The measurement of lung capacity is known as spirometry. Figure 32.1 shows a Propper spirometer used to make such measurement. There are a number of terms used in describing various volumes of air during breathing:

Tidal volume - the normal amount of air that moves in and out of the lungs during a normal breath. Average = 500 ml

Expiratory reserve volume - the amount of air which can be expelled beyond the tidal volume (i.e. beyond normal expiration). Average = 1,200 ml

Inspiratory reserve volume - the amount of air that can be drawn into the lungs after a normal inhalation. Average = 3,100 ml

Vital capacity - the sum of the tidal, expiratory reserve, and inspiratory volumes. This is the total functional capacity of the lungs. Average = 4,800 ml

Residual volume - the amount of air which cannot be expelled from a living lung. Average = 1,200 ml

Figure 32.1 Propper Spirometer

Exercise And Vital Capacity

Exercise 32.1

Measure your tidal volume, expiratory reserve volume, and vital capacity using a Propper spirometer.

1. Swab the stem of the spirometer with alcohol and place a mouthpiece over the stem.

2. Rotate the dial of the spirometer to zero.

When you exhale through the spirometer; the dial will remain at the position it attains. Exhale slowly and steadily. Hold the spirometer with the dial up.

3. After three normal breaths, exhale three normal breaths into the spirometer. Inhale through your nose. The dial of the spirometer will automatically add the volumes of the three breaths.

4. Divide the spirometer reading by three and record the result as your tidal volume.

5. Set the spirometer to zero.

6. Without the spirometer; make three normal inhalations and exhalations. Then, without a fourth inhalation, exhale all you can through the spirometer.

7. Record this volume as your expiratory reserve volume.

8 Set the spirometer to zero once again.

9 Without the spirometer, take three deep breaths and exhale completely. Take a fourth deep breath and exhale completely, slowly, and steadily through the spirometer.

10. Record this volume as your vital capacity.

Since the Propper spirometer works only during expiration, you cannot measure the inspiratory reserve volume directly. However, you can calculate the inspiratory reserve volume by subtracting the tidal and expiratory reserve volumes from the vital capacity.

11. Calculate and record your inspiratory reserve volume.

12. Discard the mouthpiece. Wipe the stem with alcohol.

13. If you are the last person to use the spirometer during a period, open the spirometer and wipe the interior with alcohol.

Average Your


Tidal Volume

500 ml

Expiratory reserve volume

1,200 ml

Vital capacity

4,800 ml

Inspiratory reserve volume

3,100 ml

(IRV = VC - ERV - TV)

1. _ What is normal tidal volume?

2. _ True/false. The vital capacity is the volume of air contained in the lungs at death.

3. _ True/false. The residual volume is the volume of air which is expelled during forced expiration.

4. _ The measurement of lung capacities is (4) .

5. _ True/false. The Propper spirometer is effective for directly measuring normal exhalations.


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