4900 Altitude

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Exercise at High AltitudeExercise at High Altitude

PED 4900PED 4900

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Gas Exchange at Sea LevelGas Exchange at Sea Level

Air has weight

Its weight is related to barometric pressure

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Dalton's Law

The total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases in the mixture.

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Partial Pressures of Air

Standard atmospheric pressure (at sea level) =760 mmHg

Nitrogen (N2) is 79.04% of air;

the partial pressure of nitrogen (PN2) = 600.7 mmHg

Oxygen (O2) is 20.93% of air;PO2 = 159.1 mmHg

Carbon dioxide (CO2) is 0.03%;PCO2 = 0.2 mmHg

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Partial Pressures of Air Partial Pressures of Air

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Partial Pressures of Air Partial Pressures of Air

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PO2 AND PCO2 IN BLOOD

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Partial Pressures of Respiratory

Gases at Sea Level

Total 100.00 760.0 760 760 0

H2O 0.00 0.0 47 47 0

O2 20.93 159.1 104 40 64

CO2 0.03 0.2 40 45 5

N2 79.04 600.7 569 573 0

Partial pressure (mmHg)

% in Dry Alveolar Venous Diffusion

Gas dry air air air blood gradient

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OXYGEN-HEMOGLOBIN DISSOCIATIONCURVE

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ALTITUDEALTITUDE

Atmospheric pressure

± Decreases at higher altitude

Partial pressure

± Same percentages of O2, CO2, and N2 in the air

± Lower partial pressure of O2, CO2, and N2

± Terms

Hypoxia: low PO2 (altitude)

Normoxia: normal PO2 (sea level)

Hyperoxia: high PO2

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Conditions at AltitudeConditions at Altitude

Reduced PO2

Reduced air temperature

Low humidity

Increased solar radiation

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Changes in Barometric Pressure (P ) and Partial

Pressure of Oxygen (PO ) at Different Altitudes2

B

0 (sea level) 760 159.2

1,000 674 141.2

2,000 596 124.9

3,000 526 110.2

4,000 462 96.9

9,000 231 48.4

Altitude (m) PB (mmHg) PO2 (mmHg)

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Sea LevelPikes Peak

Mount Everest

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Oxygen TransportOxygen Transport

VentilationVentilation

± ± DiffusionDiffusion

HemoglobinHemoglobin

± ± O2 affinityO2 affinity

Cardiac outputCardiac output

Peripheral circulationPeripheral circulation

Metabolism (aerobic energy production)Metabolism (aerobic energy production)

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Oxygen TransportOxygen Transport

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ALTITUDEALTITUDE

High altitude = 10,000 feet or 3048 meters

Moderate altitude = 4,921 feet or 1,500

meters

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Acute and Chronic Adaptations Acute and Chronic Adaptations

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PulmonaryPulmonary

HyperventilationHyperventilation

± ± Reduced arterial PO2Reduced arterial PO2 ± ± ChemoreceptorsChemoreceptors

± ± ³Hypoxic drive´³Hypoxic drive´

Variations in strength of hypoxic driveVariations in strength of hypoxic drive

± ± Stronger drive; better tolerance to altitudeStronger drive; better tolerance to altitude

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RESPIRATOR Y REGULATION

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Pulmonary ResponsePulmonary Response

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PulmonaryPulmonary

Hyperventilation leads to reduced CO2 in thealveoli

More CO2 diffuses out of the blood This increases the pH of the blood

CO2 + H20 H2CO3 HCO3 + H (acid)

³Respiratory alkalosis´.

Kidneys excrete more HCO3 The decreases the buffering of HCO3 and

increases the acid level (lowers the pH)

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PulmonaryPulmonary

Lower PO2 inside the alveoli

Less O2 saturation in the blood

Also, lower PO2 in the blood

Less pressure gradient at the muscles

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Oxygen UptakeOxygen Uptake

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VO2maxVO2max

No effect until altitudes

greater than 1,600 m

(5,249 ft). Above 1,600 meters,

VO2max decreases 8-

11% per 1,000 m

(3,281 ft) increase inelevation.

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VO2maxVO2max

VO2max decreased from

about 62 ml/kg/min at

sea level to 15 ml/kg/minat the top of Mount

Everest

If VO2max is 50

ml/kg/min at SL, then itwill be 5 ml/kg/min at ME

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Cardiovascular ResponsesCardiovascular Responses

Blood Volume

± Plasma volume decreases (up to 25%) from

respiration and increase urine production ± Increases RBC concentration and hematrocrit

± Eventually, plasma volume returns

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Cardiorespiratory and MetabolicCardiorespiratory and Metabolic

ChangesChanges

Note: Greater differences are at maximal exercise

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Metabolic DifferencesMetabolic Differences

Increase in anaerobic energy

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Altitude Altitude--Related ConditionsRelated Conditions

Acute Mountain Sickness (AMS)

High-Altitude Pulmonary Edema

(HAPE)

High-Altitude Cerebral Edema (HACE)

High-Altitude Retinal Hemorrhage

(HARH)

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MechanismsMechanisms

Reduced cerebral oxygen saturation

Decrease appetite leading to decrease in

body weight

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SymptomsSymptoms

Severe headache

Fatigue

Irritability Nausea

Vomiting

Loss of appetite

± Flatulence

± Constipation ± Sleep Disturbance

± Decreased urine output

± Indigestion

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PreventionPrevention

Gradual ascent

Diet rich in carbohydrates

Exercise

Diamox- counteracts fluid retention

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HighHigh--Altitude Pulmonary Edema Altitude Pulmonary Edema

Caused by rapid ascent

Symptoms occur within 12-96 hours

Fluid accumulation in the brain and lungs AMS symptoms present along with ³rales´ or

wheezing

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TreatmentTreatment

Descent

Supplemental O2

Medications

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PreventionPrevention

Ascending slowly

Climbing & sleeping at low altitudes

Limiting physical ability Avoiding cold exposure

Making visits brief as possible

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HighHigh--Altitude Cerebral Edema Altitude Cerebral Edema

Caused by rapid ascent

Extreme form of AMS

Can be fatal; fluid accumulation in the brain ± Vasodilation of cerebral vessels

± Tissue hypoxia

Differentiate by symptoms

± Lack of consciousness & coordination

Prevention same as AMS

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HighHigh--Altitude Retinal Hemorrhage Altitude Retinal Hemorrhage

All climbers experience if above 6700 m.

Blood pressure surges during exercise

cause ruptures in retinal capillaries.

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Acclimatization to Altitude

Decrease plasma volume

Increase hematocrit and RBCs

Possible increase in capillarization

Increase in 2, 3-DPG

Increase mitochondrial density

Increase in aerobic enzymes

Loss of body weight and lean body mass

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Hematologic Changes

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Cellular ChangesCellular Changes

Increase capillarization

Increase myoglobin

Increase mitochondria Increase 2, 3-diphosphoglycerate (2, 3-

DPG)

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PerformancePerformance

VO2max decreases 7-9%

per 1000m

Threshold for decrements

occurs at 1600 meter events and longer

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At altitude, endurance activity is affected the most due toreliance on oxygen transport and the aerobic energysystem.

Performance at AltitudePerformance at Altitude

Anaerobic sprint activities are the least affected byaltitude.

The thinner air at altitude provides less aerodynamicresistance and less gravitational pull, thus potentiallyimproving jumping and throwing events.

Endurance athletes can prepare for competitions ataltitude by performing high-intensity endurance training atany elevation to increase their VO2max.

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Fluid LossFluid Loss

Dehydration is fairly common

Water loss through the kidneys is

increased

Increased respiratory evaporation

Increased ventilation is the leading cause

of dehydration

Estimated water loss during 7 hours of

climbing is 1, 072 ml

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Fluid LossFluid Loss

Average daily water loss at altitudeincludes:

± Urination: 1.3 L ± Feces: .1-.2 L

± Sweat: .1L

± Water that passes through lungs & skin:

.7-1.1L

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Fluid RecommendationsFluid Recommendations

Additional 2 liters if at moderate altitude

Additional 4 liters if at high altitude

Urine should be light in color

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General Nutrition HintsGeneral Nutrition Hints

Gradually increase calories as activity increases

Plan one pot meals that cook in 15 minutes

Drink 3-5 L of water per day Drink frequently

Know that it takes 15 minutes to melt snow towater and 10-15 minutes to boil water

Increase carbohydrate intake drastically Avoid alcohol

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Training for Optimal Altitude Performance

Compete within 24 hours of arrival to altitude

Train at 1,500 to 3,000 m above sea level for at least 2weeks before competing

Increase VO2max at sea level to be able to compete at alower relative intensity

.

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Acute Altitude Sickness

Nausea, vomiting, dyspnea, insomnia

Appears 6 to 96 h after arrival at altitude

May result from carbon dioxide accumulation

Avoid by ascending no more than 300 m (984 ft) per dayabove 3,000 m (9,843 ft)

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High-Altitude Pulmonary Edema (HAPE)

Shortness of breath, excessive fatigue, blue lips andfingernails, mental confusion

Occurs after rapid ascent above 2,700 m (8,858 ft)

Accumulation of fluid in the lungs which interferes withair movement

Cause unknown

Administer supplemental oxygen and move to lower

altitude

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Eff t f Altit dEff t f Altit d

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Effect of Altitude onEffect of Altitude on

PerformancePerformance

Short-term anaerobic performance

± Lower PO2 at altitude should have no effect of

performance ± Lower air resistance may improveperformance

Long-term aerobic performance

± Lower PO2 results in poorer aerobicperformance

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Effect of Altitude on VOEffect of Altitude on VO2max2max

Decreased VO2max at higher altitude

Up to moderate altitudes (~4,000m)

± Decreased VO2max due to decreased arterialPO2

At higher elevations

± Rate of VO2max reduction also due to fall inmaximum cardiac output

Ch i VOCh i VO WithWith

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Changes in VOChanges in VO2max2max WithWith

Increasing AltitudeIncreasing Altitude

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ec o u e onec o u e on

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Submaximal Heart RateSubmaximal Heart Rate

ResponseResponse

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Adaptation to High Altitude Adaptation to High Altitude

Production of more red blood cells

± Counter desaturation caused by lower PO2

In those who grew up at altitude ± Have complete adaptations in arterial oxygen

content and VO2max

In those recently arriving at altitude ± Adaptations are less complete

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The Quest for EverestThe Quest for Everest

Mount Everest was climbed withoutoxygen in 1978

± Previously thought that VO2max at summitwould be just above rest

± Actually, VO2max estimated at 15mlkg-1min-1

Due to miscalculation of barometric pressure atsummit

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4900 Altitude