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32 Cards in this Set
- Front
- Back
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Why is it ideal for all alveolar capillary units to receive the same proportion of alveolar ventilation and cardiac output?
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So that air and blood can get together for exchange to occur.
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What will the PO2 and PCO2 be in an alveolus that is ventilated but not perfused? What is an alveolus called in this situation?
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-Equal to atmospheric levels
-Called Alveolar Dead Space |
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What is the normal value of inspired PO2?
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150 mm Hg
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What is the normal mixed venous PO2?
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40 mm Hg
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What is the normal alveolar PCO2?
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45 mm Hg
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What is the VQ ratio when a unit's ventilation and perfusion are perfectly matched?
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1
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What are the PAO2 and PACO2 in an alveolus with a VQ ratio of 1?
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PAO2 = 100 mm Hg
PACO2 = 40 mm Hg |
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What is the VQ ratio when a unit is perfused but not ventilated?
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0
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What are the PAO2 and PACO2 in an alveolus with a VQ ratio of 0?
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PO2 = 40 mm Hg
PCO2 = 45 mm Hg Equal to mixed venous blood |
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What is the VQ ratio when a unit is ventilated but not perfused?
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Infinity
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What are the alveolar gas tension in an alveolus that is ventilated but not perfused?
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Equal to atmospheric
PO2 = 150 mm Hg PCO2 = 0 |
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Where is bloodflow fastest in the lung?
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At the bottom
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Where is ventilation fastest in the lung?
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At the bottom
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What's higher/faster at the top of the lung; ventilation or bloodflow?
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Ventilation
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What's higher/faster at the bottom of the lung; ventilation or bloodflow?
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Bloodflow
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What is the VQ ratio at the bottom of the lung?
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A little lower than one
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What is the VQ ratio at the top of the lung?
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It shoots up to higher than 3
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So where is the VQ ratio highest in the lungs?
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At the top
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What is the VQ ratio in most of the lung?
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Much closer to 1
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Why does emphysema result in an abnormal VQ ratio in the lungs?
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-Loss of elastic tissue
-Alveoli susc to collapse -Nonuniform time constants -Pendelluft effect |
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What is a SHUNT?
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The passage of deoxygenated blood from venous circulation to arterial circulation without picking up o2.
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What is the normal Physiologic Shunt?
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Some blood returns to the left heart without getting oxygenated first due to pulmonary venous admixture
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Sources of the normal physiologic shunt (4):
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1. Thebesian circulation perfusing the left ventricle
2. Bronchial circulation empties into pulmonary veins 3. Atelectasis 4. Congenital defects |
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What is Atelectasis?
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The few collapsed alveoli that even normal people get
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What congenital defects cause shunting?
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Atrial or Ventricular septal defects
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How do you calculate the fraction of cardiac output that gets shunted normally?
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Q(shunt)= O2(end cap) – art O2
------- ------------------- Q(total)= O2(end cap) – venous O2 content |
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If arterial oxygen levels are below normal because of an abnormal VQ ratio, what might help?
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Increasing the percentage of oxygen in inspired air - only to a point though.
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Why doesn't increasing inspired oxygen content help if the shunt is 50%?
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Because in the lungs, you're at the top of the oxygen dissociation curve, where changes in blood oxygen content don't change PO2 much.
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How much does breathing 100% oxygen help if a person has a 50% shunt?
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Not much at all - the change in arterial oxygen will be only very minimal.
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What happens to blood oxygen content and pressure values as blood passing normal and blocked alveoli mixes?
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O2 content gets averaged
PO2 does NOT get averaged; it's determined by the dissociation curve. |
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What happens normally as you increase inspired air oxygen?
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Arterial oxygen rises proportionately.
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What happens as you increase inspired air oxygen and the percent severity of shunt increases?
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Increasing inspired oxygen helps less and less.
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