It is only recently that health problems of the elderly have drawn our more active attention in this country. The number of people beyond 65 years of age have significantly increased in the last one or two decades or so. This is partly because of the increase in the total population and partly because of an increase in life span. Many individuals who earlier used to die young, now live longer into old age. This has obviously happened because of the general improvements in socio-economic standards and health care. As a result, one sees more and more elderly people in the hospitals seeking solutions for their health problems.
The issues related to health care of elderly have evoked great interest of internists and the specialists. Old age is one special area of medicine which is rather specialized for handling. Yet one needs to manage an old person as a general physician more often than a specialist.
All body systems including the respiratory tract age with time. But the different alterations which occur in one particular system (e.g. respiratory) are also reflected in the functioning of the other. This is particularly true in old age.
The anatomical and physiological alterations which take place with age not only affect the normal functioning of respiratory system but also the occurrence and course of different diseases. It is important to discuss the different age related changes before we deliberate upon diagnosis and management of diseases.
Lung elasticity: The two major tissues of lung parenchyma affected by aging are lung elastin and collagen. Due to changes and loss of elastin, there is loss of elasticity resulting in alveolar dilatation, lung hyperinflation and inadequate deflation. Lungs therefore become voluminous and grounded in shape, an appearance similar to that of emphysema. It is for this reason that the terminology senile emphysema got popular although the lungs are not emphysematous in true histological sense.
There is also a progressive increase in respiratory bronchioles and alveolar ducts ductectasia. But the alveolar septae become shortened and flattened causing a decrease in the surface to volume ratio.
Collagen, which is metabolically inert, is present in abundance in lungs. Due to an increase in the number of cross-links between sub-units of collagen, there is increased rigidity.
Changes in chest wall: There is sclerosis and calcification of joints of ribs with sternum and spinal column. In addition, osteoporosis of vertebrae may cause kyphosis. The chest wall changes decrease its compliance limiting chest expansion.
Changes in compliance of lung parenchyma and chest wall take place in opposite directions. Since the increase in chest wall rigidity is far more than the decrease in lung elastic recoil, the overall change is that of a decrease in compliance of the respiratory system, causing increased work of respiratory muscles.
Respiratory muscles: Respiratory muscles atrophy with age causing decrease in respiratory muscle strength and endurance. Both maximal inspiratory (Pimax) and expiratory (Pemax) pressures decrease in both sexes. There is a marked inter-individual variability in respiratory pressures. Physically active individuals have greater muscle endurance because of the training effects.
Miscellaneous changes: There are some alterations in respiratory control i.e. a diminished responsiveness to hypoxaemia and/or hypercapnia. This could further be attributed to changes in function of the peripheral chemo-receptors or the respiratory centre or both.
Alterations in pulmonary circulation are generally mild. There is a minor increase in pulmonary vascular resistance and pulmonary artery wedge pressure during exercise. These changes have little physiological or clinical significance.
Alterations of lung functions are important and clinically relevant. There is a gradual decline in vital capacity (VC) and forced expiratory volume in first second (FEV1). On the other hand, the residual lung volume, functional residual capacity (FRC) and the total lung capacity are increased. These changes indicate some degree of air trapping in the lung. The air flows are reduced and the percent ratio of FEV1 to VC may also be low. Total airway resistance at FRC does not change but the significant increase which occurs in the peripheral airway resistance is compensated by a decrease in central airway resistance.
There is a gradual decline with age of diffusion capacity (DLCO) of the lungs. Both the membrane component (Dm) and pulmonary capillary blood volume (VC) decrease but the decline in Dm is greater. Low DLCO along with increased ventilation ? perfusion mismatching cause an age-related fall in arterial oxygen pressure (PaO2). The alveolar oxygen pressure (PAO2) remains unaltered but the alveolar arterial oxygen gradient (PA-aO2) is increased. There are no alterations in either PaCO2 or pH of arterial blood.
Besides the functions of other organ systems, exercise, sleep, psychological and sexual activities also alter with age and affect the functioning of respiratory system either directly or indirectly. Exercise capacity is decreased and sleep disturbed. The diminished gastrointestinal motility, limited neurological responses, diminished cardiac output and increased dysfunction, all affect the normal functions of respiratory systems, occurrence of diseases and their management strategies.