A simple way of measuring lung capacity that students can do at home

Using a spirometer to measure lung function is one test that doctors use to diagnose asthma. Your students can make a simple spirometer at home, using household items and use it to measure their vital capacity.

 

Each student will need:

 

• A large bottle (minimum of 3 litres but preferably 5 litres)
• A measuring jug
• Plastic tubing (a section of hose is ideal) or a bendy straw
• Large tub
• Masking tape
• Pen
• Scissors

 

Student instructions

The volume of air in your lungs that you can breathe out is called your vital capacity. It can be measured using a piece of equipment called a spirometer. In this experiment you are going to make you own and use it to measure your vital capacity.

 

1. Take any labels off the bottle and stick a strip of masking tape up the side from top to bottom of the bottle.
2. Use the measuring jug to add 250 ml of water into the bottle. Use the pen to draw a line on the masking tape to show the level of the water. Repeat this, adding 250 ml at a time until you have marks all the way up the masking tape.
3. Add a little more water so the bottle is completely full and screw on the cap.
4. Half fill the large tub with water.
5. Ask a helper to place the bottle into the tub upside down so the cap is under the water. Unscrew the cap and place the plastic tubing or the straw up inside the bottle.
6. Take a deep breath to fully inflate your lungs and then breathe out through the straw. Keep going until there is no more air left in your lungs.
7. Count how many marks down from the bottom of the bottle the water level is. Use this to work out the volume of air that you breathed out. This is your vital capacity.

 

Now try to answer these questions:

What was your vital capacity?

Students should be able to work out the volume of their vital capacity by counting the number of marks and multiplying by 250. This will give them an answer in ml. Dividing by 1000 will give them their vital capacity in litres.

What variables affect vital capacity?

Age, sex, height, lung disease and whether the person smokes will affect lung capacity. A rough guideline to work out lung capacity in children is to multiply their mass in kg by 8. So, for a child with mass 50 kg this gives a vital capacity of 400 ml. The students probably would have got a volume much lower than this. You can discuss why this is the case with them. They may have stopped exhaling early, their bottle might not have been big enough to measure all the air etc.

Asthma does not reduce vital capacity but the volume of air expelled in the first second of a forced exhalation is lower than average in asthmatics because of narrowed airways. You could discuss with the students how this could be measured using the equipment.

 

Your students can find out what happens during an asthma attack by reading Oops – when science goes wrong – what happens during an asthma attack?