Ventilation/Perfusion Abnormalities Flashcards
Consider the regional differences in ventilation between the apex and base of the lung. In relation to these differences:
Resting lung volume is lower at the bases
True. Due to the weight of the lung and higher intrapleural pressure, the resting lung volume is lower at the base than the apex.
Consider the regional differences in ventilation between the apex and base of the lung. In relation to these differences:
Compliance is lower at the bases
False. The slope of the pressure-volume curve is known as compliance. The lung is easier to inflate at low lung volumes, so compliance is higher at the base.
Consider the regional differences in ventilation between the apex and base of the lung. In relation to these differences:
The weight of the lung is uniform
True. The weight of the lung at the base is greater than at the apex.
Consider the regional differences in ventilation between the apex and base of the lung. In relation to these differences:
Intrapleural pressure is higher at the apex
False. Intrapleural pressure is higher, i.e. less negative, at the bases to support the weight of the lungs.
Consider the regional differences in ventilation between the apex and base of the lung. In relation to these differences:
Ventilation is greater at the bases
True. Regional ventilation is defined as change in volume per unit resting volume. Inflation pressure is lower at the bases as is resting volume, hence a greater change is seen when compared with the apices.
With the body in the erect position, going from the apex to the base of the lung:
Ventilation decreases
False. Due to lower resting volume and better compliance, ventilation is greater at the base of the lung.
With the body in the erect position, going from the apex to the base of the lung:
Compliance increases
True. The base of the lung is more compliant due to its position on the pressure-volume curve.
With the body in the erect position, going from the apex to the base of the lung:
Ventilation/perfusion ratio remains constant
False. It decreases from the apex to the base.
With the body in the erect position, going from the apex to the base of the lung:
Blood flow increases
True. Blood flow increases due to differences in hydrostatic pressures, i.e. West zones.
With the body in the erect position, going from the apex to the base of the lung:
Intrapleural pressure increases
True. Due to the increased weight of the lung at the base, an equal, i.e. higher, pressure is required to balance this.
Regarding the relationship between ventilation and perfusion (V/Q):
Ventilation changes more than perfusion
False. Perfusion changes more than ventilation.
Regarding the relationship between ventilation and perfusion (V/Q):
Ventilation increases from the apex to the base
True. Resting volume at the base is lower than at the apex. Ventilation is change in volume per unit volume, so ventilation is greater at the base.
Regarding the relationship between ventilation and perfusion (V/Q):
Perfusion increases from base to apex
False. Perfusion increases due to gravity and hydrostatic pressure differences.
Regarding the relationship between ventilation and perfusion (V/Q):
The ventilation/perfusion ratio at the apex is greater than at the base
True. V/Q is >1 at the apex and <1 at the base.
A reduction in PaO2 can be caused by:
Hypoventilation
True. PaO2 is determined by the rate of removal of oxygen, through metabolism, and rate of replenishment of oxygen, through alveolar ventilation.
A reduction in PaO2 can be caused by:
Breathing an hypoxic mixture
True. This is correct unless there is compensation such as hyperventilation.
A reduction in PaO2 can be caused by:
An increase in dead space
True. An example of this is a pulmonary embolus. The alveolus is ventilated but not perfused so there is no blood to oxygenate, i.e. wasted ventilation.
A reduction in PaO2 can be caused by:
Hypermetabolic states
True. This is correct unless ventilation is increased to compensate.
A reduction in PaO2 can be caused by:
An increase in shunt
True. An example of this is pneumonia. Shunted blood is not exposed to oxygen and therefore depresses arterial oxygen content.
Are these statements true or false?
Hypoventilation causes an increase in PaCO2
True. This can be predicted from the alveolar gas equation.
Are these statements true or false?
Shunt causes an increase in PaCO2
False. Any rise is detected by chemoreceptors resulting in an increase in ventilation.
Are these statements true or false?
The hypoxia caused by shunt can be abolished by increasing inspired oxygen
False. Shunted blood is never exposed to the increase in FiO2 and therefore the reduction in PaO2 persists.
Are these statements true or false?
The hypoxia caused by hypoventilation can be abolished by increasing inspired oxygen
True. The increase in inspired oxygen compensates for the hypoventilation.
Are these statements true or false?
Alveolar (PAO2) and arterial (PaO2) oxygen are usually the same
False. Under normal circumstances there is a small difference between the PAO2 and PaO2 due to incomplete diffusion.
In the shunt equation, used to calculate the degree of shunt, which of these are required?
A. Cardiac output
B. Arterial oxygen content
C. Mixed venous oxygen content
D. End-capillary oxygen content
E. Alveolar carbon dioxide concentration
F. Inspired oxygen concentration
A - D
Qs/Qt = (CcO2 - CaO2)/(CcO2 - CvO2)
E&F PACO2 and FiO2 do not feature in the equation.
Regarding a lung unit:
A normal ventilation/perfusion ratio is about 2.5
False. A normal / ratio is around 1.0.
Regarding a lung unit:
The ventilation/perfusion ratio increases as ventilation falls
False. V/Q decreases and approaches zero.
Regarding a lung unit:
If there is no ventilation, PAO2 and PACO2 are the same as inspired air
False. They become the same as mixed venous blood (shunt with raised CO2). Usually an increase in CO2 is not seen due to compensatory hyperventilation.
Regarding a lung unit:
The ventilation/perfusion ratio approaches infinity (∞) as perfusion increases
False. It approaches ∞ as perfusion decreases.
Regarding a lung unit:
If perfusion is completely abolished, PAO2 and PACO2 are the same as mixed venous levels
False. They become the same as inspired gas (dead space with no increase in CO2).
