2. 1 Section II Respiratory Gases Exchange

3. 2

4. 3 I Physical Principles of Gas Exchange

5. 4 Partial pressure –The pressure exerted by each type of gas in a mixture Diffusion of gases through liquids –Concentration of a gas in a liquid is determined by its partial pressure and its solubility

6. 5 Partial Pressures of Gases Basic Composition of Air 79% Nitrogen 21 % Oxygen ~ 0% Carbon Dioxide In a mixture of gases, each gas exerts a partial pressure proportional to its mole fraction. Total Pressure = sum of the partial pressures of each gas P gas = P b x F gas P N = 760 x 0.79 = 600.4 mm Hg P 0 2 = 760 x 0.21 = 159.6 mm Hg Total Pressure (at sea level) P barometric = 760 mm Hg PbPbPbPb 760 mm Hg PbPbPbPb

7. 6 Consider a container of fluid in a vacuum Partial Pressure of Gases in Fluids Each gas has a specific solubility O 2 Solubility coefficient = 0.003 ml/100 ml Blood C0 2 = 0.06 ml/100 ml Blood (x 20 of 0 2 ) Gases dissolve in fluids by moving down a Partial Pressure gradient rather than a concentration gradient That is opened to the air Molecules of gas begin to enter the fluid

8. 7 Partial Pressure of Gases in Fluids After a short time, the number of molecules the number of molecules ENTERING = LEAVING At equilibrium, if the gas phase has a P O 2 = 100 mm Hg, the liquid phase also has a P O 2 = 100 mm Hg An easy way to talk about gases in fluids.

9. 8 Transport of gases between the alveoli and (pulmonary) capillaries and eventually from the capillaries to the tissues diffusion dependent on perfusion and the partial pressure (pp) exerted by each gas gases diffuse from area of  conc. (pp) to  conc. (pp)

10. 9  concentration    pp of gas   diffusion CO 2 more soluble than O 2, therefore it diffuses faster Diffusion

11. 10 Diffusion: Blood Transit time in the Alveolus Alveolus Blood capillary Time for exchange P O2 Time 0 0.75 sec 40 100 Saturated very quickly Reserve diffusive Capacity of the lung 45 mm Hg P CO2

12. 11 II Gas exchange in the lung and in the tissue

13. 12 Oxygen and Carbon Dioxide Diffusion Gradients Oxygen –Moves from alveoli into blood. –Blood is almost completely saturated with oxygen when it leaves the capillary –P0 2 in blood decreases because of mixing with deoxygenated blood –Oxygen moves from tissue capillaries into the tissues Carbon dioxide –Moves from tissues into tissue capillaries –Moves from pulmonary capillaries into the alveoli

14. 13 Diffusion Gradients of Respiratory Gases at Sea Level Total100.00760.07607600 H 2 O0.000.047470 O 2 20.93159.11054065 CO 2 0.030.240466 N 2 79.04600.75695730 Partial pressure (mmHg) % inDryAlveolarVenousDiffusion Gasdry airairairbloodgradient NB. CO 2 is ~20x more soluble than O 2 in blood => large amounts move into & out of the blood down a relatively small diffusion gradient.

15. 14 PO 2 and PCO 2 in Blood

16. 15 III. A-a gradient, the efficiency of the gas exchange in alveoli

17. 16 Oxygen Content in Alveolus Gas ) (measured during exhalation) Oxygen Content in arterial blood (equivalent to that leaving lungs) What is an A - a gradient ? : The DIFFERENCE between: In a healthy person, what would you expect the A - a to be? No difference, greater than 0, or less than 0 Normal: A – a, up to ~ 10 mm Hg, varies with age

18. 17 Factors contributing to A - a Gradient 1.Blood Shunts 2.Matching 1.Blood Shunts 2.Matching

19. 18 Alveolar SPACE arterial vessel SIMPLE CONCEPT OF A SHUNT BLOOD FLOW CO 2 O2O2O2O2 No Gas Exchange = SHUNT AIR FLOW Blood Mixing Lowered O 2 /l00 ml

20. 19 Total Perfusion, Q Total Ventilation NEXT NEW CONCEPT Matching What? Blood to Air Flow Exchange Oxygen If the volumes used for exchange are aligned – We might consider the system to be “ideally matched”

21. 20 Arterial Perfusion (Q c ) Slide or Misalign the distribution volumes Alveolar Ventilation (V A ) ExchangeOxygen Dead Air Space (Airways) Shunt (Q s ) (Bronchial Artery) Some Volumes are wasted, Matching Ratio = V A /Q c = 0.8 Normal Case; Small Shunt, low volume Dead Space

22. 21 Matching ventilation & perfusion Ventilation and perfusion (blood flow) are both better at the bottom (base) of the lung than that at the top (apex). But the change in blood flow is more steep than in ventilation. Therefore the ventilation/perfusion ratio rises sharply from the base to the apex.

23. 22 Matching ventilation & perfusion (cont) Result: V/Q is greater or less than 0.8 in different regions If V/Q 0.8 little benefit, Increases A - a gradient

24. 23 Alveolar Ventilation V A Arterial Perfusion Q Exchange Oxygen Dead Air Space Shunt = Lung Disease with a Large A – a gradient

25. 24 IV Factors Affecting the Gas Diffusion in the Lung

26. 25 1.The Properties of the Gas 1)Molecular weight. Diffusion rate is inversely proportional to the square root of the molecular weight 2)Temperature 3)Solubility in water Each gas has a specific solubility O 2 Solubility coefficient = 0.003 ml 0 2 /100 ml Blood C0 2 = 0.06 ml/100 ml Blood (x 20 of 0 2 ) P O2 Time 0 0.75 sec 40 100 Saturated very quickly Reserve diffusive Capacity of the lung 45 mm HG P CO2

27. 26 2. Partial Pressure of the Gases 1)Alveoli ventilation 2)Blood perfusion in the lung capillary 3)Speed of the chemical reaction The slow speed of the chemical reaction HCO 3 - + H + ----- H 2 CO 3 ---H 2 O + CO 2 reduces the CO 2 exchange in the lung. So, during the gas exchange in the external respiration, the exchange of CO 2 is a little lower than that of O 2.

28. 27 3. Properties of the Lung 1)Area of the respiratory membrane 2)Distance of the diffusion 3)V A /Q c

29. 28 V Pulmonary Diffusion Capacity Concept: The ability of the respiratory membrane to exchange a gas between the alveoli and the pulmonary blood defined as the volume of a gas that diffuses through the membrane each minute for a pressure of 1 mmHg. D L = V/(P A – P C ) V is a gas that diffuses through the membrane each minute, P A is the average partial pressure of a gas in the air of alveoli, P C is the average partial pressure of a gas in the blood of pulmonary capillary.

30. 29 Factors Affecting the D L 1.Body posture 2.Body height and weight 3.Exercise 4.Pulmonary diseases

31. 30 VI Internal Respiration All cells require oxygen for metabolism All cells require means to remove carbon dioxide Gas exchange at cellular level

32. 31 Concept: Gas exchange between the capillary and the tissues throughout the body Process: Factors affecting the internal respiration: 1.Distance between the cells and the capillary 2.Rate of metabolic rate 3.Speed of the blood flow in capillary

33. 32 EXTERNAL AND INTERNAL RESPIRATION HEART TISSUE CELL O 2 + FOOD CO 2 + H 2 O + ATP LUNGS ATMOSPHERE PULMONARY CIRULATION SYSTEMIC CIRCULATION