the lungs in special situations
TRANSCRIPT
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Aviation and High Altitude
Physiology
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Composition of AtmosphericGases
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Barometric Pressures
Barometric pressure at sea level is 760mm Hg
As altitude increases, barometric pressuredrops while partial pressure of oxygenremains at 21% PO 2 at sea level is about 159 mm Hg while at
50,000 feet is only 18 mm Hg
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Partial Pressures of O2 andCO2
020
406080
100120140160180
Air Trachea Alveoli Tissues Cells
Oxygen Carbon Dioxide
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Alveolar PO 2 at Different Elevations
CO 2 and water vapor decrease alveolaroxygen Vapor pressure in the alveoli remain at 47 mm
Hg regardless of altitude CO 2 decreases in higher altitudes due to
hyperventilation, more so in the acclimatized
individual
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Alveolar PO 2 at Different Altitudes
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Effect on high altitude on O2saturation
0 10 20 30 40 50
50
60
70
80
90
100
Altitude (thousands of feet)
A r t e r i a
l o x y g e n s a
t u r a
t i o n
( p e r c e n
t )
Pure oxygen
Breathing air
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Acute Effects of Hypoxia
At 12,000 feet drowsiness, lassitude,mental and muscle fatigue, headache,nausea, sometime euphoria
At 18,000 feet twitching or seizures At 23,000 feet coma followed shortly by
death
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Acclimatization
Hypoxia is the primary physiological insulton ascent to high altitude
The response to hypoxia depends on boththe magnitude and the rate of onset ofhypoxia
The process of adjusting to hypoxia,termed acclimatization, is a series ofcompensatory changes in multiple organsystems over differing time courses fromminutes to weeks
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Acclimatization
Most important immediate response of thebody to hypoxia is an increase in minuteventilation Increased ventilation = higher alveolar PO 2 Lowered alveolar PCO 2 = respiratory alkalosis Renal compensation, through excretion of
bicarbonate ion, gradually brings the blood pHback toward normal and allows furtherincrease in ventilation
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Acclimatization
Ventilatory acclimatization requires 4 days Enhanced by acetazolamide
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Acclimatization
Circulatory changes increase delivery ofO2 to tissues Increase HR, CO, BP Pulmonary vasoconstriction to improve VQ Increase in cerebral blood flow Increase in RBC and Hgb concentration Alkalosis causes left shift of O2-Hgb curve
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Natural Acclimatization
Acclimatization begins at infancy Chest size is increased, body size somewhat
decreased, larger right heart Delivery of oxygen is also greatly facilitated
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Work Capacity at High Altitudes
Capacity of all muscles is greatlydepressed in hypoxia, including cardiacmuscle
Acclimatized individuals can perform morework at high altitudes
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Acute Mountain Sickness
Nonspecific symptoms with a broadspectrum of severity
Occurs in non-acclimatized persons in thefirst 48 h after ascent to altitudes above2500 m, especially after rapid ascent (1 dor less)
Exact cause is unknown but cerebraledema may play a role
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Chronic Mountain Sickness
RC mass and hct become very high Blood becomes very viscous
Pulmonary arterial pressure becomeselevated Alveolar hypoxia
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Chronic Mountain Sickness
Right side of the heart becomes greatlyenlarged
Peripheral arterial pressure begins to fall Congestive heart failure Death ensues unless moved to lower
altitude
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Physiology of Deep Sea Diving
and Other Hyperbaric Conditions
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Hyperbarism exposure of blood in thelungs to extremely high alveolar gaspressures
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Sea Depth to Pressure
Depth (feet)
Sea Level3366
100133166200300400500
Atmosphere(s)
1234567
101316
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Effect on Depth on Volume Boyles Law
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Henrys Law
The Henry law states that the solubility ofa gas in a liquid is directly proportional tothe pressure exerted upon the gas andliquid
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Effect on High Partial Pressures onGases on Body
Gases which a diver breathes is nitrogen,oxygen, and carbon dioxide
Nitrogen narcosis at high nitrogenpressures Varying degrees of narcosis at high pressures 1 st symptoms of mild narcosis appear at 120
feet for 1 hour exhibits joviality At 150 to 200 feet, diver becomes drowsy At 200 to 250 feet, too clumsy
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Effect on High Partial Pressureson Gases on Body
Nitrogen narcosis at high nitrogenpressures Characteristics similar to alcohol intoxication Narcotic effect is same as gas anesthetics Nitrogen dissolves freely in the fats of the
body
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Oxygen Toxicity at High Pressures
Effect of extremely high PO 2 on bloodoxygen transport
Effect of high alveolar PO 2 on tissue PO 2 Acute oxygen poisoning
Brain mostly affected cause seizuresfollowed by coma at 4 atm within 30 to 60minutes
Nausea, muscle twitching, dizziness,disturbance of vision, irritability anddisorientation
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Oxygen Toxicity at High Pressures
Excessive intracellular oxidation as thecause of nervous system oxygen toxicity oxidizing free radicals O 2 has little capability oxidizing other chemical
compounds must be active Oxygen free radicals (superoxide O 2-)
Tissues contain enzymes that remove freeradicals (peroxidases, catalases, superoxidedismutases)
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Decompression After Exposure toHigh Pressures
Amount of nitrogen dissolved in bodybecomes great after a person breathes airunder high pressure Blood flowing thru capillaries becomes
saturated with nitrogen saturate tissues not metabolized
When pressure in the lungs normalizes,nitrogen is removed but slowly
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Decompression After Exposure toHigh Pressures
Volume of nitrogen dissolved in body fluidsat different depths At sea level 1L of nitrogen is dissolved in the
body (half in water, half in fat) At 33 feet 2L of N 2 are dissolved, at 100 feet,
4L are dissolved
Water equilibrates in 1 hour while fat takesseveral hours to equilibrate
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Decompression sickness (Bends,Caisson Disease)
If a diver has been beneath the sea longenough and ascends rapidly,decompression sickness develops
Gas forms bubbles due to suddendecompression of gasses
Symptoms depend on where bubblesdislodge (joints, nervous system,pulmonary capillaries)
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Nitrogen Elimination
Decompression tables Tank decompression
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Treatment
Decompression tank
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Helium Oxygen in Deep Dives
Divers working at deep levels between250 to 1000 feet use helium-oxygenmixtures
Helium used due to: One fifth narcotic effects of nitrogen One half as much volume dissolves in tissues Low density of helium
Use 1 percent oxygen mixtures
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Hyperbaric Oxygen Therapy
Oxidizing free radicals responsible foroxygen toxicity are also responsible fortherapeutic benefits Treatment of gas gangrene leprosy