呼吸科呼吸系统课件2.ppt

* 5.2. Gas Exchange * * Definition Diffusion of oxygen and carbon dioxide between the alveoli and the blood inside the pulmonary capillaries. What we have to know? Basic principles of gas diffusion Factors that determine the rate of gas diffusion Partial Pressure of Individual Gases in a Gas Mixture Above the absolute temperature, all molecules of all matter are continually undergoing motion. Pressure is caused by multiple impacts of moving molecules against a surface either in air, liquid or other forms of matter. The partial pressure is directly proportional to the concentration of the gas molecule for air. * * Applied Gas Laws Question At the sea level (barometric pressure is 760 mmHg), how much is the partial pressure of oxygen if we know air consists of 21% oxygen? Hints Dalton’s law states that the total pressure exerted by a gaseous mixture is equal to the sum of the partial pressures of each gas component in the gas mixture. In a mixture of gases, the partial pressure of a given gas is directly proportional to the volume that gas contributes to the total volume. * * Answers PB = PN2 + PO2 + PHO2 + PCO2 (at the sea level, PB = 760 mmHg). Where PB = barometric pressure at the sea level. Where PN2 is the partial pressure of nitrogen. PO2 is the partial pressure of oxygen (氧分压). PO2 in the air = 760 mmHg X 0.21 = 160 mmHg . * * Partial Pressures of Individual Gases at the Seal Level (PB = 760 mmHg) * * Ambient Dry air (mm Hg) Moist Tracheal Air (mmHg) Alveolar Air (mmHg) Systemic Arterial Blood (mmHg) Mixed Venous Blood (mmHg) O2 160 150 102 95 40 CO2 0 0 40 40 46 Water Vapor 0 47 47 47 47 N2 600 563 571 571 571 Total 760 760 760 760 704 Water Vapor (水蒸汽） Lowers PO2 once Air Is Being Humidified（湿化） Air is being warmed and humidified before reaching alveoli. Water vapor does not change the percentage of O2 or N2 but does low the partial pressure of O2 or N2. In humidified air, PO2= (760 – 47) X 0.21 = 150 mmHg PN2 = (760 – 47) X 0.79 = 563 mmHg