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76 Cards in this Set
- Front
- Back
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How do you calculate the Po2 in inspired air?
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Po2 = Total pressure x FCO2
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So what is the Po2 in tracheal air?
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760 - 47 x .21 = 150 mm Hg
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Why is 47 subtracted from 760?
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To account for the pressure of water in humidified tracheal air
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What is the Physiologic shunt?
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2% of systemic CO that BYPASSES pulmonary bloodflow
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What effect does the physiologic shunt have on arterial blood Po2?
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It is slightly less than the Po2 of alveoli
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What is alveolar Po2?
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100 mm Hg
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Why is alveolar Po2 less than tracheal?
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Because air is removed by the blood circulation
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What is systemic arterial blood Po2?
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100 (minus a little bit due to the physiologic shunt)
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What is mixed venous arterial blood Po2? Why?
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40 - because the tissues remove O2
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What is the PCO2 in dry air?
In the trachea? |
0 - in both
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What is the PCO2 in alveoli? why?
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40 - because the blood delivers it from the tissues
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What is the PCO2 in Venous blood?
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46 mm Hg
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Why is Venous PCO2 higher than by the time blood reaches the alveoli?
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Because at the alveoli blood equilibrates with the alveolar air, which has lower CO2 levels.
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How do we calculate the amount of dissolved O2 in arterial blood?
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Multiply PO2 x solubility constant
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What is the normal amt of dissolved O2 in arterial blood?
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100 mm Hg x .03 = .3/100 ml blood
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What determines the RATES of diffusion of O2/CO2 from the alveoli into the blood?
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Partial pressure DIFFERENCES
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What happens when partial pressures of O2 in alveoli and pulmonary cap blood are equal?
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No net movement
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What is the most common limiting factor to the rate of O2 uptake at the alveolus? In what condition?
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PERFUSION - just normal
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What is less common of a limitation to O2 uptake? In what conditions?
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Diffusion - Emphesma, fibrosis, or exercise can limit O2 uptake
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What does Perfusion limited diffusion refer to?
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The equilibration of alveolar and capillary blood so that no more net exchange occurs
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What is the only way to increase gas diffusion when Perfusion is the limiting factor?
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Increased BLOODFLOW
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What 3 gases exhibit Perfusion-limitation?
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O2, CO2, and NO2
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What gases illustrate DIFFUSION limitation?
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CO and O2 in disease states
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Why is O2 uptake limited by diffusion capacity in Fibrosis?
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Because of thickening of the alveolar membrane
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What effect does the increased alveolar membrane thickness have for perfusion of O2?
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It is decreased; no complete equilibrium btwn Alveolar O2 and capillary O2 is reached.
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So will increasing perfusion in Fibrosis increase O2 uptake?
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No
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Why is O2 uptake diffusion limited in Emphesyma?
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Because of decreased alveolar SURFACE area
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What are the 2 forms of Oxygen carried in blood?
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-Dissolved
-Hb bound |
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Which form is most important?
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HEMOGLOBIN-bound
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How much does Hb (non-anemic) increase the blood's O2 carrying capacity?
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70X!!!
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What is the state in which Iron is when it can bind o2?
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Fe2+ - ferrous
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What is Hb called if Fe is 3+? Why is this bad?
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METhemoglobin - can NOT bind O2
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What is Adult Hb? Fetal?
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Adult = a2b2
Fetal = a2y2 |
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What is the difference of Fetal hb?
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Higher affinity for O2
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So what direction is the Hb dissociation curve shifted with Fetal hb?
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To the left
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WHY is fetal hb's affinity higher?
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Bc it binds 2,3-DPG less avidly!
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Why is it good for fetal hemoglobin to have higher affinity for oxygen?
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It facilitates it picking up O2 from maternal blood
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What is O2 capacity?
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the capacity Hemoglobin has for binding Oxygen
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What is Hb's O2 capacity determined by?
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The concentration of Hb in blood
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What is O2 CONTENT?
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The total amount of O2 in blood
-Dissolved -Hb bound |
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What are the 3 determinants of O2 content in blood?
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-Hb concentration
-Po2 of blood -P50 of hemoglobin |
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How do you calculate O2 content?
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(Hb%sat x O2 capacity) + Diss O2
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What is the normal Hb % sat?
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98%
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What is the main determinant of Hb saturation?
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The Po2 in blood
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What is the normal %sat of Hb at arterial blood PO2?
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Arterial Po2 = 100
Hb % sat = 98% (4 groups bound) |
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What is the % sat of Hb at mixed venous blood Po2?
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MV blood PO2 = 40 mm Hg
% sat Hb = 75% (3 groups bound) |
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What is the P50?
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The pressure of O2 at which Hb is 50% saturated (2 groups bound)
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What is the normal P50?
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25 mm Hg
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Why is the Hb-O2 dissociation curve sigmoidal?
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Because O2 binding has a cooperative effect; binding the first O2 increases its affinity for another
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For which molecule of O2 binding does Hb have the HIGHEST affinity?
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The 4th!
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What effect does this cooperative binding have on Hb loading/unloading oxygen?
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It WANTS to get all 4 O2's at the lungs, and more easily gets rid of the last at the tissues.
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So where does Hb have the highest affinity for o2?
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In the lungs
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What effect does the fact that the Hb dissociation curve is FLAT between 60-100 mm Hg O2 have for humans?
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Changes in atmospheric levels of O2 will have little effect on the ability for Hb to take up O2 at the lungs!
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What maintains the gradient for tissue uptake of O2 from blood?
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Constant metabolism of tissues
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What direction will the curve shift if Hb's affinity for O2 is decreased? Increased?
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Decreased = to the right
Increased = to the left |
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What is the Bohr effect?
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The shift to the right in response to CO2 or Acid
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What will happen to the curve in exercise and why?
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Shift to the right - bc of increased TEMP
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When does increased 2,3 DPG play a role in decreaseing the Hb affinity for O2?
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In chronic hypoxemia - ADAPTATION
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In addition to opposite changes of all the things that cause a right shift, what 2 things shift the curve to the left?
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-Fetal hb
-CO poisoning |
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Why does Hb F shift to the left?
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Decreased affinity for 2,3DPG
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Why does CO poisoning shift the curve to the left?
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Hb's affinity for CO is 200X higher than for O2
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What is Hypoxia?
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Decreased O2 delivery to a tissue due to low o2 CONTENT
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What is hypoxemia?
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Decreased amount of DISSOLVED O2 in the blood
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What is a condition that could be hypoxia without hypoxemia?
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Anemia - the total CONTENT is decreased, but not the PO2 of blood
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And what is dissolved O2 determined by?
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The Po2
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What are 5 causes of HypoXEMIA?
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-High altitude
-Hypoventilating -Pulmonary Fibrosis -VQ defect -Shunt |
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What are 5 causes of Hypoxia?
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-Decreased cardiac output
-Hypoxemia -Anemia -CO poisoning -Cyanide poisoning |
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What is the dominant form of CO2 transport in blood?
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Bicarbonate ion - 90%
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How is CO2 converted into Bicarb?
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By hydration in RBC's
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How does CO2 from tissues get into RBCs?
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By diffusion
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What enzyme catalyzes formation of H2CO3 in RBCs?
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Carbonic anhydrase
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What causes HCO3 to leave RBCs? Where?
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Cl shifts in to displace HCO3 - in PLASMA
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What happens to the Bicarb in plasma after Cl shift?
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Transport to lungs in plasma
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So the major form of transporting CO2 to the lungs is:
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Bicarb in Plasma!
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What happens to the H+ that comes from breaking down H2CO3 in the RBCs?
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It is BUFFERED by deoxyhemoglobin!
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What is the fate of HCO3 in the lungs?
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The opposite of what happened in the tissues; enter RBCs, reforms H2CO3, breaks down into CO2 + H2O, breathe out CO2 after diffusion out of RBC.
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