Lung Function Testing

Question 1

What are the benefits of Lung function testing?

Answer 1

Non-invasive
Cheap
Technically Simple: measurement of Volume and Flows
Technically Complex: Measurement of the composition of gases

Question 2

What is the Tidal volume?

Answer 2

The volume that enters and leaves the lungs with each breath (0.5L)

Question 3

What is the Inspiratory Reserve Volume?

Answer 3

The extra volume that can be breathed IN over that at rest (2.5L)

Question 4

What is the Expiratory Reserve Volume?

Answer 4

The extra volume that can be breathed OUT over that at rest (1.5L)

Question 5

What is Residual Volume?

Answer 5

The volume remaining after maximal expiration, cannot be measured by spirometry but contributes to lung capacity (0.8L)

Question 6

What is the difference between lung volume and lung capacity?

Answer 6

Lung volumes change with tidal volume.
Lung capacities do not change with tidal volume, as they are defined relative to fixed points in the breathing cycle. Capacities are fixed.

Question 7

How is the Vital capacity calculated?

Answer 7

Biggest breath in
(IRV+ TV+ ERV= VC
Inspiratory reserve volume + Tidal Volume + Expiratory Reserve Volume

Question 8

What is the normal Vital capacity in a typical adult?

Answer 8

~5L (3.7L F)

Question 9

What is Inspiratory Capacity?

Answer 9

The biggest breath that can be taken in from resting expiratory level (the lung volume at the end of quiet expiration)
Typically 3L

Question 10

What is the typical inspiratory capacity?

Answer 10

~3L (3.8L M, 2.7L F)

Question 11

What is the function residual capacity of the lung?

Answer 11

The volume of air in the lungs at the end of quiet respiration.
ERV + RV
typically ~ 2L

Question 12

What is the typical FRC?

Answer 12

~2.3L

Question 13

What is the total lung volume?

Answer 13

The total volume of gas in the lungs at the end of maximal inspiration
Vital Capacity + Reserve Volume
Typical 5.8 L
(4.4L F)

Question 14

What is the typical Total Lung Volume

Answer 14

~5.8L (4.4L F)

Question 15

What does Vital capacity depend on?

capacity not volume

Answer 15

Depends on maximal inspiration and maximal expiration, i.e maximal inspiratory effort and force of recoil.

- Inspiration:
Compliance of the lungs
Force of inspiratory muscles
- Expiration:
Airway resistance: increases as expiration proceeds 

Or both.

Question 16

What produces a restrictive deficit?

Answer 16

If lungs are unusually stiff, or inspriratory effort is compromised by muscle weakness, injury or deformity

Question 17

What produces a obstructive deficit?

Answer 17

During expiration (particularly forced) the small airways are compressed, increasing flow resistance, eventually to a point where no more air can be driven out of the alveoli.
if airways are narrowed, then expiratory flow is compromised much earlier in expiration.
e.g. asthma

Question 18

Discuss the affect on the FEV1/FVC ratio in an obstructive defect

Answer 18

In an obstructive defect:
- FVC is nearly normal as lungs are easy fill
However the resistance will increase on inspiration, the air will come out more slowly
- FEV1 is reduced markedly
- FEV1/FVC ratio is less than 70%

Question 19

What is the normal FEV1/FVC ratio?

Answer 19

70%

Question 20

what is FEV1?

Answer 20

The Forced Expiratory Volme in one second

Question 21

What is FEV1 used for?

Answer 21

To distinguish between restrictive and obstructive defects

Question 22

Discuss the affect on the FEV1/FVC ratio in an restrictive defect

Answer 22

In a restrictive defect:
The lungs are more difficult to fill; stiff, weak muscles, problem with chest wall
- FVC is reduced
The air will come out normally
- FEV1 is reduced proportionally
- FEV1/FVC ratio is normal (or even higher than normal)

Question 23

What is a vitalograph?

Answer 23

volume plotted against time

Question 24

What is the PEFR?

Answer 24

The peak expiratory flow rate- at the start of expiration when the lungs are expanded the airways are stretched open, the expiratory flow rate is at is maximum.
Resistance at its minimum

Question 25

Discuss the effects a obstructive deficit would have on a flow volume curve? e.g. asthma

Answer 25

The volume expired remains the same. However as the lungs are compressed, more air is expired and airways begin to narrow. Resistance increases and the flow rate falls. The narrower the airways are to start (i.e in a obstructive defect) the more rapidly the flow rate falls (scalloping of flow vol curve)

Question 26

Discuss the effects a restrictive deficit would have on a flow volume curve? e.g. emphysema

Answer 26

the lungs fail to ill normally, however the PEFR is reached as the flow rat is unaffected. the shape of the curve is generally the same, but narrower (as the volume is decreased) and flow rate is greater at than normal at comparable volumes

Question 27

How do you measure the residual volume in the lungs/

Answer 27

Using the helium dilution test

Question 28

Describe the helium dilution test

Answer 28

Helium is not metabolised The patient breathes in a known volume of air containing a known concentrate of helium. This concentration changes and helium becomes diluted as the lungs fill, because the helium comes in contact with air already in the lungs.

Question 29

What is serial/physiological dead space?

Answer 29

The volume of air inhaled that does not enter the lungs either because it does not enter the conducting airways or because of poor perfusion across the alveoli

Question 30

What test would you use to measure the dead space in the lungs?

Answer 30

Nitrogen wash out test

Question 31

Describe the nitrogen wash out test

Answer 31

The last gas in is the first gas out pt breathes in pure O2 then breathes out, % N is measured, inially only pure o" then a air which inc. N2 vol expired at transition = serial dead space.

Question 32

How would you measure diffusion capacity of the lungs?

Answer 32

The Carbon monoxide transfer factor measurement

Question 33

Describe the CO Transfer Factor measurement

Answer 33

Calculated by measuring the CO uptake following a single maximal breath of a gas mixture containing air, 14% helium and 0.1% CO. Inhaled CO is used because of its very high affinity for Hb. Since almost all the CO entering the blood binds to Hb, the concentration gradient for pCO (between alveolar gas and plasma) across the alveolar capillary membrane is maintained (and remains the same) for the entire time blood remains in contact with alveolar gas. The amount of CO transferred is an estimate of the diffusion resistance barrier

Question 34

What is diffusion conductance?

Answer 34

the resistance to diffusion across the alveolar membrane, and is estimated by the CO transfer factor

Question 35

When would a CO transfer factor measurement be indicated?

Answer 35

When spirometry suggests a reduction in Vital Capacity, Residual Volume or Total lung capacity Looks at diffusion conductance (resistance)

Question 36

True or False A 70Kg man with normal lungs Would achieve an alveolar conc of 5% when breathing in 5% helium for 2 normal breaths

Answer 36

True | He is not metabolised

Question 37

What are the benefits of interpreting a Flow vol curve in disease?

Answer 37

Sensitive Can detect problems early compared to spirometry Can discriminate where in the respiratory tract the problem lies