diffusion of gases.pptx involving carbon dioxide,nitrogen,oxygen

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1. PULMONARY GAS EXCHANGE NAME:Dr.Vidya Panda PGT 1 st year.

2. SCHEMA: HISTORY PHYSICS OF PARTIAL PRESSURES OF GASES PARTIAL PRESSURE OF DIFFERENT GASES AS THEY ENTER AND LEAVE THE LUNGS DIFFUSION OF GASES THROUGH THE RESPIRATORY MEMBRANE. DIFFUSING CAPACITY AND IT’S MEASUREMENT DIFFUSION AND PERFUSION

3. HISTORY DIFFUSION: PARTIAL PRESSURE OF GASES

4. INTRODUCTION The process of diffusion: is simply the random motion of molecules in all directions through the respiratory membrane and adjacent fluids. diffusion of oxygen (O2) from the alveoli into the pulmonary blood and diffusion of carbon dioxide (CO2) from the blood into the alveoli.

5. PARTIAL PRESSURES OF GASES Is the pressure of a single type of gas in a mixture of gases. The pressure is directly proportional to the concentration of the gas molecules. In respiratory physiology, one deals with mixtures of gases, mainly oxygen, nitrogen, and carbon dioxide. HENRY’S LAW: Partial pressure =Concentration of dissolved gas/solubility coefficient.

6. Diffusion of Gases Through Fluids—Pressure Difference Causes Net Diffusion

7. Alveolar air is slowly renewed by atmospheric air: Multiple breaths are required to exchange most of the alveolar air. The slow replacement of alveolar air is of particular importance in preventing sudden changes in gas concentrations in the blood. The concentrations and partial pressures of both O2 and CO2 in the alveoli are determined by the: Rates of absorption or excretion of the two gases. The amount of alveolar ventilation

8. Effect of alveolar ventilation on the alveolar Po2 at two rates of oxygen absorption from the alveoli—250 ml/min and 1000 ml/min. Point A is the normal operating point.

9. Effect of alveolar ventilation on the alveolar Pc o 2 at two rates of carbon dioxide excretion from the blood—800 ml/ min and 200 ml/min. Point A is the normal operating point.

10. DIFFUSION OF GASES THROUGH THE RESPIRATORY MEMBRANE

11. RESPIRATORY UNIT

12. The alveolar walls are extremely thin , and between the alveoli is an almost solid network of interconnecting capillaries. Alveolar gases are in very close proximity to the blood of the pulmonary capillaries.

13. Respiratory Membrane (Pulmonary membrane): A layer of fluid containing surfactant that lines the alveolus and reduces the surface tension of the alveolar fluid. The alveolar epithelium , which is composed of thin epithelial cells. An epithelial basement membrane. A thin interstitial space between the alveolar epithelium and the capillary membrane. A capillary basement membrane that in many places fuses with the alveolar epithelial basement membrane. The capillary endothelial membrane.

14. Despite the large number of layers, the overall thickness of the respiratory membrane in some areas is as little as 0.2 micrometer and averages about 0.6 micrometer , except where there are cell nuclei. The average diameter of the pulmonary capillaries is only about 5 micrometers , which means that red blood cells must squeeze through them. The red blood cell membrane usually touches the capillary wall, so O2 and CO2 need not pass through significant amounts of plasma as they diffuse between the alveolus and the red blood cell. This, too, increases the rapidity of diffusion. .

15. FACTORS THAT AFFECT THE RATE OF GAS DIFFUSION THROUGH THE RESPIRATORY MEMBRANE: (1) The thickness of the membrane (2) The surface area of the membrane (3) The diffusion co- effcient of the gas in the substance of the membrane (4) The partial pressure difference of the gas between the two sides of the membrane

16. DIFFUSING CAPACITY OF THE RESPIRATORY MEMBRANE: The volume of a gas that will diffuse through the membrane each minute for a partial pressure difference of 1 mm Hg . A- Diffusing Capacity for Oxygen: In the average young man, the diffusing capacity for O2 under resting conditions averages 21 ml/min/mm Hg . The mean O2 pressure difference across the respiratory membrane during normal, quiet breathing is about 11 mm Hg . Multiplication of this pressure by the diffusing capacity (11 × 21) gives a total of about 230 milliliters of oxygen diffusing through the respiratory membrane each minute, which is equal to the rate at which the resting body uses O2.

17. Example: Increased Oxygen Diffusing Capacity during Exercise: 65 ml/min/mm Hg X 11 mmHg = 715ml . More than three folds than normal. The pulmonary blood flow increased , the ventilation increased , so the oxygen diffusing capacity will increase this established by: 1- Reopening of dormant pulmonary capillary. 2- Dilating of pre existing pulmonary capillary. 3- Matching the V/Q ratio.

18. B- Diffusing Capacity for Carbon Dioxide: The diffusing capacity for CO2 has never been measured because CO2 diffuses through the respiratory membrane so rapidly that the average PCO2 in the pulmonary blood is not far different from the PCO2 in the alveoli the average difference is less than 1 mm Hg. Because the diffusion coefficient of CO2 is slightly more than 20 times that of O2 , one would expect a diffusing capacity for CO2 under resting conditions of about 400 to 450 ml/min/mm Hg and during exercise of about 1200 to 1300 ml/min/mm Hg.

19. M EASURMENT OF DC CO is used to determine the lung diffusing capacity. (1) alveolar Po2 , (2) Po2 in the pulmonary capillary blood, (3) the rate of oxygen uptake by the blood.

20. M EASUREMENT OF DC BY CARBON MONOXIDE METHOD: To measure the diffusing capacity (DC) with CO, the equation is: DC = Vco /PACO Vco , where VCO is CO uptake in ml/min and PACO is alveolar partial pressure of CO. The most common technique for making this measurement is called the single-breath test.

21. PERFUSION AND DIFFUSION LIMITATION. CARBON MONOXIDE IS DIFFUSION LIMITED. NITROUS OXIDE IS PERFUSION LIMITED OXYGEN:DIFFUSION OR PERFUSION LIMITED

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