Respiratory System Anatomical and Physiological differences between adults

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

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

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

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

Development of the respiratory system

ANATOMICAL DIFFERENCES

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

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.

Infant chest shape • Anterior view • Lateral view

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

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

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 highendurance muscle fibres and also more susceptible to fatigue • The diaphragm is the most important inspiratory muscle due to the inactivity of the intercostal muscles

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

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

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

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

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

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

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

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

PHYSIOLOGICAL DIFFERENCES

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

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

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

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.

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 apnoea.

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

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. ) 4 th ed. Churchill Livingstone elsevier. Edinburgh pp 330 -335

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