Effects of Aging on the Cardiopulmonary System
After reading this chapter you will be able to:
• Explain why health care of elderly people has taken on increasingly greater importance in the twenty-first century
• Explain why older people are more prone to falls and how this phenomenon is related to pulmonary health
• Explain why elderly people are more predisposed to infections than younger people
• Describe the nature of major age-related physiological changes of the respiratory and cardiovascular systems
• Describe the nature of the body’s compensatory responses to age-related cardiopulmonary changes
• Explain why the PaO2 of a healthy elderly person is lower than the PaO2 of a younger person when both individuals are breathing room air
• Explain why an elderly person has a lower maximum cardiac output and oxygen consumption during exercise than a younger person
• Explain the major benefits of an exercise program for elderly individuals
Implications of an Aging Population
People are increasingly surviving to older ages than they did in previous generations, owing to modern advances in medicine that affect old age mortality and because of improved diet and exercise habits. In addition, with the aging of baby boomers (individuals born in the post World War II era, generally between 1946 and 1964), increasingly greater numbers of people in the United States are entering the 65 years and older age bracket. According to the U.S. Census Bureau, the elderly population (≥65 years old) increased more than 10-fold between 1900 and 2000 (from 3.1 million to 35 million), whereas the general population only tripled in the same time span.1 Elderly people account for about 12% of the U.S. population. In 1900, the median age (half of the population younger and half older) was 23 years; in 2000, the median age was 35 years. The elderly population as a whole is aging; the fastest growing age group in the United States as well as the world is the oldest-old—80 years old and older.1,2 It is predicted that by 2050, the number of people in the world 60 years old or older will exceed, for the first time in history, the number of people younger than age 15.2
The aging population has significantly influenced the focus of health care.3 Health of older people typically worsens with increasing age because of increased vulnerability to accidents and disease. The demand for long-term health care facilities and home-based health care is ever increasing.
The clinician must be able to distinguish between the effects of normal aging and the effects of disease to treat elderly patients effectively; effects of aging and disease are often combined. It is difficult to sort and assess the subtle effects of other factors such as smoking history, environmental pollution, and physical activity. Separating the effects of normal aging from the effects of disease is complicated because age increases susceptibility to disease. Increased propensity for developing disease, especially more severe disease, is the most important physiological change of aging.3 The lung function of a healthy 70-year-old is about half that of a 30-year-old; renal function declines by about the same amount. Although decreased reserve capacity does not affect activities of daily living, it greatly affects the ability of older people to recover from severe illnesses.3
Neuromuscular systems that maintain upright posture become less effective with age; this leads to postural instability and a predisposition to falls, which are more likely to produce fractures because of bone mass loss and greater bone fragility.3 Danger of falling is exacerbated by sensory impairments such as poor eyesight, hearing loss, and balance disorders. In addition, loss of muscular mass and strength, arthritis, orthopedic problems, blood pressure instability, and medications contribute to the tendency to fall. Bone fractures lead to immobility, and when combined with an impaired gag reflex and a less effective mucociliary clearance mechanism, the susceptibility to respiratory infection and pneumonia increases.3
Effects of Aging on the Respiratory System
Structural Changes
Aging changes the compliance of the lungs and chest wall. The chest wall progressively stiffens as the thoracic cage joints and attachments calcify and become less mobile.3,4 With advancing age, vertebral column deformities produce some degree of kyphoscoliosis (abnormal front-to-back and side-to-side curvature of the spine).5 Simultaneously, intercostal and diaphragmatic muscles atrophy, losing strength and endurance. These changes combine to decrease upper and lower rib cage and abdominal expansion.5,6
In contrast to the chest wall, the lung becomes more compliant with age as it loses elastic tissue and recoil force. As a result, the chest wall expands slightly, which mildly increases lung volumes at end-tidal exhalation (functional residual capacity [FRC]) and at maximal effort exhalation (residual volume [RV]). These changes lead to slight hyperinflation and a mildly increased anterior-posterior chest diameter (barrel chest).3,4
Loss of elastic recoil forces also allows small noncartilaginous airways to remain at larger diameters after normal expiration, increasing the anatomical dead space volume and the dead space-to-tidal volume ratio (VD/VT); in addition, alveolar ducts and alveoli become wider, shallower, and less complex in shape, resulting in a marked decrease in gas-exchange surface area.4 These changes are suggestive of emphysema—hence the misleading term senile emphysema. Anatomical changes are much more extensive and debilitating in clinically significant pulmonary emphysema than they are in the healthy aged lung.
Functional Changes
Table 24-1 summarizes functional respiratory changes with aging. Loss of elastic tissue with subsequent loss of alveolar complexity decreases gas-exchange surface area and diffusion capacity. Small noncartilaginous airways become more prone to compression and collapse during forced expiration as they lose the tethering effect of surrounding elastic fibers. This tendency toward collapse decreases maximum expiratory flow rates, especially in effort-independent portions of the forced vital capacity (FVC). Expiratory flow limitation is the most consistent effect of aging during moderate and heavy exercise.4 As the lung ages, total lung capacity remains relatively constant, while residual volume increases; this causes vital capacity to decrease by about 30 mL per year after age 30 years.7
TABLE 24-1
Changes in Respiratory Function with Aging
| Function | Mechanism | Clinical Manifestation |
| Mechanics of ventilation | Loss of lung elastic recoil; decreased chest wall compliance | ↓ VC; ↑ RV; no change in TLC; ↓ expiratory flow rates |
| Decreased respiratory muscle mass and strength | ↓ Maximal inspiratory and expiratory force | |
| Perfusion, ventilation, and gas exchange | Decreased uniformity of ventilation with small airway closure during tidal breathing, especially in the supine position; ↓ cardiac output; ↓ < ?xml:namespace prefix = "mml" /> |
↑ P(A-a)O2; ↓ PaO2; no change in PaCO2 or pH |
| Increased physiological dead space | None (slightly ↑  ) |
|
| Decreased alveolar surface area | ↓ DLCO | |
| Exercise capacity | Decreased aerobic work capacity of skeletal muscle; deconditioning | ↓ Maximum  |
| Decreased efficiency of ventilation | ↑  |
|
| Regulation of ventilation | Decreased responsiveness of central and peripheral chemoreceptors | ↓  and P0.1 responses to hypoxia and hypercapnia |
| Sleep and breathing | Decreased ventilatory drive | ↑ Frequency of apneas, hypopneas, and desaturation episodes during sleep |
| Decreased upper airway muscle tone | Snoring; ↑ incidence of obstructive sleep apnea | |
| Decreased arousal and cough reflexes | ↑ Susceptibility to aspiration and pneumonia | |
| Lung defense mechanisms |
