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28 Cards in this Set
- Front
- Back
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Why does the partial pressure of O2 go down as we move into the lungs? |
Because we have water and CO2 coming out of the blood, so total pressure is the same but partial pressure of O2 is lower because these other gases take up part of it |
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Why does PO2 decrease as we enter capillaries? |
Because some venous blood that comes through does not see the alveoli |
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What are typical alveolar, arterial, and venous oxygen partial pressures at sea level? |
alveolar - 100 mmHg arterial - 100 mmHg venous - 40 mmHg |
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What are typical alveolar, arterial, and venous carbon dioxide partial pressures at sea level? |
Alveolar - 40 mmHg Arterial - 40 mmHg Venous - 46 mmHg
-driving force pushes CO2 out of body (atmosphere lower) |
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How long does it normally take the PO2 in pulmonary capillaries to reach that of alveoli? |
.25 sec -In abnormal may take full contact time of 0.75 sec but will get there eventually -In very sick ma not reach full PO2 despite contact time |
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Name two limitations on diffusion |
Pulmonary edema Interstitial fibrosis
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What is pulmonary edema? |
-Alveoli become filled with fluid -Gas exchange cannot occur since the fluid displaces the air |
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Interstitial fibrosis |
-Alveoli become inflamed and scar tissue forms in the interstitial layers of the alveolar walls. -Thickens diffusion membrane |
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Hemoglobin combines with oxygen is called... |
oxyhemoglobin, red colour |
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Hemoglobin not bound to oxygen is called... |
deoxyhemoglobin, purple colour |
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What does a pulse oximeter measure? |
% saturation = % of all of the hemoglobin molecules that are bound to oxygen |
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What does a hemoglobin molecule consist of? |
Four polypeptide chains of the protein globin. Each protein contains a heme group with an iron atom, each which binds with one O2 molecule. |
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What is the relationship between oxygen saturation and PO2? |
An S-shaped curve |
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What are two physiological advantages to an S-shaped curve? |
-Lower area with a steep curve, a small change in pressure will cause huge change in loading/unloading. Low PO2 in tissues so beneficial to have hemoglobin have low affinity at those low pressures to unload easily. -Parital pressure closer to 100 in lungs, so want hemoglobin to have high affinity to pick up more O2 here, and flattens off because you want this to stay constant even at high PO2 |
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What happens with a right shift of the hemoglobin-oxygen saturation curve? |
Decrease the affinity of Hb for oxygen. -occurs at the level of the tissues
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What causes a right shift in the hemoglobin oxygen saturation curve? |
-Increase in body temp (Warmer in body than lungs) -Decrease in pH (peripheral tissues are more acidic due to higher CO2 levels -Increased PCO2
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What happens with a left shift in the hemoglobin oxygen saturation curve? |
Increases the affinity of Hb for oxygen -happens in the lungs |
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What causes a left shift in a hemoglobin oxygen saturation curve? |
-Decreases in temperature ("cooler" in the lungs) -Increases in pH (less CO2 in lungs because dumped out) -Decreases in PCO2 |
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3 contributors to oxygenation |
-oxygen uptake - How much in alveolus? How much taken into arterial blood? (Alveolar gas equation) -oxygen content - How much O2 in arterial blood? -oxygen delivery - Blood flow needed to actually move blood through body to deliver oxygen |
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Alveolar gas equation |
PAO2 = FiO2 x (PB - PH2O) - (PaCO2/0.8) FiO2 = fraction of inspired oxygen (.21 on room air) PB = barometric pressure (760mmHg at sea level) PH2O = water vapour pressure (47 mmHg) Normal ventilation PaCO2 = 40 mmHg 0.8 = respiratory quotient
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Estimating alveolar oxygen content |
PAO2 approximately equals O2 multiplied by 5 (at sea level) |
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Hypoxemia |
Oxygen saturation of arterial blood is low - need to measure with arterial blood gas sample or pulse oximeter. -happens in shock |
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Hypoxia |
Oxygen levels are low at the levels of tissue themselves |
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Five causes of hypoxemia |
1. Low inspired oxygen 2. Hypoventilation 3. Diffusion impairment - second most common cause 4. Ventilation/Perfusion mismatch - most common cause 5. Right to left shunt - rule out by listening for murmur |
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To know oxygenation of a tissue, where do you take a sample from? |
Immediately downstream of that tissue -Will reflect metabolism and gas levels at that location only |
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What is the A-a gradient? |
The difference between PAO2 and PaO2. Normal is 0-15 mmHg. -Measures the ability of the lungs to load oxygen and blood to pick it up |
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What can we manipulate to change PAO2? |
-Increase inspired oxygen to increase levels in alveoli -ventilate patient to remove CO2 -can not influence barometric pressure, water vapour pressure or respiratory quotient
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How do you calculate oxygen content? |
content = (1.32 x Hb x O2 Sat%) + (PO2 x 0.003)
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