The normal volume moved in or out of the lungs during quiet breathing is called tidal volume. When we are in a relaxed state, only a small amount of air is brought in and out, about 500 mL. You can increase both the amount you inhale, and the amount you exhale, by breathing deeply. Breathing in very deeply is called the inspiratory reserve volume. It can increase lung volume approximately six-fold over the tidal volume of 500 mL. We can also increase expiration by contracting our thoracic and abdominal muscles.
This is called expiratory reserve volume and is about 1,400 ml of air. Vital capacity is the total of tidal, inspiratory reserve and expiratory reserve volumes; it is called vital capacity because it is vital for life, and the more air you are capable of moving, the better off you are. Vital capacity can vary depending on how much we can increase inspiration by expanding our chest and lungs. Some air that we breathe never even reaches the lungs! Instead it fills our nasal cavities, trachea, bronchi, and bronchioles. These passages aren't used in gas exchange so they are considered to be dead air space. To make sure that the inhaled air gets to the lungs, we need to breathe slowly and deeply. Even when we exhale deeply some air is still in the lungs (about 1,000 ml) and is called residual volume. This air isn't useful for gas exchange. There are certain types of diseases of the lung where residual volume builds up because the person cannot fully empty the lungs. This means that the vital capacity is also reduced because their lungs are filled with useless air.
Lung volumes and lung capacities refer to the volume of air associated with different phases of the respiratory cycle. Lung volumes are directly measured. Lung capacities are inferred from lung volumes. The average total lung capacity of an adult human male is about six liters of air, but only a small amount of this capacity is used during normal breathing. Tidal breathing is normal, resting breathing; the tidal volume is the volume of air that is inhaled or exhaled in a single such breath. Several factors affect lung volumes; some can be controlled and some cannot. The tidal volume, vital capacity, inspiratory capacity, and expiratory reserve volume can be measured directly with a spirometer. These are the basic elements of a ventilatory pulmonary function test.
A person who is born and lives at sea level will develop a slightly smaller lung capacity than a person who spends their life at a high altitude. This is because the partial pressure of oxygen is lower at higher altitude which, as a result, oxygen less readily diffuses into the bloodstream. In response to higher altitude, the body's diffusing capacity increases in order to process more air.
When someone living at or near sea level travels to locations at high altitudes (e.g., the Andes, Denver, Colorado, Tibet, the Himalayas, etc.) that person can develop a condition called altitude sickness because their lungs remove adequate amounts of carbon dioxide but they do not take in enough oxygen. In normal individuals, carbon dioxide is the primary determinant of respiratory drive.
Specific changes in lung volumes also occur during pregnancy. Decreased functional residual capacity is seen, typically falling from 1.7 to 1.35 liters, due to the compression of the diaphragm by the uterus. The compression also causes a decreased total lung capacity (TLC) by 5% and decreased expiratory reserve volume. Tidal volume increases with 30-40%, from 0.45 to 0.65 liters, and minute ventilation by 30-40% giving an increase in pulmonary ventilation. This is necessary to meet the increased oxygen requirement of the body, which reaches 50 mL/min, 20 mL of which goes to reproductive tissues. Overall, the net change in maximum breathing capacity is zero.
Determination of the residual volume is more difficult as it is impossible to "completely" breathe out. Therefore measurement of the residual volume has to be done via indirect methods such as radiographic planimetry, body plethysmography, closed circuit dilution (including the helium dilution technique), and nitrogen washout. In absence of such, estimates of residual volume have been prepared as a proportion of body mass for infants (18.1ml/kg), or as a proportion of vital capacity (0.24 for men and 0.28 for women) or in relation to height and age ((0.0275*AgeInYears+0.0189*HeightInCentimeters-2.6139) liters for normal-weight individuals and (0.0277*AgeInYears+0.0138*HeightInCentimeters-2.3967) liters for overweight individuals). Standard errors in prediction equations for residual volume have been measured at 579 ml for men and 355 ml for women, while the use of 0.24*FVC gave a standard error of 318 ml.