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Physiology of Aging
J.M. Cairo, Ph.D.
[email protected]
504-568-4246
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 >50 years of age.
Demographics

Population over 65 is fastest
growing age group in the US: >85
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
♂:♀ = 39:100; by the age of 85, this
ratio shrinks progressively thereafter
Demographics



1 of 4 patients undergoing
surgery >65 years
50% of patients over 65 years
have an operation in the
remainder of their lives
12% of patients >65 years use
65% of the total medical
resources each year
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
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 body’s resources
(bones) leaving bones pitted, brittle, and porous
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
Aging and the Respiratory
System
 Mechanics of Breathing
 Pulmonary Circulation
 Gas Exchange
 Control of Breathing
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
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
Levitzky, MG: Pulmonary Physiology,
7th Edition. New York, Lange, 2007
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.
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.
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 >70 years and their
respond to supplemental oxygen is
reduced.
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
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
Aging and the Cardiovascular
System


Heart
Blood Vessels


Central vessels (e.g., aorta)
Peripheral vessels
Aging and the Heart

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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
Aging and the Heart


Systolic function is relatively preserved
Velocity of myocardial shortening
decreases but the duration of contraction
is prolonged
Aging and the Heart


Delayed diastolic relaxation coupled with
increased myocardial stiffness leads to
increased venous filling pressures
The heart’s inotropic and chronotropic
responses, as well as, the vascular
responsiveness to catecholamines are
reduced

sympathetic nervous system stimulation is
apparently related to receptor function
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.
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
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)

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

Cardiovascular Response to Exercise: Young versus Older Subjects
Effect of Conditioning on Heart Rate Response
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 betaadrenergic blockers
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
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
Renal System
Clinical Implications

The capacity of the bladder does decline significantly (it
may retain 100 mL of urine thus diminishing its overall
capacity.

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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
Digestive System
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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
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)
Age-Related Neurological and
Psychological Changes
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•
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
Sensory Issues
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Vision
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Begins to change in mid 40’s in five major
ways:
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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).
Sensory Issues
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Touch
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Taste
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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.
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%.
Theories of Aging
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Metabolic Damage
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Free-Radicals
Glycation
Free Radicals and Aging
Theories of Aging
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Replicative Senescence
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Telomere shortening
Inadequate DNA repair
Toxic and Non-Toxic Garbage Accumulation
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Protein cross-linking and aggregation
Advanced glycation
Atherosclerotic and amyloid plaques
Lipofuscin
Metals
DDT, PCBs, etc