Chapter 5

Question 1

What are the Four Causes of Hypoxemia?

Answer 1

• Hypoventilation
• Diffusion Limitation
• Shunt
• Ventilation-Perfusion Inequality

Question 2

What does Hypoventilation do to Alveolar and Arterial Pco2?

Answer 2

• Always increases it

Question 3

What is Hypoventilation?

Answer 3

• Reduced Breathing frequency
• Reduced Breathing Intensity

Question 4

What would Hypoventilation do to Po2?

Answer 4

• Decrease unless additional O2 is inspired

Question 5

How is Hypoxemia easily reversed when it is caused by Hypoventilation?

Answer 5

• Adding O2 to the inspired gas

Question 6

What is a Shunt?

Answer 6

• Very poorly ventilated alveoli

Question 7

How does Hypoxemia respond to added inspired O2 when it is caused by a Shunt?

Answer 7

Poorly
- Arterial Po2 does not rise to the expected levels when 100% O2 is inhaled
- Useful diagnostic test

Question 8

When can the shunt size be calculated?

Answer 8

By the Shunt Equation
- Only if it is caused by mixed venous blood

Question 9

What is the Ventilation Perfusion Ratio?

Answer 9

• VA/Q

Question 10

What does the Ventilation Perfusion Ratio Determine?

Answer 10

• THe gas exchange in any single lung unit

Question 11

What do regional differences in the Ventilation-perfusion ratio of an upright lung cause?

Answer 11

• pattern of regional gas exchange

Question 12

How does a ventilation-perfusion ratio inequality impair the lung?

Answer 12

• impairs uptake of all gases by lung
• Impairs elimination of all gases by lung

Question 13

How can an impairment in CO2 elimination due to ventilation-perfusion inequality be corrected? What about Hypoxemia? Explain the reason for the answer.

Answer 13

CO2 correction
- Increasing ventilation to the alveoli
Hypoxemia
- Cannot be corrected by increased ventilation
Reason
- CO2 and O2 have different shaped dissociation curves

Question 14

What are the two main causes of Hypercapnia?

Answer 14

• Hypoventilation
• Ventilation-perfusion inequality

Question 15

What is Hypercapnia

Answer 15

• CO2 Retention

Question 16

What is the only cause of Hypoxemia that is not corrected by giving 100% O2 to breathe?

Answer 16

• Shunt

Question 17

What is the normal pressure of ambient air at sea level?

Answer 17

• 760mmHg

Question 18

What is the pressure of water molecules in humidified air? (like in the lungs)

Answer 18

• 47 mmHg

Question 19

What is the average percentage of oxygen in the air?

Answer 19

• 20.93%

Question 20

What is the equation for identifying the Partial Pressure of Oxygen in Tracheal Air?

Answer 20

Ota = 0.2093 x (760 - 47)
Ota = 149mmHg

Question 21

What are the average air pressures of different gasses in alveolar air?

Answer 21

• Oxygen: 14.5%
• Carbon Dioxide: 5.5%
• Nitrogen: 80%

Question 22

How do you determine Alveolar Partial Pressures of Oxygen and Carbon Dioxide?

Answer 22

Alveolar PO2 = 0.145 x (760-47)
Alveolar PO2 = 103mmHg

Alveolar PCO2 = 0.055 x (760-47)
Alveolar PCO2 = 39mmHg

Question 23

What does Hypoxemia mean?

Answer 23

• Low PaO2

Question 24

What happens to a small amount of coronary venous blood?

Answer 24

• Drains directly into the cavity of the left ventricle through the thebesian (in the myocardium) veins

Question 25

What happens to some Bronchial Artery Blood in a normal lung?

Answer 25

• Collected by the pulmonary veins after it has perfused the bronchi and its O2 has been partially depleted