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TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Biology > Edexcel AS Biology - Spirometers
What is a spirometer, what does it show, definitions of what it shows and how it works
- A spirometer is used to measure lung volume.
- The trace from this apparatus tells us a lot about the lungs.
- A spirometer can also be used to determine a person's rate of oxygen consumption.
- Firstly, it shows that the lungs have a total lung capacity: a maximum quantity of air that the lungs can hold during the deepest possible breath. A spirometer can be used to calculate the vital capacity of the lungs. This is the maximum usable volume of the lungs. Therefore:
- Vital capacity = total lung capacity - residual volume
- Where the residual volume is the volume of air that remains (resides) in the lungs after breathing. Some air remains in the lungs after breathing because we can never totally empty our lungs even when we have exhaled as much as possible, as there is still some air in the alveoli, bronchi and trachea (these are held open permanently by rings of cartilage).
- Secondly, the spirometer shows that during normal breathing, the volume of air in and out of the lungs in each breath is called the tidal volume. In a normal adult at rest, this is about 0.5L.
- Thirdly, the trace from the spirometer shows that after breathing in at rest, the organism breathing could inhale an extra 1.5L: the inspiratory reserve volume (IRV). He or she could also breathe out another 1L: the expiratory reserve volume (ERV).These volumes represent the extra volumes of air that we could breathe in and out during exercise.
- Finally, we can calculate the ventilation rate from the spirometer: volume of air taken into the lungs in 1 minute.
- Ventilation rate = breaths taken per minute times tidal volume.
Risk assessment when using the spirometer
- Never do investigations like this without close supervision as rebreathing your own air can be dangerous.
- The spirometer produces a trace by means of a ink pen and float (in water).
- When you breathe in, the pen goes up and the float goes down, producing a trace. And when you breathe out the float goes up so the pen goes down, producing a trace.
- Movement of the float in relation to the pen is inversely proportional. Without the proportion symbol on my keyboard though, this relationship can also be portrayed as so:
- Where f = the float and p = the pen.
Comments
These notes are aimed at people studying Edexcel Biology A Level, but will be suitable for other exam boards too.
Originally written by Elements on TSR Forums.
