Lung volumes



Lung volumes refer to physical differences in lung volume, while lung capacities represent different combinations of lung volumes, usually in relation to respiration and exhalation.

The average pair of human lungs can hold about 6 liters of air, but only a small amount of this capacity is used during normal breathing.

Breathing mechanism in mammals is called "tidal breathing". Tidal breathing means that air goes into the lungs the same way that it comes out.

Factors affecting lung volume
Several factors affect lung volumes, some that can be controlled and some that can not. These factors include:

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.) they can develop a condition called altitude sickness because their lungs cannot respirate sufficiently in the thinner air.

Measurement and values
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 :

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:

Other
The largest human lung capacity recorded is that of British rower Peter Reed at 11.68 litres, roughly twice that of an average person.