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Changes in structure, function, metabolism, and blood flow in the aging brain lead to cognitive impairments, most frequently episodic memory changes, and an increased risk of delirium in the acute setting.
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The geriatric population tends to have higher blood pressure with lower cardiac output and diminished chronotropic and inotropic responses to beta-receptor stimulation.
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Respiratory aging results in changes to mechanical properties of the respiratory system, reduction of arterial oxyhemoglobin
Physiology Considerations in Geriatric Patients
Section snippets
Key points
Nervous system
The aging of the brain is accompanied by a change in structure, function, and metabolism (Table 1).5 The volume and weight of the brain decline at a rate of approximately 5% per decade after age 40 years.6 Once the brain is 70 years old, the rate of decline is thought to increase.6 The changes in neuronal volume and affected areas may be related to gender.6 Brain atrophy starts earlier in men but is more rapid in women once it has started.5 There are longitudinal studies using MRI and reviews
Cardiovascular system
The geriatric population tends to have higher blood pressures, similar heart rates and ejection fractions, and lower left ventricular end-diastolic volumes, stroke volumes, and cardiac outputs compared with younger populations (Table 2).3 These aging-related changes in the cardiovascular system primarily start with changes in connective tissues. Connective tissue stiffens within the arteries, veins, and myocardium, causing them to become less compliant.3 This stiffening is secondary to a
Respiratory system
The lungs continue to develop throughout life, and maximal functional status is achieved in the early part of the third decade, after which lung function gradually declines.15 Changes with aging include alteration of the mechanical properties of the respiratory system, reduction of arterial oxyhemoglobin saturation, and impaired response to hypoxia (Table 3).15
The parenchyma of the lung undergoes significant structural alterations with aging, with the most important change being a reduction in
Gastrointestinal system
Age-related changes occur along most of the gastrointestinal track (Table 4). There is a decrease in the amplitude of esophageal contractions and a decrease in the number of peristaltic waves that occur with a standard swallow.19 One study found an increase in the number of disordered contractions in the body of the esophagus.19 Geriatric individuals are also subject to prolonged gastric emptying.19 One study showed that a standard mixed meal took double the time to empty compared with younger
Renal and volume regulation system
Renal function declines related to age have been well documented within multiple geographic settings and patient populations and by using a wide range of methods and parameters (Table 5).21 There is a cumulative increase in patients with end-stage renal disease with increasing age.22 Age-related renal decline is affected by gender, with men more affected than women secondary to increased damage from vascular changes and androgen production.21 Aging causes both creatinine clearance and
Endocrine system
There is a decline in endocrine function with age that includes decreased tissue responsiveness and a reduction in hormone secretion from peripheral glands (Table 6).25 Examples include reductions in thyroid-stimulating hormone and triiodothyronine (T3). Age also results in a dampening of circadian hormonal and nonhormonal rhythms.25
Impaired glucose tolerance develops in more than 50% of individuals older than 80 years of age.26 There is a decrease in insulin production by beta cells, an
Summary
No matter the mechanism, aging affects the physiology of every major organ system. The nervous system experiences cognitive decline and volume loss. The cardiovascular system changes result in lower cardiac output and higher blood pressures leading to significant changes to the structure and function of the heart. The respiratory system changes lead to impaired oxygenation, diminished ventilation/perfusion matching, and an increased risk of atelectasis. The gastrointestinal system experiences a
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Contributions: The authors performed the literature review, prepared the article, and approved the final article.
Disclosure: Dr C.G. Hughes is supported by National Institutes of Health HL111111, R03AG045085 (Bethesda, MD), and Jahnigen Career Development Award sponsored by the American Geriatrics Society (New York, NY).
Conflicts of Interest: None.