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32 Cards in this Set

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