It is one of the diseases that make up chronic obstructive pulmonary disease (COPD). This is a set of diseases where the flow of air in the lungs is obstructed. Emphysema is most often caused by smoking but can be caused by other diseases or have no known cause at all.
It occurs when the very small air sacs (called the alveoli) at the ends of the airways in the lungs start to break down from many sacs to form much bigger sacs. The alveoli are the areas of the lung where oxygen and carbon dioxide are exchanged into and out of the blood. Emphysema makes it hard for people to blow air out of the lungs because air gets trapped inside the broken alveoli due to the collapse of the walls. The trapped air in the lungs creates the characteristic "barrel chest" of emphysema.
There is no cure for emphysema. Treatment includes stopping smoking and taking medicines ('broncho-dilators' and sometimes corticosteroids). Supplemental oxygen is recommended in those with low oxygen levels at rest. It decreases the risk of heart failure and death if used 15 hours per day, and may improve people's ability to exercise. In those with normal or mildly low oxygen levels, oxygen supplementation may improve shortness of breath. There is a risk of fires and little benefit when those on oxygen continue to smoke.
Emphysema is commonly associated with chronic bronchitis. As it is rather difficult to delineate "pure" cases of emphysema or chronic bronchitis they are classed together into chronic obstructive pulmonary disease (COPD).
Oxygen
Oxygen is a chemical element. It has the symbol O and atomic number 8. It is the third most common element in the universe, after hydrogen and helium. Oxygen is more than a fifth of the Earth's atmosphere by volume. In the air, two oxygen atoms usually join to make dioxygen (), a colourless gas. This gas is often just called oxygen. It has no taste or smell. It is pale blue when it is liquid or solid.
Oxygen is part of the chalcogen group on the periodic table. It is a very reactive nonmetal. It makes oxides and other compounds with many elements. The oxygen in these oxides and in other compounds (mostly silicate minerals, and calcium carbonate in limestone) makes up nearly half of the Earth's crust, by mass.
Most living things use oxygen in respiration. Many molecules in living things have oxygen in them, such as proteins, nucleic acids, carbohydrates and fats. Oxygen is a part of water, which all known life needs to live. Algae, cyanobacteria and plants make the Earth's oxygen gas by photosynthesis. They use the Sun's light to get hydrogen from water, giving off oxygen.
Oxygen gas () was isolated by Michael Sendivogius before 1604. It is often thought that the gas was discovered in 1773 by Carl Wilhelm Scheele, in Sweden, or in 1774 by Joseph Priestley, in England. Priestley is usually thought to be the main discoverer because his work was published first (although he called it "dephlogisticated air", and did not think it was a chemical element). Antoine Lavoisier gave the name "oxygène" to the gas in 1777. He was the first person to say it was a chemical element. He was also right about how it helps combustion work.
At the top of the Earth's atmosphere is ozone (), in the ozone layer. It absorbs ultraviolet radiation, which means less radiation reaches ground level.
Oxygen gas is used for making steel, plastics and textiles. It also has medical uses and is used for breathing when there is no good air (by divers and firefighters, for example), and for welding. Liquid oxygen and oxygen-rich compounds can be used as a rocket propellant.
One of the first known experiments on how combustion needs air was carried out by Greek Philo of Byzantium in the 2nd century BC. He wrote in his work "Pneumatica" that turning a vessel upside down over a burning candle and putting water around this vessel meant that some water went into the vessel. Philo thought this was because the air was turned into the classical element fire. This is wrong. A long time after, Leonardo da Vinci worked out that some air was used up during combustion, and this forced water into the vessel.
In the late 17th century, Robert Boyle found that air is needed for combustion. English chemist John Mayow added to this by showing that fire only needed a part of air. We now call this oxygen (O). He found that a candle burning in a closed container made the water rise to replace a fourteenth of the air's volume before it went out. The same thing happened when a live mouse was put into the box. From this, he worked out that oxygen is used for both respiration and combustion.
Robert Hooke, Ole Borch, Mikhail Lomonosov and Pierre Bayen all made oxygen in experiments in the 17th and 18th centuries. None of them thought it was a chemical element. This was probably because of the idea of the "phlogiston theory". This was what most people believed caused combustion and corrosion.
J. J. Becher came up with the theory in 1667, and Georg Ernst Stahl added to it in 1731. The phlogiston theory stated that all combustible materials were made of two parts. One part, called phlogiston, was given off when the substance containing it was burned.
Materials that leave very little residue when they burn, like wood or coal, were thought to be made mostly of phlogiston. Things that corrode, like iron, were thought to contain very little. Air was not part of this theory.
Polish alchemist, philosopher and physician Michael Sendivogius wrote about something in air that he called the "food of life", and this meant what we now call oxygen. Sendivogius found, between 1598 and 1604, that the substance in air is the same as he got by heating potassium nitrate. Some people believe this was the discovery of oxygen while others disagree. Some say that oxygen was discovered by Swedish pharmacist Carl Wilhelm Scheele. He got oxygen in 1771 by heating mercuric oxide and some nitrates. Scheele called the gas "fire air", because it was the only gas known to allow combustion (gases were called "airs" at this time). He published his discovery in 1777.
On 1 August 1774, British clergyman Joseph Priestley focused sunlight on mercuric oxide in a glass tube. From this experiment he got a gas that he called "dephlogisticated air". He found that candles burned more brightly in the gas and a mouse lived longer while breathing it. After breathing the gas, Priestley said that it felt like normal air, but his lungs felt lighter and easy afterwards. His findings were published in 1775. It is because his findings were published first that he is often said to have discovered oxygen.
French chemist Antoine Lavoisier later said he had discovered the substance as well. Priestley visited him in 1774 and told him about his experiment. Scheele also sent a letter to Lavoisier in that year that spoke of his discovery.
Lavoisier did the first main experiments on oxidation. He was the first person to explain how combustion works. He used these and other experiments to prove the phlogiston theory wrong. He also tried to prove that the substance discovered by Priestley and Scheele was a chemical element.
In one experiment, Lavoisier found that there was no increase in weight when tin and air were heated in a closed container. He also found that air rushed in when the container was opened. After this, he found that the weight of the tin had increased by the same amount as the weight of the air that rushed in. He published his findings in 1777. He wrote that air was made up of two gases. One he called "vital air" (oxygen), which is needed for combustion and respiration. The other (nitrogen) he called "azote", which means "lifeless" in Greek. (This is still the name of nitrogen in some languages, including French.)