Physiological ageing of the respiratory system is associated
with changes in the compliance of the chest wall
and lung parenchyma, which result in static air-trapping,
increased functional residual capacity and increased work
of breathing. Expiratory flow rates decrease with ageing,
with characteristic changes in the flow±volume curves suggesting
increased collapsibility of peripheral airways. Respiratory
muscle function is affected by geometric changes
in the rib cage and is strongly correlated with nutritional
status (lean body mass, body weight), peripheral muscle
mass and strength and cardiac index. In subjects aged $80
yrs, values of maximal inspiratory pressure may reach
critically low values, which may be associated with alveolar
hypoventilation in circumstances such as left-sided
heart failure or pneumonia. Gas exchange is well preserved
at rest and during exertion in spite of a reduced alveolar
surface area and increased ventilation±perfusion heterogeneity.
In fact, in elderly subjects with regular training, the
respiratory system can adapt to high levels of exercise.
However, age-associated alterations of the respiratory system
tend to diminish the subjects' reserve in cases of infection
or heart failure. Decreased sensitivity of respiratory
centres to hypoxia or hypercapnia will result in a diminished
ventilatory response in cases of acute disease such
as heart failure, infection or aggravated airway obstruction.
Furthermore, decreased perception of added resistive loads
(i.e. bronchoconstriction) and diminished physical activity
may result in less awareness