10b.5 Understanding Partial Pressure

Question 1

What does partial pressure describe?

Answer 1

The amount of a specific gas (O₂ or CO₂) in air, the alveoli, or the blood.

Question 2

Why is partial pressure important in physiology?

Answer 2

It drives gas exchange between the lungs and blood.

Question 3

What is atmospheric pressure at sea level?

Answer 3

Approximately 760 mmHg.

Question 4

What causes atmospheric pressure?

Answer 4

The weight of the air above us pushing down.

Question 5

How is the pool analogy related to pressure?

Answer 5

Deeper = more water above = more pressure; similarly, lower altitude = more air above = more pressure.

Question 6

What happens to pressure as altitude increases?

Answer 6

Atmospheric pressure decreases.

Question 7

What is absolute pressure?

Answer 7

Pressure compared to a vacuum (which has zero pressure).

Question 8

What is the formula for partial pressure of a gas?

Answer 8

Partial Pressure = (% of gas) × (Atmospheric Pressure)

Question 9

What percentage of air is oxygen at sea level?

Answer 9

Approximately 21% oxygen.

Question 10

Calculate the partial pressure of oxygen at sea level.

Answer 10

0.21 × 760 mmHg ≈ 160 mmHg.

Question 11

At high altitude, what happens to the % of O₂ in the air?

Answer 11

It stays the same (21%).

Question 12

Why is there “less oxygen” at high altitude?

Answer 12

Atmospheric pressure is lower, so the partial pressure of oxygen is lower.

Question 13

If atmospheric pressure is 600 mmHg at altitude, what is PO₂?

Answer 13

0.21 × 600 ≈ 126 mmHg.

Question 14

How can we increase partial pressure clinically?

Answer 14

Increase the fraction of inspired oxygen (FiO₂) using supplemental O₂.

Question 15

What happens when FiO₂ is increased to 50% at sea level?

Answer 15

PO₂ = 0.50 × 760 ≈ 380 mmHg.

Question 16

Why is partial pressure used instead of gas concentration in blood gases?

Answer 16

Partial pressure determines gas diffusion across membranes (not % concentration).