Lung Volumes and Function Testing

Question 1

When is lung compliance higher? When is it lower?

Answer 1

. Compliance higher at lower pressure (more pliable)

. Compliance lower at high pressures (stiffer)

Question 2

Define compliance.

Answer 2

The ease with which the lungs can expand under pressure.

Question 3

When is lung compliance highest?

Answer 3

At moderate lung volumes (very high or low volumes give lower compliance)

Question 4

What does surfactant do?

Answer 4

Reduces surface tension of alveoli to make them more stable and less likely to collapse. Means that alveoli inflate to equal sizes with same pressure (e.g. smaller volume alveoli have more surfactant so inflate faster than larger volume alveoli so they ultimately inflate to the same size)

Question 5

Define tidal volume. What is a normal value for this?

Answer 5

Volume of air entering and leaving the lungs when breathing normally (normal is around 0.5l)

Question 6

Define inspiratory reserve volume (IRV)

Answer 6

The additional volume of air that can be forcibly inhaled after a normal tidal volume is inhaled

Question 7

Define expiratory reserve volume (ERV)

Answer 7

The additional volume of air that can be exhaled after a normal tidal volume is exhaled

Question 8

Define vital capacity

Answer 8

The greatest volume of air that can be expired from the lungs after taking the deepest possible breath in

Question 9

Define residual volume

Answer 9

The volume of air remaining in the lungs after the ERV is exhaled

Question 10

Define functional residual capacity

Answer 10

Volume of air in the lungs after passive expiration (at equilibrium with no exertion by diaphragm or respiratory muscles)

Question 11

Define total lung capacity

Answer 11

Maximum volume of air that the lungs can hold

Question 12

Define forced vital capacity (FVC)

Answer 12

Total volume of air forcibly exhaled after taking in the deepest breath possible

Question 13

Compare the similarities and difference of vital capacity (VC) and forced vital capacity (FVC).

Answer 13

. With both, the person (using spirometer) needs to take in the deepest possible breath and a volume plateau should eventually be reached
. With vital capacity, the person breathes out in a relaxed slow way. In forced vital capacity, the person breathes out hard and fast

Question 14

How can total lung capacity/residual volume be measured?

Answer 14

Can’t be measured using spirometer because can’t expire the residual air, so can use helium dilution or nitrogen washout

Question 15

How do you work out forced residual capacity from helium dilution?

Answer 15

FRC= Reservoir vol x [(initial conc helium - final conc helium)/ final conc helium)

Question 16

How does helium dilution work?

Answer 16

. Closed system with set amount of helium in reservoir
. Helium can’t cross alveoli barrier, so closed system
. Patient breathes in helium from reservoir until equilibrium is reached
. Volume of helium in reservoir shows volume of helium in lungs, so can determine lung capacity/volume

Question 17

How does nitrogen washout work?

Answer 17

. Patient breathes in 100% oxygen and expires into spirometry system
. Procedure repeated until nitrogen in lungs is replaced with oxygen
. FRC calculated from exhaled nitrogen and estimated alveolar nitrogen

Question 18

What are vitalographs used for?

Answer 18

Measure volume of air expired in a given time, so can work out FEV1 and FVC

Question 19

What does the flow-volume curve show?

Answer 19

Expiratory flow rate and expiratory volume

Question 20

What does the initial steep rise of the curve represent?

Answer 20

FVC

Question 21

What does the maximum volume of the flow-volume curve show?

Answer 21

Total lung capacity

Question 22

What does the minimum volume of the flow-volume curve show?

Answer 22

Residual volume

Question 23

What are on the axis of a flow-volume curve?

Answer 23

Volume on the x-axis, flow expiration on the y-axis

Question 24

At what point are the airways the widest?

Answer 24

When the lungs are fully expanded (max flow)

Question 25

Which parts of the curve are effort-dependent?

Answer 25

From TLC to PEF because as effort increases, flow rate increases

Question 26

Which parts of the curve are effort-independent?

Answer 26

From PEF to RV because increase in effort doesn’t decrease flow rate

Question 27

Draw a flow-volume curve.

Answer 27

(Check notes in purple folder!)

Question 28

What does gas transfer-diffusion conductance measure?

Answer 28

Used to measure how easily carbon monoxide crosses from alveoli into blood

Question 29

How is gas transfer-diffusion conductance carried out?

Answer 29

. Patient inhales single breath of dilute CO and holds breath for 10 secs
. Use lung vols and % CO in alveoli at start and end of the 10 sec breath hold to measure gas diffusion
. E.g. with fibrosis gas exchange across the alveoli would be a lot slower due to the thickened alveolar walls

Question 30

What is the normal value for forced vital capacity?

Answer 30

5 litres

Question 31

Name 4 factors that would decrease gas exchange in the lungs.

Answer 31

. Decreased alveolar surface area (e.g. emphysema)
. Decreased blood flow (e.g. due to clot- decreases concentration grad for gas exchange)
. Fibrosis (thickens diffusion pathway)
. Decreased surfactant means alveoli have higher surface tension (causes infant respiratory distress syndrome)

Question 32

Which alveolar cells secrete surfactant?

Answer 32

Type II (small, round, secretory)