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22 Cards in this Set
- Front
- Back
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Give the values of the PO2 gradient between the atmosphere and the tissues.
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Atmosphere = 150
Nasal cavity = 140 Alveoli = 100 Pulmonary capillary = 98 artery = 96 tissues = 20 |
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What is the alveolar gas equation (in its simplified form)?
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PAO2 = PiO2 - (PACO2/0.8)
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What is a normal value for the A-a difference? List three causes for inflation of this value.
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*2-12mmHg
1.diffusion barrier 2.Anatomical shunt 3.Perfusion-ventilation inequality |
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What is an anatomical shunt?
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Any circulation that bypasses the lungs and does not contribute to the oxygenation of blood leaving the left heart.
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What are two non-pathological examples of an anatomical shunt?
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*the thebesian veins, which drain into the left ventricle
*the bronchial veins, which drain into the pulmonary veins |
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What percentage of cardiac output is normally shunted around the lung? What is the percentage in cases of atrial septal defect?
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*1-2%
*50-60% |
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What is a pathological shunt? Does supplemental oxygen help patients with pathological shunts?
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*An airway is blocked, thus blood perfusing that area of the lung is not oxygenated
*no, the airways are still blocked and thus the blood does not come into contact with oxygen |
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How is PaCO2 affected in cases of pathological shunt?
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PaCO2 is usually normal, as increased PCO2 triggers hyperventilation thus allowing the lungs to breath off excess CO2.
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What two factors determine the PO2 of blood exiting a pulmonary capillary bed?
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*rate of perfusion (Q)
*rate of alveolar ventilation (V) |
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What is a normal value for the ratio of ventilation to perfusion?
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0.8-1, indicating that ventilation and perfusion are nearly equal.
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How is an alveolar obstruction reflected in the ventilation-perfusion ratio? Track the PO2 of the blood as it enters and leaves the capillary perfusing this alveolus.
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In this case, V/Q will be less than 1 as alveolar ventilation is reduced while perfusion remains constant. The blood passing through remains at the same PO2. This is equivalent to a pathological shunt.
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How is capillary blockage reflected in V/Q? What happens to the PAO2 of the alveoli ventilating such a capillary?
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In this case, V/Q is greater than 1 because Q decreases while V remains constant. PAO2 rises to 150mmHg because no oxygen is being drawn out by blood.
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Describe the vertical gradient of V/Q through the lung. What value do the majority of alveoli operate at?
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It is highest in the upper regions (4) and decreases through the middle (1) and lower (0.7-0.8) regions. The majority of alveoli operate at V/Q = 1.
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What happens to the value of V/Q in patients with emphysema? What causes this effect?
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*V/Q becomes greater than 1
*alveoli coelesce such that some capillaries continue to serve unventilated areas and this reduces the effective perfusion *similar to physiological dead space *ventilation remains ~constant |
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What happens to the value of V/Q in patients with bronchitis? What causes this effect?
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*V/Q is less than 1
*airways are blocked and ventilation decreases *perfusion remains constant *this can be thought of as a pathological shunt |
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What happens to the vertical gradient of V/Q during exercise?
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The gradient disappears as the entire lung is used to provide oxygen to the body.
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List four pulmonary causes for pathophysiological hypoxemia.
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1.V/Q mismatch
2.Physiological shunt 3.Diffusion impairment 4.Hypoventilation |
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Name three clinical conditions that result in a V/Q mismatch. What happens to the A-a difference in these cases?
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*Asthma, bronchitis, cystic fibrosis
*A-a difference increases |
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Name two clinical conditions that cause physiological shunts. What happens to the A-a difference in these cases? Will supplemental oxygen help these patients?
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*ARDS, COPD, arterial-venous fistulas
*A-a difference increases *supplemental oxygen will not help (except for a minimal increase in dissolved gas) |
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Where is the pathology in cases of hypoventilation? What happens to the A-a difference in these cases? Will supplemental oxygen help these patients?
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*Typically in the regulation of respiration, rather than in the lung itself
*no change in A-a *supplemental O2 will help |
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Name two clinical conditions that cause diffusion impairment. What happens to the A-a difference in these cases? Does supplemental O2 help?
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*fibrosis, pulmonary edema
*A-a increases *patients will respond to supplemental O2 |
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Name 3 non-pulmonary causes of hypoxemia.
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1.Low atmospheric PO2 (altitude)
2.Intercardiac right-to-left shunt 3.Low O2 carrying capacity of blood (anemia, CO poisoning) |
