ASPECTS OF AGING AND REHABILITATION OF OLDER ADULTS

PHYSIOLOGY OF AGING

Robert S. Stall, MD

Last updated December 27, 1995

1. Changes in Body Composition--altered medication pharmacokinetics
   1. Increased fat (esp. centrally)
   2. Decreased muscle mass
   3. Decreased body water
2. Skin changes--increased susceptibility to infection, trauma, and external environment
   1. Decreased vascularity and subcutaneous fat
   2. Decreased # sebaceous and sweat glands
   3. Increased pain threshold (i.e., pain less noticeable)
   4. Decreased sensory acuity
3. The Senses--affect functional ability, apparent cognitive status, and nutritional status
   1. Decreased vision/hearing
   2. Decreased taste/smell/touch
4. Immune Function--increased susceptibility to infection
   1. Decreased cell-mediated immunity
   2. Decrease antibody response to foreign antigens
   3. Increased autoantibodies
5. Renal Function--decreased creatinine clearance despite "normal" creatinine (140-age/serum creatinine=approximate creatinine clearance)
   1. Decreased # functional nephrons
   2. Structural & functional changes (sclerosis of glomeruli and vasculature, basement membrane thickening, decreased levels of renin and aldosterone) cause impaired regulation of water and electrolytes
6. GU--obstruction, incontinence & infection extremely common
   1. Decreased bladder capacity
   2. Prostatic hypertrophy
   3. Mucosal atrophy in women
7. Liver--altered drug metabolism
   1. Atrophy
8. Heart--impaired perfusion of all body tissues
   1. Calcification and sclerosis of fibrous cardiac skeleton-->predisposes to conduction abnormalities and valvular dysfunction
   2. Increased peripheral resistance-->cardiac hypertrophy
   3. Decreased diastolic filling rate, increased filling from atrial contraction-->end diastolic volume constant (but will be compromised in atrial fibrillation)
9. Lungs--impaired oxygenation of all body tissues
   1. Decreased surface area of alveolar capillary membranes, increased alveolar size-->ventilation-perfusion mismatch, decreased PaO2
   2. Decreased respiratory muscle strength/mucociliary clearance-->predisposes to infection
   3. Decreased responsivity to hypoxia and hypercarbia-->breathing disorders and perioperative respiratory complications
10. Reference
    1. Physiology of Aging--A Synopsis (Second Edition), Richard A. Kenney, Year Book Medical Publishers, 1989.