lung volumes

Question 1

spirometry
- how did it used to work
- how has it modernised
- what is it used for (+ a test for lung function)

Answer 1

• Originally, breathing air through a tube into a water column moving the water up and down, a pen was connected and drew waves in sequence with the movements of the water. Could measure the volumes and durations so could calculate ventilation.
• Now we have compact, sophisticated equipment that uses sensors to measure amount of air moved and is expressed in a graph of numbers
• It is used to evaluate lung volumes, also lung function by measuring variables such as the force expired volume in 1 second (FEV1)- test showing the proportion of total expiration a person can achieve in first second of movement, higher percentage, better function.

Question 2

what can be found from a spirometry trace
- tidal volume
- Expiratory and inspiratory reserve volumes
- Vital capacity
- Functional residual capacity
- Residual volume

Answer 2

1- Tidal volume- shows volume of air in and out under normal
circumstances
2- Expiratory and inspiratory reserve volumes- amount of
additional air that can be moved up during heavier breathing
(either side of tidal volume, end at max voluntary expiration or
max possible inspiration)
3- Vital capacity- max amount of air that can be moved in and out
of lungs (from max insp to exp)
4- Functional residual capacity- amount of air in lungs after
normal expiration (bottom of TV to 0)
5- Residual volume- amount of air left in lungs after max
expiration (never 0 as cant get all air out)
- 4 and 5 cannot be measured using a spirometer

Question 3

respiratory dead space
- what does it do
- fixed volume?
- where is the alveolar dead space and why does it exist

Answer 3

• delivers air from envro to the gas exchange system in alveoli.
• has a fixed volume around 150ml that wont contribute to gas exchange no matter how big breath.
• in top right of lungs where alveoli and blood do not contact so no exchange occurs even though O2 reaches it, due to gravity

Question 4

air movements in the airways during ventilation
- think the fixed volume of dead space
- eg. of breathing in 500ml of air

Answer 4

• Breathe in 500ml- the first 150ml of old remaining expired air enters alveoli first, 350ml new inspired air enters alveoli, and the last 150ml stays in the airways and is expired in expiration first.
• Total ventilation 500ml, but alveolar ventilation 350ml as 150ml doesn’t make it.

Question 5

minute ventilation
- what is it
- what is the calc
- normal values in rest and exercise
- what is hyperpnoea
- what is hyper ventilation
- what these two look like on a graph

Answer 5

• Amount of air moved by lungs in 1 min
• VE= tidal volume x breathing frequency
• Normal at rest around 6l/min (0.5l x 12br/min)
• Max in exercise around 150l/min (3l x 50br/min)
• Hyperpnoea- when VE increases in proportion to metabolic rate
• Hyper ventilation- when VE increases more than metabolic rate does
• Linear relationship between ventilation and metabolism (Hyperpnoea until around 80l/min), then anaerobic threshold is met and non linear relationship occurs (hyperventilation).

Question 6

3 schemes volumes can be measured
- ATPS
- BTPS
- STPD

Answer 6

• ambient temp and pressure saturated
  Measure it under ambient conditions- temperature, atmospheric pressure, water vapour in air
• body temp and pressure saturated
  Is a Correction taking into account body temperature (37degC) so the numbers make sense in context of human body allowing comparison between different individuals. With temp of air and water vapour at 37degC and ambient atmospheric pressure.
• standard temp and pressure dry
  Is a correction with no water vapour considered, so can make sense of results in different locations eg. Someone at low and high altitude can compare results. Put atmospheric pressure at sea level (760mmHg) and temperature 0degC