Respiratory System: Anatomical and Physiological differences between adults and children Robyn Smith Department of Physiotherapy UFS 2012

Learning outcomes At the end of this module the learner should:  Be able to identify both key 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

The main reason for hospital admissions in children under the age of 4 years worldwide is respiratory illness

Important to understand children are not simply mini adults

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

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

Chest wall anatomy

Muscles of the chest wall

Mechanics of respiration Air moves in and out of the lungs due to changes in pressure gradients created by movement of the chest wall and muscular action Inspiration active process –Diaphragm –Intercostals –Accessory muscles Expiration is passive Forced expiration involves abdominal muscles e.g. cough

Components of respiratory system Most of the components of the respiratory system are present at birth but –are underdeveloped, –and immature This poses certain challenges to the child regarding breathing

Development of the respiratory system

ANATOMICAL DIFFERENCES

Anatomical differences include: The chest or thorax – Shape – Ribcage – Mechanism of breathing Breathing pattern Diaphragm Internal organs Airway diameter Bronchial walls Surfactant Alveoli Collateral ventilation Exposure to toxins and allergens

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

Infant chest shape Anterior view Lateral view

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.

Thorax: Ribcage The bucket handle movement of ribcage as seen in older children and adults is therefore not possible. This mechanism is used to increase lung volumes during inspiration.

Thorax: Ribcage Infant can therefore only increase the anterior-posterior or transverse diameter of their chest The intercostal muscles are inactive and poorly developed in infancy. The abdominal muscles are not yet stabilising the ribcage (only from about 3-4 months) The interaction of gravity and the musculoskeletal system play an important role in the development of the thorax.

Thorax.... clinical implications With the limited chest expansion the child can only increase their lung volumes by increasing their respiration rate, this explains why small children have a higher RR than adults NB!!!! No head down position for postural drainage premature infants or neonates (1month). Even older infants need to monitored on how they copes when put in a head down position. Infants are diaphragmatic breathers, therefore they are positioned in a head up position to ease the work of breathing

Thorax.... clinical implications Premature infants & children with hypotonic need to be positioned correctly to avoid chest deformities e.g. scoliosis or kyphosis Rib flaring and a high riding ribcages are common in children with weak abdominal muscles and children with cerebral palsy as it does not anchor and pull down the ribcage Infants with chronic cardio-respiratory conditions associated with prematurity or CHD paradoxal breathing may occur over a long period of time resulting in chest deformities forming over time e.g. pectus excavatum or carniatum because the chest wall is still so pliable.

Abnormal chest forms Flaring ribs Barrel chest

Abnormal chest forms Pectus carniatum Pectus excavatum

Postural deformities Scoliosis Kyphosis

Preferential nasal breathing Shape and orientation of the head and neck in babies means that the airway prone to obstruction NB!!! Infants up to about 6 months are preferential nose breathers

Preferential nasal breathing...clinical implications Children with upper respiratory tract infections and nasal secretions may have compromised respiration if the nose is blocked Constant oxygen therapy dries out the mucociliary escalator. As physiotherapists we need to ensure adequate humidification e.g. saline inhalations or saline nose drops and Keep the nose clear by suctioning or aspiration

Preferential nose breathing

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

Diaphragm The diaphragm is the most important inspiratory muscle in children due to the immaturity and inactivity of the intercostal muscles Weak accessory muscles and the abdominals as well in small babies

Diaphragm...clinical implications Ventilation is compromised in infants where the function of the diaphragm is impaired: Examples of such cases include: – abdominal distension –Phrenic nerve paralysis –When placed in the head down position –Congenital diaphragmatic hernia

Internal organs Heart and other organs are relatively large in relation to the infants size

Internal organs... clinical implications This leaves less place for chest expansion

Airway diameter Trachea is short and narrow about a 1/3 of diameter adult in neonate. Generally all airways are narrower. This makes respiratory resistance higher and the work of breathing greater. Narrowest part of the airway is the cricoid ring Right bronchus less angled During the first few years of life there is significant growth in the diameter of the airways

Airway diameter...clinical implications Tracheal swelling as a result of intubation can heighten the resistance Inflexible cricoid ring leaves child more vulnerable to post extubation mucosal oedema and stridor Children are often intubated into the right bronchus resulting in collapse of left lung Children more likely to have tracheal injury after intubation (stenosis/ulceration)

Bronchial walls Bronchial walls are supported by cartilaginous rings. However the support provided in children is far less than in adults making airways more prone to collapse The bronchial wall has proportionally more cartilage, connective tissue and goblet cells than in adults and less muscle tissue is present Beta adrenergic receptors are immature

Bronchial walls...clinical implications Airways are more prone to collapse Lung tissue less complaint Less smooth muscles makes them less responsive to bronchodilator therapy until the age of 12 years (but especially in the first 1-2 years of life)

Cilia At birth cilia are poorly developed

Cilia Clinical implication... Ineffective mucociliary escalator Risk of secretion retention and airway obstruction is greater in premature infants and neonates

Primary Ciliary Dyskinesia Rare genetic disorder Also known as Kartagener’s Syndrome Cilial motility is severely reduced Due to structural defect in the cilia Results in recurrent sinusitis or bronchiectasis due to the impaired sputum clearance

Surfactant Surfactant is a phospholipid produced by the type II pneumocytes in the lungs Function is to reduce the surface tension at the air liquid interface in the alveoli making it easier to expand the alveoli Secreted from 23 weeks gestation, with a surge in production at weeks as the lungs become fully mature

Surfactant.... clinical implications Premature infants have insufficient surfactant resulting in: – ↑ surface tension with alveoli that are difficult to expand –↑ Work of breathing – more easily develop respiratory distress and- failure than adults –More easily develop atelectasis/lung collapse

Alveoli Very few, small alveoli are present at birth Alveoli develop after birth in terms of increasing numbers and in size. The majority of the development occurs within the first 2 years. Alveoli are important for gaseous exchange

Alveoli structures critical to gaseous exchange

Alveoli....clinical implications Smaller alveoli in infants make them more susceptible to collapse and atelectasis Smaller alveoli also provides a smaller area for gaseous exchange

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

Collateral ventilation.... clinical implications... Makes the child more susceptible to alveolar collapse

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 Passive smoking

PHYSIOLOGICAL DIFFERENCES

Physiological differences include: Lung compliance V/Q matching Closing volume Oxygen consumption Muscle endurance Breathing pattern

Lung 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

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. Substernal, subcostal and intercostal recession is common in such cases. This is the reason for paradoxal breathing, if this persists over long period of time it can result in chest deformities

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

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 in a natural V/Q mismatch Clinically significant in unilateral lung disease where the affected lung is placed uppermost for postural drainage but impairs ventilation perfusion matching.

Ventilation & perfusion Children have a natural ventilation perfusion mismatch. 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.

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

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 respiratory distress and apnoea.

Breathing pattern Irregular breathing and episodes of apnoea are more common in neonates and premature infants and is related to immature cardiorespiratory control centre of the brain

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

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