Author(s): Louis D’Alecy, 2009

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3

O2 and CO2 Transport

M1 – Cardiovascular/Respiratory Sequence Louis D’Alecy, Ph.D.

Fall 2008

4

Tuesday 11/18/08, 9:00 O2 and CO2 Transport

35 slides, 50 minutes 1.  Describe the amount of oxygen dissolved and combined in blood. 2.  Define oxygen delivery to a tissue. 3.  Describe the characteristics of the oxygen-Hb saturation curve. 4.  Describe the shifts produced in the oxygen-Hb saturation curve. 5.  Describe the effects of anemia on oxygen content and PO2. 6.  State the three forms in which CO2 is carried in the blood. 7.  Describe the role of carbonic anhydrase in CO2 transport. 8.  Describe the chemical events associated with the

uptake and release of CO2. 9.  Defines chloride shift.

5

O2 content of blood = Dissolved + Hb bound O2

Liquid blood

Alveolar gas

Source Undetermined

6

How much gas is dissolved ?

A gas dissolves in a liquid in direct proportion to

its partial pressure and solubility.

“Henry’s Law”

7

Henry’s Law for O2

C d O = a O 2 P O 2

C d O 2 content of dissolved O2 mL/dL

a 2

solubility coefficient for O2 in blood =

=

= 0.0031 mL/mm Hg/dL a O 2

The content of dissolved oxygen is equal to the product of the oxygen solubility coefficient and oxygen partial pressure.

Linear straight line Relationship like

y = mx.

dL = 100 mL

8

Dissolved O2 At PO2 of 100 mmHg X 0.0031

you get 0.3 mL O2/dL dissolved oxygen in blood.

With cardiac output of 5000 ml/min or 50 dL/min you would deliver (50 dL X 0.3 mL/dL) or 15 mL O2/min.

BUT We consume 20 X that or 250 mL O2/min

so dissolved just will not do it!!

You need hemoglobin to bind and transport O2.

dL = 100 mL

9 Hemoglobin

Zephyris (wikipedia),

10

Air Air

RBC Hb-O2 bound + O2 dissolved

Not all Hb has O2

Plasma Dissolved only

D’Alecy

11

How much O2 is in blood?Concentration = Content

mL/dL = mL/100mL = Vol% (mL of O2 in 100 mL blood)

i.e. arterial blood has 20 Vol% O2

Content ≠ %Hb Saturation % Hb Saturation = O2 bound to Hb X 100%

O2 capacity of Hb

12

O2 content (with flow) determines O2 delivery.

So why do we talk about O2 saturation?

O2 Content ≠ %Hb Saturation

O2 saturation is relatively easier to measure and O2 content is much more difficult to measure.

We need to understand the differences!!!!

Thus O2 content is more important to O2 delivery than is O2 saturation.

13

Hb Saturation Curve

Normal Arterial Blood

~ 27 mmHg Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed.

14

Linear straight line relationship.

Most O2 combined. “% Hb Sat”

Or Sat

O2 C

onte

nt (m

L / 1

00m

L)

Source Undetermined

15

Different amounts of Hb but all 100% saturated !

Hb=10 Hb=15 Hb=20

Normal blood Hb = 15 gm/dL

O2 C

onte

nt (m

L / 1

00m

L)

HbO

2 Sat

urat

ion

(%)

Source Undetermined

16

DO

2 (cc

/m2 /m

in)

CI (L/m2 /min)

Anemia or Blood loss

Bartlett, Critical Care Physiology

17

i.e. ANEMIA

1. Decreased number of RBC

2. Decreased Hb content per RBC

Decreased Hb concentration so that % saturation can be normal (97-100%) but O2 content is decreased.

Normal blood Hb = 15 gm/dL

18

Breathing 100% O2.

Denver ? O2 bars?

O2 C

onte

nt (m

L / 1

00m

L)

Source Undetermined

19

Hemoglobin Bound Oxygen Content mL O2 /dL

C b O = S O 2

[ Hb ] Hb s 2

S O = % Hb saturation

[ Hb ] = hemoglobin content gm/dL blood

Hb s = saturated Hb O2 content mL O2 /gm Hb

Hb s = 1.36 mL O2 /gm Hb = O2 capacity

= O2 bound to Hb X 100% O2 capacity of Hb

20

Typical Arterial Blood Oxygen Content

O P 2 = 100 mm Hg S O 2

= 97% [ Hb ] = 15 gm/dL

C d O 2 a O 2

P O 2 = 0.0031 x 100 = 0.31 mL / dL

Dissolved O

Bound O

C b O = S O

2 [ Hb ] Hb

2 = 0.97 x 15 x 1.36 = 19.79 mL / dL

Total Oxygen Content

C d O 2 + C b O 2 = 0.31 + 19.79 = 20.1 mL / dL

=

s

21

673

100%

Bound CbO2 19.97 mL / dL 20.1

Dissolved CdO2 0.31 2.1

Total CO2 20.1 22.2

HbO

2 Sat

urat

ion

(%)

Source Undetermined

22

Breathing 100% O2

P a O 2 C a O 2

S O 2 mm Hg mL / dL %

Normal Hb 15 g/dl

Anemia Hb 7.5 g/dl

673 22 100

673 12 100

Breathing Room Air

Normal Hb 15 g/dl

Anemia Hb 7.5 g/dl

100 20 97

100 10 97

Thus breathing 100% O2 does not “fix” reduced oxygen transport capacity due to anemia.

Content

23

DO

2 (cc

/m2 /m

in)

CI (L/m2 /min)

Anemia or Blood loss

2X or 3X CO could compensate

Bartlett, Critical Care Physiology

24

pH on O2 Saturation of Hb

Acid unloads O2 from Hb (Bohr Effect) At any PO2 less O2 bound

Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed.

25

CO2 on O2 Saturation of Hb

CO2 unloads O2 from Hb (Bohr Effect) At any PO2 less O2 bound

Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed.

26

Temperature on O2 Saturation of Hb

Temperature unloads O2 from Hb At any PO2 less O2 bound

Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed.

27

2,3-BPG on O2 Saturation of Hb

More 2,3-BPG unloads O2 from Hb Lost in stored blood ~ canʼt unload O2

Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed.

28

Venous blood on O2 Saturation of Hb

Venous blood unloads O2 from Hb P50 is PO2 at 50% O2 saturation.

Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed.

29

right shift

(tissues)

↓ H+ ↓ CO2 ↓ temperature ↓ 2,3 BPG

left shift

(lungs)

At any PO2 less O2 bound.

At any PO2 more O2 bound.

Source Undetermined

30

O 2 Hb O 2

H Temperature CO

+

2

right shift

tissue metabolism

O2 is “unloaded” in tissues

D’Alecy

31

tissue ISF

plasma RBC

CO2 CO2 CO2 + H2O

H2CO3

HCO3- + H+

HbO2

O2 + HHb

C.A. = carbonic anhydrase

Cl-

O2 O2

Bohr shift

chloride Shifts in

In tissues O2 is “unloaded” from blood.

In tissues CO2 is “stored” in blood (for transport).

Buffer Action.

Source Undetermined

32

alveolus plasma RBC

CO2 CO2 CO2 + H2O

H2CO3

HCO3- + H+

HbO2

O2 + HHb

Cl-

O2 O2

Haldane shift

chloride Shift out

HCO3-

In lungs CO2 is “unloaded” from blood.

In lungs O2 is “stored” in blood.

C.A. = carbonic anhydrase

Source Undetermined

33

C d x = a x P x

C d x = dissolved gas content mL/dL

= 0.003 mL / mm Hg /dL a O 2

= 0.06 mL / mm Hg /dL a CO 2

How is CO2 Transported? CO2 is about 20 x more soluble than O2

But still only 5% (art.) to 10% (ven.) of transport is dissolved!! The content of dissolved gas (Cdx) is the product of the

solubility coefficient (ax) and the partial pressure of the gas (Px).

34

Most Some

H+ + Hb-NHCOO- = Hb + CO2 + H2O = H+ + HCO3-

Carbonic Anhydrase

Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed.

35

Reduced (de-ox)Hb binds more CO2 than HbO2

Source Undetermined

36 Source Undetermined

37

Reduced (de-ox)Hb binds more CO2 than HbO2 , venous blood can carry more CO2 then arterial blood.

Venous blood

Arterial blood

Venous

Arterial

Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed.

38

right shift

(tissues)

↓ H+ ↓ CO2 ↓ temperature ↓ 2,3 BPG

left shift

(lungs)

At any PO2 less O2 bound.

At any PO2 more O2 bound.

Source Undetermined

Slide 5: Source Undetermined Slide 9: GFDL, Zephyris (wikipedia), http://en.wikipedia.org/wiki/GNU_Free_Documentation_License Slide 10: D’Alecy Slide 13: Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed. Slide 14: Source Undetermined Slide 15: Source Undetermined Slide 16: Bartlett, Critical Care Physiology Slide 18: Source Undetermined Slide 21: Source Undetermined Slide 23: Bartlett, Critical Care Physiology Slide 24: Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed. Slide 25: Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed. Slide 26: Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed. Slide 27: Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed. Slide 28: Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed. Slide 29: Source Undetermined Slide 30: D’Alecy Slide 31: Source Undetermined Slide 32: Source Undetermined Slide 34: Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed. Slide 35: Source Undetermined Slide 36: Source Undetermined Slide 37: Levitzky. Pulmonary Physiology. McGraw-Hill, 2003. 6th ed. Slide 38: Source Undetermined

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