Physiology of Aging

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Physiology of Aging

• J.M. Cairo, Ph.D.
• jcairo_at_lsuhsc.edu
• 504-568-4246

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Demographics

• Life expectancy has nearly doubled since the
  beginning of the 20th century
• It is estimated that by the year 2020, 47 of the
  population will be gt50 years of age.

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Demographics

• Population over 65 is fastest growing age group
  in the US gt85 years is the fastest growing
  segment of this group
• People over 65 years constitute 14 of the total
  US population and will account for 20 of the
  total US population over the next 50 years
• ?? 39100 by the age of 85, this ratio
  shrinks progressively thereafter

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Demographics

• 1 of 4 patients undergoing surgery gt65 years
• 50 of patients over 65 years have an operation
  in the remainder of their lives
• 12 of patients gt65 years use 65 of the total
  medical resources each year

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Searching for Answers

• The medical literature is predominantly composed
  of cross-sectional studies rather than
  longitudinal studies
• Published studies indicated that cardiopulmonary,
  hepatic, renal, neurological, and immune
  functions are reduced in the elderly and
  susceptible to decompensation

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Metabolism

• There is no consensus on the best method of
  assessing nutritional status in the elderly
• Increased mortality in underweight people
• There is a progressive loss of skeletal mass,
  renal mass, and liver mass with a reciprocal
  increase in lipid composition of the body
• Calcium and phosphorus metabolism are adversely
  affected with age thus mineral levels in blood
  are maintained by drawing on the bodys resources
  (bones) leaving bones pitted, brittle, and porous

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Metabolism

• 10-15 reduction in metabolic requirements in
  elderly versus young
• Decrease in body heat production coupled with
  impairment of thermoregulatory vasoconstriction
• Delayed drug clearing due to reductions in
  hepatic and renal elimination

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Aging and the Respiratory System

• Mechanics of Breathing
• Pulmonary Circulation
• Gas Exchange
• Control of Breathing

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Mechanics of Breathing

• Rounding of the thorax
• Calcification of the costal cartilages (Decreased
  thoracic compliance)
• Decreased space between the spinal vertebrae and
  a greater degree of spinal curvature

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Mechanics of Breathing

• Progressive enlargement of the respiratory
  bronchioles and alveolar ducts
• Loss of functional alveolar surface area and
  alveolar surface tension
• 15 reduction by the age of 70 years
• Negative effects on forced expiratory flow
• Decreased respiratory muscle strength and
  endurance

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Levitzky, MG Pulmonary Physiology, 7th Edition.
New York, Lange, 2007
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Pulmonary Circulation

• Changes in the pulmonary circulation are
  difficult to separate from those attributable to
  the heart and circulatory system
• In contrast to comparatively similar resting
  values with the young, older persons demonstrate
  significantly higher PA, PAWP, and PVR during
  exercise.

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Gas Exchange

• Gas exchange declines at 0.5/yr
• Ventilation-perfusion ratios are adversely
  affected by increasing age.
• Increased areas of high V/Q thus causing an
  increase in physiological dead space from 20 at
  20 year old subject to 40 at 60 years of age.
• There is also an increase in the proportion of
  alveoli that have a low V/Q resulting in an
  increase in venous admixture.

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Gas Exchange

• Baseline arterial oxygenation is lower with age
• PaO2 declines by 1 torr/yr after the age of 60
  years
• The risk of hypoxemia and hypercarbia is higher
  in patients gt70 years and their respond to
  supplemental oxygen is reduced.

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Control of Breathing

• Elderly individuals have a significantly
  diminished response to hypoxia and hypercapnia
• Higher incidence of apnea and periodic breathing
  with narcotics
• There is a markedly diminished response for vocal
  cord closure thus increasing the risk of
  aspiration and its consequences

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Implications for Clinicians

• Decreased maximum breathing capacity, vital
  capacity, and maximal O2 uptake
• Decreased mucociliary clearance and cellular and
  humoral lung defense mechanisms
• Increased risk for respiratory infections
• Acute and chronic respiratory conditions can have
  severe consequences as a result of hypoxemia and
  hypercapnia

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Aging and the Cardiovascular System

• Heart
• Blood Vessels
• Central vessels (e.g., aorta)
• Peripheral vessels

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Aging and the Heart

• There is a linear loss of myocardial cells
  beginning during infancy (38 million per year)
• The remaining myocardial cells hypertrophy
  (ventricular wall thickness is therefore
  preserved over time)
• Increase in fibrous connective tissue matrix

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Aging and the Heart

• Systolic function is relatively preserved
• Velocity of myocardial shortening decreases but
  the duration of contraction is prolonged

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Aging and the Heart

• Delayed diastolic relaxation coupled with
  increased myocardial stiffness leads to increased
  venous filling pressures
• The hearts inotropic and chronotropic responses,
  as well as, the vascular responsiveness to
  catecholamines are reduced
• sympathetic nervous system stimulation is
  apparently related to receptor function

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Aging and the Vasculature

• Changes in the systemic arterial wall occur
  predominantly in the medial layer
• The changes that occur with aging involve elastin
  fibers undergoing progressive disorientation,
  fragmentation, and degeneration, with subsequent
  collagen deposition, calcification, and cystic
  degeneration.

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Aging and the Vasculature

• Central elastic vessels dilate and become more
  tortuous. The increase in stiffness of the aorta
  and central elastic arteries is not found in the
  peripheral arteries.
• This results in a doubling of the pulse wave
  velocity in the aorta, a quadrupling of the
  descending aorta impedance, and a progressive
  rise in systolic pressure

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Hemodynamic Effects

• Resting cardiac output, stroke volume, and peak
  aortic flow may change little with age
• Systemic Blood Pressure
• Systolic pressure rises 6.0-7.0 mmHg per decade
• Diastolic pressure remains relatively constant
  (it may actually fall with increases in systolic
  pressure)

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Hemodynamic Effects

• The cardiovascular response to exercise declines
  progressively
• Maximal HR, SV, CO, Ejection Fraction, and VO2
  decrease
• End-systolic and end-diastolic volumes increase
• The age-related diastolic dysfunction makes the
  elderly more susceptible to the effects of
  tachycardia

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Cardiovascular Response to Exercise Young
versus Older Subjects
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Effect of Conditioning on Heart Rate Response
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Perioperative Implications

• Small decreases of venous filling from narcotics,
  diuretics, volume depletion, and positive
  pressure ventilation can have profoundly negative
  effects on stroke volume and cardiac output.
• Inhalation anesthetics exaggerate the negative
  inotropic and chronotropic effects of calcium
  channel blockers and beta-adrenergic blockers

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Perioperative Implications

• Fluid overloads may precipitate heart failure and
  pulmonary edema in the elderly more easily than
  in young subjects
• Perioperative hypotension is more frequent and
  severe in the elderly than in the young

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Renal System

• Although kidney function declines with age, it
  does not cause any major problems unless blood
  flow is severely restricted due to heart problems

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Renal SystemClinical Implications

• The capacity of the bladder does decline
  significantly (it may retain 100 mL of urine thus
  diminishing its overall capacity.
• The frequency and urgency may be frustrating
  because the urgency to urinate does not occur
  until the bladder is near capacity
• Incontinence affects about 15 of patients over
  65 years and 60 of all patients
  institutionalized over the age of 65 years
• Bladder problems may result from weakness of the
  bladder outlet or distension of the bladder
• In males, prostate problems may increase
  frequency or loss of control

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Digestive System

• Eating habits may change due to changes in
  ability to taste food, loss of teeth due to
  periodontal diseases, or the presence of dentures
• There is an decrease in digestive enzymes and the
  beginning of atrophy of glands in the stomach
  causing food to move slower through the digestive
  tract.
• Increased incidence of diverticulitis and rupture

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Age-Related Neurological and Psychological Changes

• Decline in receptors, fewer afferent conduction
  pathways, fewer brain cells (i.e., decreased mass
  and increase in CSF) and connections and slower
  corticospinal transmission
• Baroreceptor responsiveness, postural response
  and vasoconstrictor response are all impaired in
  rate and magnitude
• Sensory thresholds for stimuli are blunted
  (vision, hearing, taste, pain, temperature)

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Age-Related Neurological and Psychological Changes

• Psychomotor response-reaction time
• Problem-solving
• Memory
• Cognitive impairment
• Delirium
• Can results from a variety of causes, including
  hypoxia, electrolyte disturbances, hypotension,
  and pharmacologic toxicity
• Associated with increased perioperative mortality
• Dementia
• Can result from undernutrition, acute situational
  stress, family history of mental illness, and
  personal history of substance abuse
• Depression

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Sensory Issues

• Vision
• Begins to change in mid 40s in five major ways
• Lens thickens
• Lens tends to harden and is more sensitive to
  glare
• Lens becomes more yellow which changes color
  perception
• Pupil becomes smaller letting in less light
• Muscles controlling opening and closing respond
  slower making it harder to perceive quick-moving
  objects
• Hearing
• One in three people over 65 years have some
  degree of hearing impairment (i.e., conductive
  versus nerve loss).

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Sensory Issues

• Touch
• As the skin thins and loses nerve cells, it is
  more difficult to distinguish changes in
  temperature. At the age of 25 years, a person
  can perceive a 1 degree drop in temperature by
  touch at age 65 years, it would take a 9 degree
  change to be equivalent.
• Taste
• Loss of taste alters eating habits. A 30 year
  old has about 245 taste buds on each papilla on
  the tongue the number begins to decrease at age
  50 and will progress to a loss of about 65 of
  those taste buds at the age of 80 years. Of the
  four basic taste sensations, sweet taste buds
  diminish the most, sour the least, with bitter
  and salty fitting in the middle.
• Smell
• Odors must be 2 to 12 times more intense for a 70
  year old than a 25-35 year old. 25 of people
  between 65 and 80 have major smell dysfunctions
  and after 80 years it increases to 50.

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Theories of Aging

• Metabolic Damage
• Free-Radicals
• Glycation

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Free Radicals and Aging
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Theories of Aging

• Replicative Senescence
• Telomere shortening
• Inadequate DNA repair
• Toxic and Non-Toxic Garbage Accumulation
• Protein cross-linking and aggregation
• Advanced glycation
• Atherosclerotic and amyloid plaques
• Lipofuscin
• Metals
• DDT, PCBs, etc