Oxygen dissociation curve

ALL ABOUT OXYGEN AND CO2 DISSOCIATION CURVE

1. OXYGEN AND
CARBON DIOXIDE
TRANSPORT
-DR.DHAIRAL MEHTA

2. WHY IS IT IMPORTANT
TO KNOW???????

3. The normal protective response to hypoxia is reduced by
anaesthetic drugs and this effect extends into the post-operative
period.
Following induction of anaesthesia :
FRC ↓
V/Q mismatch is ↑ed
Atelectasis develops rapidly
This 'venous admixture' increases from N 1% to around 10%
following induction of anaesthesia.
Volatile anaesthetic agents suppress hypoxic pulmonary
vasoconstriction.
Many anaesthetic agents depress CO and therefore ↓ O2 delivery.
Anaesthesia causes a 15% ↓ in metabolic rate and therefore a
reduction in oxygen requirements.
Artificial ventilation causes a further 6% ↓ in oxygen requirements
as the work of breathing is removed.

4. O2 TRANSPORT
The oxygen transport system comprises the following consecutive
processes:
1.Mass transport from the environment to the pulmonary alveolar
spaces, powered by the contraction/relaxation cycling of the
respiratory muscles whose action is regulated mainly by the
medullary and pontine respiratory centers and peripheral
chemoreceptors.
2.Passive diffusion occurs across the alveolo-capillary membrane,
through the plasma and across the erythrocyte membrane finally
binding to hemoglobin ‘‘driven’’ by a partial-pressure gradient for
oxygen (pAO2 – paO2).
3.Mass transport from the alveolar capillaries and the heart
through the vascular distribution system to all systemic
capillaries,and return to the heart, powered by the
contraction/relaxation cycling of the myocardium, regulated by
the autonomic nervous system, various hormones,and other local
vascular regulatory functions affecting the distribution of blood
flow.

5. OXYGEN TRANSPORT
Carried in bld in 2 forms:
1.By red blood cells
 Bound to Hb.
 97-98%.
2.Dissolved O2 in plasma
Obeys Henry’s Law (“Amount of gas dissolved in a solution is
directly proprtional to its partial pressure”)
PO2 x α = O2 conc in sol
α = Solubility Coefficient (0.003mL/100mL/mmHg at 37C)
Low capacity to carry O2 i.e <2%.

6. OXYGEN TRANSPORT
Oxyhemoglobin Formation:
Oxygen + Hb  Oxyhemoglobin (Reversible)
When oxygen binds to haemoglobin, it forms
OXYHAEMOGLOBIN.
•In the lungs where the partial pressure of oxygen is high, the
reaction proceeds to the right forming Oxyhemoglobin.
•In the tissues where the partial pressure of oxygen is low, the
reaction reverses. OxyHb will release oxygen, forming
deoxyhemoglobin.

7. HAEMOGLOBIN
Haemoglobin molecules can
transport up to four O2’s
When 4 O2’s are bound to
haemoglobin, it is 100% saturated,
with fewer O2’s it is partially
saturated.
Oxygen binding occurs in
response to the high PO2 in the
lungs
Co-operative binding:
haemoglobin’s affinity for
O2 increases as its
saturation increases.

8. O
2
CONTENT OF THE BLOOD
It is the total amount of O
2
carried by blood.
= dissolved O
2
+ O
2
combined with Hb.
= 0.3 ml/100ml + 19.5 ml/100ml

= 19.8 ml/100 ml blood.
It depends mainly on the O
2
bound to Hb, as it represents
the main component.
Plasma (0.3 ml)Plasma (0.3 ml)Hb of RBCs (19.5 ml)Hb of RBCs (19.5 ml)
100 ml blood100 ml blood

9. O
2
CARRYING CAPACITY
OF THE BLOOD
It is the maximum amount of O
2
that can be carried by
Hb.
Each gram Hb, when fully saturated with O
2
, can carry
1.34 ml O
2
.
As Hb content = 15 gm/100 ml blood.
So, O
2
carrying capacity = 1.34 x 15

= 20.1 ml O
2
/100 ml blood.
100 ml blood100 ml blood
Hb = 15 gmHb = 15 gm
Each gm: 1.34 ml OEach gm: 1.34 ml O
22

10. THE PERCENT OF HB SATURATION
WITH O
2
(% HB SATURATION)-
It is an index for the extent to which Hb is
combined with O
2
.
O
2
bound to Hb
% Hb saturation = X 100
O
2
carrying capacity
When all Hb molecules are carrying their maximum O
2

load,
Hb is said to be fully saturated (100 % saturated).
PO
2
of the blood is the primary factor that determines %
Hb saturation.

11. THE OXYGEN DISSOCIATION CURVE(ODC)
Reveals the amount of Haemoglobin saturation
at different PO
2
values.

12. CHARACTERISTICS OF THE CURVE
Sigmoid Shaped Curve.
The amount of oxygen that is saturated on the
hemoglobin (SO2) is dependent on the amount
dissolved (PO2).
Amount of O2 carried by Hb rises rapidly upto
PO2 of 60mmHg(Steep Slope) but above that
curve becomes flatter(Flat Slope).
Combination Of 1st Heme with O2 increases
affinity of 2
nd
Heme for the 2
nd
O2 and so on. It is
known as “Positive Co-Operativity”.

13. THE OXYGEN DISSOCIATION CURVE
In the lungs the partial
pressure is approximately
100mm Hg at this Partial
Pressure haemoglobin has
a high affinity to 02 and
is 98% saturated.
In the tissues of other
organs a typical PO2 is
40 mmHg here
haemoglobin has a lower
affinity for O2 and
offloads O2 to the tissues.

14. The curve is S-shaped because each Hb molecule contains four
subunits;
each binding of O
2
to each subunit facilites the binding of the next
one.
 This combination of oxygen with hemoglobin is an example of
cooperativity,
Explanation
The globin units of DeoxyHb are tightly held by electrostatic bonds in
a conformation with a relatively low affinity for oxygen.
 The binding of oxygen to a heme molecule breaks some of these bonds
between the globin units, leading to a conformation change such that
the remaining oxygen-binding sites are more exposed.
Thus, the binding of one O
2
molecule to DeoxyHb increases the affinity
of the remaining sites on the same hemoglobin molecule, and so on.

15. THE UPPER FLAT (PLATEAU)
PART OF THE CURVE
POPO
22
%

H
b

s
a
t
u
r
a
t
i
o
n
%

H
b

s
a
t
u
r
a
t
i
o
n
1001006060
97 %97 %
90 %90 %
In the pulmonary capillaries (lung, POIn the pulmonary capillaries (lung, PO
22 range of 100-60 mmHg). range of 100-60 mmHg).
- At PO
2
100 mmHg 97% of Hb is saturated with O
2
.
- At PO
2
60 mmHg 90% of Hb is saturated with O
2
(small change in %
Hb saturation).

16. Physiologic significance:
- Drop of arterial PO
2
from 100 to 60 mmHg
little decrease in Hb saturation to 90 % which will
be sufficient to meet the body needs.
This provides a good margin of safety against blood
PO
2
changes in pathological conditions and in
abnormal situations.
- Increase arterial PO
2
(by breathing pure O
2
)

little increase in % Hb saturation (only 2.5%) and in
total O
2
content of blood.

17. THE STEEP LOWER PART
OF THE CURVE
POPO
22
%

H
b

s
a
t
u
r
a
t
i
o
n
%

H
b
s
a
t
u
r
a
t
i
o
n
1001006060
97 %97 %
90 %90 %
In the systemic capillaries (tissue, POIn the systemic capillaries (tissue, PO
22 range of 0-60 mm Hg). range of 0-60 mm Hg).
- At PO
2
40 mmHg (venous blood) 70% of Hb is saturated with
O
2
(large change in % Hb saturation).
At PO
2
20 mmHg (exercise) 30% of Hb is saturated with O
2
.
30 %30 %
70 %70 %
2020 4040

18. THE STEEP LOWER PART
OF THE CURVE
Physiologic significance:
- In this range, only small drop in tissue PO
2

rapid desaturation of Hb to release large amounts
of O
2
to tissues.
- If arterial PO
2
falls below 60 mmHg
desaturation of Hb occurs very rapidly
release of O
2
to the tissues.
This is important at tissue level.

19. THE “P50”
A common point of reference on the oxygen dissociation
curve is the P50.
The P50 represents the partial pressure at which the
hemoglobin is 50% saturated with oxygen, typically
26.6 mm Hg in adults.
The P50 is a conventional measure of hemoglobin
affinity for oxygen.
19

20. SHIFTS IN THE P50
In the presence of disease or other conditions that
change the hemoglobin’s oxygen affinity and,
consequently, shift the curve to the right or left, the
P50 changes accordingly.
An increased P50 indicates a rightward shift of
the standard curve, which means that a larger
partial pressure is necessary to maintain a 50%
oxygen saturation, indicating a decreased
affinity.
Conversely, a lower P50 indicates a leftward
shift and a higher affinity.
20

21. RIGHT SHIFT
Right shift decrease the loading of oxygen
onto Hb at the Alveolo-Capillary
membrane.
The total oxygen delivery may be much
lower than indicated by a particular Pao2
when the patient has some disease process
that causes a right shift.
Right shift curves enhance the unloading
of oxygen at the tissue level.
21

22. LEFT SHIFT
Left shift curves enhance the loading
capability of oxygen at the Alveolo-
Capillary membrane.
The total oxygen delivery may be higher
than indicated by a particular PaO2 when
the patient has some disease process that
cause a left shift.
Left shift curves decreases the unloading of
oxygen at the tissue level.
22

23. SHIFT TO THE LEFT
As In Pulmonary Capillaries
High pH
Decreased Temp.
Decreased Co2
Fetal Hb
Methaemoglobinemia
Increased Affinity Of Hb
To Oxygen –Less Release
Of Oxygen
SHIFT TO THE RIGHT
As In Placenta And
Muscles
Low pH
Increased Temp.
Increased CO
2
Increased 2,3 DPG
Decreased Affinity Of
Hb To Oxygen- More
Release Of Oxygen
From Hb
OO
XX
YY
GG
EE
NN
--
HH
BB
CC
UU
RR
VV
EE

24. FACTORS AFFECTING DISSSOCIATION
BLOOD TEMPERATURE
increased blood temperature
reduces haemoglobin affinity for O
2
hence more O
2
is delivered to warmed-up
tissue
Respiratory Response to Exercise
BLOOD pH
•lowering of blood pH (making blood
more acidic)
•caused by presence of H
+
ions from lactic
acid or carbonic acid
•reduces affinity of Hb for O
2
•and more O
2
is delivered to acidic sites
which are working harder
CARBON DIOXIDE CONCENTRATION
•the higher CO
2
concentration in tissue
•the less the affinity of Hb for O
2
•so the harder the tissue is working, the
more O
2
is released

26. Bohr's Effect
The Bohr effect is a physiological phenomenon first
described in 1904 by the Danish physiologist Christian
Bohr, stating that the “oxygen binding affinity of Hb
is inversely related to the concentration of carbon
dioxide & H
+
concentration.”
- At tissues: Increased PCO
2
& H
+
conc. shift of O
2
-Hb
curve to the
right.
-
At lungs: Decreased PCO
2
& H
+
conc. shift of O
2
-Hb
curve to the
left.
So, Bohr's effect facilitates -
i)O
2
release from Hb at tissues.
ii)O
2
uptake by Hb at lungs.

27. ROLE OF 2,3-DPG
(DiPhosphoGlycerate):
•2,3 DPG is an
organic phosphate
normally
found in the RBC.
•Produced during
Anaerobic
glycolysis in
RBCS.

28. CONTD..
2,3 DPG has a tendency to bind to β chains
of Hb and thereby decrease the affinity of
Hemoglobin for oxygen.
HbO2 + 2,3 DPG → Hb-2,3 DPG +
O2
It promotes a rightward shift and
enhances oxygen unloading at the tissues.
This shift is longer in duration than that
due to [H+] or PCO2 or temperature.

29.  The levels increase with:
Cellular hypoxia.
Anemia
Hypoxemia secondary to
COPD
Congenital Heart Disease
 Ascent to high altitudes
The levels decrease with:
 Septic Shock
 Acidemia
 Stored blood has No
DPG after 2 weeks of
storage.
In banked blood,the 2,3-
BPG level falls and the
ability of this blood to
release O2 to the tissues
is reduced.

30. FACTORS AFFECTING ODC

31. MYOGLOBIN
Myoglobin is single
chained heme pigment
found in skeletal
muscle.
Myoglobin has an
increased affinity for
O2 (binds O2 at lower
Po2)
Mb stores O2
temporarily in muscles
& acts as a reserve in
muscles, which can be
used during exercise.

32. O
2
Dissociation Curve Of Myoglobin
One molecule of myoglobin has one ferrous atom (Hb has 4 ferrous
atoms).
One molecule of myoglobin can combine with only one molecule of
O
2
.
The O
2
–myoglobin curve is rectangular in shape and to the left of the
O
2
-Hb dissociation curve.

So, it gives its O
2
to the tissue at very low PO
2
.

So, it acts as O
2
store used in severe muscular exercise when PO
2

becomes very low.

33. O
2
Dissociation Curve Of Fetal Hb
Fetal Hb (HbF) contains 2a and 2g polypeptide chains and has no b
chain which is found in adult Hb (HbA).

So, it cannot combine with 2, 3 DPG that binds only to b chains.

So, fetal Hb has a dissociation curve to the left of that of adult Hb.
So, its affinity to O
2
is high increased O
2
uptake by the
fetus from the mother.

34. FETAL HAEMOGLOBIN

35. •
EFFECTS OF ANEMIA & CARBON MONOXIDE ON
THE OXYGEN DISSOCIATION CURVE
↓O2 content.
SaO2remains normal
Carbon Monoxide [CO]
affinity of Hb for CO is 250
fold relative to O2 competes
with O2 binding
 L shift- interfere with O2
unloading at tissues causing
severe tissue hypoxia.
Sigmoidal HbO2 curve
becomes Hyperbolic.

36. HAEMOGLOBIN SATURATION AT HIGH
ALTITUDES
Lungs at sea level:
PO2 of 100mmHg
haemoglobin is 98%
SATURATED
Lungs at high
elevations: PO2
of 80mmHg,
haemoglobin 95
% saturated
At pressures above
60mm Hg, the standard
dissociation curve is
relatively flat.
This means the oxygen
content does not change
significantly even with
large changes in the
partial pressure of
oxygen.

37. HAEMOGLOBIN SATURATION DURING EXERCISE

38. DURING EXERCISE
There will be:
Decreased PO
2
in capillaries of active muscles.
Increased temperature in active muscles.
Increased CO
2

Decreased pH due to acidic metabolites.
Increased 2, 3 DPG in RBCs by anaerobic glycolysis.
All these factors lead to:
Shift of O
2
-Hb dissociation curve to the right.
Decrease affinity of Hb to O
2
.
More release of O
2
to tissues.

39. CARBON DIOXIDE
TRANSPORT

40. CARBON DIOXIDE TRANSPORT
Once carbon dioxide is released from the cells, it
is carried in the blood primarily in three ways..
Dissolved in plasma.
As bicarbonate ions resulting from the
dissociation of carbonic acid.
Bound to haemoglobin.

41. When CO
2
molecules diffuse from the tissues
into the blood
7% remains dissolved in plasma
23% combines in the erythrocytes with
deoxyhemoglobin to form carbamino
compounds.
70% combines in the erythrocytes with water
to form carbonic acid, which then dissociates
to yield bicarbonate and H
+
ions.

42. MOST CO2 TRANSPORTED
AS BICARBONATE (HCO 3
-
)*

43. CHLORIDE SHIFT AND
REVERSE CHLORIDE SHIFT
Most of the bicarbonate then moves out of the
erythrocytes into the plasma in exchange for Cl
-
ions &
the excess H
+
ions bind to deoxyhemoglobin,known as
Chloride Shift.
The reverse occurs in the pulmonary capillaries and
CO
2
moves down its concentration gradient from blood
to alveoli,known as Reverse Chloride Shift.
Hematocrit of venous blood is 3%>arterial
 Venous RBC are more fragile
 Cl content of RBCs V>A

44. CHLORIDE SHIFT
PHENOMENON
It is the movement of Cl
-
in exchange with HCO
-
3
across
RBC membrane.
It is responsible for carrying most of the tidal CO
2
in
the bicarbonate form.
It prevents excessive drop of blood pH.

45. TissueTissue
RBCRBC
PlasmaPlasma
HCOHCO
--
33
+ + HH
22OO
Plasma Plasma
proteinsproteins
HbHb
CACA
COCO
22
ClCl
--
HH
22OO
COCO
22 HCOHCO
33 +H +H
++
HH
22COCO
33
COCO
22 + + HH
22OO HH
22COCO
33 HCOHCO
33 +H +H
++
ClCl
--
HH
22OO
HbOHbO

46. CHLORIDE SHIFT
PHENOMENON
Mechanism:
-CO
2
entering the blood diffuses into RBCs rapidly
hydrated to H
2
CO
3
in the presence of the carbonic anhydrase
enzyme.
-H
2
CO
3
dissociates into H
+
and HCO
-
3
.
-H
+
is buffered by the reduced (not oxygenated) Hb.
-HCO
-
3
concentration in RBCs increases.
-some of the HCO
-
3
diffuses out to the plasma.
-In order to maintain electrical neutrality, chloride ions
(Cl
-
) migrate from the plasma into the red cells.

47. CHLORIDE SHIFT
PHENOMENON
Net effect:
-Increased HCO
-
3
in both the RBCs and plasma.
-Increased Cl
-
inside the RBCs.
-Increased osmotic pressure inside RBCs
water shift from the plasma.
-Increase RBCs volume increase in the
hematocrit value.
-Buffering of the tidal CO
2
with very little change in
the pH.

48. REVERSE CHLORIDE SHIFT
PHENOMENON
 It is the movement of Cl
-
in exchange with HCO
-
3

across RBC membrane.
It is responsible for removal of the tidal CO
2
by lungs.

49. Lung Lung
alveolialveoli
RBCRBC
PlasmaPlasma
HCOHCO
--
33
Carbamino Carbamino
proteinsproteins
COCO
22
COCO
22
ClCl
--
HH
22OO
COCO
22
COCO
22HbHb COCO
22
+ + HH
22OO
HH
22COCO
33 HCOHCO
33 +H +H
++
ClCl
--
HH
22OO

50. CARBON DIOXIDE DISSOCIATION CURVE
Carbon dioxide
dissociation curves
relate PaCO2 to the
amount of
carbon dioxide carried
in blood

51. Lower the saturation of
Hb with O2 , larger the
CO2 conc for a given
PaCO2.
CO2 curve is shifted to
right by increase in
SpO2

52. GRAPH ILLUSTRATES THE
DIFFERENCE
BETWEEN THE CONTENT IN BLOOD
OF
OXYGEN AND CARBON DIOXIDE
WITH
CHANGE IN PARTIAL PRESSURE
•CO2 content rises throughout
the increase in partial
pressure.
• O2content rises more steeply
until a point at which the hb is
fully saturated. After that, the
increase is small because of
the small increased amount in
solution.
• Consequently, the CO2 curve
is more linear than the O2Hb
dissociation curve.

53. Deoxygenation of Hb
­ qty of CO2 bound to
Hb.
For any given PCO
2
,
the blood will hold
more CO
2
when the
PO
2
has been
diminished.
Reflects the tendency
for an increase in PO
2

to diminish the affinity
of hemoglobin for CO
2
.
HALDANE EFFECT

54. Combination of oxygen with hemoglobin in the lungs
causes the hemoglobin to become a stronger acid.
Therefore:
1)The more highly acidic hemoglobin has less
tendency to combine with CO
2
to form CO
2
Hb
2)The increased acidity of the hemoglobin also
causes it to release an excess of hydrogen ions thus
causing a further rise in the ph and decreased
tendency of CO2 to combine with hemoglobin in
the presence of oxygen.
MECHANISM OF HALDANE EFFECT

55. Haldane effect

56. DIFFERENCES BETWEEN
BOHR’S AND HALDANE’S
EFFECT
BOHR’S EFFECT
1.It is the effect by
which the presence of
CO2 decreases the
affinity of Hb for O2
HALDANE EFFECT
1.It is the effect by which
combination of O2 with Hb
displaces CO2 from Hb

57. 2. Was postulated by Bohr
in 1904.
3. Occurs at tissues and
systemic capillaries.
4. In tissues, body
metabolism causes
↑PCO2(45 mmHg) &
↓ PO2(40mmHg) with
respect to arterial
PCO2 and PO2.
2. Described by John Scott
Haldane in 1860.
3. Occurs at alveolar and
pulmonary capillaries.
4. In lungs,
Hb+O2HbO2
HbO2 has low tendency
to combine with CO2.

58. CO2 enters the blood
and O2 released from
blood to tissues..
Shifting O2
disosiciation curve to
right and unloading
O2 to the tissues.
O2+HbH+ and CO2

H+ + HCO3-
H2CO3H2O
+CO2..
CO2 is thus released
from blood to alveoli to
be expelled out.

59. SUMMARY
Bohr's effect:
- Increased CO
2
decrease the affinity of Hb to O
2
shift of O
2
-Hb dissociation curve to the right.
Haldane effect:
- Increased O
2
decrease the affinity of Hb to CO
2

(because binding of O
2
with Hb displacement of CO
2

from the blood).
 The presence of O
2
or CO
2
carried by Hb interferes
with the carriage of the other gas.