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3 O 2 and CO 2 Transport M1 – Cardiovascular/Respiratory Sequence Louis D’Alecy, Ph.D. Fall 2008

4 Tuesday 11/18/08, 9:00 O 2 and CO 2 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 PO 2. 6.State the three forms in which CO 2 is carried in the blood. 7.Describe the role of carbonic anhydrase in CO 2 transport. 8.Describe the chemical events associated with the uptake and release of CO 2. 9.Defines chloride shift.

5 O 2 content of blood = Dissolved + Hb bound O 2 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 O 22 C d O = a O 2 P O 2 C d O 2 content of dissolved O 2 mL/dL a O 2 solubility coefficient for O 2 in blood = = = 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 O 2 At PO 2 of 100 mmHg X you get 0.3 mL O 2 /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 O 2 /min. BUT We consume 20 X that or 250 mL O 2 /min so dissolved just will not do it!! You need hemoglobin to bind and transport O 2. dL = 100 mL

9 Hemoglobin Zephyris (wikipedia),

10 Air RBC Hb-O 2 bound + O 2 dissolved Not all Hb has O 2 Plasma Dissolved only D’Alecy

11 How much O 2 is in blood? Concentration = Content mL/dL = mL/100mL = Vol% (mL of O 2 in 100 mL blood) i.e. arterial blood has 20 Vol% O 2 Content ≠ %Hb Saturation % Hb Saturation = O 2 bound to Hb X 100% O 2 capacity of Hb

12 O 2 content (with flow) determines O 2 delivery. So why do we talk about O 2 saturation? O 2 Content ≠ %Hb Saturation O 2 saturation is relatively easier to measure and O 2 content is much more difficult to measure. We need to understand the differences!!!! Thus O 2 content is more important to O 2 delivery than is O 2 saturation.

13 Hb Saturation Curve Normal Arterial Blood ~ 27 mmHg Levitzky. Pulmonary Physiology. McGraw-Hill, th ed.

14 Linear straight line relationship. Most O 2 combined. “% Hb Sat” Or Sat O 2 Content (mL / 100mL) Source Undetermined

15 Different amounts of Hb but all 100% saturated ! Hb=10 Hb=15 Hb=20 Normal blood Hb = 15 gm/dL O 2 Content (mL / 100mL) H b O 2 Saturation (%) Source Undetermined

16 DO 2 (cc/m 2 /min) CI (L/m 2 /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 O 2 content is decreased. Normal blood Hb = 15 gm/dL

18 Breathing 100% O 2. Denver ? O 2 bars? O 2 Content (mL / 100mL) Source Undetermined

19 Hemoglobin Bound Oxygen Content mL O 2 /dL C b O = S O 2 [ Hb ] Hb s 2 S O 2 = % Hb saturation [ Hb ]= hemoglobin content gm/dL blood Hb s = saturated Hb O 2 content mL O 2 /gm Hb Hb s = 1.36 mL O 2 /gm Hb = O 2 capacity = O 2 bound to Hb X 100% O 2 capacity of Hb

20 Typical Arterial Blood Oxygen Content O P 2 = 100 mm HgS O 2 = 97%[ Hb ] = 15 gm/dL C d O 2 a O 2 P O 2 = x 100 = 0.31 mL / dL Dissolved O 2 Bound O 2 C b O = S O 2 [ Hb ] Hb 2 = 0.97 x 15 x 1.36 = mL / dL Total Oxygen Content C d O 2 + C b O 2 = = 20.1 mL / dL = s

% O 2 breathing 100% O 2 100% Bound Cb O mL / dL 20.1 Dissolved Cd O Total C O H b O 2 Saturation (%) Source Undetermined

22 Breathing 100% O 2 P a O 2C a O 2 S O 2 mm HgmL / dL % Normal Hb 15 g/dl Anemia Hb 7.5 g/dl Breathing Room Air Normal Hb 15 g/dl Anemia Hb 7.5 g/dl Thus breathing 100% O 2 does not “fix” reduced oxygen transport capacity due to anemia. Content

23 DO 2 (cc/m 2 /min) CI (L/m 2 /min) Anemia or Blood loss 2X or 3X CO could compensate Bartlett, Critical Care Physiology

24 pH on O 2 Saturation of Hb Acid unloads O 2 from Hb (Bohr Effect) At any PO 2 less O 2 bound Levitzky. Pulmonary Physiology. McGraw-Hill, th ed.

25 CO 2 on O 2 Saturation of Hb CO 2 unloads O 2 from Hb (Bohr Effect) At any PO 2 less O 2 bound Levitzky. Pulmonary Physiology. McGraw-Hill, th ed.

26 Temperature on O 2 Saturation of Hb Temperature unloads O 2 from Hb At any PO 2 less O 2 bound Levitzky. Pulmonary Physiology. McGraw-Hill, th ed.

27 2,3-BPG on O 2 Saturation of Hb More 2,3-BPG unloads O 2 from Hb Lost in stored blood ~ can’t unload O 2 Levitzky. Pulmonary Physiology. McGraw-Hill, th ed.

28 Venous blood on O 2 Saturation of Hb Venous blood Venous blood unloads O 2 from Hb P 50 is PO 2 at 50% O2 saturation. Arterial blood Levitzky. Pulmonary Physiology. McGraw-Hill, th ed.

29 right shift (tissues)  H + (Bohr shift)  CO 2  temperature  2,3 BPG   H +  CO 2   temperature   2,3 BPG left shift (lungs) Summary At any PO 2 less O 2 bound. At any PO 2 more O 2 bound. Source Undetermined

30 O 2 HbO 2 H Temperature CO + 2 right shift tissue metabolism O 2 is “unloaded” in tissues D’Alecy

31 tissue ISF plasma RBC CO 2 + H 2 O H 2 CO 3 HCO H + HbO 2 O2O2 + HHb C.A. = carbonic anhydrase Cl - O2O2 O2O2 Bohr shift chloride Shifts in In tissues O 2 is “unloaded” from blood. In tissues CO 2 is “stored” in blood (for transport). Buffer Action. Source Undetermined

32 alveolus plasma RBC CO 2 + H 2 O H 2 CO 3 HCO H + HbO 2 O2O2 + HHb Cl - O2O2 O2O2 Haldane shift chloride Shift out HCO 3 - In lungs CO 2 is “unloaded” from blood. In lungs O 2 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 CO 2 Transported? CO 2 is about 20 x more soluble than O 2 But still only 5% (art.) to 10% (ven.) of transport is dissolved!! The content of dissolved gas (C dx ) is the product of the solubility coefficient (a x ) and the partial pressure of the gas (P x ).

34 Most Some H + + Hb-NHCOO - = Hb + CO 2 + H 2 O = H + + HCO3 - Carbonic Anhydrase Levitzky. Pulmonary Physiology. McGraw-Hill, th ed.

35 Reduced (de-ox)Hb binds more CO 2 than HbO 2 Source Undetermined

36 Source Undetermined

37 Reduced (de-ox)Hb binds more CO 2 than HbO 2, venous blood can carry more CO 2 then arterial blood. Venous blood Arterial blood Venous Arterial Levitzky. Pulmonary Physiology. McGraw-Hill, th ed.

38 right shift (tissues)  H + (Bohr shift)  CO 2  temperature  2,3 BPG   H +  CO 2   temperature   2,3 BPG left shift (lungs) Summary At any PO 2 less O 2 bound. At any PO 2 more O 2 bound. Source Undetermined

Slide 5: Source Undetermined Slide 9: GFDL, Zephyris (wikipedia), Slide 10: D’Alecy Slide 13: Levitzky. Pulmonary Physiology. McGraw-Hill, th 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, th ed. Slide 25: Levitzky. Pulmonary Physiology. McGraw-Hill, th ed. Slide 26: Levitzky. Pulmonary Physiology. McGraw-Hill, th ed. Slide 27: Levitzky. Pulmonary Physiology. McGraw-Hill, th ed. Slide 28: Levitzky. Pulmonary Physiology. McGraw-Hill, th ed. Slide 29: Source Undetermined Slide 30: D’Alecy Slide 31: Source Undetermined Slide 32: Source Undetermined Slide 34: Levitzky. Pulmonary Physiology. McGraw-Hill, th ed. Slide 35: Source Undetermined Slide 36: Source Undetermined Slide 37: Levitzky. Pulmonary Physiology. McGraw-Hill, th ed. Slide 38: Source Undetermined Additional Source Information for more information see: