The rise and rise of asthma

Activity 2

Measure the volume of air you can exhale

Note: Students suffering from respiratory or heart problems should not act as subjects for this activity.

During an asthma attack the smooth muscle lining the air passages of the lungs becomes constricted and the volume of the air that can be exhaled is decreased. Using a large plastic bottle, you can approximately measure, the maximum volume of air that can be exhaled during forced breathing.

Materials (for each small group)

  • 5-litre (or larger) plastic bottle with lid (bottle should be marked with 100 mL gradations);
  • half a metre of tubing (rubber or plastic);
  • sink or large plastic container.

Procedure

  1. Fill a sink or large plastic container with water.

  2. Fill the plastic bottle to the top with water and put the lid on.

  3. Turn the bottle upside down in the sink and take off the lid under water.

  4. Insert a length of tubing into the bottle as shown in the diagram.

  5. Take a deep breath and expel all the air in your lungs through the tubing and into the bottle.

  6. Record the volume of air you have forced into the bottle.

  7. Refill the bottle and set up the apparatus as before.

  8. Relax for a few minutes until your breathing pattern returns to normal.

  9. Repeat the experiment twice.

  10. Average the values you obtain.

Questions

  1. How is oxygen used in your body?

  2. When does your body need more oxygen?

  3. How is the carbon dioxide that you exhale produced?

Teachers notes

Students suffering from respiratory or heart problems should not act as subjects for this activity.

Make sure students do not become competitive in their exhaling.

This activity should be done in groups of two (or more). While one student is exhaling another is needed to stabilise the bottle. Provide a new length of tubing for each student.

You may want students to calculate a class average and determine the standard deviation. Students could compare the average volume exhaled by females with that exhaled by males or they could look for a correlation between volume of air exhaled and height of the student.

Remind students the volume they are measuring is the vital capacity of the lungs which is more than that exhaled during normal breathing (tidal volume) but less than the total lung capacity. (Some air always remains in the lungs because the thorax cannot be completely collapsed.)

Students can also measure the tidal volume of their lungs using the set-up for this activity. They could use the large plastic bottle or a 500-mL cylinder. The plastic bottle will only give a very approximate reading but will show students that the tidal volume is only small compared to the vital capacity.

  1. Oxygen is used for aerobic cellular respiration, the process by which sugar molecules are broken down and energy is released.

  2. More oxygen is need when more energy is required. More oxygen is required during exercise.

  3. During cellular respiration, carbon dioxide is produced. The general equation is:

    oxygen + sugars = carbon dioxide + water + energy.
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Posted March 1997.