Mesuring Lung Volumes

Question 1

Precautions:

Answer 1

•Subject should be healthy and asthma free.
•Soda lime should be fresh and functioning, drum should be filled with fresh air (ensure normal levels
of O2 and no build-up of CO2), sterilised mouthpiece (avoid infection).
•No air leaks in apparatus, nose clip (for valid measurements).

Question 2

Lung volumes:

Answer 2

Graph on right shows vol of air in the lungs (note vol of air in spirometer traces have decreasing gradient). Total lung capacity = vital capacity + residual volume.
Vital capacity: the maximum volume of air that can be
expelled from the lungs in one breath. Measured by
taking the deepest possible breath and expiring al the
air possible. Depends on:
• Size of person
• Age and gender
• Level of regular exercise
Usually in the region 2.5 - 5dm3

Question 3

Residual volume:

Answer 3

Residual volume: the volume of air that remains in the lungs after forced expiration (approx. 1.5dm3).

Question 4

Tidal volume:

Answer 4

the volume of air inhaled/exhaled in one breath, usually measured at rest (approx. 0.5dm3) – this is usually sufficient to supply all the oxygen required by the body at rest.

Question 5

Oxygen uptake:

Answer 5

Volume of oxygen absorbed by blood in one minute.
A higher oxygen uptake will result from increased demand (exercise), when muscles are respiring more, increased breathing rate and/or deeper breaths.

Question 6

Rate of oxygen uptake

Answer 6

gradient of spirometer trace: Measure decrease in volume from point A to B, and time taken and divide the two. The rate of oxygen uptake will be in dm3s-1 or per min.

Question 7

Breathing rate:

Answer 7

measured from spirometer trace by counting number of peaks per minute. At rest, usually approx. 12-14 breaths per min.

Question 8

What does spirometer measure?

Answer 8

Spirometers measure the movement of air into and out of the lungs. The spirometer consists of a chamber of medical-grade oxygen which the person breathes in through a tube.

Question 9

Chambers during inspiration and exportation,
Breathing supplies :

Answer 9

•During inspiration, the chamber is pulled down as air is drawn out of the chamber, the movements are recorded on paper on a rotating drum by a pen attached to the lid.

•In expiration, air returns into the chamber, raising the lid. The CO2 rich air exhaled is passed through a chamber of soda lime, which absorbs the CO2 so the person doesn’t inhale CO2. This allows the measurement of O2 consumption – therefore the volume of air in the chamber decreases over time.

Breathing supplies O2 and removes CO2, as a person breathes from the spirometer O2 is absorbed by the blood and replaced by CO2, which is absorbed by the soda lime. The volume of CO2 released and absorbed by the soda lime can be assumed to equal the volume of O2 absorbed by the blood.