Lung volumes
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Lung volumes and lung capacities refer to the
volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). ...
of air in the
lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of ...
s at different phases of the respiratory cycle. The average total lung capacity of an adult human male is about 6 litres of air. Tidal breathing is normal, resting breathing; the tidal volume is the volume of air that is inhaled or exhaled in only a single such breath. The average human
respiratory rate The respiratory rate is the rate at which breathing occurs; it is set and controlled by the respiratory center of the brain. A person's respiratory rate is usually measured in breaths per minute. Measurement The respiratory rate in humans is me ...
is 30–60 breaths per minute at birth, decreasing to 12–20 breaths per minute in adults.


Factors affecting volumes

Several factors affect lung volumes; some can be controlled, and some cannot be controlled. Lung volumes vary with different people as follows: A person who is born and lives at
sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardis ...
will develop a slightly smaller lung capacity than a person who spends their life at a high
altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...
. This is because the partial pressure of oxygen is lower at higher altitude which, as a result means that oxygen less readily diffuses into the bloodstream. In response to higher altitude, the body's diffusing capacity increases in order to process more air. Also, due to the lower environmental air pressure at higher altitudes, the air pressure within the breathing system must be lower in order to inhale; in order to meet this requirement, the thoracic diaphragm has a tendency to lower to a greater extent during inhalation, which in turn causes an increase in lung volume. When someone living at or near sea level travels to locations at high altitudes (e.g. the
Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...
;
Denver, Colorado Denver () is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 at the 2020 census, a 19.22% increase since 2010. It is the 19th-most populous city in the Unit ...
;
Tibet Tibet (; ''Böd''; ) is a region in East Asia, covering much of the Tibetan Plateau and spanning about . It is the traditional homeland of the Tibetan people. Also resident on the plateau are some other ethnic groups such as Monpa people, ...
; the
Himalayas The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 10 ...
) that person can develop a condition called
altitude sickness Altitude sickness, the mildest form being acute mountain sickness (AMS), is the harmful effect of high altitude, caused by rapid exposure to low amounts of oxygen at high elevation. People can respond to high altitude in different ways. Sympt ...
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.) Lung function development is reduced in children who grow up near motorways although this seems at least in part reversible. Air pollution exposure affects FEV1 in asthmatics, but also affects FVC and FEV1 in healthy adults even at low concentrations. Specific changes in lung volumes also occur during pregnancy. Functional residual capacity drops 18–20%, typically falling from 1.7 to 1.35 litres, due to the compression of the
diaphragm Diaphragm may refer to: Anatomy * Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Pelvic diaphragm or pelvic floor, a pelvic structure * Urogenital diaphragm or triangular ligament, a pelvic structure Other * Diap ...
by the uterus. The compression also causes a decreased
total lung capacity Lung volumes and lung capacities refer to the volume of air in the lungs at different phases of the respiratory cycle. The average total lung capacity of an adult human male is about 6 litres of air. Tidal breathing is normal, resting breath ...
(TLC) by 5% and decreased expiratory reserve volume by 20%. Tidal volume increases by 30–40%, from 0.5 to 0.7 litres, and
minute ventilation Minute ventilation (or respiratory minute volume or minute volume) is the volume of gas inhaled (inhaled minute volume) or exhaled (exhaled minute volume) from a person's lungs per minute. It is an important parameter in respiratory medicine d ...
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.


Values

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''. 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 (18.1 ml/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* Age ears0.0189*Height mˆ’2.6139) litres for normal-mass individuals and (0.0277*Age ears0.0138*Height mˆ’2.3967) litres 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.
Online calculators are available
that can compute predicted lung volumes, and other spirometric parameters based on a patient's age, height, weight, and ethnic origin for many reference sources. British rower and three-time Olympic gold medalist, Pete Reed, is reported to hold the largest recorded lung capacity of 11.68 litres; US swimmer, Michael Phelps is also said to have a lung capacity of around 12 litres.


Weight of breath

The mass of one breath is approximately a gram (0.5-5 g). A litre of air weighs about 1.2 g (1.2 kg/m3). Atmosphere of Earth#Density and mass A half litre ordinary tidal breath weighs 0.6 g; a maximal 4.8 litre breath (average vital capacity for males) weighs approximately 5.8 g.


Restrictive and obstructive

The results (in particular FEV1/FVC and FRC) can be used to distinguish between restrictive and obstructive pulmonary diseases:


See also

*
Pulmonary function testing Pulmonary function testing (PFT) is a complete evaluation of the respiratory system including patient history, physical examinations, and tests of pulmonary function. The primary purpose of pulmonary function testing is to identify the severity ...
(PFT) *
Spirometry Spirometry (meaning ''the measuring of breath'') is the most common of the pulmonary function tests (PFTs). It measures lung function, specifically the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. Spirometry is ...


References


External links


Lung function fundamentals (anaesthetist.com)Volume of human lungs
{{Respiratory physiology Respiratory physiology Pulmonary function testing