V: Regional Distributions of Ventilation

Question 1

To awaken the respiratory system to life, the volumes of the lung must be _______ as a function of time.

Answer 1

dynamically ventilated

Question 2

What is the total ventilation of the system defined as?

Answer 2

the exhaled tidal volume multiplied by the breathing frequency (VE=VTxf)

Question 3

What does the dead space of the lungs refer to?

Answer 3

wherever there are no alveoli present and where gas exchange cannot take place with the pulmonary capillary blood (aka, upper airways)

Question 4

What is the volume of the alveolar space equal to?

Answer 4

tidal volume (above FRC) minus dead space volume
VA=VT-VD (~350 mL on average)

Question 5

What is PaCO2 normally regulated at, independent of activity levels?

Answer 5

40 mmHg (whether CO2 production is high or low, arterial content of CO2 remains the same)

Question 6

What is the best clinical indicator of effective or ineffective ventilation?

Answer 6

the PaCO2 of the arterial blood (partial pressure of CO2 in systemic arterial blood)

Question 7

Do the alveoli at the apex or base of the lung have higher compliance? Why?

Answer 7

Alveoli at the base of the lung have higher compliance (more easily stretched) because the alveoli are under-stretched due to less gravity pulling down on them and elongating them compared to apical alveoli.

Question 8

Is the lung designed for diffusion? Why or why not?

Answer 8

Yes it is, due to its very large area for diffusion (70 m^2) and its very thin wall (<1 um).

Question 9

What are the units for conductance?

Answer 9

mL/min x mmHg

Question 10

What is the first air to reach the alveolar space vs. the first air to be exhaled?

Answer 10

“dirty” air left over in dead space from the previous exhalation is the first air to reach the alveolar space, and the left over clean air that was not able to reach the alveolar space is the first to leave

Question 11

Is PACO2 directly or inversely proportional to alveolar ventilation?

Answer 11

inversely proportional (lower PACO2 indicates better ventilation)

Question 12

What is the difference between hyperpnea and hyperventilation?

Answer 12

In hyperpnea, the increased alveolar ventilation rate is desirable, as it meets the body’s needs by matching increased CO2 production. In hyperventilation, increased alveolar ventilation is inappropriate for the body’s needs. (the same thought process can be applied to hypopnea vs. hypoventilation)