αo 2 : solubility coefficient of O 2

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Caitlin Bond
5 years ago
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limit gas transfer 3) diffusion capacity gas volume gaseous phase

α diffusion gradient C : of (ml. /ml. solution) P : tension of (mm.

1 Version 2006 Dr. Puntarica Suwanprathes 1) Fick s law of diffusion 2) facts which limit gas transfer 3) diffusion capacity gas volume gaseous phase dissolved gas exert pressure*** Solubility of Gas C =P. α diffusion gradient C : of (ml. /ml. solution) P : tension of (mm.hg) μ C diffusion gradient α : coefficient of (ml. in 1 ml. solution / 1 ATP) 37 0 C : α = αc = diffuse faster

gas Low pressure equilibrium Low dissolved gas Double the pressure equilibrium Double the volume

gas mixture (A+ B +C) PA + PB + PC independence Gas transptation in blood dissolved /C exert

Pressure gradient A = B Gas diffusion in Lungs Gas diffusion in Lungs pressure gradient gradient

2 gas Low pressure equilibrium Low dissolved gas Double the pressure equilibrium Double the volume = x coefficient () in solution volume = x coefficient constant in solution volume α of that gas gas mixture (A+ B +C) PA + PB + PC independence Gas transptation in blood dissolved /C exert pressure Binding /C (chemical reaction) Diffusion gas X in A > B A B A > B diffuse from A to B Pressure gradient A = B Gas diffusion in Lungs Gas diffusion in Lungs pressure gradient gradient gaseous phase PAC 40 mmhg PA 104 mmhg alveolar-capillaries membrane PVC 46 mmhg liquid phase PV 40 mmhg

Diffusion rate Duffusion rate: in gaseous medium in gaseous medium diffusion rate: faster Graham s law molecular wt.

of diffusion rate molecular wt. of C = 32 = 5.6 44 6.

(80%) volume α of that gas diffusion rate α C diffusion rate = 0.592 = 24.3 diffusion rate 0.0244 1.

3 Diffusion rate Duffusion rate: in gaseous medium in gaseous medium diffusion rate: faster Graham s law molecular wt.: lighter Duffusion rate: in liquid medium FACTORS: Diffusion rate diffusion rate α 1 square root of density C diffusion rate = molecular wt. of diffusion rate molecular wt. of C = 32 = alveolar duct Diffusion rate in liquid medium diffusion distance ~1 mm pressure gradient gradient interface almost complete in sec. (80%) volume α of that gas diffusion rate α C diffusion rate = = 24.3 diffusion rate Diffusion rate > C in gaseous medium Graham s law C > in liquid medium FACTORS: Diffusion rate Fick s law (Law of diffusion) V gas α A. D. (P 1 -P 2 ) T MW C diffusion rate = 5.6 x = 20.6 diffusion rate 6.6 x V = diffusion rate A = area of diffusion D = diffusion constant T = length of diffusion path P 1 -P 2 = difference in

Pressure difference across membrane difference in diffusion rate Pv 40 mmhg PvC 45 mmhg C Pa 100 mmhg PaC 40 mmhg

during exercise??? B 75 ml = 6 L/min pulm.

Thickness of membrane RBC (max 4μ) causes?

4 Pressure difference across membrane difference in diffusion rate Pv 40 mmhg PvC 45 mmhg C Pa 100 mmhg PaC 40 mmhg alveoli equilibrium pulm. capillary blood A time in pulmonary capillary = 0.75 sec. diffusion time = 0.25 sec. during exercise??? B 75 ml = 6 L/min pulm. blood flow mixed venous P Pa alveoli fluid layer alveolar epithelial layer Interstitial fluid layer Capillary endothelial layer ~ μ Plasma layer cell membrane of red blood cell Intracellular fluid layer in RBC Hb length of diffusion path Thickness of membrane RBC (max 4μ) causes? thickness diffusion rate block Total respiraty surface area area of diffusion = surface areas (both lungs) ~ 70 m rest: active use only 20% (14 m 2 ) e.g. Emphysema Alveolar dead space destroy alveolar wall (+ capillary surface) areas of diffusion diffusion P: 1 mmhg V (ml) time: 1 min membrane Gas volume: ml time: 1 min pr. gradient: 1 mmhg ml/min/mmhg membrane

5 V gas α A. D. (P 1 -P 2 ) T can not measure V gas = D L. (P 1 -P 2 ) D L = V gas P 1 - P 2 mean P of capillary gas mean P of alveolar gas Measuring: CO D DcO Affinity: > 210 Single-breath method CO = 0.3% 1 breath: TLC breath-holding: 10 sec exhale completely DL = V gas P 1 -P 2 DCO = V CO P A CO -P C CO D = DCO x 1.23 Nmal value: DCO = 25 ml/min/mmhg D = 31 ml/min/mmhg D exercise D aging pulm. edema pulm. emphysema Impaired diffusion! arterial blood gas tension? Version 2006 mild. rest exercise Pa PaC

I Physical Principles of Gas Exchange

Respiratory Gases Exchange Dr Badri Paudel, M.D. 2 I Physical Principles of Gas Exchange 3 Partial pressure The pressure exerted by each type of gas in a mixture Diffusion of gases through liquids Concentration