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1、VentilationVentilationMeasurement of Gases Total Pressurecombined pressure of all atmospheric gases760 mm Hg or torr at sea level Partial PressurePressure exerted by each gas of a mixtureAtmosphericNitrogen 597.0 torr (78.62%); Oxygen 159.0 torr (20.84%); Carbon Dioxide 0.3 torr (0.04%); Water 3.7 t
2、orr (0.5%)Measurement of GasesPartial PressuresAlveolar Nitrogen 569.0 torr (74.9%); Oxygen 104.0 torr (13.7%); CO2 40.0 torr (5.2%); Water 47.0 torr (6.2%)RespirationVentilation vs. RespirationExchange of gases between a living organism and its environmentExternal Respirationexchange between lungs
3、& blood cellsInternal Respirationexchange between blood cells & tissuesRespirationHow are O2 and CO2 transported?Diffusiondefinitiongases dissolved in water and pass through alveolar membraneFiO2% of oxygen in inspired air (e.g. FiO2 = 0.95)RespirationOxygen Content of Blooddissolved O2 crosses pulm
4、 cap membrane and binds to Hgb of RBCTransport = O2 bound to hemoglobin (97%) or dissolved in plasmaO2 Saturation: % of hemoglobin saturated with oxygen (usually carries 96% of total)O2 content divided by O2 carrying capacityRespirationOxygen saturation affected by:low Hgb (anemia, hemorrhage)inadeq
5、uate oxygen availability at alveolipoor diffusion across pulm membrane (pneumonia, pulm edema, COPD)Ventilation/Perfusion (V/Q) mismatch blood moves past collapsed alveoli (shunting)alveoli intact but blood flow impairedRespirationCarbon Dioxide content of bloodByproduct of work (cellular respiratio
6、n)Transported as bicarbonate (HCO3- ion) 20-30% bound to hemoglobinPressure gradient causes CO2 diffusion into alveoli from bloodincreased level - hypercarbiaAnatomy of the Lower AirwayAlveoli PO2 100 & PCO2 40PO2 40 & PCO2 46 - Pulmonary circulation - PO2 100 & PCO2 40 HeartPO2 40 & PCO2 46 - Systemic circulation - PO2 100 & PCO2 40 Tissue cell PO2 46 Inspired Air: PO2 160 & PCO2 0.3OxygenatedDeoxygenated
