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15 Cards in this Set
- Front
- Back
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Define Oxygen cascade. (OC)
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The OC is the process of diminishing or declining O2 tension from the atmospheric environment down to the cellular level, specifically the mitochondria.
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Within atmospheric conditions, what is the partial pressure of O2?
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It is about 159mm/Hg.
O2, being a gas exerts a partial pressure within the environmental atmosphere. At sea level the AP is 760mm/Hg, and O2 makes up about 21% (20.094) of inspired air. 760 X 0.21 = 159mm/Hg. |
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What is the starting point of the O2 cascade?
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As it moves down through the body to the cell, O2 will be diluted down, extracted or lost, so that at cellular level the PO2 may be 3 or 4 mm/Hg.
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Technically, does O2 ever encounter obstacles in its path?
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Yes. O2 encounters water vapor, which will humidify the inspired air, and dilutes the quantity of O2. This will reduce the partial pressure by the saturated vapor pressure which is about 47mm/Hg.
This will influence affect the PIO2 which is recalculated as (760-47) X 0.2094 = 149mm/Hg. |
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What is PIO2?
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PIO2,
It is the symbol for partial pressure of inspired oxygen. |
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Air consists of O2 and N2, but as gas moves into the alveoli, a third gas such as CO2 is present. True/False
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True. The alveolar CO2 level (PACO2) is about the same as the arterial CO2 level.
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How can one calculate the alveolar partial pressure of O2?
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It is calculated thusly:
PAO2=PIO2 - PaCO2/R. R is the respiratory quotient, which is the quantity of CO2 excreted for the amount of O2 utilized. |
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In reference to question 7, what will the PAO2 be if the respiratory quotient is 0.8?
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149-(40/0.8) = about 100mm/Hg.
PAO2 = PIO2(149) - PaCO2(40)/R (0.8) The next step would be movement of O2 from alveolus to artery due to 5-10mm/Hg gradients. |
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O2 is continuously extracted through the capillary network, such that the partial pressure of O2 in mixed venous blood, PVO2, is about 47mm/Hg. TRUE/FALSE
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TRUE.
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What is PVO2?
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PVO2 is the symbol for Mixed Venous Oxygen Tension.
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Give an example of regarding the delivery of O2 at any point in the cascade.
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At 19,000 feet, the barometric pressure is half with respect to that at sea level. The FiO2 is 21%, the PIO2 is only 70mm/Hg, half that at sea level.
If the barometric pressure is increased, (hyperbaric chambers), the PIO2 will be higher. |
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What is FiO2?
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The air around us is made up of 78.1% nitrogen, 20.9% oxygen, 0.9% argon and 0.1% carbon dioxide and other gases. Therefore, your FiO2 is 0.21 (21%). If someone in the hospital is on a breathing machine that is delivering pure 100% oxygen, then his/her FiO2 would be 1.00 (100%).
They named it such because, as you point out, it stands for "fraction of inspired oxygen". In other words, it is the "fraction" of the "inspired" air (inspire means to breathe in) that is made up of "oxygen", O2. |
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List four factors that affect O2 delivery from the alveoli to the capillaries.
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1. V/Q mismatch (ventilation/perfusion)
2. Right to left shunt 3. Diffusion defects 4. Cardiac output. |
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List several factors that determine the quantity of O2 in the blood.
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1.O2 carrying capacity
2. Serum Hb level 3. Percentage of Hb saturated with o2 4. CO (cardiac output) 5. Quantity of O2 dissolved. |
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How is the PVO2 determined?
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It is determined by whole body O2 demand, and the capacity of the tissues to extract O2. In infectious states, there is usually is an abnormality of tissue O2 extraction.
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