Ch 5 Ventilation Part 1 Flashcards
(42 cards)
What is the primary function of the lung?
Gas exchange
This includes the movement of gases between the atmosphere and the tissues.
What are the three mechanisms of hypoxemia?
- Hypoventilation
- Diffusion limitation
- Shunt
What determines the level of alveolar Po2?
The balance between the rate of removal of O2 by the blood and the rate of replenishment by alveolar ventilation
The removal of O2 is influenced by tissue metabolic demands.
What happens to alveolar Po2 during hypoventilation?
It falls
This occurs because of reduced alveolar ventilation.
What is hypoventilation?
Abnormally low alveolar ventilation
This leads to increased arterial Pco2.
What are common causes of hypoventilation?
- Drugs (e.g., morphine, barbiturates)
- Damage to the chest wall
- Respiratory muscle paralysis
- High resistance to breathing
What is the relationship between alveolar ventilation and Pco2?
If the alveolar ventilation is halved, the Pco2 is doubled
This is derived from the alveolar ventilation equation.
What is diffusion limitation in the context of gas exchange?
Inability of O2 to fully equilibrate between alveolar gas and end-capillary blood
This can occur during exercise or with a thickened blood-gas barrier.
What is a shunt in respiratory physiology?
Blood that enters the arterial system without passing through ventilated areas of the lung.
Which types of blood contribute to shunt?
- Bronchial artery blood
- Coronary venous blood
- Abnormal vascular connections in some patients
What is the effect of a shunt on arterial Po2?
It depresses the arterial Po2
This is due to the addition of poorly oxygenated blood.
Can hypoxemia caused by a shunt be corrected by breathing 100% O2?
No
Shunted blood bypasses ventilated alveoli and does not benefit from the higher alveolar Po2.
What is the response of arterial Pco2 to shunt?
Usually does not raise
Chemoreceptors respond to elevated Pco2 by increasing ventilation.
What is the impact of ventilation-perfusion inequality on gas exchange?
It impairs overall gas exchange for both oxygen and carbon dioxide.
What is the ventilation-perfusion ratio?
The relationship between the amount of air reaching the alveoli and the amount of blood flow in the pulmonary capillaries.
What is the significance of the alveolar gas equation?
It relates the components of alveolar gas to the rates of ventilation and metabolism.
What factors can lead to hypoxemia?
- Hypoventilation
- Diffusion limitation
- Shunt
- Ventilation-perfusion mismatch
Fill in the blank: The Po2 of inspired air at sea level is approximately _______.
150 mm Hg
True or False: Diffusion limitation is a common cause of hypoxemia at rest at sea level.
False
It rarely causes hypoxemia at rest due to sufficient time for equilibration.
What is the shunt fraction?
The ratio of shunt flow to total flow in the pulmonary circulation.
What happens to arterial Po2 during 100% O2 breathing in the presence of a shunt?
The arterial Po2 does not rise to the expected level despite the addition of shunted blood with low O2 concentration
This indicates that hypoxemia responds poorly to added inspired O2.
What is the main diagnostic test for hypoxemia caused by shunt?
Inspiring 100% O2
This test reveals that the arterial Po2 does not reach the anticipated level.
How can the size of a shunt caused by mixed venous blood be calculated?
Using the shunt equation.
What is the ventilation-perfusion ratio?
It is the ratio of ventilation (V) to blood flow (Q) in a lung unit.
