The respiratory system of children differs anatomically and physiologically from adults in several important ways. Anatomically, children have a more horizontal ribcage, larger internal organs relative to size, narrower airways, and less developed alveoli and cilia. Physiologically, children have greater airway resistance, lower respiratory compliance, higher oxygen consumption, and more easily fatigued respiratory muscles. These developmental differences impact a child's respiratory function and make them more susceptible to respiratory illnesses.

1. Respiratory System:
Anatomical and Physiological differences
between adults and children
Robyn Smith
Department of Physiotherapy
UFS
2011

2. Learning outcomes
• At the end of this module the learner should:
Be able to identify both anatomical and
physiological differences between the respiratory
systems of child and a adult
Understand and explain the impact of these
differences on the clinical findings, observations
and respiration of a child
Describe the impact of preferential nasal breathing
on respiration in babies

3. Background
• The respiratory system of children differs both
anatomically and physiologically from that of adults
• These differences have important consequences for
the physiotherapy care of children in terms of
assessment, treatment and choice of techniques
• The principle reason for hospital admissions in
children under the age of 4 years is respiratory illness

4. Background
• The principles of adult chest physiotherapy cannot
be directly transposed to a child.
• Chest physiotherapy as provided to children has
become a specialised area on its own for this reason

5. Development of the
respiratory system

6. ANATOMICAL DIFFERENCES

7. Thorax: Chest shape
• Cross sectional area of the thorax is
cylindrical and not elliptical as in adults

8. Thorax: Ribcage
• The ribcage of the newborn and
infant is relatively soft and
cartilaginous compared to the rigid
chest wall of older children and
adults
• Ribs run horizontally to the
vertebrae and sternum compared to
the more oblique angle of older
children and adults. The bucket
handle movement as seen in older
children and adults is therefore not
possible.
• Infant can therefore increase the
anterior-posterior or transverse
diameter of their chest
• The intercostal muscles are inactive
and poorly developed in infancy.
And the abdominal muscles are not
yet stabilising the ribcage
• The interaction of gravity and the
musculoskeletal system play an
important role in the development of
the thorax.

9. Infant chest shape
• Anterior view • Lateral view

10. Thorax.... clinical implications
• Clinical implications....
• With the limited chest expansion
the child can only increase their
lung volumes by increasing their
respiration rate
• No postural drainage in
premature infants or neonates
• Infants are diaphragmatic
breathers
• Premature infants & children
with low tone especially
hypotonia need to be
positioned correctly to avoid
chest deformities, rib flaring and
a high riding ribcage
• Infants with chronic
caqrdiorespiratory conditions
e.g. BPD, RDS or paradoxal
breathing may also develop
chest deformities over times

11. Preferential nasal breathing
• Shape and orientation of the
head and neck in babies
means that the airway prone
to obstruction
• Infants up to about 6 months
are preferential nose
breathers
clinical implications .....
Children with upper
respiratory tract
infections and nasal
secretions may have
compromised
respiration of the nose
is blocked

12. Diaphragm
• Angle of insertion of the
diaphragm in infants is more
horizontal
• Diaphragm works at a
mechanical disadvantage
• Diaphragm in infants has a
lower-content of high-
endurance muscle fibres and
also more susceptible to
fatigue
• The diaphragm is the most
important inspiratory muscle
due to the inactivity of the
intercostal muscles

13. Diaphragm...clinical implications
• Ventilation is
compromised in infants
where the function of
the diaphragm is
impaired
e.g. abdominal
distension and phrenic
nerve palsy

14. Internal organs
• Heart and other organs
are relatively large in
relation to the infants
size
clinical implications
This leaves less place
for chest expansion

15. Airway diameter
• Trachea is short and narrow
(1/3 of diameter adult) in
neonate. This makes respiratory
resistance higher and the work
of breathing greater.
• Narrowest part of the airway is
the cricoid ring (adult vocal
cords)
• Right bronchus less angled than
left
• During the first few years of life
their is significant growth in the
diameter of the airways
clinical implications .....
• Tracheal swelling as a result
of intubation can heighten
the resistance
• Inflexible cricoid ring leaves
child more vulnerable to post
extubation mucosal odema
and stridor
• Children are often intubated
into the right bronchus

16. Bronchial walls
• Bronchial walls are supported
by cartilaginous rings. However
the support provided in children
is far less than in adults making
airways
• The bronchial wall has
proportionally more cartilage,
connective tissue and mucus
cells and less muscle tissue
than in adults
• Beta adrenergic receptors
immature
clinical implications ...
• Airways more prone to
collapse
• Lung tissue less complaint
• Less smooth muscles makes
them less responsive to
bronchodilator until the age
of 12 years

17. Cilia
• At birth cilia are poorly
developed
Clinical implication...
• Risk of secretion
retention and airway
obstruction is greater in
premature infants and
neonates

18. Alveoli & surfactant
• Alveoli develop after birth in
terms of increasing numbers
and in size. The majority of the
development occurs within the
first 2 years.
• Surfactant which reduces the
surface tension at the air liquid
interface in the alveoli are
secreted from 23 weeks
gestation
Clinical implications ....
• Smaller alveoli in infants
make them more susceptible
to collapse
• Smaller alveoli also provides
a smaller area for gaseous
exchange
• Premature infants have
insufficient surfactant
resulting in the development
of RDS

19. Collateral ventilation
• Ensures that distal lung
units are ventilated
despite the obstruction
of a main airway
• The collateral
ventilatory channels are
poorly developed in
children under 2-3
years
Clinical implications...
• Makes the child more
susceptible to alveolar
collapse

20. Height and exposure to
pollution
• Children have a higher RR,
spend more time outdoors
exposing them to allergens
and pollutants
• Their height also exposes
the child to other pollutants
e.g. exhaust fumes

21. PHYSIOLOGICAL
DIFFERENCES

22. Respiratory compliance
• Measure of the pressure required to increase the
volume air in the lungs
• Combination of lung- and chest wall compliance
• Lung compliance in a child is comparable to an adult
and is directly proportional to the child’s size
• Compliance in a child is reduced by the high
proportion of cartilage in the airways
• Premature infants with insufficient surfactant show
reduced compliance

23. Chest wall compliance
• The chest wall of the infant is cartilaginous and
very soft and compliant. In the case of respiratory
distress the chest is drawn inwards .
• This is the reason for paradoxal breathing

24. Closing volume
• Lung volume at which the small airways close
• In infants the closing volume is greater than the FRC, airway
closure may thus occur before the end of expiration, a
consideration when using manual techniques e.g. Vibrations. One
may further reduce the lung volumes resulting in widespread
atelectasis
In respiratory distress children grunt (adducting the vocal cords) in
an attempt to reduce the expired volume of air in order to minimise
alveolar collapse
• It is harder to re-inflate collapsed alveoli in children

25. Ventilation & perfusion
• Ventilation and perfusion in both adults and children are
preferentially distributed to the dependant lung.
• The best ventilation/perfusion and gaseous exchange will occur
in the dependent lung areas
• In child the ventilation is best in the uppermost lung whilst
perfusion remains best in the dependent area, resulting a V/Q
mismatch
• Clinically significant in unilateral lung disease where the affected
lung is placed uppermost for postural drainage but impairs
ventilation

26. Ventilation & perfusion
• The difference in ventilation distribution in infants is due to
compliance of the ribcage, compressing the dependent areas of
the lung.
• In adults the abdominal content provides a preferential load on
the dependant diaphragm, improving its contractility. This does
not happen in the infant die to the smaller and narrower
abdomen.

27. Oxygen consumption
• Infants have a higher resting metabolic rate than an adult
• Higher oxygen consumption rate, therefore they develop
hypoxia more quickly
• Infants respond to hypoxia with
bradycardia and pulmonary
vasoconstriction whilst adults
become tachycardic and systemic
vasoconstriction

28. Muscle fatigue
• Respiratory muscles of infants
tire more easily than that of an
adult due to the smaller
proportion of fatigue resistant
type I muscle fibres (30%) in
their diaphragms than in adults
(55%).
• This proportion is brought inline
with that of an adult by the age
of 1 year.
• Excessive muscle fatigue in
infants results in apnoea.

29. Breathing pattern
• Irregular breathing and episodes of apnoea are more
common in neonates and premature infants and is
related to immature cardiorespiratory control

30. References
• Smith, M. & Ball, V. 1998. Paediatric Management in
Cardiovascular/Respiratory Physiotherapy. Mosby,
London pp 254-256
• Ammani Prasad, S & Main, E. 2009. Paediatrics in
Physiotherapy for respiratory and cardiac problems.
Adults and children. Pryor, J.A. & Ammani Prasad, S
(eds.) 4th ed. Churchill Livingstone elsevierEdinburgh
pp 330-335

31. References
• van der Walt, R. 2009. Development of the chest wall
presented at the Baby NDT course 2010,
Bloemfontein (unpublished)
• Images courtesy of GOOGLE images