The function of lungs is to exchange gases. The large surface area of the lungs increases the risk of toxic exposure as the lungs are directly exposed. The changes in lungs as the person ages is not only due to aging of the lung, but also the insults that the lung has suffered over the years. Most common toxic exposure to the lungs is the exposure to smoke (smoke from industrial emission, vehicular pollution and more importantly cigarette smoke).
The key exposure is from breathing in the direct cigarette smoke but passive smoking also is a major factor, which is only now being recognized.
Age related changes in the lungs
Lungs provide the surface for exchange of oxygen, one of the most important molecules for survival. Oxygen unfortunately, also causes damage to the epithelial lining of the lung by the formation free radicals. These cause the release of inflammatory molecules leading to tissue damage.
Basically, oxygen free radicals cause the lung to injure itself and age before its time. The free radicals generated in a smoker’s lungs are far more in number and are far more dangerous than in a non-smoker’s lungs.
There are other risk factors which can cause early aging of the lung which are as follows:
- Environmental toxins, pollution
- Poor nutrition (more significant in elderly)
- Respiratory infections
- Sedentary life style with reduced physical activity
Breathing units are basically made of three kinds of tissues: the lung tissue containing the alveoli and airways, the chest wall and the respiratory muscles.
Changes in the lung tissue:
The alveoli enlarge and the elastic tissue in them degenerates leading to reduced recoil and permanent stretching of the alveoli. This is called “Senile Emphysema”. The alveolar surface area drops by as much as 20%. This leads to an increased tendency of the airways to collapse during the breathing out phase (expiration).
The airways also stiffen due to deposition of a variety of substances related to aging.
The epithelial cells lining the airways perform an important function of secreting mucous that serves as a lubricant in the airways, preventing them from damaging. With age the epithelial cells also decrease in number, leading to dryness and irritation of airways, exposing them to higher risk of infection.
Chest wall changes
Changes occurring in the chest wall are:
- calcification of rib cartilages,
- changes in the inter-vertebral discs of the vertebral column
- changes in the muscle of the chest wall.
The chest wall becomes stiff and the effort of breathing increases. Collapse of the inter-vertebral disc leads to kyphosis in about 10% of elderly, leading to hunch back and barrel shaped chest.
Changes in the respiratory muscles
The major age related changes in the respiratory muscles is the reduction in both strength and endurance of the muscles and thus causing an increase in the effort of breathing.
Other co-existing illnesses like congestive cardiac failure, chronic obstructive pulmonary disease and poor nutrition contribute to the respiratory limitations.
The functional lung capacity decreases with age leading to increase in the effort of breathing by 120% in elderly compared to a young healthy adult.
The breathing volumes per minute in elderly are about the same as in young adults but breathing in elderly is faster and shallower. The breath rate increases more compared to that in a young adult in response to exercise. This means that even a healthy elderly person seems much more breathless than a healthy young adult after similar exercise.
Sleep disordered breathing is much more common in healthy elderly. Snoring, taking sleeping pills and other concurrent illnesses lead to un-reported cases of oxygenation insufficiency and increase the risk of stroke in sleep.
Respiratory obstruction, Alzheimer’s disease and congestive cardiac failure seem to be very common clinical combination with a bad outcome.
Effects of aging on the immune function of the lung
The mucous barrier becomes weaker in old age leading to dryness of airways and increased risk of airborne infections. Smoking contributes to a large extent in causing damage to the defense mechanisms. This decrease in immunity explains to a large extent, the increased incidence of lower respiratory tract infections in the elderly.
Malnutrition and diabetes are common co-existing conditions in old-age. These too contribute to increased incidence of pneumonia. Age related immunity decline also leads to decreased response to vaccination ultimately leading to overall increase of risk of respiratory infections and delay in recovery.
Ask a question regarding Aging of Respiratory System