1
Q
Normoxia
A
Adequate supply of oxygen
2
Q
Hypoxia
A
Insufficient oxygen to main normal tissue function
3
Q
Hypoxemia
A
Low levels of oxygen in the arterial blood
4
Q
Anoxia
A
Absence of oxygen in the blood or tissue
5
Q
Hypobaric hypoxia
A
Barometric pressure decreases as altitude increases
6
Q
Normobaric hypoxia
A
Experimentally manipulate fraction of inspired O2 without manipulating barometric pressure
7
Q
Hypoxic hypoxia
A
Reduction in arterial PO2
8
Q
Examples of hypoxia hypoxia
A
High altitude
Hyperventilation
9
Q
Anemic hypoxia
A
Reduction in O2 carrying capacity of the blood
10
Q
Anemic hypoxia examples
A
Decreased RBC levels (hemorrhage)
Reduced hemoglobin concentration (anemia)
Reduced O2 binding capability of hemoglobin (carbon monoxide inhalation)
11
Q
Circulatory hypoxia
A
Decreased blood flow to tissues
12
Q
Circulatory hypoxia examples
A
Heart failure
Local vasoconstriction (cold)
13
Q
Histotoxic hypoxia
A
Inability of tissues to use distribution of electron transport chain in mitochondira
14
Q
Histotoxic hypoxia examples
A
Cyanide poisoning
15
Q
PIO2 equation
A
(PB- 47mmHg) x 0.2093
16
Q
Alveolar gas equation
A
(PAO2 - (PACO2/R) + F
17
Q
Alveolar ventilation equation
A
VCO2/ PACO2 x 0.863
18
Q
Flow equation
A
Pressure x conductance
19
Q
Cardiac output equation
A
MAP x Vascular conductance
MAP/ vascular resistance
20
Q
MAP equation
A
Cardiac output x vascular resistance
21
Q
What causes vasodilation?
A
Hypoxia
22
Q
What causes vasoconstriction?
A
Increased sympathetic nerve activity
23
Q
What decreases vascular resistance?
A
Hypoxia-mediated vasodilation stimulated by arterial O2
24
Q
What increases vascular resistance?
A
Sympathetically mediated vasoconstriction stimulated by arterial PO2
25
Pulmonary Vascular Physiological Responses
Hypoxic pulmonary vasoconstriction
Increase pulmonary artery pressure
26
High-altitude Pulmonary Edema
Pulmonary vasoconstriction
Pressure induced leak
Pulmonary edema
Clinical features of HAPE
27
What counteracts reduced O2 in hypoxia?
Greater ease of O2 offloading from Hb (smaller pressure gradient required to release O2)
28
Neurological responses to hypoxia
Hyperventilation
Brain blood flow is altered
Reduced tissue PO2 and decreased cerebral oxygenation (accelerates supraspinal fatigue)
29
Hyperventilation and hypocapnia relationship
Hyperventilation causes hypocapnia and decreases PACO2
30
Hypercapnia causes
Cerebrovascular vasodilation
31
Hypocapnia causes
Cerebrovascular vasoconstriction
32
Determinants of physiological responses to hypoxia
Degree of hypoxia
Individual variability
Physical activity
Temperature
Illness/disease
Drugs
33
Describe the first demonstration of the dangers of rapid high-altitude ascent
Zenith balloon ascent
Reached an altitude of 28,000 feet (8600 meters). Two never regained consciousness and died during, one survived to write about it but became deaf.
34
Why study hypoxia?
Aviation physiology
Military (airforce, navy)
Tourism
Railway and highway mountain passes
Rescue at high altitude
Shift work (mining, observations/telescopes)
35
How many people live at high altitude?
>1500m - greater than 500 million
>2500m - greater than 83 million
>3500m - greater than 14 million
36
Where has most high altitude research been done?
Climbing
Aviation
Male researchers testing each other
Women deemed "distractions" and high-altitude residents as "unintelligent"
37
Acclimatization
Physiological adjustments derived from exposure to a natural environment
38
Decrease in PAO2 causes?
Carotid body - increase ventilation - decrease PACO2 - back to beginning
39
What is essential for normal respiratory acclimatization?
Peripheral chemoreceptors (Carotid bodies)
Animals who have had their carotid bodies denervated fail to acclimatize properly (similar to humans with unilateral and/or bilateral resection of their carotid bodies)
40
Ventilatory response to exercise
Larger ventilatory response causes increase in climbing performance (however, there is a trade off at extreme altitude)
41
The most successful climbers had what response to hypoxia?
Smaller responses - because of lowered HVR, their ventilatory efficiency was higher.
42
Describe the trade off of high HVR
Useful at moderate altitudes, but at extreme altitudes the metabolic cost of excessive breathing is counterproductive.
43
Describe the ventilation process
Ventilation - pulmonary O2 diffusion - circulatory O2 delivery - muscle O2 diffusion - muscle O2 utilization - muscle ATP turnover
44
Alveolar to arterial PO2 causes
Thickening of the diffusion barrier, decrease in the surface area, breathing low O2 mix
45
Circulation changes with altitude
Cerebral circulation increases CBF on initial exposure
Hypoxic pulmonary vasoconstriction
Increased sympathetic outflow
Increased heart rate
Reduced stroke volume (due to reduced blood volume)
46
How many people does acute mountain sickness affect?
Up to 25% travellers to 2500m and 75% with rapid ascent to 5000m
47
When does AMS occur?
Within 6-48 hours of ascent
48
Symptoms of AMS
Headache and one of:
Malaise
Nausea
Vomitting
Anorexia
Light headedness/dizziness
49
What causes AMS?
Increase in intracranial pressure
50
How to minimize risk of AMS?
Slow, gradual ascent (let yourself acclimatize); no more than 300m higher/night above 3000m
Acetazolamide (diamox)
51
Acetazolamide effects
Produces metabolic acidosis and stimulates ventilation
52
What causes high-altitude cerebral edema?
Increased intracranial pressure
53
When does high-atltitude cerebral edema occur?
1-2 days after onset of AMS symptoms
54
Symptoms of high-altitude cerebral edema
Impaired level of consciousness
Hallucinations
Swelling of optic disk
55
Treatment for high-altitude cerebral edema
Medications (dexamethasone)
O2
Descent
56
When does high-altitude pulmonary edema occur?
24-72 hours after rapid ascent
57
Symptoms of high-altitude pulmonary edema
Breathlessness
Cough
Lung crackles
58
Treatment of high-altitude pulmonary edema
O2
Medications
Descent
59
High-altitude pulmonary edema impairs what?
Diffusion from alveoli to capillary
60
Function of the gamow bag
Generates internall pressure using 10-15 pumps/minute (2-3 with CO2 bladder)
61
How long must gamow bag be used?
1-2 hours for minimal treatment for AMS
4 hours for HAPE
6 hours for HACE
62
Aids to acclimatization
Climb high, sleep low
High carbohydrate diet
Guides pace - avoid overexertion
Avoid alcohol and sleeping medications
Pre-acclimatization strategies
63
The highest city in the world
La Rinconada
64
Arterial O2 content equation
Increased [Hb] x O2 saturation + dissolved O2
65
How many people does chronic mountain sickness effect?
~5-20% of high-altitude residents (Andean)
66
Chronic mountain sickness causes
Excessive erythrocytosis (Hb > 21)
Increased cardio and cerebral vascular risk
67
Outcomes from excessive erythrocytosis and chronic mountain sickness
Pulmonary hypertension
Right heart failure
Neurological problems
Increased cardiovascular risk
Mortality
68
Treatment for chronic mountain sickness
Descent (not always possible)
Bloodletting
Acetazolamide
Drugs that lower blood viscosity
69
Why is bloodletting not preffered?
RBC production can bounce back even worse than before
70
Describe benefits of the tibetan advantage compared to lowlanders
More effective breathing pattern
Increased lung diffusion capacity
Some cardiac and brain adaptations
Higher capillary density
Greater mitochondria
71
Describe "unairness" of olympic events
Western countries objected to "Training advantages" of Kenyans and Ethiopians (were competing and winning in international distance running)
Most people couldn't spend >4-6 weeks at altitude
72
Why altitude train?
Erogenic benefit of acclimatization
Hypoxic exercise > normoxic exercise
Variety (added stressor to boost ceiling in elite athletes)
73
Correlation and causation relationship
Correlation DOES NOT equal causation
74
VO2 max exercise at altitude
VO2 max remains reduced at high altitude, as well as reduced max cardiac output (reduced max heart rate and stroke volume)
75
Live high-train high
Acclimatization and hypoxic exercise
76
Live high - train low
Acclimatization
Environmental Physiology Final
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