Ch 5 Ventilation Part 1 Flashcards
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.
What does a low ventilation-perfusion ratio indicate in a lung unit?
It indicates impaired O2 and CO2 transfer due to mismatched ventilation and blood flow.
What determines the concentration of O2 in a lung unit?
The ratio of ventilation to blood flow (V/Q).
What happens to O2 and CO2 levels when the ventilation-perfusion ratio is decreased?
O2 levels fall and CO2 levels rise.
What is the expected O2 and CO2 composition when ventilation is completely abolished?
It will be the same as that of mixed venous blood.
What is the effect of increasing the ventilation-perfusion ratio by obstructing blood flow?
O2 rises and CO2 falls, approaching the composition of inspired gas.
How is the relationship between Po2 and Pco2 depicted graphically?
Using an O2-CO2 diagram where Po2 is on the x-axis and Pco2 is on the y-axis.
What happens to the ventilation-perfusion ratio from the apex to the base of the lung?
It decreases.
What is the consequence of the high ventilation-perfusion ratio at the apex of the lung?
It results in high Po2 and low Pco2.
What is the main reason a lung with ventilation-perfusion inequality cannot maintain high arterial Po2?
The majority of blood flow comes from lower zones where Po2 is low.
What is the relationship between regional differences in ventilation and blood flow?
Ventilation increases slowly from top to bottom, while blood flow increases more rapidly.
Fill in the blank: The _______ equation is used to calculate the ventilation-perfusion ratio.
[ventilation-perfusion ratio equation]
True or False: A lung with uniform ventilation and perfusion can transfer more O2 and CO2 than one with inequality.
True.
What is the impact of uneven ventilation and blood flow on arterial Pco2?
It will be elevated due to higher Pco2 at the base than at the apex.
What does the O2-CO2 diagram illustrate regarding gas exchange?
It shows the changes in alveolar gas composition with varying ventilation-perfusion ratios.
What is the significance of the differences in pH down the lung?
They reflect the considerable variation in Pco2 of the blood.
What happens to overall gas exchange in the presence of ventilation-perfusion inequality?
The lung cannot transfer as much O2 and CO2 as a uniformly ventilated and perfused lung.
What is the respiratory exchange ratio at the apex compared to the base?
It is higher at the apex due to lower blood flow.
What is the effect of exercise on blood flow distribution in the lung?
It becomes more uniform, increasing O2 uptake at the apex.
