Resp 5 - Lung function tests + O2/CO2 in the blood

Question 1

Define tidal volume:

Answer 1

The amount of air in and out at each breath

~ 0.5 L

Question 2

Define inspiratory reserve volume:

Answer 2

Air volume that can be inspired ‘on top of’ tidal inspiration
~ 2.5 L

Question 3

Define expiratory reserve volume:

Answer 3

Air volume that can be expired ‘on top of’ tidal expiration

~ 1.5 L

Question 4

Define residual volume:

Answer 4

Volume remaining in lungs after maximal expiration

~ 0.8 L

Question 5

Define inspiratory capacity:

Answer 5

Amount of air that can be inspired from the Resting Expiratory Level
~ 3 L

Question 6

Define functional residual capacity:

Answer 6

Volume of air in lungs at resting expiratory volume

~ 2 L

Question 7

Define vital capacity:

Answer 7

Measured from maximum inspiration to maximum expiration

~ 5 L

Question 8

Define total lung volume:

Answer 8

The volume of gas at the end of maximum inspiration

~ 5.8 L

Question 9

Define FVC:

Answer 9

Forced Vital Capacity

= Total volume of air that can be breathed out with maximal effort in 1 breath

Question 10

Define FEV1:

Answer 10

Forced Expiratory Volume in 1 sec

= Volume of air that can be breathed out with maximal effort in 1 second (calculated from FVC)

Question 11

How does an obstructive deficit affect:
FEV1
FVC
FEV1/FVC

Answer 11

FEV1 < 80%
FVC may be reduced
FEV1/FVC < 0.7

Question 12

How does a restrictive deficit affect:
FEV1
FVC
FEV1/FVC

Answer 12

FEV < 80%
FVC < 80%
FEV1/FVC > 0.8

Question 13

Give some examples of obstructive lung diseases:

Answer 13

• Asthma
• COPD
• Emphysema
• Chronic bronchitis
• Cystic fibrosis

Question 14

Give some examples of restrictive lung diseases:

Answer 14

• Fibrosis
• Tumours
• Interstitial lung disease
• Pneumothorax
• Weak muscles (ie Muscular dystrophy)

Question 15

What is the normal range for respiratory rate in an adult?

Answer 15

16-20 breaths per min

Question 16

What changes would you see on a flow-volume loop if the patient has obstructive disease?

Answer 16

• Scalloped expiratory flow
• Normal expired volume
• Normal inspiratory flow

Question 17

What changes would you see on a flow-volume loop if the patient has restrictive disease?

Answer 17

• Narrowed curve
• Reduced expiratory volume
• Fast expiratory flow rate
• Normal inspiratory flow

Question 18

How can we measure the residual volume of the lungs?

Answer 18

Helium dilution:
- Patient breaths a known volume of gas containing a known concentration of Helium
- As patient breaths, [He] changes as it is diluted by the residual air in the lungs
(Helium is not metabolised)

Question 19

What are the properties of Hb which facilitate O2 transport in the blood?

Answer 19

• 4x Haem groups

- Cooperative binding (T and R states)

Question 20

How does a fall in pH affect the O2-Hb dissociation curve?

Answer 20

BOHR EFFECT

Curve shifts to right

Question 21

How does a rise in temperature affect the O2-Hb dissociation curve?

Answer 21

Curve shifts to the right

Question 22

How does an increase in 2,3-BPG affect the O2-Hb dissociation curve?

Answer 22

Curve shifts to the right

Question 23

Why do red blood cells usually contain 2,3-BPG?

Answer 23

To stabilise deoxy-Hb, promoting O2 release at the tissues

Question 24

How does high altitude and anaemia affect the concentration of 2,3-BPG in the blood?

Answer 24

Increases conc of 2,3-BPG

Question 25

Why is it important that foetal haemoglobin binds 2,3-BPG less tightly?

Answer 25

Allows O2 to be passed from maternal blood to foetal blood

Question 26

Define cyanosis:

Answer 26

Bluish discolouration of skin and mucous membranes due to unsaturated haemoglobin in systemic circulation, or poor circulation

Question 27

What test specifically measures the level of haemoglobin saturation in arterial blood (bound O2)?

Answer 27

Pulse oximetry

Question 28

What does pulse oximetry test, and how?

Answer 28

The level of haemoglobin saturation in arterial blood

Red and infared light emitting detector detects the difference in absorption of light between Oxy-Hb and Deoxy-Hb

Question 29

What are the units of a pulse oximetry test?

Answer 29

% saturation

Question 30

What is the main disadvantage of a Pulse Oximetry test?

Hint - An anaemic could have 100% O2 saturation

Answer 30

It doesn’t measure the amount of Haemoglobin in the blood

Question 31

What test measures the pO2 in arterial blood?

Answer 31

Arterial blood gas analysis

Question 32

What are the units of an arterial blood gas analysis?

Answer 32

kPa

Question 33

What does an Arterial Blood Gas Analysis measure?

Answer 33

PO2, PCO2 and pH of arterial blood

Question 34

What is the normal range of [HCO3-] in the blood?

Answer 34

~ 22-26 mmol/L

Question 35

What is the pKa of H2CO3 in the plasma?

Answer 35

pKa = 6.1

Question 36

What is the Henderson-Hasselbach equation for plasma pH?

Answer 36

pH = pKa + log( [HCO3-] / (PCO2 x 0.23) )

Question 37

What acids can be produced by the body to buffer HCO3-?

Answer 37

• Keto acids
• Lactic acid
• Sulphuric acid

Produces H2O and CO2 which can be removed by expiration

Question 38

How is CO2 transported in the blood?

Answer 38

8% dissolves in plasma
12% as carbamino compounds (Carbaminohaemoglobin)
80% as HCO3-

Question 39

What are the functions of carbaminohaemoglobin?

Answer 39

• Transport of CO2

- More formed at tissues = reduces Hb affinity for O2 = favours O2 release at tissues

Question 40

What is the colour of Carbaminohaemoglobin?

Answer 40

Blue = darker venous blood

Question 41

What is the [CO2] in whole arterial and venous blood?

In what form is the majority of CO2 transported?

Answer 41

[CO2] in whole arterial blood = 21.31 mmol/L
[CO2] in whole venous blood = 23.21 mmol/L
Majority of CO2 carried as HCO3- in the plasma

Question 42

What percentage of blood is plasma vs cells?

Answer 42

Blood=
~ 60% plasma
~ 40% cells