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Physical Changes With Aging

by Richard W. Besdine, MD

Most age-related biologic functions peak before age 30 and gradually decline linearly thereafter ( Selected Physiologic Age-Related Changes); the decline may be critical during stress, but it usually has little or no effect on daily activities. Therefore, disorders, rather than normal aging, are the primary cause of functional loss during old age. Also, in many cases, the declines that occur with aging may be due at least partly to lifestyle, behavior, diet, and environment and thus can be modified. For example, aerobic exercise can prevent or partially reverse a decline in maximal exercise capacity (O 2 consumption per unit time, or Vo 2 max), muscle strength, and glucose tolerance in healthy but sedentary older people (see Exercise).

The unmodifiable effects of aging may be less dramatic than thought, and healthier, more vigorous aging may be possible for many people. Today, people > 65 are in better health than their ancestors and remain healthier longer. Because health has improved, decline tends to be most dramatic in the oldest old.

Selected Physiologic Age-Related Changes

Affected Organ or System

Physiologic Change

Clinical Manifestations

Body composition

Lean body mass

Muscular mass

Creatinine production

Skeletal mass

Total body water

Percentage adipose tissue (until age 60, then until death)

Changes in drug levels

Strength

Tendency toward dehydration

Cells

DNA damage and DNA repair capacity

Oxidative capacity

Accelerated cell senescence

Fibrosis

Lipofuscin accumulation

Cancer risk

CNS

Number of dopamine receptors

α-Adrenergic responses

Muscarinic parasympathetic responses

Tendency toward parkinsonian symptoms (eg, muscle tone, arm swing)

Ears

Loss of high-frequency hearing

Ability to recognize speech

Endocrine system

Menopause, estrogen and progesterone secretion

Testosterone secretion

Growth hormone secretion

Vitamin D absorption and activation

Incidence of thyroid abnormalities

Insulin resistance and glucose intolerance

Bone mineral loss

Secretion of ADH in response to osmolar stimuli

↑ Incidence of diabetes

Muscle mass

Bone mass

Fracture risk

Vaginal dryness, dyspareunia

Changes in skin

Tendency toward water intoxication

Eyes

Lens flexibility

Time for pupillary reflexes (constriction, dilation)

Incidence of cataracts

Presbyopia

Glare and difficulty adjusting to changes in lighting

Visual acuity

GI tract

Splanchnic blood flow

Transit time

Tendency toward constipation and diarrhea

Heart

Intrinsic heart rate and maximal heart rate

Blunted baroreflex (less increase in heart rate in response to decrease in BP)

Diastolic relaxation

Atrioventricular conduction time

Atrial and ventricular ectopy

Tendency toward syncope

Ejection fraction

Rates of atrial fibrillation

Rates of diastolic dysfunction and diastolic heart failure

Immune system

T-cell function

B-cell function

Tendency toward some infections and possibly cancer

Antibody response to immunization or infection but autoantibodies

Joints

Degeneration of cartilaginous tissues

Fibrosis

Glycosylation and cross-linking of collagen

Tightening of joints

Tendency toward osteoarthritis

Loss of tissue elasticity

Kidneys

Renal blood flow

Renal mass

Glomerular filtration

Renal tubular secretion and reabsorption

Ability to excrete a free-water load

Changes in drug levels with risk of adverse drug effects

Tendency toward dehydration

Liver

Hepatic mass

Hepatic blood flow

Activity of P-450 enzyme system

Changes in drug levels

Nose

Smell

Taste and consequent appetite

Likelihood (slightly) of nosebleeds

Peripheral nervous system

Baroreflex responses

β-Adrenergic responsiveness and number of receptors

Signal transduction

Muscarinic parasympathetic responses

Preserved α-adrenergic responses

Tendency toward syncope

Response to β-blockers

Exaggerated response to anticholinergic drugs

Pulmonary system

Vital capacity

Lung elasticity (compliance)

Residual volume

FEV 1

V/Q mismatch

Likelihood of shortness of breath during vigorous exercise if people are normally sedentary or if exercise is done at high altitudes

Risk of death due to pneumonia

Risk of serious complications for patients with a pulmonary disorder

Vasculature

Endothelin-dependent vasodilation

Peripheral resistance

Tendency toward hypertension

= decreased; = increased; FEV 1 = forced expiratory volume in 1 sec; V/Q = ventilation/perfusion.

Adapted from the Institute of Medicine: Pharmacokinetics and Drug Interactions in the Elderly Workshop . Washington DC, National Academy Press, 1997, pp. 8–9.

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  • CRINONE
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  • DELATESTRYL

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