1、Overview of Key Steps in RespirationPulmonary Ventilation Pulmonary Gas ExchangeTissue Gas ExchangeTransportExternal RespirationInternal RespirationPulmonary Gas Exchange&Gas Transportation(O2 transportation)Pulmonary Gases ExchangePrimary Force for Gas Exchange Diffusion of a gas from higher pressu

2、re to lower pressure-Dependent on Pressure Gradient Partial Pressure: The pressure exerted by each type of gas in a mixture Dalton Law:In a mixture of gases, partial pressure is directly proportional to the concentration of gas moleculesTotal Pressure = Sum of partial pressures of each gasHow about

3、each gas pressure in a mixture of gases?Partial Pressures of Gases in Air Basic Composition of Air 78.62% Nitrogen 20.84 % Oxygen 0.04% Carbon Dioxide 3.7% H2O PN2 = 760 x 0.7862 = 597.5 mm Hg PO2 = 760 x 0.2084 = 158.4 mm Hg PCO2 = O.3 mmHg PH2O = 3.7mmHg Total Pressure (at sea level) Pbarometric =

4、 760 mm HgPb760 mmHg PbHow about Gas Dissolved in Water or Liquid?D(P x A x S) / (d x MW)Fick Law D: Diffusion Rate P: Partial Pressure A: Area of Diffusion S: Solubility d: Distance of DiffusionMW: Molecular Weight Laws Governing the Gas Diffuse into Liquid Diffusion Coefficient= MWCO2 is 44，MWO2 i

5、s 32 CO2 diffusion coefficient is 20 times O2 S /MW Amount of air dissolved in blood under 37 O2 0.003ml/100ml.mmHg CO2 0.064ml/100ml.mmHg CO2 is more than 20 times soluble as O2Graham Law:P1CO2P2CO2 CO2 diffusion coefficient is 20 times O2 Gas Partial Pressure (mmHg)Atmosphere Alveoli Arterial Veno

6、us TissuePO2 159 104 100 40 30PCO2 0.3 40 40 46 50 PO2 & PCO2 in Blood Thickness of Respiratory Membrane: 0.20.6um Total surface area: 50100m2, 2550 times to body surface areaRespiratory Membrane Diffusion Capacity of Lung (DL)Definition: Volume of a gas that diffuses through the membrane for 1 minu

7、te for a pressure of 1 mmHgDL = V/(PA PC)V: A gas that diffuses through the membrane each minutePA: Partial pressure of the gas in alveoliPC: Partial pressure of the gas in pulmonary capillaryO2 : 20ml/min.mmHgCO2 : 400ml/min.mmHgBlood Transit Time in the Alveoli- Fibrosis Factors Affecting the Pulm

8、onary Gas DiffusionD(P x A x S) / (d x MW) Under normal condition, for a given gas, S ,MW, P are constant 1. A & d, that is Properties of Respiratory Membrane (Surface Area & Thickness) are the key factors Pulmonary Edema or Fibrosis -Increase the membrane thickness Emphysema - Decrease the membrane

9、 surface area - Many of alveoli coalesce, as the area decreased to 1/3 or 1/4 of normal, gas exchange will be impeded even at the resting condition 2. Ventilation & Perfusion ratio: the ration of alveolar ventilation per minute (VA) with pulmonary blood flow per minute (Q)Factors Affecting the Pulmo

10、nary Gas Diffusion Normally, (VA/Q)=0.84 0.84 Physiologic dead space air increased 0.84 functional A-V shunt Lung itself have the ability to adjust the blood flow towards the alveoli with better O2 ventilation Due to : The vessel located at the alveoli with low ventilation will constrict, decrease t

11、he blood flow, thus push the blood flowing into the alveoli with better ventilation People entering the high altitude area: -Pulmonary arterial high pressureVA/Q in the Upper & Lower Lungin upright positionVA/Q=3.3 VA/Q=0.63 Gas Transportationin the Blood(O2 transportation) Physical Dissolution Chem

12、ical Combination Most of oxygen & carbon dioxide in the blood is transported in chemical combination Only the gas in physical dissolution express partial pressure & diffusionForm of Gases TransportedAlveoli Blood Tissue O2CO2 Dissolve Combine DissolveDissolve Combine DissolveO2CO2 Oxygen Transport D

13、issolved in Plasma 1.5 % Combined with Hemoglobin 98.5 %Hemoglobin (Hb) Structure 1 Globin 4 HemeFe2+O2Formation of OxyhemoglobinO2 + HbHbO2High PO2Low PO2(Oxyhemoglobin)(Deoxyhemoglobin) O2 with Hemoglobin to form oxyhemoglobin is an oxygenation, not an oxidation O2 released from oxyhemoglobin is a

14、 deoxygenation, not a reduction The reaction is rapid, requiring less than 0.01 second Theoretically, 1 mol Hb can combine with 4 mol O2 Hb have two forms: Tense form (T form) & Relaxed form (R form). R form is 500 times ability combining with O2, then change to T form O2 + HbHbO2High PO2Low PO2 Oxy

15、gen Capacity: The maximum amount of oxygen can combine with Hb per 100ml blood 1.34 ml/gHb, 15gHb/100ml blood20ml/100ml blood Oxygen Content: Actual amount of oxygen can combine with Hb per 100 ml blood Oxygen Saturation: (Oxygen ContentOxygen Capacity) x100%Basic ConceptsEvaluation of Hb Combine wi

16、th O2Oxygen Dissociation CurveT: 37, pH: 7.4, PCO2: 40 mm Hg, Hb concentration: 15g/100ml Flattened upper portion (60100mmHg) Steep middle portion (4060mmHg)3. Lower portion (1540mmHg)P50-Affinity of Hb with O226.5Factors that Affect the Oxygen Dissociation Curve H+ CO2 Temperature 2,3,-DPG H+ & PCO

17、2:Bohr Effect Temperature 2,3-diphosphoglycerate (2,3,-DPG)2, 3-DPG2, 3-DPGAnalyze the curve shift under exercise & why? 缺 氧hypoxia 你能想到的缺氧狀態？高原貧血室間隔缺損休克氰化物：氫氰酸 氧代謝環節 低張性缺氧 hypotonic hypoxia 空氣呼吸系統動靜脈血摻雜 室間隔缺損 法洛四聯癥 動靜脈瘺 高原、高空 通風不良 麻醉藥稀釋 氣道 肺 胸膜腔 呼吸肌 血液性缺氧 hemic hypoxia 數 量 質 量CO中毒（碳氧血紅蛋白血癥）高鐵血紅蛋白血癥亞硝酸鹽中毒血紅蛋白病Hb與氧的親和力輸入庫存血