Ventilation - Trachte

Question 1

What does ventilation refer to?

Answer 1

The amount of air entering and leaving the lungs per minute.

Describes how gas (oxygen) gets to the alveoli.

Question 2

What is alveolar ventilation?

Answer 2

The amount of air exchanging with blood.

Question 3

What are the different lung volumes?

Answer 3

• Total lung capacity
• Vital capacity
• Tidal volume
• Residual volume
• Functional residual capacity

Question 4

What is the total lung capacity?

Answer 4

• Vital capacity + residual volume
  
  • usually about 6,000 mL depending on size of person & altitude

Question 5

Can the total lung capacity be measured directly?

Answer 5

NO

Measured indirectly by dilution of a nonexchangeable gas (He) or with a body plethysmograph.

Question 6

What is the Vital Capacity?

Answer 6

• The maximum volume of air that can be exhaled after a maximum inspiration
  
  • usually about 6,000 mL
    
    • depends on size & altitude
    • decreases with age

Question 7

Can the Vital Capacity be measured directly?

Answer 7

Yes

(measured with spirometer)

Question 8

What is the Residual Volume?

Answer 8

• The amount of air remaining in the lungs after a maximal expiration.
  
  • usually about 1,500 mL

Question 9

Can the Residual Volume be measured directly?

Answer 9

NO

Measured indirectly by dilution of a nonexchangeable gas (He) or with a body plethysmograph.

Question 10

What is the Functional Residual Capacity?

Answer 10

• The amount of air remaining after a typical exhalation
  
  • the natural resting state when the lungs and chest wall are not expanded (at rest)
    
    • usually about 2,500 mL

Question 11

Can the functional residual capacity be measured directly?

Answer 11

NO

Measured indirectly with a gas dilution technique using a nonexchangeable gas (He) or with a body plethysmograph.

Question 12

What is the Tidal Volume?

Answer 12

• The amount of air normally inhaled & exhaled per breath
  
  • usually 500 mL per breath
    
    • 500 mL x 15 breaths/min = 7,500mL/min

Question 13

Can the Tidal Volume be measured directly?

Answer 13

Yes

Question 14

What is the relationship between CO₂ concentration in alveolar gas and ventilation?

Answer 14

• [CO₂] in alveolar gas is INVERSELY related to ventilation
  
  • Alveolar ventilation = V_CO2/P_CO2 x K
    
    • amount of CO₂ in the exhaled air divided by the fractional concentration of CO₂ in the expired air

Question 15

What is anatomic dead space?

Answer 15

• Conducting airways
  
  • The amount of a breath not reaching alveoli.

Question 16

How do you measure the dead space volume?

Answer 16

• Measured by breathing in pure O₂
  
  • _​expired gas is plotted vs. N₂ in expired gas
  • the [N₂] increases with expiration until it reaches a constant level = pure alveolar gas
  • Dead Space = the volume that corresponds with the midpoint [N₂] or half-maximal [N₂]​
    
    • it measures the midpoint in the transition from dead space to alveolar ventilation

Question 17

What is physiologic dead space?

Answer 17

The amount of a breath not exchanging with blood.

Question 18

How can physiologic dead space be measured?

Answer 18

• Measured by ration of CO₂ in expired air vs. arteries
• taking the fraction of CO₂ in expired gas and comparing it to alveolar gas
  
  • Vd/VT = (PA_CO2 – PE_CO2)/PA_CO2
    
    • ​Called the Bohr equation

Question 19

Are the lower or upper regions of the lungs more/better ventilated? Why?

Answer 19

LOWER

Lower regions of the lung are perfused better (more blood goes to lower region due to gravity)