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Lung Capacities

HOW DOES IT WORK?                                                                

Lung capacity tests are used to test for diseases in humans such as Asthma and Emphysema which affect the volume of air a person can breathe in and out during normal and deep or excessive breathing. The lung capacities kit shows the volume of air trapped in the bag, which is measured in Litres, and for practical purposes will represent a person’s lung volume, it is a hypothetical representation as a small amount of air always remains in the lungs. Comparisons can be made between a person’s lung volume and factors such as height, age, physical activities and smoking habits, which can ultimately tell us how healthy our lungs are.

The most important lung volumes that will be tested is:

  • Tidal Volume
  • Inspiratory Reserve Volume
  • Expiratory Reserve Volume
  • Residual Volume
  • Vital Capacity
  • The total Lung Capacity



Time allocation: 45 Min

A human’s average total lung capacity (how much air the lungs can hold) is about six litres, although many factors – such as gender, height, altitude, working out, and smoking – can cause this to vary. We can use the lung capacities kit to calculate the lung capacities of our fellow students and determine and compare their individual lung capacities.

The tidal volume (TV), about 500 mL, is the amount of air inspired during normal, relaxed breathing.

The inspiratory reserve volume (IRV), about 3,100 mL, is the additional air that can be forcibly inhaled after the inspiration of a normal tidal volume.

The expiratory reserve volume (ERV), about 1,200 mL, is the additional air that can be forcibly exhaled after the expiration of a normal tidal volume.

Residual volume (RV), about 1,200 mL, is the volume of air still remaining in the lungs after the expiratory reserve volume is exhaled.

The vital capacity (VC), about 4,800 mL, is the total amount of air that can be expired after fully inhaling. The value varies according to age and body size.

The inspiratory capacity (IC), about 3,600 mL, is the maximum amount of air that can be inspired.

The functional residual capacity (FRC), about 2,400 mL, is the amount of air remaining in the lungs after a normal expiration

Summing specific lung volumes produces the following lung capacities: The total lung capacity (TLC), about 6,000 mL, is the maximum amount of air that can fill the lungs. Use all the values calculated in order to determine what the lung capacity of the individual is.

Some of the air in the lungs does not participate in gas exchange. Such air is located in the anatomical dead space within bronchi and bronchioles—that is, outside the alveoli




Time allocation: 45 Min

To measure the Tidal Volume, Expiratory reserve, Inspiratory reserve, Vital Capacity and Residual volume of a student’s Lung capacity.



  • 1 x Bag of cotton balls
  • 1 x isopropyl alcohol 250ml
  • 1 x Lung Volume kit



PART 1 : Assembly
  1. Start by sterilizing the mouth piece, vales, coupler and tee, with a cotton ball dipped into the isopropyl alcohol (Rubbing alcohol) you will see these pieces in the figure 1 below.
  2. Place one valve on each end of the tee so the I’s on the valve tabs face the same direction.
  3. Insert the coupler halfway into the bag opening and fold it tightly around the coupler(Figure 2)
  4. Use the rubber band to secure the bag to the coupler as seen in figure 2.
  5. Tightly insert the coupler with the bag attached into the valve outlet, the O- tab should be facing out as seen in figure 3.
  6. Insert a mouthpiece into the opening at the centre of the tee.
  7. From the mouthpiece and tee, detach only the coupler which is attached to the bag from the valve.
  8. Lay the closed end of the bag flat against a hard surface holding it down with your palm.
  9. With your other hand smooth out the remaining air in the bag till it is flat and there is no excess air in it. ( See figure 4)


PART 2: Experiment

Carry out each measurement as follows:
  1. The bag has litre and 1/10 litre graduations, when you are done with the breathing instruction after each step, wrap the bag tightly against your fist until the bag becomes stiff (Figure 5) in order to take an accurate reading.
  2. Take a normal breath in, hold your nose and take a normal breath out into the lung volume bag mouthpiece, record this as tidal volume.
  3. Remove all the air from the lung volume bag by sliding your hand along its length.
  4. Take a normal breath, exhale normally, then hold your nose and breathe out as hard as you can into the lung volume bag mouthpiece.
  5. Slide your hand along the bag to push all the air to the end and measure the volume of air it contains. Record this as expiratory reserve.
  6. Remove all the air from the lung volume bag by sliding your hand along its length.
  7. Breathe in the largest breath possible, hold your nose and breathe out as much air as possible into the lung volume bag mouthpiece, record this as vital capacity.
  8. Remove all the air from the lung volume bag by sliding your hand along its length.
  9. Make sure to sterilize the mouthpiece before the next student does their readings.
  10. The inspiratory reserve can be calculated by subtracting tidal volume and expiratory reserve from vital capacity.
  11. Calculate your average lung capacity from these values in the practical table.
  12. Allow at least 4 students to do readings and compare their findings.


In the observation table below record your initial values in order to calculate the Functional Residual capacity, Inspiratory Reserve volume, Vital capacity and Total lung capacity in the practical table.


  • Do not test any subjects with breathing problems, such as asthma.
  • Ensure the mouth pieces are sterilized when taken out of the kit with the rubbing alcohol and cotton balls.
  • Ensure that after a student uses the apparatus that it is sterilized before the next student uses it.
  • Ensure it is once again sterilized before it is packed away.

If a person that is being tested struggles to breath during the experiment discontinue testing immediately and place person in the semi-fouler position.