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Interpretation Standard: Reflects changes in Hb saturation with changes in P O 2 Variant: Changes in O2 content with changes in P O 2. Oxy-hemoglobin dissociation curve. Interpretation Standard: Reflects changes in Hb saturation with changes in P O 2 - PowerPoint PPT Presentation
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Oxy-hemoglobin dissociation curveOxy-hemoglobin dissociation curve
• Interpretation• Standard: Reflects changes in Hb saturation with changes in PO2
• Variant: Changes in O2 content with changes in PO2
Oxy-hemoglobin dissociation curveOxy-hemoglobin dissociation curve
• Interpretation• Standard: Reflects changes in Hb saturation with changes in PO2
• Variant: Changes in O2 content with changes in PO2
• Dynamics
100
80
60
40
20
020 40 60 80 100
%S
atu
rati
on
PO2 (mmHg)
P50
Temp, CO2 , 2-3 DPG; pH(favors unloading)
OxygenTransport
P50
Temp, CO2 , 2-3 DPG; pH(favors loading) Bohr Effect
Oxy-hemoglobin dissociation curveOxy-hemoglobin dissociation curve
• Interpretation• Standard: Reflects changes in Hb saturation with changes in PO2
• Variant: Changes in O2 content with changes in PO2
• Dynamics• Changes in position affect the tendency to load or unload oxygen: Bohr effect
Volume rate transfer(oxygen)
OxygenTransport
VO2 = D * A * (PcO2 - PtO2)
L2
• Lung 0.5-1.0 microns
• Skeletal Muscle 80 microns
• Brain 40 micronsdistance (L) can usually be decreased by recruitment
• Myocardium 12 microns(approximately one capillary per muscle cell)
At The Lung:• 70-80% of alveolar surface is covered by a single
cell layer of red blood cells
• Maximal capacity is ~200 ml blood• Normal blood volume in the capillaries is ~70 ml
• Alveolar-hemoglobin distance is 0.5 to 1.0 µm
• Capillaries cover several contiguous alveoli• capillaries travel ~600-800 µm before
joining a venule
• In a normal resting individual, it takes ~750 msec for an RBC to traverse a gas exchange section
Transit Time (msec)
0 250 500 750
PO
2 (m
mH
g)
0
50
100
Alveolar PO 2
NormalAbormal
Grossly abnormal
2Blood PO
Transit Time (msec)
0 250 500 750
PO
2 (m
mH
g)
0
50
100
Alveolar PO 2
Blood PO2
How about if transit time is decreased???
• Oxygen uptake by blood (at the lung) is normally considered perfusion-limited • The amount of oxygen taken up by blood at the lungs is
normally limited only by the rate of blood flow
• Oxygen uptake by tissue (from blood) is normally considered diffusion-limited• The amount of oxygen taken up by tissue from the blood
is normallly limited by diffusion characteristics (partial pressure gradient, distance)
PO2
0
50
100
OxygenTransport
OxygenTransport
100
0
50
PO2
Adequate
Rc
Critical
Anoxic
Inadequate
PO2
100
100
80
80
80
80
40
OxygenTransport
60
6060
PO2
100
5030
50100
30
20
20
100
Lethal Corner
OxygenTransport
2
Hb
Sat
ura
tion
(%
)100
80
60
40
20
0 20 40 60 80 100
P O (mmHg)
OxygenTransport
PO2
100
70
40
70
100
50
50
100
PO2
100
100
70
70
70
70
10
40
40
40 2
Hb
Sat
ura
tion
(%
) 100
80
60
40
20
0 20 40 60 80 100PO (mmHg)
No Bohr effect
Bohr effect
Oxy-hemoglobin dissociation curveOxy-hemoglobin dissociation curve
• Interpretation• Standard: Reflects changes in Hb saturation with changes in PO2
• Variant: Changes in O2 content with changes in PO2
• Dynamics• Changes in position affect the tendency to load or unload oxygen: Bohr effect
• Changes in shape usually reflect chemical alteration of the molecule
• Methemoglobin
• Thalessemias
• Carbon monoxide
OxygenTransport
SaO2 = 97
SaO2 = 62
(CO Hb=35%)O2 C
onte
nt
(ml O
2 /d
l blo
od)
0
20
16
12
8
4
PO2 (mmHg)20 40 60 80 100
Hypoxia: Inadequate tissue oxygenation
• At the lung: hypoxic hypoxia
• At the blood:• Anemia (reduced # RBCs or Hb)
• Carbon monoxide: left-shifted O2-Hb curve and decreased carrying capacity
• Hypoxemia due to hemoglobin mutation (thalassemia)
• Perfusion-related (stagnant hypoxia)
• Tissue level• Metabolic disorders
• Poisons
• Cyanide: inhibits oxidative phosphorylation
• Dinitrophenol: uncouples oxidative phosphorylation
• Carbon monoxide (cytochrome binding): prevents electron transfer to oxygen
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