Journal of Gerontological Nursing

Physiological Parameters of Aging Part 1

Anna M Tichy; Lois J Malasanos

Abstract

In addition to decreased inspiratory and expiratory pulmonary function, loss of elastic tissue surrounding alveoli and changes in pulmonary circulation result in a decreased diffusing capacity between the alveolar-capillary membrane. The capillaries at the base of the lung have the greatest blood flow but most ventilation occurs in the upper zones. A consequence of the mismatch of air distribution and pulmonary circulation is reflected in the arterial oxygen tension, Pao, values which decrease progressively throughout life to approximately 70 to 80 mm Hg in the seventh decade.6

Unlike the brain, lung tissue actually increases in size *due to a loss of elasticity somewhat analogous to the skin changes characteristic of aging. A physiological consequence of a diminished force of lung recoil is an increase in compliance, closing volume, and residual volume. The latter is the amount of air remaining in the lungs following maximal expiration. Compliance, which describes the change in volume as a result of a change in pressure, is rate dependent in the elderly, decreasing with rapid respiration. Due to the diminished elastic recoil of the lungs, the smaller airways begin to close at a greater lung volume. This phenomenon describes the closing volume, which increases linearly with age. When the closing volume approaches the functional residual capacity, the airways at the base of the lung begin to close, while those in the apex remain open. These factors contribute to nonuniform ventilation. Deep breathing minimizes premature airway closure, therefore the aged person can raise the Pao, value by increasing the depth of respiration.5

Pulmonary blood flow in the older person is decreased subsequent to a decrease in cardiac output. In the resting state, changes that could be associated'with aging have not been identified in pulmonary artery pressure, however, exercise results in an increase in this pressure.7 Morphological changes in the pulmonary system include a decreased number of capillaries and an excess of the fibrous connective tissue of the intima of the vessel wall. As a result of the thickened capillary membrane and the diminished number of capillaries surrounding the alveoli, pulmonary diffusingcapacity of oxygen decreases progressively with aging. Thus, gaseous exchange is hampered not only by an altered ventilation perfusion ratio, but also as a result of the ^anatomical changes in the alveolar-capillary membrane.

Despite the age related respiratory changes, the ability to maintain adequate oxygenation is not * seriously impaired under conditions of health and moderate activity. However, a challenge such as marked physical exertion or respiratory illness may compromise ventilation as man grows older. Exercise vincreases the minute volume of air ventilated in the aged person; this excessive ventilation may be responsible for the exertional dyspnea associated with marked activity. The inability to perform sustained work increases with aging. The major limiting factor seems " to reside in oxygen transport and utilization of oxygen by the active muscles. Lung disease, whether of an acute or chronic nature, poses a threat to the older person. 'With advancing years secretions are handled less effectively. Ciliary action, responsible for the movement of secretions, is compromised as a result of epithelial atrophy. The cough reflex is frequently depressed with a minimized sensitivity to stimuli and decreased muscle tone. These factors along with impaired gaseous exchange are responsible for the - -seriousness of respiratory problems in old age.

The nurse has a significant role in legislation concerned with environmental pollutants and in the health education of the public regarding the deleterious effects of smoking. Assessment of the elderly patient's ^respiratory status, including blood gases, is an integral part of the nursing process. Coughing, deep breathing exercises, and positioning to facilitate lung…

Presently the number of persons 65 years of age or older approximates 23 million, or more than 10% of the total population. This number can be compared to the 1900 figure of three million people or 3.1%.' Though 65 years has been designated by social and governmental agencies as indicative of old age, biological factors are far more significant than chronological ones in determining the vitality of the person. Aging is a "wearing out" process that affects virtually every system, organ, and cell in the body to a varying degree. An understanding of the age related effects upon body systems is an integral part of the scientific basis for nursing care of the elderly person.

Nervous System

Some of the most frequently discussed changes that occur with aging focus upon the neural structures. The most dramatic alterations occur in the central nervous system as compared to the peripheral motor neurons or autonomic nervous system whose functions remain relatively unimpaired throughout life. The most readily recognizable feature of the aged central nervous system is a diminished brain weight. Cerebral cellular loss begins in the early 30s and continues steadily thereafter though functional ability may not be significantly affected as a result of the compensatory activity of reserve cells. However, a possible Consequence of decreased brain mass, particularly interneurons, may be a reduction or weakening of signal strength. Approximately 99% of all nerve cells that originate and terminate within the central nervous system are interneurons. These small neurons function in amplification, divergence, and refinement of signal input. Complex processes such as learning, memory, language, and mentation involve thousands of interneurons.

In addition to the reduced cell number, electro-physiological alterations such as a decrease in conduction velocity and a diminished activity of the enzymes associated with synaptic transmission occur with aging. A consequence of these biological changes may be manifested in a progressive slowing of response.s Electroencephalographic data indicates that the cerebral activity of the aged is characterized by long-lasting "after effects" following stimulus input. The result of persistent "aftereffect" activity is to obscure subsequent stimuli, impede short-term memory and hinder learning. Long-lasting "after effects" may also be involved in increased response time. Simple tasks may be delayed until signal strength is increased sufficiently through the reinforcing effect of simultaneous "after effect" input.2

Short-term memory loss is frequently a problem for the elderly person, though long-term memory may remain intact. Two distinctly different physiological processes are involved in recent and long-term memory storage. Short-term, recent memory storage is a limited depository process contingent upon stimulus input into a closed reverberating neuronal circuit. Maintenance of the circuitous electrical activity, which is dependent upon adequate tissue oxygenation, is" necessary for retention of the mental impression of the input. The aging brain may be considered to be chronically hypoxic. The diminished oxygen supply is due in part to atherosclerosis as well as a decreased-cellular respiratory activity which may be ascribed to an intracellular accumulation of metabolic end products. Thus the elderly person may experience difficulty remembering what he had for breakfast that morning but may recall childhood experiences with ease. Long- term memory storage, which is not affected by chronic cerebral tissue hypoxia, may be attributed to permanent structural alterations of the neuron. These changes may be morphological, involving dendritic processes and new synapses, or molecular with the establishment of the nucleotide sequence of ribonucleic acid and other cellular proteins.3

Other neurologic parameters that exhibit age related alterations include temperature regulation, pain per-* ception, and tactile discrimination. The elderly person has a low tolerance for extremes in temperature which may be attributed to a diminished vascular tone. The diameter of the vessel lumen is dependent in part upon the nervous system. Research may also reveal an age related alteration in thevhypothalamic temperature setpoint, though evidence for this at the present time is lacking. Pain and tactile perception involve peripheral sensory receptors, a relay pathway and cortical integration. A decrease in the number and sensitivity of sensory receptors, dermatomes and neurons" in the central nervous system contributed to a general dulling of these sensations.

Since the neurological changes characteristic of aging occur gradually, the elderly person is often able to < compensate by an avoidance of new, stressful situations and temperature extremes, and by the accomplishment of tasks at a leisurely pace. Any stressor, such as illness or a new environment, may seriously interfere with these compensatory mechanisms contributing to confusion and disorientation.

Respiratory System

Tests of pulmonary physiology have revealed a number of age related alterations in lung function. The effects of environmental toxins, which increase over time, are difficult to separate from the changes , attributable solely to aging. Forced vital capacity, vital capacity, inspiratory reserve volume, and maximum breathing capacity decrease progressively with age.4 These findings are due to: (1) atrophy and weakening of the respiratory musculature and (2) an increase in the anteroposterior diameter of the chest as a result of vertebral decalcification, kyphosis, and calcification of costal cartilage.5

In addition to decreased inspiratory and expiratory pulmonary function, loss of elastic tissue surrounding alveoli and changes in pulmonary circulation result in a decreased diffusing capacity between the alveolar-capillary membrane. The capillaries at the base of the lung have the greatest blood flow but most ventilation occurs in the upper zones. A consequence of the mismatch of air distribution and pulmonary circulation is reflected in the arterial oxygen tension, Pao, values which decrease progressively throughout life to approximately 70 to 80 mm Hg in the seventh decade.6

Unlike the brain, lung tissue actually increases in size *due to a loss of elasticity somewhat analogous to the skin changes characteristic of aging. A physiological consequence of a diminished force of lung recoil is an increase in compliance, closing volume, and residual volume. The latter is the amount of air remaining in the lungs following maximal expiration. Compliance, which describes the change in volume as a result of a change in pressure, is rate dependent in the elderly, decreasing with rapid respiration. Due to the diminished elastic recoil of the lungs, the smaller airways begin to close at a greater lung volume. This phenomenon describes the closing volume, which increases linearly with age. When the closing volume approaches the functional residual capacity, the airways at the base of the lung begin to close, while those in the apex remain open. These factors contribute to nonuniform ventilation. Deep breathing minimizes premature airway closure, therefore the aged person can raise the Pao, value by increasing the depth of respiration.5

Pulmonary blood flow in the older person is decreased subsequent to a decrease in cardiac output. In the resting state, changes that could be associated'with aging have not been identified in pulmonary artery pressure, however, exercise results in an increase in this pressure.7 Morphological changes in the pulmonary system include a decreased number of capillaries and an excess of the fibrous connective tissue of the intima of the vessel wall. As a result of the thickened capillary membrane and the diminished number of capillaries surrounding the alveoli, pulmonary diffusingcapacity of oxygen decreases progressively with aging. Thus, gaseous exchange is hampered not only by an altered ventilation perfusion ratio, but also as a result of the ^anatomical changes in the alveolar-capillary membrane.

Despite the age related respiratory changes, the ability to maintain adequate oxygenation is not * seriously impaired under conditions of health and moderate activity. However, a challenge such as marked physical exertion or respiratory illness may compromise ventilation as man grows older. Exercise vincreases the minute volume of air ventilated in the aged person; this excessive ventilation may be responsible for the exertional dyspnea associated with marked activity. The inability to perform sustained work increases with aging. The major limiting factor seems " to reside in oxygen transport and utilization of oxygen by the active muscles. Lung disease, whether of an acute or chronic nature, poses a threat to the older person. 'With advancing years secretions are handled less effectively. Ciliary action, responsible for the movement of secretions, is compromised as a result of epithelial atrophy. The cough reflex is frequently depressed with a minimized sensitivity to stimuli and decreased muscle tone. These factors along with impaired gaseous exchange are responsible for the - -seriousness of respiratory problems in old age.

The nurse has a significant role in legislation concerned with environmental pollutants and in the health education of the public regarding the deleterious effects of smoking. Assessment of the elderly patient's ^respiratory status, including blood gases, is an integral part of the nursing process. Coughing, deep breathing exercises, and positioning to facilitate lung expansion are especially important in the postoperative period or in the immobilized patient. Postural drainage to aid in the removal of secretions may be modified with consideration of the aged person's cardiovascular status, skeletal changes, and level of tolerance.

Cardiovascular System

Anatomically there is little specificity in the cardiac parameters of aging. In the absence of cardiovascular ^ disease, heart size remains unchanged or decreases slightly due to a shrinkage or loss of myocardial fibrils. As a result of the deposition of an intracellular pigment, lipofuchsin, the myocardium assumes a dark brown color but myocardial contractility does not seem to be affected adversely.

Another age related change is the deposition of subpericardial adipose tissue in certain regions of theheart. The sites particularly involved are the entry of the pulmonary vein, the superior vena cava posteriorly, the base of the aorta, the sinoatrial node, and the intercaval band.9 The constant hemodynamic challenge induces endocardial alterations. Aging results in the develop-., ment of whitish patches, fibrosis, and sclerosis in the endocardium which lines the cavities of the heart and aids in forming the valves. The anatomical areas of the heart subject to high pressure are most affected. The right ventricle, which is a low pressure chamber, is generally spared.9 Histologically these changes are characterized by alterations in the insoluble collagen of the myocardium associated with an increased stabilization of body collagen. This rigidity in the myocardium could lead to a decrease in myocardial contractility, distensibility, and a decline in a number of physiological parameters of cardiac function.10 '

A lifetime of hemodynamic stress is reflected in alterations in all the heart valves, however, the mitral and aortic are the most seriously affected. The valves become rigid because of nodular thickening and fibrosis. The aortic valve, located at the exit of the left ventricle, prevents a regurgitation of blood from the arterial system. The three cusps of the aortic valve are functionally important not only in the closed state but also in the open position. The coronary orifice is located in a widened portion of the aorta just above the aortic valve ring. The position of the aortic cusps is important in the maintenance of coronary blood flow. Eddy currents, a swirling motion of flowing liquid, are generated when fluids flow from a small orifice into a. large vessel. The eddy currents in the aorta swirl about the cusps in such a manner that they prevent apposition of the cusps and aortic vessel wall, thereby preventing blockage of the coronary orifice. Distortion of the aortic; valve, as occurs with aging, may result in blockage of the coronary orifice. Coronary blood flow in the elderly person, because of valvular vessel changes, may be reduced by as much as 35%.11 The heart sounds Si and S2 result partially from the effects of closure of the atrioventricular and semilunar (aortic and pulmonic) valves. With advancing age, clinical manifestations of valvular rigidity and incomplete closure may include the presence of a murmurs

The blood vessels of the heart and systemic circulation, particularly the arteries, are characterized by age related changes that may begin as early as the first or second decade of life. A degree of intimai thickening and calcification is evident in the coronary artery and* aorta in youth.12 Arterial dilation, vessel lengthening, tortuosity, and rigidity are due in part to the age specific changes in the molecular structure of collagen.13 The ubiquitous deposition of arteriosclerotic plaque, a fatty material, in the intimai layer of arteries also enhances vessel rigidity and circulatory insufficiency. These changes in the aorta are responsible for the increased work load of the heart. A clinically measurable parameter of the arterial rigidity is the nature of the pulse and the pulse pressure. With aging the pulse assumes a forceful character and the pulse pressure widens. By 70 years of age, the systolic blood pressure increases to approximately 150 mm Hg and the diastolic to 90 mm Hg. The reason for this is that aging results in decreased hemodynamic reflexes from the mechanoreceptors of the carotid sinus located in the aortic arch and the carotid sinus region. These baroreceptor reflexes are decreased as a result of an inelasticity of the vessel wall and possibly an altered set-point of the mechanoreceptors. These factors are responsible for the common occurrence of persistent arterial hypertension in old age.14

The resting cardiac output, which is the amount of blood pumped by the heart each minute, decreases 30 to 40% between the ages of 25 and 65 years.15 The diminished cardiac output reflects a decreased heart rate and a decreased stroke volume. Despite the diminished cardiac output, cerebral blood flow is maintained. Other organ systems, such as the liver and kidneys, receive a diminished blood supply. However, because of reduced function even the lessened blood supply is generally adequate for functional integrity. A challenge such as exercise may compromise this balance. At rest skeletal muscles have a relatively small blood flow requirement; exercise increases the perfusion need several fold. Inability to meet this need is apparent in the ischemia induced intermittent claudication evident in some elderly persons following exercise of the lower« extremities. On a cellular level, the aging heart has a decreased capacity to utilize oxygen.13 The diminished tissue oxygenation may be a significant factor in the elderly person's reduced tolerance for physical work. ,,

Anatomical and physiological age changes in the myocardium and blood vessels are secondary to shifts occurring at the molecular and cellular levels. Despite, the identification of a number of these shifts, the aging heart can provide valiant service provided that coronary insufficiency or the challenge of a superimposed illness do not occur. Health education in the areas of nutrition,», exercise, and behavior modification is an integral component of the nursing process. Teaching should be directed toward a decrease in the intake of sodium and' cholesterol and gradual position changes to minimized orthostatic hypotension and possible injury.

References

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  • 2. Timiras PS: Developmental Physiology and Aging. New York, MacMillan Co, 1972, pp 502-524.
  • 3. Vander A, Sherman J, Luciano D; Human Physiology, The Mechanisms of Body Function, 2nd ed. New York, McGraw Hill Co, 1975, pp 565-568.
  • 4. Morris JF, Koski A, Johnson LC: Spirometrie standards for healthy non-smoking adults. Am Rev Respir Dis 103:57-67, 1971.
  • 5. Dhar S, Shastri SR, Lenora, RAK: Aging and the respiratory system. Med Clin Ν Am 60(6): 1121-1139, (November) 1976.
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  • 10. Zwolinski RJ. Hamlin CR, Kohn RR: Age-related alteration in human heart collagen. Proc Soc Exp Biol Med 152:362-365, 1976.
  • 11. Selkurt EE, Bullard RW: The heart as a pump: Mechanical correlates of caridac activity. In Selkurt EF. (ed): Physiology. Boston, Little, Brown and Co, 1971, pp 275-295.
  • 12. Lansing AI. Blumenthal HT, Gray SH: Aging and calcification of the human coronary artery. J Gerontol 3:87, 1948.
  • 13. Harris R: Special features of heart disease in elderly patients. In Chinn AB (ed): Working with Older People, vol 4, Clinical Aspects of Aging. Maryland, US Department of Health, Education and Welfare, July 1971. pp 81-101.
  • 14. Frolkis VV, Bezrukov VV. Shevchuk VG: Hemodynamics and its regulation in old age. Exp Gerontol 10:251-271, 1975.

10.3928/0098-9134-19790101-10

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