Question

Short / long answer type questions.
Give the definition and normal values of lung volumes and lung capacities.

Answer 1

There are following respiratory volumes and capacity :

1. Tidal volume (TV): It is the volume of air normally inspired or expired in one breath (i.e. inspiration and expiration) without any extra effort. It is about 500 ml in the normal healthy adult.

2. Inspiratory reserve volume (IRV): By taking a very deep breath, you can inspire a good deal more than 500 ml. This additional inhaled air, called IRV is about 3000 ml.

3. Expiratory reserve volume (ERV): If you inhale normally and then exhale as forcibly as possible, you should be able to push out 1200 ml of air in addition to 500ml. of T.V. The extra 1200 ml is called ERV.

4. Residual volume (RV): Even after expiratory reserve volume is expelled, considerable air remains in the lung, this volume, which cannot be measured by spirometry, and it is called residual volume is about 1200 ml.

5. Functional residual capacity (FRC): It is the amount of air that remains in the lungs after a normal expiration. It is about 2300 ml.

FRC = ERV + RV = 1100 + 1200 = 2300 ml.

6. Vital capacity (VC): This is the maximum amount of air that can be expired forcefully from his lungs after first filling these with a maximum deep inspiration. It is about 4600 ml.

VC = IRV + TV + ERV

= 3000+500+1100 = 4600 ml.

7. Total lung capacity (TLC): TLC is the sum of vital capacity (VC) and residual volume (RV). It is about 5800ml.

TLC = VC + RV

= 4600 + 1200 = 5800 ml.

8. Inspiratory capacity (IC): It is the total amount of air a person can inspire by maximum distension of his lungs.

I.C. = TV + IRV