GASEOUS EXCHANGE & FACTORS DETERMINING
GASEOUS EXCHANGE & FACTORS DETERMINING
- Diffusion of gases from alveoli to blood (O2) or from blood to alveoli (CO2), happens via alveolocapillary (respiratory) membrane.
- This is gaseous exchange process.
Factors affecting gasous diffusion:
1. Thickness of respiratory membrane:
- Normal thickness – 0.5 µm,
Thickening of membrane seen in:
- Pneumonia, TB, Lung carcinoma, Emphysema & Cystic fibrosis.
2. Surface area of membrane:
- Total surface area in two lungs = 100 m2.
- Time taken by blood to traverse pulmonary capillaries at rest: 0.75 s.
3. Diffusion coefficient of gas:
- Diffusion – Net movement of fluid from one compartment to another due to concentration difference.
- Gas diffuses from high to low pressure.
Diffusion rate (D) is directly proportionol to,
- Pressure gradient (P).
- Solubility of gas (S).
- Surface area of respiratory membrane (A).
Diffusion rate (D) is inversely proportionol to,
- Thickness of respiratory membrane (d).
- Molecular weight of gas (MW).
- Diffusion coefficient – S/√ MS.
- Main characteristics determining rate of diffusion of gas – S & MW.
- Diffusion coefficient of oxygen = 1
- Diffusion coefficient of carbon-dioxide = 20.3.
- Diffusion coeficient of CO2 > O2 – Due to more solubility of CO2.
- CO2 diffuses more rapidly into respiratory membrane than O2.
4. Solubility coefficient:
- Denotes the solubility characteristics of particular gas in water.
- Solubility coefficiency for oxygen – 0.024
- Solubility coefficiency for CO2 – 0.57
- CO2 is 20 times more soluble than O2.
- Solubility coefficiency for N2 – 0.012
- Solubility coefficiency for CO – 0.018
5. Diffusion capacity:
- Is the overall ability of respiratory membrane to transfer a gas between alveolar air & pulmonary blood.
- Also referred as “transfer factor”.
- Diffusion capacity of O2 – 25 ml/min/mm Hg (At rest).
- Diffusion capacity of O2 – 65 ml/min/mm Hg (At exercise).
- Diffusion capacity of CO2 (theoretical value) – 400 ml/min/mm Hg (At rest).
- Diffusion capacity of CO – Used as index for measuring normalcy.
- (Note: Diffusion of Co & O2 are same).
Factors affecting diffusion capacity of CO:
Decreasing factors:
- Restrictive/interstitial lung disease, COPD (emphysema), pulmonary embolism, pulmonary hypertension, CHF, anemia & drugs (amiodarone).
Increasing factors:
- Polycythemia, asthma, left to right shunt, alveolar hemorrhage, increased pulmonary blood volume (during exercise).
Exam Important
- Normal thickness of respiratory membrane 0.5 µm.
- Thickening of membrane seen in pneumonia, TB, Lung carcinoma, Emphysema & Cystic fibrosis.
- Total surface area in two lungs = 100 m2.
- Time taken by blood to traverse pulmonary capillaries at rest: 0.75 s.
- Diffusion rate (D) is directly proportional to pressure gradient (P), solubility of gas (S) & surface area of respiratory membrane (A).
- Diffusion rate (D) is inversely proportional to thickness of respiratory membrane (d) & molecular weight of gas (MW).
- Diffusion coefficient of oxygen = 1.
- Diffusion coefficient of carbon-dioxide = 20.3.
- Diffusion coefficient of CO2 > O2 – Due to more solubility of CO2.
- CO2 diffuses more rapidly into respiratory membrane than O2.
- Solubility coefficiency for oxygen – 0.024.
- Solubility coefficiency for CO2 – 0.57.
- CO2 is 20 times more soluble than O2.
- Diffusion capacity of O2 – 25 ml/min/mm Hg (At rest).
- Diffusion capacity of O2 – 65 ml/min/mm Hg (At exercise).
- Diffusion capacity of CO2 (theoretical value) – 400 ml/min/mm Hg (At rest).
- Diffusion capacity of CO – Used as index for measuring normalcy.
- Factors decreasing diffusion capacity of CO are restrictive/interstitial lung disease, COPD (emphysema) & pulmonary embolism.
- Factors increasing diffusion capacity of CO are polycythemia.
Don’t Forget to Solve all the previous Year Question asked on GASEOUS EXCHANGE & FACTORS DETERMINING
