2.4 Ventilation/Perfusion

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What is the consequence of having high ventilation but low perfusion in the lung?

Increased dead space

Which of the following describes a reason for nonuniform ventilation of the alveoli?

Different metabolic demands in different lung regions

What is the purpose of the shunt equation in understanding pulmonary physiology?

To quantify the amount of blood bypassing the lungs

How does physiologic dead space affect gas exchange in the lungs?

It decreases alveolar ventilation

Which statement accurately summarizes regional differences in ventilation and perfusion?

V/Q ratios vary across different lung regions

How do V/Q ratios relate to gravity in the lungs?

V/Q ratios are highest at the lung's apex due to gravity

What influences mixed venous blood to bring CO2 into the lungs and take up alveolar O2?

Both neural and humoral/chemical regulation

Which of the following is a pulmonary vasoconstrictor that increases pulmonary vascular resistance (PVR)?


What effect does sympathetic innervation have on pulmonary vascular resistance (PVR)?

Increases PVR

Which chemical is known to produce vasodilation in the pulmonary vasculature?


What intrinsic autoregulation mechanism produces vasoconstriction in the pulmonary vasculature?

Hypoxic pulmonary vasoconstriction

How does parasympathetic innervation affect the pulmonary vasculature?

Causes vasodilation

What is the impact on the V/Q ratio when the airway is occluded, preventing ventilation?

V/Q = 0

What does a shunt in the context of gas exchange refer to?

Allows blood to reach the arterial system without passing through ventilated lung regions

How does a pulmonary embolus affect the V/Q ratio?

V/Q increases

What happens if there is matched ventilation and perfusion at the alveolar-capillary unit?

Optimal gas exchange

What is the impact of an intrapulmonary shunt on alveoli?

Alveoli are underventilated or overperfused

How are small shunts typically identified?

By measuring partial pressures during 100% inspired oxygen

What can cause nonuniform ventilation of the alveoli?


What is one cause of nonuniform ventilation due to obstruction according to the text?

Decreased lumen

How can one assess the distribution of inspired gas in the lungs?

Lung scans after IV administration of dissolved Xe

What may lead to nonuniform compliance in different lung regions?

Regional variations in surfactant production

What is the physiological shunt equal to?

Physiological dead space

What does a pathological right-to-left intracardiac shunt involve?

An abnormal passage between the right and left sides of the heart

What is the equation to calculate venous admixture in the context of shunting?

Shunt equation

Supplemental oxygen will not improve which type of shunt?

Absolute intrapulmonary shunt

Intrapulmonary shunts are associated with which of the following?

Collapsed alveoli

What does increased arterial-alveolar CO2 difference indicate?

An increase in physiological dead space

What is the primary cause of a normal (A-a) DO2?

Ventilation-perfusion mismatch

Which regions of the lung have high VA/Q ratios?

"Apical regions"

Absolute intrapulmonary shunts are also known as 'true shunts' and can be improved with supplemental oxygen.


Physiological shunt corresponds to anatomic dead space in the lungs.


Anatomic shunts include venous blood from bronchial, thebesian, and pleural veins entering the left ventricle without passing through pulmonary capillaries.


Absolute intrapulmonary shunts are associated with well-ventilated alveoli.


What is the key feature of an anatomic shunt?

Blood from pleural veins entering the left ventricle without passing through pulmonary capillaries

How do absolute intrapulmonary shunts differ from shunt-like states?

Absolute shunts cannot be improved with supplemental oxygen, while shunt-like states can

What does the shunt equation conceptually divide all alveolar-capillary units into?

Well-ventilated and poorly ventilated units

Which is a pathologic characteristic of the pulmonary vasculature that may contribute to nonuniform ventilation of the alveoli?

Compression by tumors causing regional compliance issues

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