1、e.g. Asthma / Bronchitis/ EmphysemaObstructive Hypovenlitation Decreased airway diameter or airway obstruction Expiration is more difficult than inspiration, why? FRC increasesNormal Lung VolumeLung Volume in Obstructive DiseaseEmphysemaTimed Vital Capacity (Restrictive & Obstructive)Maximal expirat

2、ory flow-volume curves Overview of Key Steps in RespirationPulmonary Ventilation Pulmonary Gas ExchangeTissue Gas ExchangeTransportExternal RespirationInternal RespirationPulmonary Gas Exchange&Gas TransportationPUMC & CAMS Xue Gao(O2 transportation)Pulmonary Gases ExchangePrimary Force for Gas Exch

3、ange Diffusion of a gas from higher pressure 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

4、of partial pressures of each gasHow about 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 T

5、otal Pressure (at sea level) Pbarometric = 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

6、 Graham Law: Diffusion Coefficient= MWCO2 is 44，MWO2 is 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 O2P1CO2P2CO2 CO2 diffusion coefficient is 20 times O2 Analysis: O2 & C

7、O2 exchange, which one will get worse if area decrease or thickness increase? Gas Partial Pressure (mmHg)Atmosphere Alveoli Arterial Venous 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

8、surface areaRespiratory Membrane Diffusion Capacity of Lung (DL)Definition: Volume of a gas that diffuses through the membrane for 1 minute 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 t

9、he gas in pulmonary capillaryO2 : 20ml/min.mmHgCO2 : 400ml/min.mmHgBlood Transit Time in the Alveoli- Fibrosis Factors Affecting the Pulmonary 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 (Sur

10、face Area & Thickness) are the key factors Pulmonary Edema or Fibrosis -Increase the membrane thickness Emphysema - Decrease the membrane 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

11、& Perfusion ratio: the ration of alveolar ventilation per minute (VA) with pulmonary blood flow per minute (Q)Factors Affecting the Pulmonary Gas Diffusion Normally, (VA/Q)=0.84 0.84 Physiologic dead space air increased 5g/100ml (Cyanosis) Color of HbO2 & Deoxyhemoglobin CO+Hb=HbCO is cherry red CO

12、competes the position for O2 in Hb CO has extremely high affinity for Hb, 250 times to O2 CO inhibit the release of O2 from HbCO Poisoning Clinical Correlate“Chronic Obstructive Pulmonary Disease” (COPD) Chronic bronchitis: is an inflammatory condition that affects one or more bronchi Emphysema: ste

13、ms from an overdistension of the alveoli & a loss of lung elastic recoil Chronic bronchitis & Emphysema often coexist Asthma: is marked by apasmodic contractions of smooth muscle in the bronchi FEV1, FVC, FEV1/FVC TLC, FRC, RV RV/TLC% may increase exceed 40% (less than 30% in young healthy person) Elastic recoil of the lung The pressure-volume curve is displaced up & to the left The transpulmonary pressure Airway resistance Ventilation-perfusion ratio