Why smokers' emphysema starts at the top of the lungs
In emphysema the thin walls between the lungs' tiny air sacs break down, merging them into larger, useless spaces and shrinking the surface available to absorb oxygen. The kind linked to smoking usually begins in the upper lobes, where gravity changes air and blood flow and particles are filtered less well.
Healthy lung tissue is spongy, packed with alveoli where oxygen crosses into the blood. As their walls break down, the enlarged spaces reduce gas exchange and the lung loses elasticity. Because the damage builds slowly, the disease usually shows up in middle age or later. When it significantly restricts airflow it counts as a major form of chronic obstructive pulmonary disease. Worldwide it accounts for about 3 per cent of all deaths, and in the United States in 2016 it was recorded as the cause of 6,977 deaths.
Pathologists recognise four main types. Centrilobular emphysema begins around the smallest airways at the centre of each lung lobule and is the only type tied to smoking; it is about 20 times more common than panlobular emphysema, which damages whole lobules, tends to hit the lower lungs and is linked to the inherited condition alpha-1 antitrypsin deficiency. The upper lobes are prone to the centrilobular form because gravity gives them a higher ratio of air to blood flow, and they have less blood and lymph flow to clear particles. Paraseptal emphysema forms air blisters just under the lung's lining and can grow into giant bullae filling a third of one side of the chest, a state nicknamed vanishing lung syndrome.
Smoking is the commonest cause, but not the only one. Coal dust, silica and radon exposure in uranium mining are all linked to it. About 20 per cent of people with HIV show increased emphysematous change regardless of whether they smoke, and that form develops faster. Injecting methylphenidate tablets, sold as Ritalin and never meant for injection, can cause a panlobular pattern called Ritalin lung; suspicion falls on talc filler, although other injected drugs containing talc do not seem to do this.
Early signs such as coughing, wheezing and breathlessness on exertion overlap with many other conditions, so emphysema is often underdiagnosed. It also raises the risk of lung cancer, especially in smokers. Diagnosis may become gentler: a 2025 simulation study of dark-field chest X-rays in 93 people suggested emphysema could still be detected at doses as low as 11 microsieverts, with accuracy close to full-dose images.
Source: Emphysema
