4Concentration of a gas in a liquid Partial pressureThe pressure exerted by each type of gas in a mixtureConcentration of a gas in a liquiddetermined by its partial pressure and its solubility coefficient
5Partial Pressures of Gases Total Pressure (at sea level)Pbarometric = 760 mm HgPb760 mm HgBasic Composition of Air79% Nitrogen21% Oxygen~ 0% Carbon DioxideIn a mixture of gases, each gas exerts a partial pressure proportional to its mole fraction.Total Pressure = sum of the partial pressures of each gasPgas = Pb x FgasPN2 = 760 x 0.79 = mm HgP02 = 760 x 0.21 = mm Hg
6Partial Pressure of Gases in Fluids Each gas has a specific solubility O2 Solubility coefficient = ml/100 ml BloodC02 = 0.06 ml/100 ml Blood (x 20 of 02)Gases dissolve in fluids by moving down a Partial Pressure gradient rather than a concentration gradientConsider a container of fluid in a vacuumThat is opened to the airMolecules of gas begin to enter the fluid
7Partial Pressure of Gases in Fluids After a short time, the number of molecules the number of molecules ENTERING = LEAVINGAt equilibrium, if the gas phase has a PO2 = 100 mm Hg,the liquid phase also has a PO2 = 100 mm HgAn easy way to talk about gases in fluids.
8Diffusion: Blood Transit Time in the Alveolus Blood capillaryTime for exchangePO2Time0.75 sec40100Saturated very quicklyReserve diffusive Capacity of the lung45mm HgPCO2
10Diffusion Gradients of Respiratory Gases at Sea Level TotalH2OOCONPartial pressure (mmHg)% in Dry Alveolar Venous Diffusion Gas dry air air air blood gradientNB. CO2 is ~20x more soluble than O2 in blood => large amounts move into & out of the blood down a relatively small diffusion gradient.
12III. A-a gradient, the efficiency of the gas exchange in alveoli
13The DIFFERENCE between: What is an A - a gradient ?The DIFFERENCE between:Oxygen Content in arterial blood(equivalent to that leaving lungs)Oxygen Content inAlveolus Gas(measured during exhalation)In a healthy person, what would you expect the A - a to be?No difference, greater than 0, or less than 0Normal: A – a, up to ~ 10 mm Hg, varies with age
14Factors contributing to A - a Gradient Blood ShuntsBlood MixingMatching
15Alveolar SPACE Blood Mixing SIMPLE CONCEPT OF A SHUNT AIR FLOW CO2 O2 arterial vesselBLOOD FLOWBloodMixingLowered O2/l00 mlNo Gas Exchange = SHUNT
16Matching Blood to Air Flow ImportantOn the testNEXT NEWCONCEPTMatching What?Blood to Air FlowTotal VentilationExchangeOxygenTotal Perfusion, QIf the volumes used for exchange are aligned– We might consider the system to be “ideally matched”
17Matching Dead Air Space (Airways) Alveolar Ventilation (VA) Oxygen ExchangeOxygenArterial Perfusion (Qc)Slide or Misalign the distribution volumesShunt (Qs)(BronchialArtery)Some Volumes are wasted,Matching Ratio = VA/Qc = 0.8Normal Case; Small Shunt, low volume Dead Space
18Matching ventilation & perfusion Ventilation and perfusion (blood flow) are both better at the bottom (base) of the lung than that at the top (apex).the change in blood flow is more steep than in ventilation.the ventilation/perfusion ratio rises sharply from the base to the apex.
19Matching ventilation & perfusion (cont) Result: V/Q is greater or less than 0.8 in different regionsIf V/Q <0.8 = shunt like, If V/Q > 0.8 little benefit, Increases A - a gradient
20= Lung Disease with a Large A – a gradient Severe MismatchDead Air SpaceAlveolar VentilationVAExchangeOxygenArterial Perfusion Qblood mixingShunt= Lung Disease with a Large A – a gradient
21IV Factors Affecting the Gas Diffusion in the Lung Area of the respiratory membraneDistance of the diffusionVA/Q
22V Pulmonary Diffusion Capacity Concept:The ability of the respiratory membrane to exchange a gas between the alveoli and the pulmonary blooddefined as the volume of a gas that diffuses through the membrane each minute for a pressure of 1 mmHg.DL = V/(PA – PC)V is a gas that diffuses through the membrane each minute,PA is the average partial pressure of a gas in the air of alveoli,PC is the average partial pressure of a gas in the blood of pulmonary capillary.
23Factors Affecting the DL Body postureBody height and weightExercisePulmonary diseases
24VI Internal Respiration All cells require oxygen for metabolismAll cells require means to remove carbon dioxideGas exchange at cellular level
25Concept: Gas exchange between the capillary and the tissues throughout the body Process:Factors affecting the internal respiration:Distance between the cells and the capillaryRate of metabolic rateSpeed of the blood flow in capillary
26EXTERNAL AND INTERNAL RESPIRATION TISSUECELLO2 + FOODATMOSPHERESYSTEMICCIRCULATIONHEARTPULMONARYCIRULATIONLUNGSCO2 + H2O+ ATP