With age, muscle function declines and the nervous system that sends the impulse to breathe becomes less responsive, meaning that less oxygen enters the lungs on breathing in, and more carbon dioxide stays behind on breathing out.
It becomes harder to clear mucus that collects in the lungs, especially when people lie in bed or sit for long periods -- a high risk factor for lung infections like bronchitis or pneumonia because of the accumulation of mucus.
At the same time, a weakening immune system means the body is less able to fight infection, according to the US National Institutes of Health (NIH).
"When we are young and fit, we cough up (mucus) vigorously. When we are old, we cough less easily and if we already have weakened lungs the mucus stays behind and there is a high risk of congestion," said French pulmonologist Bertrand Dautzenberg.
"This is why old people are prone to respiratory infections, which are a key cause of death among the elderly."
Also, he said, most people on reaching the age of 90 use about 50 percent of their lung capacity, compared to 20 percent in youth.
"If, in addition, a part of one's lung has previously been damaged by tuberculosis... one is left with very little spare capacity."
Mandela has a long history of lung problems, and was most recently treated for an infection in December last year, when he spent nearly three weeks in hospital.
He was previously briefly hospitalized for an acute respiratory infection in January 2011.
In 1988, while serving a 27-year prison term, Mandela was diagnosed with early stage TB after complaining of dampness in his cell.
Two liters (1.1 pints) of fluid were drained from his chest at the time and he spent six weeks recuperating in hospital.
According to Dautzenberg, respiratory infections are often a contributing factor to death in the elderly.
The symptoms can be dire and resemble the eating disorder anorexia, he said: patients stop eating and become exhausted over time.
If they suffer a shortage of oxygen, this could affect other organs like the brain or kidneys.
In hospital, though doctors can provide oxygen and physiotherapy to loosen and expel any mucus.
source: interaksyon.com
