Lung volumes refers to physical differences in lung volume, while lung capacities represent different combinations of lung volumes, usually in relation to inhalation and exhalation.
Breathing mechanism in mammals is called "tidal breathing". Tidal breathing means that air goes into the lungs the same way that it comes out.
Several factors affect lung volumes; some can be controlled and some cannot. Lung volumes can be measured using the following terms:
|Larger volumes||Smaller volumes|
|taller people||shorter people|
|people living at high altitudes||people living at low altitudes|
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 atmosphere is less dense at higher altitude, and therefore, the same volume of air contains fewer molecules of all gases, including oxygen. In response to higher altitude, the body's diffusing capacity increases in order to be able to process more air.
When someone living at or near sea level travels to locations at high altitudes (eg. the Andes, Denver, Colorado, Tibet, the Himalayas, etc.) s/he can develop a condition called altitude sickness because their lungs cannot respirate sufficiently in the thinner air.
These values vary with the age and height of the person; the values that follow are for a 70 kg (154 lb), average-sized adult male :
|Total lung capacity (TLC)||= 6.0 L||= IRV + TV + ERV + RV||The volume of gas contained in the lung at the end of maximal inspiration. The total volume of the lung (i.e.: the volume of air in the lungs after maximum inspiration).|
|Vital capacity (VC)||= 4.6 L||= IRV + TV + ERV||The amount of air that can be forced out of the lungs after a maximal inspiration. Emphasis on completeness of expiration. The maximum volume of air that can be voluntarily moved in and out of the respiratory system.|
|Forced vital capacity (FVC)||= 4.8 L||measured||The amount of air that can be maximally forced out of the lungs after a maximal inspiration. Emphasis on speed.|
|Tidal volume (Vt)||= 500 mL||measured||The amount of air breathed in or out during normal respiration. The volume of air an individual is normally breathing in and out.|
|Residual volume (RV)||= 1.2 L||measured||The amount of air left in the lungs after a maximal exhalation. The amount of air that is always in the lungs and can never be expired (i.e.: the amount of air that stays in the lungs after maximum expiration).|
|Expiratory reserve volume (ERV)||= 1.2 L||measured||The amount of additional air that can be breathed out after the end expiratory level of normal breathing. (At the end of a normal breath, the lungs contain the residual volume plus the expiratory reserve volume, or around 2.4 litres. If one then goes on and exhales as much as possible, only the residual volume of 1.2 litres remains).|
|Inspiratory reserve volume (IRV)||= 3.6 L||measured IRV=VC-(TV+ERV)||The additional air that can be inhaled after a normal tidal breath in. The maximum volume of air that can be inspired in addition to the tidal volume.|
|Functional residual capacity (FRC)||= 2.4 L||= ERV + RV||The amount of air left in the lungs after a tidal breath out. The amount of air that stays in the lungs during normal breathing.|
|Inspiratory capacity (IC)||= 4.1 L||= TV + IRV||The volume that can be inhaled after a tidal breathe-out.|
|Anatomical dead space||= 150 mL||measured||The volume of the conducting airways. Measured with Fowler method.|
|Physiologic dead volume||= 155 mL||The anatomic dead space plus the alveolar dead space.|
The tidal volume, vital capacity, inspiratory capacity and expiratory reserve volume can be measured directly with a spirometer. Determination of the residual volume can be done by radiographic planemetry, body plethysmography, closed circuit dilution and nitrogen washout.
These are the basic elements of a ventilatory pulmonary function test. The results (in particular FEV1/FVC and FRC) can be used to distinguish between restrictive and obstructive pulmonary diseases:
|restrictive diseases||pulmonary fibrosis||volumes are decreased||often in a normal range (0.8 - 1.0)|
|obstructive diseases||asthma or COPD||volumes are essentially normal but flow rates are impeded||often low (Asthma can reduce the ratio to 0.6, Emphysema can reduce the ratio to 0.3 - 0.4)|
Unofficially Grant Hackett, an Australian Olympic Swimmer, has a lung capacity of 13 litres