Spirometry

Key words

Tidal volume
- amount of air exchanged in a single breath
- approx. 500cm³ at rest
expiratory reserve volume
- the extra volume that can be exhaled with an extra deep breath
inspiratory reserve volume
- the extra volume that can be taken in with an extra deep breath
vital capacity
- the max volume of air that can be breathed in when the strongest possible exhalation is followed by the deepest possible inhalation
residual volume
- the volume of air that remains in your lungs after fully breathing out
- cannot be measured directly
total lung capacity
- residual volume + vital capacity
ventilation rate
- total volume of air inhaled in one minute
- tidal volume x breathing rate

Measuring lung volumes

peak flow meter
- measures the rate at which air can be expelled from the lungs
- PEFR = peak expiratory flow rate (l/min)
- measurements are compared to tables of expected values
vitalograph
- measure FEV1
- forced expiratory volume in 1 second
- a measure of how fast air can be breathed out
spirometer
- more detailed investigation of lung function
  - different lung volumes
  - breathing patterns

Spirometer function

breathe via tube into oxygen filled chamber
- chamber is hinged and floats on a tank of water
- exhale and chamber rises
- inhale and chamber falls
CO2 scrubber (soda lime) to remove CO2 from recirculated air
movement of spirometer is recorded on a revolving drum or kymograph
each up and down trace represents a single breath
drum revolves at a set speed so can calculate:
- breathing rate
- breathing depth
- tidal volume
- expiratory reserve volume
- inspiratory reserve volume
- vital capacity
spirometer should be filled with medicinal grade O2
subject should have no heart or respiratory problems

Spirometer trace

Oxygen consumption

the air breathed into the spirometer has the CO2 removed by the soda lime
- volume of gas decreases
- decrease = oxygen consumption
- gradient = rate of oxygen consumption
  - gradient is steeper during exercise as more oxygen is needed