Lecture 4: Ventilation and Perfusion Relationships

Question 1

What is the alveolar gas equation?

Answer 1

PA O2 = PI O2 - [(Pa CO2)/R]

Question 2

How do you calculate for the inspired partial pressure of oxygen?

Answer 2

PI O2 = (barometric pressure - water vapor pressure)(fraction of inspired oxygen)

Normal: PI O2 = (760 - 47)(oxygen %)
*all values can change if stated otherwise

Question 3

Ideally, what should the alveolar-arterial gradient be?

Answer 3

<20 mm Hg

Question 4

What can an increase in the alveolar-arterial gradient indicate?

Answer 4

Diffusion Impairment

-something wrong with alveoli

Question 5

At the apex of the lung, we find ____ intrapleural fluid and the intrapleural pressure is ____ negative, so the alveoli are ____ at rest.

Answer 5

At the apex of the lung, we find LESS intrapleural fluid and the intrapleural pressure is MORE negative, so the alveoli are LARGE at rest.

Question 6

At the base of the lung, we find ____ intrapleural fluid and the intrapleural pressure is ____ negative, so the alveoli are ____ at rest.

Answer 6

At the base of the lung, we find MORE intrapleural fluid and the intrapleural pressure is LESS negative, so the alveoli are SMALL at rest.

Question 7

With inspiration, alveoli will get tend to get larger where?

Answer 7

More change in volume seen at base of lung compared to apex

Question 8

What does a high V/Q mean?

Answer 8

Ventilation is HIGH relative to perfusion

Question 9

What does a low V/Q mean?

Answer 9

Ventilation is LOW relative to perfusion

Question 10

What happens during a low V/Q ratio?

Answer 10

Extreme condition: airway blocked

• oxygen content in blood decreases
• carbon dioxide in blood increases
• low pH
• right to left shunt

Question 11

What happens during a high V/Q ratio?

Answer 11

Extreme condition: no blood to alveoli

• pressure in alveolus will become closer to atmospheric conditions (very high oxygen, very low carbon dioxide)
• blood not benefitted
• high pH

Question 12

At the apex of the lung, there is a ____ V/Q ratio:
____ arterial oxygen content
____ arterial carbon dioxide content

Answer 12

At the apex of the lung, there is a HIGH V/Q ratio:

• higher arterial oxygen content
• lower arterial carbon dioxide content

Question 13

At the middle region of the lung, there is a ____ V/Q ratio:
____ arterial oxygen content
____ arterial carbon dioxide content

Answer 13

At the middle region of the lung, there is a NORMAL V/Q ratio:

• normal arterial oxygen content
• normal arterial carbon dioxide content

Question 14

At the base of the lung, there is a ____ V/Q ratio:
____ arterial oxygen content
____ arterial carbon dioxide content

Answer 14

At the base of the lung, there is a LOW V/Q ratio:

• lower arterial oxygen content
• higher arterial carbon dioxide content

Question 15

What is hypoxic vasoconstriction?

Answer 15

Constriction of pulmonary vessels to redirect blood away from hypoxic regions
-minimizes differences in V/Q ratios