Lecture 16: O2 and CO2 exchange

Question 1

How do we exchange gas?

How do gases get across the barrier?

Answer 1

• Gases moves across the alveolar capillary via diffusion
• The difference in partial pressures of oxygen and carbon dioxide drives the gases to exchange so that the pressure equilibrate

Question 2

What is partial pressure determined by?

Answer 2

• Composition of inspired air
• Alveolar venitilaiton
• O2 consumption of CO2 production
• Matching of alveolar ventilation to pulmonary capillary blood flow

Question 3

What does alveolar ventilation measure?

Answer 3

VA - measures the flow of fresh gases into and out of the alveoli during a particular time

Question 4

What is dead space?

Answer 4

Air that is inhaled by the body in breathing BUT does not take partake in the gas exchange
- some of the inhaled air never get to the alveoli so cannot gas exchange - known as dead space

Question 5

What is Fick’s law of diffusion?

What does gas transfer diffusion depend on?

Answer 5

• Describes the movement of gas across the alveolar capillary membrane
  DEPENDS ON:
• Thickness (T) of alveolar membrane; reduction in (T) pulmonary fibrosis
• Alveolar area for diffusion; reaction is SA - emphysema
• Pressure difference which drives diffusion = alveolar - arterial

Question 6

How much oxygen is consumed by the body?

How much oxygen is consumed during exercise?

Answer 6

O2 consumption VO2 = 250 - 3– ml/min

This increases with exercise to VO2 = up to 4L/min

Question 7

How much carbon dioxide is consumed by the body?

How much carbon dioxide is consumed during exercise?

Answer 7

CO2 production VCO2= 200 - 250 ml/min

This can increase >5L/min with exercise due to ANAEROBIC metabolism

Question 8

What is the volume of a single breath?

What is respiratory exchange?

Answer 8

Volume of a single breath = tidal volume = Vt = 500ml
- Due to dead space we consume less O2
Respiratory exchange = VCO2 / VO2 = o.8

Question 9

What factors effect PAO2? (arterial oxygen pressure)

What is the PAO2 level?

Answer 9

PAO2 is dependant on:
- PO2 of inspired air
- oxygen consumption
- Alveolar ventilaiton
It is kept constant at 100mmHg

Question 10

What factors effect PACO2?

What is the PACO2 level?

Answer 10

PACO2 is dependant on:

• PCO2 of inspired air
• carbon dioxide production
• Alveolar ventilation