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