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| Stress, Health and Aging |
| Module 3: Normal Change of Aging |
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Electronic Reserve Readings
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The primary health concerns in later life are chronic conditions (i.e., disease), disability, and dependency. The epidemiology of aging is concerned with diseases that cause morbidity and mortality and also with the causes of disability and how they affect functional independence. These topics will be the major focus of this lecture. But first, let us begin by discussing the health status of older adults. |
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In this chapter we will discuss some of the major changes that occur with normal aging. We will help you apply what you are learning about aging to real life situations by illustrating these changes using patient studies that will be introduced during the course of the lesson. Before we start, it may be helpful to discuss a few aspects of normal aging.
A number of physiological changes occur as we grow older. Some of the common changes that we thought represented aging have turned out to be the result of disease. Most of the normal changes of aging have no impact on normal functioning, although they become apparent when the body is placed under stress (e.g., acute illness, physical exertion). For example, the maximum heart rate of older adults is lower than that of younger adults. However, the resting pulse of a younger and older adults would not show this change. It is important to be able to recognize the changes of normal aging versus the effects of disease. Untreated disease can result in "excess disability" and reduce the quality of life of individuals. In this lecture we identify and describe the most important changes in the body that occur with aging. Take the following quiz to see how much you know about the normal changes of aging. Healthy aging is an issue of increasing importance as the size of the older population continues to grow. Poor health in later life is not inevitable. Much of the illness and disability associated with aging is related to modifiable lifestyle factors that are present in middle age.
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The cardiovascular system includes the heart which pumps the blood throughout the body and the network of blood vessels through which the blood is transported. In healthy people, the changes that normally occur in the cardiovascular system with aging do not significantly limit the normal work capacity of the heart. Most of the changes that cause clinically significant declines in cardiovascular function are the result of disease.
As we age, the heart muscle becomes slightly stiffer and may increase slightly in size. Despite this slight increase in heart size, the amount of blood the chamber can hold may actually decrease because the heart wall thickens. The maximum heart rate (the highest rate at which your heart can pump) decreases even among the most fit athlete. However, the resting heart rate and the cardiac output (amount of blood pumped over a period of time) do not change. In response to stress or exertion, older adults compensate for their lower maximum heart rate by increasing their stroke volume (i.e., amount of blood pumped with each contraction of the heart) to maintain cardiac output. Among older adults it takes longer for the heart rate and blood pressure to return to normal resting levels following stress. Our blood vessels, including the aorta and other arteries also become stiffer and are less responsive to hormones that relax the blood vessel walls. The stiffening of blood vessels contributes to the increasing systolic blood pressure with aging observed in most cultures. In Western countries, systolic blood pressure tends to increase throughout a persons life span, while diastolic blood pressure rises until age 60 and then levels off. Nearly 50% of older adults have chronic hypertension. Increases in systolic blood pressure do not occur in many nonindustrialized societies which suggests that risk for hypertension is affected by environmental factors such as diet and lifestyle as well as heredity. An elevated blood pressure increases risk for stroke, heart attack and kidney failure. Our heart rate may be slightly slower as we grow older due to a loss in the number of pacemaker cells. The electrical pathways may develop fibrous tissue and fat deposits that can make dysrhythmias more common. Shifts in the circulation of blood to various organs can also change-- the blood flow to the kidneys may decrease by 50 percent and to the brain by 15 to 20 percent. Finally, heart murmurs are more common with age because our heart valves become less flexible and calcium deposits build up. Finally, the baroreceptors which monitor the blood pressure and adjust your blood pressure when you change position become less sensitive with aging. This can cause orthostatic hypotension (a condition where the blood pressure falls when you go from lying or sitting to standing) and cause dizziness when you change position. Therefore, if you (or your client) gets dizzy in the morning when getting out of bed, you should change position more slowly-- sit for a few minutes before standing up.
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The respiratory system reflects changes that occur in many other body systems,
including the cardiovascular, nervous and musculoskeletal systems. The Framingham
Heart Study and other studies show that respiratory function is one of the
best predictors of mortality. Most of the normal respiratory changes with
age are of little functional significance in healthy older adults. However,
they do reduce reserve capacity and increase vulnerability to respiratory
disease.
As we age, the lungs become stiffer, respiratory muscle strength and endurance diminishes, and the chest wall becomes more rigid. Total lung capacity is relatively constant across the life span but vital capacity (the volume of air that can be forcibly exhaled) decreases because our residual volume increases (the amount of air remaining in the lungs after maximum expiration). At age twenty, about twenty percent of our total lung capacity is residual air; at age sixty the residual air volume increases to about 35 percent (Williams, 1998). In the normal aging lung, alveolar surface area decreases by up to 20 percent which reduces our maximal oxygen uptake (the volume of air that can be moved in and out by forced voluntary breathing) by as much as 55% by age 85. Thus, over time our exercise capacity declines because we have less "reserve". In addition, the alveoli of older adults tend to collapse sooner on expiration than in younger peoples. This tendency is exacerbated by reduced mobility, illness, and hypoventilation and increases the risk for respiratory diseases such as atelectasis. In addition, the number of cilia decline in number as we grow older. Cilia protect against infection by clearing irritants and obstruction. At the same time, the number of mucus producing cells may increase resulting in mucus clogging your airways. These changes make older adults more vulnerable to respiratory infections. These changes make older adults less efficient in monitoring and controlling breathing. For example, they are less sensitive to hypoxia and less able to recognize acute bronchoconstriction. Although the causes are not well understood, the implications are clear. Older adults may be at greater risk for mortality from acute respiratory problems if they are less aware of respiratory symptoms and seek medical care later rather than sooner.
Older adults are less efficient in monitoring and controlling breathing. For example, they are less sensitive to hypoxia and less able to recognize acute bronchoconstriction. Although the causes are not well understood, the implications are clear. Older adults may be at greater risk for mortality from acute respiratory problems if they are less aware of respiratory symptoms and seek medical care later rather than sooner.
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The gastrointestinal (G.I.) system consists of the esophagus, the stomach, the small intestine, the large intestine or colon, the liver, gallbladder, and the pancreas. Generally, the physiological changes of an aging digestive system are minor. With this in mind, it is important to recognize and actively treat most new G.I. problems in healthy older people, rather than ascribing symptoms to aging. The following section reviews some of the most common changes among older adults that can affect the functioning of the G.I. system. Stomach Atrophic gastritis is a stomach disorder that is unique to the elderly. It involves a shrinking and inflammation of the inner lining of the stomach. While it may not cause any symptoms, it can increase the risk for stomach cancer. While this was once thought to be a normal process of aging, more recent evidence indicates that it is caused by a prolonged infestation with helicobactor pylori (H. pylori) or campylobactor pylori (C. Pylori), which is common in older adults. Achlorhydria refers to an insufficient production of stomach acid. It may be caused by atrophic gastritis. The National Academy of Sciences estimates that up to 30% of people over age 50 have achlorhydria. Achlorhydria is the most common cause of B12 deficiency. The stomach must secrete adequate amounts of gastric acid and a protein known as "intrinsic factor" as well as produce the digestive enzyme pepsin for vitamin B12 to be absorbed. Changes in the G.I. tract can affect absorption of vitamin B12. Since the liver is able to store large amounts of B12 it can take up to 5 years before symptoms of deficiency appear. However, it's important to recognize symptoms early since any neurological damage may be irreversible. Symptoms of B12 deficiency can be misdiagnosed since they can look like Alzheimer's or other chronic condition. Symptoms include extreme fatigue, dementia, confusion, and tingling and weakness in the arms and legs. Ulcers. About 20 million Americans suffer from an ulcer during their lifetime. An ulcer is an area of the stomach that has been eroded by digestive juices and stomach acid. Normally, the lining of the stomach and duodenum (small bowel) are protected from the digestive juices of the stomach. The most common symptom of an ulcer is a burning pain in the abdomen. The pain can last minutes to hours and often occurs between meals. The pain may be relieved by eating food or taking antacids. Gastric ulcers (ulcers in the stomach) are more common after the age of 60 and can be benign or malignant. Duodenal ulcers are more common between the ages of 30 and 50 and are twice as common among men. Duodenal ulcers are always benign. There are two major causes of ulcers. Most ulcers are caused by an infestation of H. pylori, this bacterium can also reduce absorption of vitamin B12. Another cause of ulcers is regular use of pain medications called non-steroidal anti-inflammatory drugs (NSAIDS), such as aspirin or ibuprofen, which irritate the stomach. Antibiotics can permanently cure 80 to 90 percent of peptic ulcers. The healing of an ulcer usually requires medication (e.g., Tagamet) to block production of stomach acid. Liver The liver plays an important role in processing the body's waste products of metabolism, as well as affecting the uptake of medications, and serum cholesterol. The major functional changes with age include reduced blood flow, altered clearance of some drugs, and a diminished capacity to regenerate damaged liver cells. Among older adults, the half life of certain drugs such as benzodiazepines, chlordiazepoxide, diazepam, and aminopyrine may be doubled due to decreased metabolism by the liver.
In general, aging does not affect the transport of food through the intestines. Our intestines do not change significantly in their ability to absorb foods as well as drugs, although there are a few exceptions. For example, changes in the metabolism and absorption of lactose, calcium and iron can occur. As we age the small intestines absorb less calcium. Therefore, we need more calcium to prevent bone mineral loss and osteoporosis in later life. Some enzymes, such as lactase which aids the digestion of lactose (a sugar found in diary products) decline with age. The prevalence of diverticulosis increases with age. Almost all of us, if we live long enough, will have diverticula-- small outpouches in the colon. This condition is caused by increased pressure in the colon as a result of impaired intestinal muscle function and weakness in the intestinal wall. Diverticula can be uncomplicated or they can become inflamed (called diverticulitis) and result in great pain. Diverticulitis can be prevented by maintaining a high intake of fiber. Studies of motility in older adults show reduced peristalsis (intestinal muscle contractions) of the large intestine (colon). This slower rate of food transport can contribute to constipation. However, constipation is aggravated by a low intake of fiber and water, inactivity, medications, and overuse of laxatives.
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The urinary system includes the kidneys, ureters, urethra and bladder. It undergoes substantial changes in function as we grow older. In both men and women, urinary changes are often associated with changes in the reproductive system. To learn about "The Aging Urinary System", click below: Kidneys There are several important changes that occur in kidney function as we grow older. The kidneys filter the blood and dispose of wastes and excess fluid as urine. The kidneys also play a vital role in the "acid-base" balance of the body. Beginning in our mid-40s, most of us experience a decline in kidney function, although they continue to function more than adequately under ordinary circumstances. Most of the clinically important changes in renal function with age are probably due to changes in the intrarenal vasculature. Blood flow to the kidneys decreases by as much as 10 percent per decade can be decreased by nearly half that of younger people (600 ml/min) in those who are age 80 or older (300ml/min). As we age, the kidneys lose one quarter to one third their mass as both the number and size of nephrons (filtering units) decreases. By age 80, the total number of glomeruli fall by 30 to 40 percent and another 30% may become sclerotic and nonfunctional. These changes reduce the rate at which the blood is filtered by the kidneys. In addition, the regulation of hormones that respond to dehydration (i.e., vasopressin) and the ability to conserve salt may decline. These renal changes make older adults particularly vulnerable to dehydration. As a result of physiologic changes, the kidneys are less efficient in concentrating urine and eliminate solutes from the blood stream. For the most part, kidney function is well preserved although it may be slower. Most changes do not cause clinically significant disease or disability, but they do leave the kidney vulnerable to illness or medications that can depress renal function and lead to acute or chronic renal failure. Medication dosages often need to be reduced in the elderly because the reduction in kidney function can affect clearance of some drugs and lead to toxicity or adverse effects. Drugs that are renal toxic should be used cautiously in older adults. Bladder The aging bladder is characterized by a decrease in capacity and urinary flow, and an increase in urgency and amount of residual urine. The changes contribute to a increase in nocturia (frequent urination at night) as well as a higher rate of urinary tract infections among the elderly.
This figure shows the difference in glomerular filtration rate (GFR) for a young and an old kidney. The process is based on two stages. First, the oxygenated blood flows in the kidney (the kidney is more RED). Secondly, as the larger particles are being taken out of the blood (the cup is filling up) and the de-oxygenated blood (the kidney is more BLUE) is flowing out of the kidney. The older kidney has a lower concentration of the urine (lighter yellow with fewer particles in it).
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The endocrine system is a complex network of glandular tissues that secrete hormones directly into the blood which are used by "target" organs. The endocrine system controls a variety of important functions such as energy metabolism, reproduction, and stress response. The pituitary gland is often referred to as the "master gland" because it regulates the hormones used by the thyroid, adrenal cortex, ovaries, testes, and the breasts (in women). The pituitary is located in the brain below the hypothalamus. It peaks in size in middle age and then gradually shrinks. Pancreas: Insulin Response The pancreas secretes insulin, a hormone which is critical to the metabolism of glucose (blood sugar). Insulin continues to be produced in sufficient quantities in older adults but their muscle cells may become less sensitive to the effects of insulin (probably due to a loss in the number of insulin receptor sites in the cell wall). After age 50, the "normal" fasting glucose level rises 6 to 14 milligrams per deciliter every 10 years. Adult onset diabetes or Type II diabetes occurs when the body develops resistance to insulin. It is usually managed through diet, exercise, and oral hypoglycemic medications. Sometimes people stop producing insulin and then insulin injections are needed. A number of studies indicate that adult onset diabetes is related to obesity and inactivity. Adrenal Glands The adrenals are located just above the kidney's and secrete several hormones including aldosterone and cortisol.
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The aging of the central nervous system is often portrayed as an irreversible loss of functions and decline in abilities. In the past, scientists reported that we "lose a million neurons every day". Fortunately, that's not correct. The adult brain retains a remarkable plasticity in it's ability to compensate functionally for those losses that do occur. Further, some cognitive abilities, such as wisdom and life experience, are stable or may increase with age. The weight of your brain peaks around age 20 and then a modest decline occurs with age that is limited to the gray matter (outer surface of the brain) in healthy older people. Older nerve cells may have fewer dendrites (branches) and some may become demyelinated (lose its coating) which can slow the speed of message transmission. Most of these changes do not appear to affect ordinary activities of living. People often fear cognitive decline in later life more than any other disabling condition. Cognitive ability is crucial to the capacity to live independently. Most of us do not want to be dependent on others as we age. Impairment in cognitive capacity can threaten autonomy and the ability to manage our daily activities.
Most neurological declines occur after age 60 and are not that severe. At age 65, less than 2% of older Americans have cognitive impairment. The incidence of cognitive impairment increases with age so that by age 85, up to 1/3 of older persons have some degree of cognitive impairment.
The cognitive abilities of older adults vary tremendously both within individuals and across age groups. Within individuals some functions may change while others do not. For example, the verbal I.Q. of an individual may be stable while his performance I.Q. declines. Across age groups the average scores may decline with age, however, we can find many older adults who continue to perform at the level of a younger adult.
The concept of attention involves both sustained attention (i.e., ability to focus) and selective attention (the ability to distinguish relevant from irrelevant information). Older adults appear to perform tasks requiring sustained attention or selective attention extremely well into old age.
One aspect of language-- semantic knowledge-- appears to decline with age, although significant differences are not found until relatively late in the life span (greater than 70 years). Semantic knowledge involves word retrieval and is tested by having respondents name common objects. Linguistic abilities that are not affected include phonologic knowledge (use of sounds of language), lexical knowledge (i.e. the name of an item and the meaning of a word), and syntactic knowledge (i.e. ability to combine words correctly). Memory Memory has been more widely studied than almost any other aspect of cognitive function, other than intelligence. After arthritis, memory problems are the second most frequent complaint among older adults. From age 45, the overall frequency of complaints of memory problems increases steadily. Despite this seeming consensus on memory complaints, the literature reveals a discrepancy between subjective reports of memory failure and objective abilities. Subjective impressions are a poor predictor of objective performance. In part this discrepancy reflects the nature of memory and how we asses our own competency. The efficiency of memory may differ considerably depending on the situation or context. For example, reliable recall of visual images such as paintings may be accompanied by a relatively poor recall of verbal words. Older adults perform less well on tasks involving encoding, retention, and retrieval of information. Currently we know very little about when competence first begins to decline, how rapidly these declines progress, and how decline in memory efficiency compares with other cognitive functioning. Although there is a general progressive trend in poorer memory performance with age, the magnitude of changes in memory competence are small and marked changes in ability do not generally occur until late in life. As people grow older, the rate at which they process information declines. Information processing has three phases:
Encoding is particularly vulnerable to age. As we age it takes more time to encode information than when they were younger. This slower rate of encoding may be due to changes in our vision, hearing and other senses that reduce the efficiency of memory. The slower rate of encoding is most likely the reason for age-related declines in short-term memory. Two types of memory tasks are recall (retrieving information) and recognition (matching information). Regardless of age, recognition is better than recall. Recognition does not decline as we age, but recall does. Long-term memory may decline as we age depending on the extent to difficulty with encoding information. Very long-term memory which spans months or years is relatively stable until well after age 70. Older adults show declines in visual-spatial abilities which affect visual tasks such as identifying incomplete figures, recognizing embedded objects, or arranging blocks into a design. Aging also appear to affect both the ability to perceive and the ability to reproduce figures in three dimensions. Mental flexibility and the capacity for abstraction do appear to decline with age however, the greatest age differences appear among those who are seventy or older.
In measures of intelligence, older adults display what is called the "classic aging pattern". Performance scores which measure problem solving ability tend to decline with age. Verbal scores which measure learning knowledge such as comprehension, arithmetic, and vocabulary, tend to remain stable. Considerable debate continues regarding the point at which declines occur and the magnitude of the declines. Relatively little decline in performance occurs prior to age 50. Substantial declines appear to occur after age 70.
Tests of reaction time indicate a decline in the processing of information among adults age 40 and older, and that the more complex the required processing, the larger the age differences in processing time (Columbia, 1998). However, in real world terms these differences represent about 10 seconds difference and are not clinically detectable. Many of the abilities in which declines occur can be improved through training and practice in memory techniques, problem-solving skills, and other cognitive strategies. Short-term memory loss is common and determining whether "forgetfulness" is benign or a precursor of dementia is often impossible. The average 70 year old can take up to 4 times longer than a 20 year old in tests involving basic memory skills (Moody, p.406). Older adults are also slower in reaction time than younger adults as is clearly shown by the declines in the speed of information processing. |
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Age-related changes in the immune (lymphatic) system increase vulnerability to infections, tumors and immune disease. Factors that affect immune system function include hormonal changes, age, nutrition, and psychological factors (e.g., stress). As we grow older, our bodies are less able to produce antibodies which are important in fighting infections. As a result older adults are at greater risk for infections and the mortality rate from infection is much higher than in the young. Older adults are 3 times more likely to die of pneumonia or sepsis, 5 to 10 times more likely to die of urinary tract infections, and 15 to 20 times more likely to die of appendicitis. The thymus gland produces hormones that are important for the development of white blood cells. White blood cells are the "phages" of the immune system-- they attack and isolate foreign materials. The involution (shrinking) of the thymus gland begins after adolescence and the level of thymic hormones decreases by age 30. By age 60 thymic hormones cannot be detected in the blood. As we age, the immune system also responds less vigorously to skin tests in which a foreign substance is injected below the skin surface, indicating a diminished response to antigens. Age-Related Changes in the Immune System
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By the time we reach age 80, most of us will lose an average of about 2
inches of height. The primary factors contributing to this reduction in
height include compression of vertebrae, changes in posture, and increased
curvature of the hips and knees. In addition, most older Americans gain
weight until about age 60, after which it declines. This pattern of weight
change is more likely the result of reductions in activity and changes in
eating rather than aging itself. There are a number of other changes in
the body with aging that affect the bones, muscle, and skin.
Bone Bone loss seems to be a universal and inevitable consequence of aging. The age of onset and rate of bone loss depends on gender and type of bone. Nearly 90 percent of adult skeletal mass is formed by the end of the teenage years. Osteoporosis has been described as a "pediatric disease with geriatric consequences" (Duane Alexander, Director of the National Institute of Child Health and Human Development). Prevention must begin early. Once peak bone mass is reached between by the age of 30, you can work to maintain what you have but you can't build any more. Around middle age, bone mass begins to gradually decline as aging disrupts the balance between the cells that produce bone and the cells that absorb bone. As the growth of bone slows it begins to thin and become more porous. Women have a more rapid rate of bone loss than men, with the most rapid losses occurring in the 5 years following menopause. Osteoporosis affects about 8 million American women. Eventually, the bones have the strength of an egg shell and even minor trauma can cause the bone to collapse and fracture. Protecting Your Skin
Muscle As we age, our muscles generally decrease in strength, endurance, size and weight. Typically, we lose about 23 percent of our muscle mass by age 80 as both the number and size of muscle fibers decrease. These changes may be more the result of inactivity, poor nutrition, and chronic illness or disease than the result of age per se. Much of this decrease in muscle mass can be prevented by maintaining physical fitness. Both men and women experience an increase in body fat with age. In women, body fat increases linearly from about 25% at age 25 to about 41% at age 74. In men, the increase in body fat is similar to that of women until age 50 when it slows. Even in those who do not gain weight as they age, the body fat increases as the lean body mass decreases. Exercise can reduce but not totally prevent this age-related increase in body fat. The distribution of body fat also differs by gender. In men, the increase in fat mass occurs primarily around the abdomen. In women, the increase in fat is more often found in the thighs. Skin One of the most common physical changes that people associate with aging is the wrinkling, pigment alteration and thinning of the skin. We now know that these changes reflect the amount of exposure to the sun (i.e., ultraviolet light) more than aging per se. Most of the "aging" of the skin is due to the effects of environment and disease. The most common changes in the skin include:
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The
maximum heart rate decreases and it takes longer for heart rate
and blood pressure to return to normal resting levels after exertion.
You
can prevent most but not all of the "aging" of the skin by avoiding
sun exposure. Ultraviolet light causes the pathological effects that
produce wrinkles, thin skin, pigmentation changes and benign and malignant
tumors. If you compare the sun exposed areas of your skin with those
areas that rarely see the sunlight, you will notice increased wrinkling,
graying of air, and other evidence of advanced aging in the sun exposed
skin.