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Lung volumes

Lung volumes

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Encyclopedia
Lung
Human lung
The human lungs are the organs of respiration in humans. Humans have two lungs, with the left being divided into two lobes and the right into three lobes. Together, the lungs contain approximately of airways and 300 to 500 million alveoli, having a total surface area of about in...

 volumes
and lung capacities refer to the volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....

 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 6 litres 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.

An average human breathes some 12-20 times per minute.

Factors affecting volumes



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
smokers
Tobacco smoking
Tobacco smoking is the practice where tobacco is burned and the resulting smoke is inhaled. The practice may have begun as early as 5000–3000 BCE. Tobacco was introduced to Eurasia in the late 16th century where it followed common trade routes...

 
non-smokers
people who live at higher altitudes people who live at lower altitudes


A person who is born and lives at sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

 will develop a slightly smaller lung capacity than a person who spends their life at a high altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often 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.

When someone living at or near sea level travels to locations at high altitudes (e.g., the Andes
Andes
The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...

, Denver, Colorado
Denver, Colorado
The City and County of Denver is the capital and the most populous city of the U.S. state of Colorado. Denver is a consolidated city-county, located in the South Platte River Valley on the western edge of the High Plains just east of the Front Range of the Rocky Mountains...

, Tibet
Tibet
Tibet is a plateau region in Asia, north-east of the Himalayas. It is the traditional homeland of the Tibetan people as well as some other ethnic groups such as Monpas, Qiang, and Lhobas, and is now also inhabited by considerable numbers of Han and Hui people...

, the Himalayas
Himalayas
The Himalaya Range or Himalaya Mountains Sanskrit: Devanagari: हिमालय, literally "abode of snow"), usually called the Himalayas or Himalaya for short, is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau...

, etc.) that person can develop a condition called altitude sickness
Altitude sickness
Altitude sickness—also known as acute mountain sickness , altitude illness, hypobaropathy, or soroche—is a pathological effect of high altitude on humans, caused by acute exposure to low partial pressure of oxygen at high altitude...

 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 occur also during pregnancy. Decreased functional residual capacity
Functional residual capacity
Functional Residual Capacity is the volume of air present in the lungs, specifically the parenchyma tissues, at the end of passive expiration...

 is seen, typically falling from 1.7 to 1.35 litres, due to the compression of the diaphragm
Thoracic diaphragm
In the anatomy of mammals, the thoracic diaphragm, or simply the diaphragm , is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity from the abdominal cavity and performs an important function in respiration...

 by the uterus. The compression also causes a decreased total lung capacity (TLC) by 5% and decreased expiratory reserve volume. Tidal volume
Tidal volume
Tidal volume is the lung volume representing the normal volume of air displaced between normal inspiration and expiration when extra effort is not applied.Typical values are around 500ml or 7ml/kg bodyweight.-Mechanical Ventilation:...

 increases with 30-40%, from 0.45 to 0.65 litres, 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.

Values

Average lung volumes in healthy adults
Volume Value (litres)
In men In women
Inspiratory reserve volume 3.3 1.9
Tidal volume 0.5 0.5
Expiratory reserve volume 1.0 0.7
Residual volume 1.2 1.1

Lung capacities in healthy adults
Volume Average value (litres) Derivation
In men In women
Vital capacity 4.8 3.1 IRV plus TV plus ERV
Inspiratory capacity 3.8 2.4 IRV plus TV
Functional residual capacity 2.2 1.8 ERV plus RV
Total lung capacity 6.0 4.2 IRV plus TV plus ERV plus RV


The tidal volume, vital capacity, inspiratory capacity and expiratory reserve volume can be measured directly with a spirometer
Spirometer
A spirometer is an apparatus for measuring the volume of air inspired and expired by the lungs. It is a precision differential pressure transducer for the measurements of respiration flow rates. The spirometer records the amount of air and the rate of air that is breathed in and out over a...

. 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
Body plethysmography
Body plethysmography or "Body Box" for short, is a very sensitive lung measurement used to detect lung pathology that might be missed with conventional pulmonary function tests. This method of obtaining the absolute volume of air within one's lungs may also be used in situations where several...

, closed circuit dilution (including the helium dilution technique
Helium dilution technique
The helium dilution technique is the way of measuring the functional residual capacity of the lungs ....

) 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*HeightInCentimetres-2.6139) litres for normal-weight individuals and (0.0277*AgeInYears+0.0138*HeightInCentimeters-2.3967) litres for overweight individuals). Standard errors in prediction equations for residual volume have been measured at 579ml for men and 355ml for women, while the use of 0.24*FVC gave a standard error of 318ml.

Restrictive and obstructive


The results (in particular FEV1/FVC and FRC) can be used to distinguish between restrictive and obstructive pulmonary diseases:
Type Examples Description FEV1/FVC
>-
| restrictive diseases
pulmonary fibrosis
Pulmonary fibrosis
Pulmonary fibrosis is the formation or development of excess fibrous connective tissue in the lungs. It is also described as "scarring of the lung".-Symptoms:Symptoms of pulmonary fibrosis are mainly:...

, Infant Respiratory Distress Syndrome, weak respiratory muscles, pneumothorax
volumes are decreased >-
| obstructive diseases
asthma
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...

 or COPD
Chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease , also known as chronic obstructive lung disease , chronic obstructive airway disease , chronic airflow limitation and chronic obstructive respiratory disease , is the co-occurrence of chronic bronchitis and emphysema, a pair of commonly co-existing diseases...

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 0.78 - 0.45)

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