Respiratory Physiology Lecture 5 Part 22: Ventilation-perfusion Relationship

Question 1

What area of the lung should inspired air be delivered to? What effects this?

Answer 1

It is important that inspired air is delivered to regions of the lung
where the blood is going and vice versa

The ventilation/perfusion (V/Q) ratio may effect this

Question 2

ventilation

Answer 2

V
Ventilation (V) refers to the flow of air into and out of the alveoli, while perfusion (Q) refers to the flow of blood to alveolar capillaries. Individual alveoli have variable degrees of ventilation and perfusion in different regions of the lungs

Question 3

Perfusion

Answer 3

Q
Perfusion refers to the blood flow to tissues and organs. Alveoli are perfused by capillaries so the diffusion of oxygen and carbon dioxide can take place

Question 4

ventilation/perfusion (V/Q) ratio

Answer 4

ventilation/perfusion (V/Q) ratio is the balance between the ventilation (Bringing O2 in to/removing CO2 from the alveoli) and the perfusion (Removing O2 from the alveoli and adding CO2)

• Ventilation (V) refers to the flow of air into and out of the alveoli, while perfusion (Q) refers to the flow of blood to alveolar capillaries. Individual alveoli have variable degrees of ventilation and perfusion in different regions of the lungs

Question 5

What does the V/Q ration strongly effect?

Answer 5

The ratio between the ventilation and the perfusion is one of the major factors affecting the alveolar (And therefore arterial) levels of O2 and CO2

Question 6

What happens to the gases with greater ventilation?

Answer 6

The greater the ventilation, the more closely alveolar PO2 and PCO2 approach their respective values in inspired air (more closely resemble the atmosphere)

⇡ PO2

⇣ PCO2

Question 7

What happens to the gases with greater perfusion?

Answer 7

The greater the perfusion, the more closely the composition of local alveolar air approaches that of mixed venous blood

⇣ PO2

⇡ PCO2

Question 8

Normal V/Q ration

Answer 8

Question 9

High V/Q ratio

Answer 9

High V/Q ratio = alveolar or physiologic dead space

Ventilated alveoli that lack perfusion

• Alveolar dead volume is region of high ventilation to low perfusion due to pathological condition in which alveoli are over-ventilated because of being underperfused
• No/ little O2 passes through lungs to vascular
• gases become similar to atmosphere

Question 10

Alveolar dead volume

Answer 10

Alveolar V_D

Regions of lung with high V/Q ratios. Regions that are relatively over ventilated (UNDERPERFUSED) so that a portion of the fresh air reaching these alveoli can not be taken up by the blood.

Question 11

Anatomical dead volume

Answer 11

Anatomical V_D

Volume of conducting airways that do not participate in gas exchange

Question 12

Low V/Q ratio

Answer 12

Low V/Q ratio = airway obstruction → shunt

• The blood and alveoli eventually equilibrate because not enough new fresh O2 is being delivered from alveoli to blood since there is no gas exchange with the atmosphere

Question 13

What is a shunt?

Answer 13

A portion of the venous blood doesn’t get oxygenated and goes back to arterial blood

• the passage of deoxygenated blood from the right side of the heart to the left without participation in gas exchange in the pulmonary capillaries. … A pulmonary shunt often occurs when the alveoli fill with fluid, causing parts of the lung to be unventilated although they are still perfused.