Static Lung Volumes

Question 1

What can be measured directly

Answer 1

IRV
TV
ERV
VC
IC

Question 2

What is measured indirectly

Answer 2

Residual volume (RV)
TLC
Functional residual volume (FRC

Question 3

What is FRC?

Answer 3

Functional residual volume

Gas present in lung at the end of normal tidal breathing

Question 4

What is TLC

Answer 4

Total lung capacity

Has in lungs after max insp

Question 5

What is RV

Answer 5

Residual volume

Gas left in lungs after max exhalation

Question 6

Uses of static lung volumes

Answer 6

Functional status of lungs

Disease progression

Elastic properties of lungs

Identify any gas trapping

Useful when used with spirometry

Question 7

Techniques for measuring static lung volume

Answer 7

Whole body plethysmography (gold std)

Helium dilution

Nitrogen washout

Question 8

Limitations of nitrogen washout and helium dilution

Answer 8

Can only measure ventilated areas of lung, so not accurate in obstructive disease due to areas of unventilated lung

Question 9

Performing whole body plethysmography

Answer 9

Tidal breathing 2-4 mins

Shutter on mouthpiece closed and pt pants against at 1 per second

Pressure changes in the box and pressure changes in mouth plotted

Shutter open, pt breath in maximally and breath out maximally to record dynamic lung volumes.

Question 10

What is the principle for whole body plethysmography

Answer 10

Boyles Law

Question 11

What is Boyles law

Answer 11

At constant temp, the volume of a gas is inversely proportional to its pressure

PV=K

If volume of a closed container doubles-the pressure halves

Question 12

How is Thoracic Gas Volume measured using Boyles law

Answer 12

Lungs treated as a closed container and assume mouth pressure changes are equal to alveolar pressure changes.

At FRC alveolar pressure is ~ equal to mouth pressure

Question 13

Why is pt asked to pant against shutter for static lung volume measurements

Answer 13

Causes rarefaction of gas in lungs during insp (increase vol, decrease pressure)

Compression of gas during expiration (decrease vol, increase pressure)

Question 14

What represents FRCpleth

Answer 14

Changes thoracic volume recorded by changes in box pressure, which are used to calculate the TGV

Comparing changes in alveolar pressure to changes in TGV. FRC pleth can be calculated at moment of occlusion of mouthpiece (end of normal breath) =FRC

Question 15

What is plotted to generate the angle of for panting

Answer 15

Changes in box pressure plotted against changes in mouth pressure and a line of best fit is used to determine the angle

Question 16

Calculation equation for TGV (FRCpleth)

Answer 16

PV = (v + changeV) x (p - changeP)

Equations multiplied out into
V= P x changeV/changeP

TGV= (PB - PH20) x (changeV/changePA)

PB= atmospheric pressure
PH20= partial pressure of water vapour in air at 37 degs

Question 17

What does the TGV equation become if you consider the angle

Answer 17

TGV= (Pb- PH2O) x (1/Tan0) x Cbox

Question 18

What can FRC be used to calculate once it has been determined?

Answer 18

RV and TLC

Question 19

RV equation

Answer 19

FRC - ERV

OR

TLC - VC (if TLC has been calculated using FRC)

Question 20

TLC calculation

Answer 20

FRC + IC

OR

RV + VC (if RV has been calculated)

Question 21

FRC accurate results criteria

Answer 21

X3 measurements within 5%

Mean of the 3 results should be calculated and reported

Question 22

Compliance equation

Answer 22

ChangeV/changeP

Question 23

Static lung volume results in restrictive pattern

Answer 23

Decreased FRC, TLC, RV

Due to stiff lungs that don’t expand but have increased elasticity e.g pulmonary fibrosis

Question 24

Static volume results for obstructive pattern

Answer 24

Increased FRC, TLC and RV

Due to increased compliance in floppy lungs expand easily but don’t contract resulting in gas trapping and hyperinflation