Principles of gas exhange

Question 1

What is ECMO?

Answer 1

A treatment that uses a pump to circulate blood through an artificial lung back into the bloodstream of a very ill baby.

Question 2

Equation for rate

Answer 2

Rate of diffusion directly proportional to A x ΔP

Question 3

What is diffusion dependent on

Answer 3

Diffusion is also dependent on the physicochemical properties of the gas and nature of the membrane (thickness, physicochemical properties- what the membrane is made up of).

Question 4

Pressure gradient

Answer 4

The pressure gradient is the difference in partial pressures of the respective gases in the alveolus and the blood.

Question 5

Partial pressure of a gas in a mixture of gases

Answer 5

The partial pressure of a gas in a mixture of gases is the pressure that it would exert if it was the only gas in the container

Question 6

What is Dalton’s law?

Answer 6

The partial pressure of a gas in a gas mixture = Total pressure x fractional concentration of the gas

Question 7

Why does partial pressure decrease the further you go up?

Answer 7

Higher you go up the earth less partial pressure- 20 tonnes of air above us, further up less air so less partial pressure.

Question 8

Is partial pressure of oxygen in alveoli lower then in room air? Why?

Answer 8

Yes- Lower than in room air because our gases we breathe in mix with our gases we breathe out

Question 9

Why does inspired air need to be humidified?

Answer 9

Inspired air is humidified in the upper airway- need to do this as dry air causes drying out of tissues- which causes it to become the saturated vapour pressure of water

Question 10

What happens to the partial pressure in the alveoli when CO2 is added?

Answer 10

In the alveoli oxygen is taken up while carbon dioxide is added- CO2 dilutes the amount of O2 coming in so partial pressure drops

Question 11

Why does the body consume more oxygen than it produces CO2?

Answer 11

This is due to the R quotient dependent on your diet e.g. carbohydrates for every molecule of oxygen you produce 1 molecule of CO2 – diets have R quotient of about 0.8 means for every 1 molecule of CO2 you produced you consume 1.2 molecules of oxygen as fat has less oxygen than carbohydrate so need more water to produce oxygen and CO2.

Question 12

What effect does humidification have on partial pressure?

Answer 12

• At 37oC the saturated vapour pressure of water ≈ 6.3 kPa
• i.e., the partial pressure of water vapour is 6.3 kPa as it gets down alveolus
• Therefore, in fully humidified air at 37oC the partial pressure of oxygen =
(101.3 (partial pressure at sea level) – 6.3) x 0.21 (fractional conc. of oxygen) = 19.95 kPa

Question 13

What effect does CO2 have on partial pressure?

Answer 13

• A typical value of the alveolar partial pressure of CO2 is 5 kPa
• If one CO2 molecule was produced for every O2 molecule consumed the alveolar partial pressure of oxygen would be 19.95 – 5 = 14.95 kPa
• But, typically 1.25 x as many O2 molecules are consumed as CO2 molecules produced – respiratory quotient as produce less carbon dioxide than oxygen consumed
• Thus, alveolar partial pressure of oxygen = 19.95 – 6.25 = 13.7 kPa

Question 14

What is a shunt?

Answer 14

A shunt is a hole or a small passage which moves, or allows movement of, fluid from one part of the body to another.

Question 15

What is a cardiac shunt?

Answer 15

Where the alveoli oxygen conc. is 13.5kPa and by the time it gets back to the heart, have a cardiac shunt where some of the blood from the right V drops straight into the L atrium which is deoxygenated so when blood comes out of artery is 13.3 kPa.

Question 16

What is Henry’s law?

Answer 16

Henry’s law- for a solution in eq with gas on top of it the partial P of gas in solution = partial P of gas on its surface

Question 17

Is a gas more or less molecules to exert a partial pressure?

Answer 17

Gases are differentially soluble. A gas that is less soluble requires less molecules to exert the partial pressure of that gas in solution to dissolve in that solution.

Question 18

What is the difference between low and high soluble molecules when they drop out of gas into solution?

Answer 18

Low soluble gas molecules drop out of gas into solution and stop as they eq. High soluble gas molecules more molecules dropping into solution much more and only stop once they eq. Exert same partial P eventually but need more highly soluble gas to achieve that.

Question 19

Is CO2 more soluble in water than in oxygen?

Answer 19

Carbon dioxide is approximately 24 times more soluble in water than is oxygen. For every molecule of O2 you can dissolve 24 CO2. CO2 is less partial pressure than O2 for a given number of particles of oxygen.

Question 20

Is relative diffusing capacity a soluble or insoluble process?

Answer 20

Relative diffusing capacity diffusion across membrane is a soluble process as needs to get into blood.

Question 21

Why does oxygen take longer to diffuse across?

Answer 21

Partial pressure is faster than CO2.
O2 we generate a partial pressure (PP) of 8 kPa you have to add the same or similar amount of oxygen molecules which takes longer. This is why oxygen takes longer to diffuse across and generate the PP needed than CO2. This is why it doesn’t follow the role of low solubility gases will eq quicker.

Question 22

Healthy person during exercise speed of oxygen to muscles?

Answer 22

Blood cell now crosses the alveolus in about 0.25 of a second helps generate enough oxygen to your muscles in a quick amount of time. Healthy person still able to oxygenate their blood optimally at max capacity and not having shunting or partial oxygenation.

Question 23

Patient with a restrictive lung disease during exercise what is affected?

Answer 23

Thickening of alveolus which decreases the ability of oxygen to diffuse in. Can’t diffuse quick enough O2 in that time frame to equilibrate it in the blood.

CO2 can as takes less time to equilibrate so normal CO2 but less oxygenation. This is type 1 respiratory failure.

Question 24

What is type 2 restrictive disease?

Answer 24

Type 2 is when they are hypoxic and hypercapnic (too much carbon dioxide (CO2) in your bloodstream).

Question 25

What is the equation for oxygen diffusing capacity?

Answer 25

Oxygen uptake/ Alveolar PO2- mean pulmonary capillary PO2

Question 26

What is the carbon monoxide diffusing capacity equation

Answer 26

Carbon monoxide diffusing capacity = CO uptake/ alveolar PCO

Question 27

What is alveolar thickening?

Answer 27

Pulmonary fibrosis- cause scaring down alveolar- thickening of basement membrane and epithelium- increase time for oxygen to diffuse

Question 28

What is alveolar consolidation?

Answer 28

Pneumonia- fills up lung- shunting- blood goes around alveolus but doesn’t participate in diffusion- blocks off the alveolus

Question 29

What are frothy excretions?

Answer 29

Pulmonary Edema- Mismatch of the R heart pumping well and L heart not pumping well- build-up of fluid in the lungs and L heart won’t get fluid out of lungs

Question 30

What is interstitial edema?

Answer 30

ARDS (adult respiratory distress system)- inflammation of the lungs

Question 31

What is alveolar- capillary destruction?

Answer 31

Emphysema-No tissue inside lungs to keep lungs down so chest moves easily

Question 32

What is alveolar collapse?

Answer 32

Atelectasis- Lose lung elasticity- partial lung collapse- some alveolus shut down so less oxygenation to the body

Question 33

What is ARDS?

Answer 33

Adult respiratory distress syndrome (ARDS)- Alveolus -thick membrane, macrophages moved into alveolus as inflammatory state. Capillary pores opening so fluid and macrophages attack the alveolus.

Question 34

What is atelactasis?

Answer 34

Atelectasis- whiter at the back is where the lungs are starting to collapse on themselves and not part of oxygen exchange anymore

Question 35

What is the problem with obesity?

Answer 35

Compliance is the ability of us to expand our lungs and the amount of gas is moved in change in pressure

Compliance of lungs defined by thoracic wall- lungs have a tendency want to collapse inwards

Obesity causes reduced lung compliance by putting a massive force down on the chest- have a reduced FRC