Respiratory System:Anatomical and Physiological differences

between adults and children

Robyn SmithRobyn Smith

Department of PhysiotherapyDepartment of Physiotherapy

UFSUFS

20112011

Learning outcomes• At the end of this module the learner should:At the end of this module the learner should:

Be able to identify both anatomical and Be able to identify both anatomical and physiological differences between the respiratory physiological differences between the respiratory systems of child and a adultsystems of child and a adult

Understand and explain the impact of these Understand and explain the impact of these differences on the clinical findings, observations differences on the clinical findings, observations and respiration of a childand respiration of a child

Describe the impact of preferential nasal breathing Describe the impact of preferential nasal breathing on respiration in babieson respiration in babies

Background

• The respiratory system of children differs both The respiratory system of children differs both anatomically and physiologically from that of adultsanatomically and physiologically from that of adults

• These differences have important consequences for These differences have important consequences for the physiotherapy care of children in terms of the physiotherapy care of children in terms of assessment, treatment and choice of techniquesassessment, treatment and choice of techniques

• The principle reason for hospital admissions in The principle reason for hospital admissions in children under the age of 4 years is respiratory illnesschildren under the age of 4 years is respiratory illness

Background

• The principles of adult chest physiotherapy cannot The principles of adult chest physiotherapy cannot be directly transposed to a child.be directly transposed to a child.

• Chest physiotherapy as provided to children has Chest physiotherapy as provided to children has become a specialised area on its own for this reasonbecome a specialised area on its own for this reason

Development of the respiratory system

ANATOMICAL DIFFERENCES

Thorax: Chest shape

• Cross sectional area of the thorax is Cross sectional area of the thorax is cylindrical and not elliptical as in adultscylindrical and not elliptical as in adults

Thorax: Ribcage• The ribcage of the newborn and The ribcage of the newborn and

infant is infant is relatively soft relatively soft and and cartilaginous compared to the rigid cartilaginous compared to the rigid chest wall of older children and chest wall of older children and adultsadults

• Ribs run horizontally Ribs run horizontally to the to the vertebrae and sternum compared to vertebrae and sternum compared to the more oblique angle of older the more oblique angle of older children and adults. The children and adults. The bucket bucket handle movement handle movement as seen in older as seen in older children and adults is therefore not children and adults is therefore not possible. possible.

• Infant can therefore increase the Infant can therefore increase the anterior-posterior or transverse anterior-posterior or transverse diameter of their chest diameter of their chest

• The The intercostal muscles are inactive intercostal muscles are inactive and and poorly developed poorly developed in infancy. in infancy. And the And the abdominal muscles are not abdominal muscles are not yet stabilising the ribcageyet stabilising the ribcage

• The interaction of gravity and the The interaction of gravity and the musculoskeletal system play an musculoskeletal system play an important role in the development of important role in the development of the thorax. the thorax.

Infant chest shape

• Anterior viewAnterior view • Lateral viewLateral view

Thorax.... clinical implications

• Clinical implications....Clinical implications....

• With the limited chest expansion With the limited chest expansion the child can only increase their the child can only increase their lung volumes by increasing their lung volumes by increasing their respiration raterespiration rate

• No postural drainage in No postural drainage in premature infants or neonatespremature infants or neonates

• Infants are diaphragmatic Infants are diaphragmatic breathersbreathers

• Premature infants & children Premature infants & children with low tone especially with low tone especially hypotonia need to be hypotonia need to be positioned correctly to avoid positioned correctly to avoid chest deformities, rib flaring and chest deformities, rib flaring and a high riding ribcagea high riding ribcage

• Infants with chronic Infants with chronic caqrdiorespiratory conditions caqrdiorespiratory conditions e.g. BPD, RDS or paradoxal e.g. BPD, RDS or paradoxal breathing may also develop breathing may also develop chest deformities over timeschest deformities over times

Preferential nasal breathing

• Shape and orientation of the Shape and orientation of the head and neck in babies head and neck in babies means that the airway means that the airway prone to obstructionprone to obstruction

• Infants Infants up to about 6 months up to about 6 months are preferential nose are preferential nose breathersbreathers

clinical implications .....clinical implications .....

Children with upper Children with upper respiratory tract respiratory tract infections and nasal infections and nasal secretions may have secretions may have compromised compromised respiration of the nose respiration of the nose is blockedis blocked

Diaphragm

• Angle of insertion of the Angle of insertion of the diaphragm in infants is diaphragm in infants is more more horizontalhorizontal

• Diaphragm works at a Diaphragm works at a mechanical disadvantagemechanical disadvantage

• Diaphragm in infants has a Diaphragm in infants has a lower-content of high-lower-content of high-endurance muscle fibres and endurance muscle fibres and also also more susceptible to more susceptible to fatiguefatigue

• The diaphragm is the most The diaphragm is the most important inspiratory muscle important inspiratory muscle due to the inactivity of the due to the inactivity of the intercostal musclesintercostal muscles

Diaphragm...clinical implications

• Ventilation is Ventilation is compromised in infants compromised in infants where the function of where the function of the diaphragm is the diaphragm is impaired impaired

e.g. e.g. abdominal abdominal distension distension and phrenic and phrenic nerve palsy nerve palsy

Internal organs

• Heart and other organs Heart and other organs are relatively large in are relatively large in relation to the infants relation to the infants sizesize

clinical implications clinical implications

This leaves less place This leaves less place for chest expansionfor chest expansion

Airway diameter

• Trachea is short and Trachea is short and narrow narrow (1/3 of diameter adult) in (1/3 of diameter adult) in neonate. This makes respiratory neonate. This makes respiratory resistance higher and the work resistance higher and the work of breathing greater.of breathing greater.

• Narrowest part of the airway is Narrowest part of the airway is the cricoid ring (adult vocal the cricoid ring (adult vocal cords)cords)

• Right bronchus less angled than Right bronchus less angled than leftleft

• During the first few years of life During the first few years of life their is significant growth in the their is significant growth in the diameter of the airwaysdiameter of the airways

clinical implications .....clinical implications .....

• Tracheal swelling as a result Tracheal swelling as a result of intubation can heighten of intubation can heighten the resistancethe resistance

• Inflexible cricoid ring leaves Inflexible cricoid ring leaves child more vulnerable to post child more vulnerable to post extubation mucosal odema extubation mucosal odema and stridorand stridor

• Children are often intubated Children are often intubated into the right bronchusinto the right bronchus

Bronchial walls

• Bronchial walls are supported Bronchial walls are supported by by cartilaginous ringscartilaginous rings. However . However the support provided in children the support provided in children is far less than in adults making is far less than in adults making airways airways

• The bronchial wall has The bronchial wall has proportionally more cartilage, proportionally more cartilage, connective tissue and mucus connective tissue and mucus cells and less muscle tissue cells and less muscle tissue than in adultsthan in adults

• Beta adrenergic receptors Beta adrenergic receptors immatureimmature

clinical implications ...clinical implications ...

• Airways Airways more prone to more prone to collapsecollapse

• Lung tissue less complaintLung tissue less complaint

• Less smooth muscles makes Less smooth muscles makes them them less responsive to less responsive to bronchodilator bronchodilator until the age until the age of 12 yearsof 12 years

Cilia

• At birth cilia are poorly At birth cilia are poorly developeddeveloped

Clinical implication...Clinical implication...

• Risk of Risk of secretion secretion retention retention and airway and airway obstruction is greater in obstruction is greater in premature infants and premature infants and neonatesneonates

Alveoli & surfactant

• Alveoli develop after birth in Alveoli develop after birth in terms terms of increasing numbers of increasing numbers and in sizeand in size. The majority of the . The majority of the development occurs within the development occurs within the first 2 years.first 2 years.

• Surfactant which reduces the Surfactant which reduces the surface tension at the air liquid surface tension at the air liquid interface in the alveoli are interface in the alveoli are secreted from secreted from 23 weeks 23 weeks gestationgestation

Clinical implications ....Clinical implications ....

• Smaller alveoli in infants Smaller alveoli in infants make them more susceptible make them more susceptible to collapseto collapse

• Smaller alveoli also Smaller alveoli also provides provides a smaller area for gaseous a smaller area for gaseous exchangeexchange

• Premature infants have Premature infants have insufficient surfactant insufficient surfactant resulting in the development resulting in the development of RDSof RDS

Collateral ventilation

• Ensures that distal lung Ensures that distal lung units are ventilated units are ventilated despite the obstruction despite the obstruction of a main airwayof a main airway

• The collateral The collateral ventilatory channels are ventilatory channels are poorly developed in poorly developed in children under 2-3 children under 2-3 yearsyears

Clinical implications...Clinical implications...

• Makes the child more Makes the child more susceptible to alveolar susceptible to alveolar collapsecollapse

Height and exposure to pollution

• Children have a higher RR, Children have a higher RR, spend more time outdoors spend more time outdoors exposing them to allergens exposing them to allergens and pollutantsand pollutants

• Their height also exposes Their height also exposes the child to other pollutants the child to other pollutants e.g. exhaust fumese.g. exhaust fumes

PHYSIOLOGICAL DIFFERENCES

Respiratory compliance• Measure of the pressure required to increase the Measure of the pressure required to increase the

volume air in the lungsvolume air in the lungs• Combination of lung- and chest wall complianceCombination of lung- and chest wall compliance• Lung compliance in a child is comparable to an adult Lung compliance in a child is comparable to an adult

and is directly proportional to the child’s sizeand is directly proportional to the child’s size• Compliance in a child is reduced by the high Compliance in a child is reduced by the high

proportion of cartilage in the airwaysproportion of cartilage in the airways• Premature infants with insufficient surfactant show Premature infants with insufficient surfactant show

reduced compliancereduced compliance

Chest wall compliance

• The chest wall of the infant is cartilaginous and The chest wall of the infant is cartilaginous and very soft and compliant. In the case of respiratory very soft and compliant. In the case of respiratory distress the chest is drawn inwards . distress the chest is drawn inwards .

• This is the This is the reason for paradoxal breathingreason for paradoxal breathing

Closing volume• Lung volume at which the small airways closeLung volume at which the small airways close

• In infants the closing volume is greater than the FRC, airway In infants the closing volume is greater than the FRC, airway closure may thus occur before the end of expiration, a closure may thus occur before the end of expiration, a consideration when using manual techniques e.g. Vibrations. One consideration when using manual techniques e.g. Vibrations. One may further reduce the lung volumes resulting in widespread may further reduce the lung volumes resulting in widespread atelectasisatelectasis

In respiratory distress children grunt (adducting the vocal cords) in In respiratory distress children grunt (adducting the vocal cords) in an attempt to reduce the expired volume of air in order to minimise an attempt to reduce the expired volume of air in order to minimise alveolar collapsealveolar collapse

• It is harder to re-inflate collapsed alveoli in childrenIt is harder to re-inflate collapsed alveoli in children

Ventilation & perfusion

• Ventilation and perfusion in both adults and children are Ventilation and perfusion in both adults and children are preferentially distributed to the dependant lung.preferentially distributed to the dependant lung.

• The best ventilation/perfusion and gaseous exchange will occur The best ventilation/perfusion and gaseous exchange will occur in the dependent lung areasin the dependent lung areas

• In child the ventilation is best in the uppermost lung whilst In child the ventilation is best in the uppermost lung whilst perfusion remains best in the dependent area, resulting a V/Q perfusion remains best in the dependent area, resulting a V/Q mismatchmismatch

• Clinically significant in unilateral lung disease where the affected Clinically significant in unilateral lung disease where the affected lung is placed uppermost for postural drainage but impairs lung is placed uppermost for postural drainage but impairs ventilationventilation

Ventilation & perfusion

• The difference in ventilation distribution in infants is due to The difference in ventilation distribution in infants is due to compliance of the ribcage, compressing the dependent areas of compliance of the ribcage, compressing the dependent areas of the lung.the lung.

• In adults the abdominal content provides a preferential load on In adults the abdominal content provides a preferential load on the dependant diaphragm, improving its contractility. This does the dependant diaphragm, improving its contractility. This does not happen in the infant die to the smaller and narrower not happen in the infant die to the smaller and narrower abdomen. abdomen.

Oxygen consumption

• Infants have a higher resting metabolic rate than an adultInfants have a higher resting metabolic rate than an adult

• Higher oxygen consumption Higher oxygen consumption rate, therefore they develop rate, therefore they develop hypoxia more quicklyhypoxia more quickly

• Infants respond to hypoxia with Infants respond to hypoxia with

bradycardia and pulmonary bradycardia and pulmonary

vasoconstriction whilst adults vasoconstriction whilst adults

become tachycardic and systemic become tachycardic and systemic

vasoconstrictionvasoconstriction

Muscle fatigue

• Respiratory muscles of infants Respiratory muscles of infants tire tire more easily more easily than that of an adult than that of an adult due to the smaller proportion of due to the smaller proportion of fatigue resistant type I muscle fatigue resistant type I muscle fibres (30%) in their diaphragms fibres (30%) in their diaphragms than in adults (55%).than in adults (55%).

• This proportion is brought inline This proportion is brought inline with that of an adult by the age of with that of an adult by the age of 1 year.1 year.

• Excessive muscle fatigue in Excessive muscle fatigue in infants results in apnoea.infants results in apnoea.

Breathing pattern

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

References

• Smith, M. & Ball, V. 1998. Paediatric Management in Smith, M. & Ball, V. 1998. Paediatric Management in Cardiovascular/Respiratory Physiotherapy. Mosby, Cardiovascular/Respiratory Physiotherapy. Mosby, London pp 254-256London pp 254-256

• Ammani Prasad, S & Main, E. 2009. Paediatrics in Ammani Prasad, S & Main, E. 2009. Paediatrics in Physiotherapy for respiratory and cardiac problems. Physiotherapy for respiratory and cardiac problems. Adults and children. Pryor, J.A. & Ammani Prasad, S Adults and children. Pryor, J.A. & Ammani Prasad, S (eds.) 4(eds.) 4thth ed. Churchill Livingstone elsevierEdinburgh ed. Churchill Livingstone elsevierEdinburgh pp 330-335pp 330-335

References

• van der Walt, R. 2009. Development of the chest wall van der Walt, R. 2009. Development of the chest wall presented at the Baby NDT course 2010, presented at the Baby NDT course 2010, Bloemfontein (unpublished)Bloemfontein (unpublished)

• Images courtesy of GOOGLE imagesImages courtesy of GOOGLE images