheep: the parietal pleura and endothoracic fascia

African elephant (Loxodonta africana)African elephant (Loxodonta africana).

Parietal pleura Viscerel pleura

What happens when elephants raise their trunk to drink water?

• Hydraulic pressure in trunk = 200cm H20

• Alveolar pressure is below atmospheric pressure?pressure?

• Open mouth, no low pressure exerted by buccal muscle

• Only last for several seconds