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22 Cards in this Set

  • Front
  • Back
Give the values of the PO2 gradient between the atmosphere and the tissues.
Atmosphere = 150
Nasal cavity = 140
Alveoli = 100
Pulmonary capillary = 98
artery = 96
tissues = 20
What is the alveolar gas equation (in its simplified form)?
PAO2 = PiO2 - (PACO2/0.8)
What is a normal value for the A-a difference? List three causes for inflation of this value.
1.diffusion barrier
2.Anatomical shunt
3.Perfusion-ventilation inequality
What is an anatomical shunt?
Any circulation that bypasses the lungs and does not contribute to the oxygenation of blood leaving the left heart.
What are two non-pathological examples of an anatomical shunt?
*the thebesian veins, which drain into the left ventricle
*the bronchial veins, which drain into the pulmonary veins
What percentage of cardiac output is normally shunted around the lung? What is the percentage in cases of atrial septal defect?
What is a pathological shunt? Does supplemental oxygen help patients with pathological shunts?
*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
How is PaCO2 affected in cases of pathological shunt?
PaCO2 is usually normal, as increased PCO2 triggers hyperventilation thus allowing the lungs to breath off excess CO2.
What two factors determine the PO2 of blood exiting a pulmonary capillary bed?
*rate of perfusion (Q)
*rate of alveolar ventilation (V)
What is a normal value for the ratio of ventilation to perfusion?
0.8-1, indicating that ventilation and perfusion are nearly equal.
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.
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.
How is capillary blockage reflected in V/Q? What happens to the PAO2 of the alveoli ventilating such a capillary?
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.
Describe the vertical gradient of V/Q through the lung. What value do the majority of alveoli operate at?
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.
What happens to the value of V/Q in patients with emphysema? What causes this effect?
*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
What happens to the value of V/Q in patients with bronchitis? What causes this effect?
*V/Q is less than 1
*airways are blocked and ventilation decreases
*perfusion remains constant
*this can be thought of as a pathological shunt
What happens to the vertical gradient of V/Q during exercise?
The gradient disappears as the entire lung is used to provide oxygen to the body.
List four pulmonary causes for pathophysiological hypoxemia.
1.V/Q mismatch
2.Physiological shunt
3.Diffusion impairment
Name three clinical conditions that result in a V/Q mismatch. What happens to the A-a difference in these cases?
*Asthma, bronchitis, cystic fibrosis
*A-a difference increases
Name two clinical conditions that cause physiological shunts. What happens to the A-a difference in these cases? Will supplemental oxygen help these patients?
*ARDS, COPD, arterial-venous fistulas
*A-a difference increases
*supplemental oxygen will not help (except for a minimal increase in dissolved gas)
Where is the pathology in cases of hypoventilation? What happens to the A-a difference in these cases? Will supplemental oxygen help these patients?
*Typically in the regulation of respiration, rather than in the lung itself
*no change in A-a
*supplemental O2 will help
Name two clinical conditions that cause diffusion impairment. What happens to the A-a difference in these cases? Does supplemental O2 help?
*fibrosis, pulmonary edema
*A-a increases
*patients will respond to supplemental O2
Name 3 non-pulmonary causes of hypoxemia.
1.Low atmospheric PO2 (altitude)
2.Intercardiac right-to-left shunt
3.Low O2 carrying capacity of blood (anemia, CO poisoning)