KMJ
Kosin Medical Journal 2016;31:11-18. http://dx.doi.org/10.7180/kmj.2016.31.1.11
Review Article
Aging of the respiratory system Seung Hun Lee, Su Jin Yim, Ho Cheol Kim
Department of Internal Medicine, Gyeongsang National University School of Medicine, Jinju-si, Gyeongsangnam-do, Korea Changes in the respiratory system caused by aging generally include structural changes in the thoracic cage and lung parenchyma, abnormal findings on lung function tests, ventilation and gas exchange abnormalities, decreased exercise capacity, and reduced respiratory muscle strength. Decreased respiratory system compliance caused by reduced elastic recoil of the lung parenchymaand thoracic cage is related to decreased energy expenditure by the respiratory system. Lung function, as measured by 1-second forced expiratory volume and forced vital capacity (FVC), decreases with age, whereas total lung capacity remains unchanged. FVC decreases because of increased residual volume and diffusion capacity also decreases. Increased physiological dead space and ventilation/perfusion imbalance may reduce blood oxygen levels and increase the alveolar-arterial oxygen difference. More than 20% decrease in diaphragmstrength is thought to beassociated withaging-related muscle atrophy. Ventilation per minute remains unchanged, and blood carbon dioxide concentration does not increase with aging. However, responses to hypoxia and hypercapnia are decreased. Exercise capacity also decreases, and maximum oxygen consumption decreases by >1%/year. Consequence of these changes, many respiratory diseases occur with aging. Thus, it is important to recognize these aging-related respiratory system changes. Key Words: Aging, Respiratory system
The worldwide aging population is rapidly in-
Changes in the respiratory system with aging
creasing and Korea also expects to become an
do not cause serious problems such as airway
ultra-aging society as elderly individuals aged
obstruction or parenchymal lung disease in
65 years or older will comprise more than 25
healthy people because they have reserve lung
% of its total population by 2025.1
capacity. However, when the affected person
The human body undergoes a variety of ag-
has comorbid underlying lung disease due to pre-
ing-related changes including changes in the res-
vious infections or smoking, the reserve is re-
piratory system. However, normal variations of
duced, and therefore, lung problems can arise
such changes may not be easily distinguishable
more easily. The changes in the respiratory sys-
from pathological changes because of marked
tem caused by aging generally include structural
interindividual differences.2
changes in the thoracic cage and lung paren-
Corresponding Author: Ho Cheol Kim, Research Building No.205, Gyeongsang National University School of Medicine, 79, Gangnam-ro, Jinju-si, Gyeongsangnam-do, 52727, Korea Tel: +82-55-750-8684 Fax : +82-55-750-8618 E-mail:
[email protected]
Received: Jan. 08, 2016 Revised: Jan. 08, 2016 Accepted: Jan. 11, 2016
11
Kosin Medical Journal 2016;31:11-18.
chyma, abnormal findings on pulmonary func-
changes in elastic fibers of small airways
tion tests, ventilation and gas exchange abnor-
(reduction by about 0.1~0.2 cm H2O each year),
mality, reduced respiratory muscle strength, and
reduction in the proportion of lung parenchyma
decreased exercise capacity. In this review, the
versus the lung volume, and mucous gland hyper-
authors intend to present the physiological alter-
trophy in addition to structural changes in lung
ations caused by aging such as changes in respi-
parenchyma.3,4
ratory system dynamics, gas exchange abnormalities, and changes in exercise capacity and respiratory muscle strength.
Change in Lung Function Aging-induced changes in the respiratory sys-
Changes in respiratory system structures
tem, such as reduction of compliance and of
and dynamics
respiratory muscle strength, result in changes in the results of pulmonary function tests.5-11
Structural changes induce an increase in the
Lung function reaches its peak when in-
anterior and posterior diameters of thoracic
dividuals are in their early 20s, is maintained
cage, causing it to assume a round shape.
for some time, and then decreases normally with
Increased stiffness and reduced compliance of
aging. In general, it is known that 1-second
the thoracic wall is induced by aging-related cal-
forced expiratory volume (FEV1) reduces by
cification of the joint cartilage of the thorax and
about 20 mL/year up to the age of 25~39 years,
spinal scoliosis caused by osteoporotic changes.
whereas it reduces by 35 mL/year in those over
A study that measured the compliance of the
65 years of age.12,13 The reduction rates of forced
thoracic wall in 61 healthy adults ranging from
vital capacity (FVC) and FEV1 increase with in-
24 to 75 years old, reported that the thoracic
creasing age, but they do not display a linear
compliance was reduced according to the partic-
reduction and the reduction rates are faster in
ipants’ age.1 Reduced compliance of the thorax
men than in women.
causes a reduction of energy efficiency increas-
Total lung capacity (TLC) does not change or
ing the effort required for breathing.2 Additional
slightly reduces during aging, but residual volume
aging-related changes include periphery airway
(RV) is increased and vital capacity (VC) is
calcification, reduction of elasticity due to
reduced. Compared to a 20-year-old person, the
12
Aging of the respiratory system
residual volume increases by about 50% and vital
blood vessel. A study by Stam et al. reported
capacity reduces by 75% in a 70-year-old person.
a decrease in the diffusing capacity of 55 healthy
Therefore, the ratio of RV/TLC increases with
persons compared with aged ≥70 years, even
age, and this increase is considered to be due
after adjusting for the dimension of the alveoli.
to reduced lung elasticity and thoracic wall com-
This decrease in diffusing capacity may likely
pliance, weakened expiratory muscle strength,
be caused by aging-induced changes in the al-
and increased closing lung volume.6,14
veolar- capillary membrane.16
The peak expiratory flow rate (PEFR) reaches
With aging-induced ventilation/perfusion im-
its peak at the age of approximately 30~35 years
balance, physiological dead space increases. At
and subsequently declines, particularly after the
the age ranged 15 to 20 years old, the dead space
age of 45. After the age of 50, PEFR reduces
is about 13% of alveolar ventilation, but it in-
at the rate of 4 L/min/year in men and 2.5
creases to 32% at the age ranged from 61 to
L/min/year in women. These reductions indicate
75 years.17 In study of Miller et al., it was reported
small airway disease based on the flow rate-vol-
that the physiological dead space in old healthy
ume curve.14
person was about 235 ± 67.5 ml and it showed
Small changes in airway resistance occur dur-
it was increased by more than 50% compared
ing aging, which can be explained by a reduction
to young healthy person whose physiological
in the diameter of the peripheral airway; how-
dead space was 150 ml.18 With the increase of
ever, the diameter of the central airway is in-
dead space, the normal arterial oxygen’s partial
creased with aging and this offsets the effects
pressure in the elderly people is lowered than
of increased peripheral airway resistance,15
in younger people while the differences in the
which comprises only 10% of the total airway
concentrations of alveolar arterial oxygen, that
resistance.
is, (Aa) DO2, is increased. However, the minute
The diffusion capacity for carbon monoxide
ventilation is not decreased and there is no occur-
(DLCO) also decreases with age by 0.2
rence of the carbon dioxide exchange impair-
mLCO/min/mmHg/year in men and by 0.15
ment by aging, therefore, the occurrence of res-
mLCO/min/mmHg/year in women. The degree
piratory acidosis should be considered as patho-
of decreases in women is reported to be lesser
logical in old ages as well.
than that in men, possibly due to the influence of estrogen, which maintains integrity of the 13
Kosin Medical Journal 2016;31:11-18.
Changes in the respiratory muscle strength
lem in healthy individuals, but if the ventilation demands are increased due to pulmonary dis-
Decreased muscle strength is a general consequence of aging, and affects the respiratory
ease, it can be a major problem resulting in respiratory failure
muscles as well.19,20 Respiratory muscle strength
The cross-sectional area of the intercostal
can be determined by measuring various param-
muscles is slightly reduced, while that of the ex-
eters such as the maximum trans-diaphragmatic
piratory muscles is reduced to a much greater
pressure (Pdi max), maximal voluntary ven-
extent, at the age of 50 years or higher.24 In
tilation (MVV), and maximal inspiratory pressure
contrast, no change in the thickness the dia-
(MIP). All these parameters have been found to
phragm occurs during aging. However, the re-
be decreased in elderly people.21,22
duction of compliance in the chest wall results
In a study that measured the muscle strength of the diaphragm, it was found that elderly people
in a reduction in the curvature causing a reduction in Pdi max.
(65 to 75 years old) show a decrease of approx-
Reduction in respiratory muscle strength in
imately 25% in the Pdi max compared to young
the elderly has shown to be associated with nutri-
adults (19 to 28 years old).19 A study by Polkey
tional status, and BMI has been reported to have
et al. also showed similar results,23 and the MIP
a significant correlation with the MIP as well
was 30% higher in men than in women irre-
as with the maximal expiratory pressure.25
spective of age. The change in H2O/year in men ranging from 65 to 85 years old was found to be 0.8-2.7 cm.
Responses to hypoxia and hypercapnia
The reduced strength of the diaphragm with aging is associated with muscle atrophy and with
Minute ventilation remains the same between
decrease of fast fibers that create a higher level
the younger and the older age groups. Although
of tension. Reduction of diaphragmatic muscle
the tidal volume is reduced with age, the minute
strength increases the respiratory rate in the eld-
ventilation is maintained by increasing the respi-
erly, which results in fatigue to the diaphragm,
ration rate. However, the ventilator response to
and may eventually cause ventilatory failure.
hypoxemia or to increased carbon dioxide con-
Thus, the reduction of respiratory muscle
centration may be inadequate in the elderly.26
strength due to aging may not be a serious prob-
A study conducted by Kronenberg and Drage
14
Aging of the respiratory system
in 8 healthy young and 8 healthy elderly partic-
lung function at rest and during exercise in
ipants, revealed that the response to hypoxia
healthy older people, McClaran et al. confirmed
was reduced by 50% and the response to hyper-
that VO2max decreased by 11% over 6 years.15
capnia was also reduced by 40% in the elderly individuals. Although the mechanism is unclear, these changes might have been caused by dys-
Changes in cough reflex
function of chemosensory receptors and by structural changes in the lung and thoracic
The cough reflex weakens with aging. This
cage.27 Poulin et al. reported that the ventilation
change may be attributed to the decrease in
demands for the generation of carbon dioxide
cough sensation, increased activation threshold
were increased during aging in 224 healthy per-
of the vagus and occipital nerves, decreased ten-
sons aged between 56 and 85 years old. This
sion of smooth muscles, and reduction of cogni-
change was considered to be caused by aging-in-
tive capacity.29,30 Respiratory muscle strength al-
duced increases in the end expiratory-arterial
so decreases so that coughing cannot adequately
carbon dioxide concentration and the ven-
remove a foreign material or secretion. Such
tilation/ perfusion imbalance.28
weakening of the cough reflex contributes to the increase in the incidence of aspiratory pneumonia in elderly individuals.30
Changes in exercise capacity The maximal oxygen consumption (VO2max)
Conclusion
which is an indicator of exercise capacity, reaches its peak level when individuals are between
The various changes that occur in the respira-
the ages of 20 and 30 years and then decreases
tory system of elderly individuals result in an
by approximately 1% every year depending on
increased risk for a variety of respiratory
the individual capacity of physical activity.
diseases. In order to understand respiratory dis-
Generally, VO2max decreases at a rate of 32
eases that occur in elderly individuals, it is im-
mL/min/ year in men and at a rate of 14 mL/min/
portant to recognize aging-related changes in
year in women after the age of 20-30 years. In
the respiratory system. Based on a thorough un-
a longitudinal study on the effects of aging on
derstanding of these changes, it might be possible 15
Kosin Medical Journal 2016;31:11-18.
to take appropriate steps to protect elderly in-
7. Janssens JP. Aging of the respiratory system:
dividuals against respiratory diseases and to
Impact on pulmonary function tests and adapta-
manage these diseases adequately when they
tion to exertion. Clin Chest Med 2005;26:469-84.
occur.
8. Meyer KC. Aging. Proc Am Thorac Soc 2005;2:433-9. 9. Sprung J, Gajic O, Warner DO. Review article:
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Kosin Medical Journal 2016;31:11-18.
Peer Reviewer’s Commentary Lung function, as measured by 1-second forced expiratory volume and forced vital capacity (FVC), decreases with age, whereas total lung capacity remains unchanged. FVC decreases because of increased residual volume and diffusion capacity also decreases. Increased physiological dead space and ventilation/perfusion imbalance may reduce blood oxygen levels and increase the alveolar-arterial oxygen difference. If we make understand the changes in respiratory function that occur with increasing age, there is meaningful results in maintaining a healthy life. (Editorial Board)
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