transport of o2 and co2

8/2/2019 Transport of O2 and CO2

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Oxygen and Carbon Dioxide

Transport in the BloodMichael Donahoe MD

www.pitt.edu/~paccm/medicalstudent.htm


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Partial pressure

Index of molecular motion of a gas

Diffusion of a gas is proportional to the

pressure gradient


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O2CO

2

O2 CO2


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Oxygen Transport

Dissolved oxygen

Linear relationship

0.003 ml 02 / 100 ml blood x P02 Chemical combination with Hg

Non - linear relationship

1.34 ml 02 / 100 ml blood x Hgb x % sat


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PO2% sat of

Hgb

02 with

Hgb

dissolved

O2

10.0 13.5 2.7 0.0320.0 35.0 7.0 0.06

30.0 57.0 11.5 0.09

40.0 75.0 15.1 0.12

50.0 83.5 16.8 0.15

60.0 89.0 17.9 0.18

70.0 92.7 18.6 0.21

80.0 94.5 19.0 0.24

90.0 96.5 19.4 0.27

100.0 97.4 19.6 0.30


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Saturation

Calculated ml O2 combined with Hgb x 100maximum ml O2 combined with Hgb

Measured


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PaO2 vs SaO2

Physiological significance

Clinical significance


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PaO2 vs SaO2

Oxygen diffusion (PaO2)

Lung (A-a)

Tissues Oxygen transport (SaO2)

Arterial oxygen content

Venous oxygen content


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Oxygen Transport

Arterial oxygen content (CaO2 ml/dL) Hgb associated O2 + dissolved O2

Arterial oxygen delivery (DO2) CaO2 x cardiac output (CO)


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Arterial oxygen content (CaO2) ml/dL

Hgb associated O2 +

dissolved O2

(A-a) Gradient

Arterial oxygen delivery (DO2) ml/min

CaO2 xcardiac output (CO)

Venous oxygen content (CvO2) ml/dL

Hgb associated O2 +

dissolved O2

Venous oxygen delivery (DO2) ml/min

CvO2 x

cardiac output (CO)

V02

PAO2

PaO2


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Tissue oxygen uptake (V02)

V02 = {(CaO2) - (CvO2)} CO

Arterial oxygen content (CaO2) Hgb associated O2 + dissolved O2

Venous oxygen content (CvO2) Hgb associated O2 + dissolved O2


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Arterial oxygen content (CaO2) = 19.5 ml/dL

15 gms/dl x 1.34 ml O2 /gm x 96%

91 x 0.003

Arterial oxygen delivery (DO2) = 1000 ml/min

19.5 ml / dL x 50 dL / min

Venous oxygen content (CvO2) = 15 ml/dL

15 gms/dl x 1.34 ml/gm x 70%

40 x 0.003

Venous oxygen delivery (DO2) = 750 ml / min

15 gms/dl x 1.34 ml O2/gm x 70% x50 dL / min

V02 = 250 ml/min

8

99

91


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DO2

PaO2(mm Hg)

SaO2(%)

Hgb(gms/dl)

CO(dl/min)

DO2(ml/min)

100 100 15 50 1020


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DO2

PaO2(mm Hg)

SaO2(%)

Hgb(gms/dl)

CO(dl/min)

DO2(ml/min)

100 100 15 50 1020

50 87 15 50 882


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DO2

PaO2(mm Hg)

SaO2(%)

Hgb(gms/dl)

CO(dl/min)

DO2(ml/min)

100 100 15 50 1020

50 87 15 50 882

100 100 7.5 50 518


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DO2 (Oxygen Delivery)

PaO2(mm Hg)

SaO2(%)

Hgb(gms/dl)

CO(dl/min)

DO2(ml/min)

100 100 15 50 1020

50 87 15 50 882

100 100 7.5 50 518

100 100 15 25 510


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O2 Stores

Oxygen Stores

Lung 400 ml

Hemoglobin 850 ml

Oxygen Utilization

Tissues 250 ml / min


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Carbon Dioxide Transport

Diffusion of CO2 from tissue cells

Chemical reactions in the plasma

Chemical reactions in the erythrocyte


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Plasma (minor)

Dissolved (0.067 ml CO2 * pCO2)

Hydration

H2O + CO2 H2CO3 H+ + HCO3

-

Reaction with plasma proteins (carbamino cmpds)


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Erythrocyte (major)

Dissolved

Hydration


-

(H+ buffered by Hgb / 02 unloaded = Bohr)

Reaction with NH2 groups of Hg to form

carbamino groups R- NH2 + CO2 R- NHCOO

- + H+


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Bohr Effect

H2O + CO2 H+ + HCO3

-

H+ binds to Hgb

Hgb and H+ = Reduces Hgb O2 Affinity

Haldane Effect

Unoxygenated Hgb favors CO2 + Hgb tocarbamino compounds


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Gas Transport

Haldane

Hgb Hb + O2

Better buffer

Promotes carbamino compounds

Bohr


-

Unloads O2


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Gas Transport

Haldane

Oxygen saturation influences CO2 content

Bohr CO2 content influences O2 saturation


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CO2 Stores

Carbon Dioxide Stores (> 100 liters)

Dissolved (plasma and RBC)

HCO3

- plasma, cells, interstitial fluid

Bone

Carbon Dioxide Production

Tissues 200 ml / min


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O2CO

2

O2 CO2

transport of o2 and co2

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