The normal values for the ratio of residual air volume to total lung volume vary according to age and gender. The ratio for adult males is 0.307, for adult females it is 0.29, and for the elderly it reaches 0.50. Residual air volume is the amount of gas that remains in the lungs after a deep inhalation, and total lung volume is the maximum total amount of gas that the lungs can hold. The indicators of residual gas volume and total lung volume, as well as the ratio between them, are very important indicators of lung function. Their clinical significance is mainly due to the fact that high ratios can be seen in diseases such as chronic obstructive pulmonary emphysema and chronic pulmonary heart disease.