Intro

Question 1

What is alveolar ventilation?

Answer 1

Volume of gas per minute that reaches the alveoli

Question 2

What is diffusion (with respect to breathing)?

Answer 2

Movement of CO2 and O2 across the blood-air barrier

Question 3

What is perfusion?

Answer 3

The movement of gas into blood flow/capillary

Question 4

List and describe the 2 types of dead space and approximate volume of each in a normal healthy individual.

Together they are called…

Answer 4

Anatomic dead space

• Includes non-perfusing areas (ex. conducting airways) ~150mL

Alveolar dead space

• Includes alveoli not participating in gas exchange ~25mL

Together they are called Physiological Dead Space.

Question 5

What is the normal PO2? (in venous blood)

Answer 5

PO2 = 40mmHg

Question 6

What is the normal PCO2? (in venous blood)

Answer 6

PCO2 = 46mmHg

Question 7

What is the normal PAO2? (in Alveoli)

Answer 7

PAO2 = 100mmHg

Question 8

What is the normal PACO2 (in Alveoli)

Answer 8

PACO2 ~ 40mmHg

Question 9

What is the normal PaO2? (in arterial blood)

Answer 9

PaO2 ~ 95mmHg

Question 10

What is the normal PaCO2 (in arterial blood)

Answer 10

PaCO2 ~ 40mmHg

Question 11

What is the Alveolar Ventilation Equation?

Answer 11

P_aCO₂ = (Vol CO₂) / (Alveolar Ventilation)

Question 12

What is the Alveolar Air Equation? (ie. equation used to determine PAO2)

Answer 12

P_AO₂ = FIO₂*(Patm-PH₂O) - P_aCO₂/R

Question 13

The ambient air is ____ % O₂ and ____% N₂.

Answer 13

Air is ~21% O₂ and ~79% N₂.

Question 14

What is the normal tidal volume of a healthy individual at rest?

What volume normally reaches the alveoli?

What volume remains in conducting airways?

Answer 14

Tidal Vol = 500mL

Vol reaching alveoli ~ 350mL

Vol remaining in conducting pathways ~ 150mL

- (This 150mL is the dead space volume and remains relatively constant in a normal individual)

Question 15

What does P_aO₂ measure?

Answer 15

The partial pressure of free O₂ in arterial blood. (Does NOT measure O₂ bound to Hb).

Question 16

True/False… Having a P_aO₂ > 100mmHg will increase ability of O₂ to bind to Hb.

Answer 16

False.

Question 17

What percent of O₂ in the blood is…

• dissolved in plasma?
• bound to Hb?

Answer 17

For O₂:

..in plasma ~ 2%

..bound to Hb ~ 98%

Question 18

What percent of CO₂ in the blood is…

• dissolved in plasma?
• bound to Hb?
• dissolved as bicarbonate?

Answer 18

For CO₂:

..in plasma ~ 5-10%

..bound to Hb ~ 30%

..dissolved as bicarb ~ 60%

Question 19

What is O₂ content?

Write the equation to determine O₂ content.

Answer 19

O₂ content is the total amount of O₂ in the blood.

C_aO₂ = (O₂ bound to Hb) + (O₂ dissolved in plasma)

C_aO₂ = (1.34 * Hb * SaO₂) + (0.003 * P_aO₂)

Breaking it down (and adding units) we get:

HbO₂ = 1.34 (mLO₂/gHb) * Hb (g/100mL) * SaO₂ (%) PlasmaO₂ = 0.003 * P_aO₂

Question 20

What is O₂ capacity?

Answer 20

The max amount of O₂ that can be bound to Hb.

Question 21

What is O₂ saturation (SaO₂)?

Answer 21

The % of O₂ binding sites (on Hb) that are bound to O₂.

Question 22

What is the Bohr effect?

Answer 22

H⁺ binds to Hb and reduces its affinity for O₂.

Therefore at lower pH (higher [H⁺]) near the tissues the O₂ is released.

Hb-O₂ binding affinity is inversely proportional to both [CO₂] and [H⁺].

**Think of the Hb dissociation Curve**

Question 23

What is the difference between Hypoxia and Hypoxemia?

Answer 23

Hypoxia = decreased O₂ in the tissues

Hypoxemia = decreased O₂ in the blood

Question 24

What are the 5 main causes of Hypoxemia? Which is the most common?

Answer 24

5 is the most common.

1. Decreased O2 content in air/ Low Inspired O2 “bad air”
2. Hypoventilation “no air”
3. Diffusion Abnormality “slow mixing”
4. Shunting “no mixing”
5. V/Q (Ventilation/Perfusion) Mismatch “bad mixing”

Question 25

What is an example of pathology that causes diffusion abnormality?

Answer 25

Fibrosis of lung tissue

Question 26

What are common causes of V/Q Mismatch?

Answer 26

• PE
• COPD
• Asthma
• Fibrosis
• Pulm HTN

Question 27

Which causes of Hypoxemia have elevated…

          - PaCO2?
          - A-a DO2 gradients?

Can they be treated with Supplemental O2?

Answer 27

_Cause /// PaCO2 /// A-a DO2 grad /// Treat _

**Low inspired O2 **N N Tx with O2

**Hypoventilation ** Inc N Tx with O2

**Diffusion Problem **N E Tx with O2

**Shunting **N Inc O2 ineffective

**V/Q mismatch ** N Inc Tx with O2

*N = normal

*E = elevated with exercise, but normal at rest