pedsRespPhys - Pediatric Respiratory Physiology Drs. Greg...

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Pediatric Respiratory Physiology Drs. Greg and Joy Loy Gordon February 2005
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Pediatric Respiratory Physiology Prenatal – Embryo Ventral pouch in primitive foregut becomes lung buds projecting into pleuroperitoneal cavity Endodermal part develops into airway alveolar membranes glands Mesenchymal elements develop into smooth muscle cartilage connective tissue vessels
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Pediatric Respiratory Physiology Pseudoglandular period – starting 17 th week of gestation Branching of airways down to terminal bronchioles Canalicular period Branching in to future respiratory bronchioles Increased secretary gland and capillary formation Terminal sac (alveolar) period 24 th week of gestation Clusters of terminal air sacs with flattened epithelia Prenatal Development
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Pediatric Respiratory Physiology Surfactant Produced by type II pneumocytes appear 24-26 weeks (as early as 20 weeks) Maternal glucocorticoid treatment 24-48 hours before delivery accelerates lung maturation and surfactant production Premature birth – immature lungs -> IRDS (HMD) due to insufficient surfactant production
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Pediatric Respiratory Physiology Proliferation of capillaries around saccules sufficient for gas exchange 26-28 th week (as early as 24 th week) Formation of alveoli 32-36 weeks saccules still predominate at birth Prenatal Development
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Pediatric Respiratory Physiology Lung Fluid expands airways -> helps stimulate lung growth contributes of total amniotic fluid prenatal ligation of trachea in congenital diaphragmatic hernia results in accelerated growth of otherwise hypoplastic lung ( J Pediatr Surg 28:1411, 1993) Prenatal Development
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Pediatric Respiratory Physiology Perinatal adaptation First breath(s) up to 40 (to 80 cmH 2 O needed to overcome high surface forces to introduce air into liquid-filled lungs adequate surfactant essential for smooth transition Elevated P a O 2 Markedly increased pulmonary blood flow -> increased left atrial pressure with closure of foramen ovale
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Pediatric Respiratory Physiology Postnatal development Lung development continues for 10 years most rapidly during first year At birth: 20-50x10 7 terminal air sacs (mostly saccules) only one tenth of adult number Development of alveoli from saccules essentially complete by 18 months of age
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Pediatric Respiratory Physiology Infant lung volume disproportionately small in relation to body size VO 2 /kg = 2 x adult value => ventilatory requirement per unit lung volume is increased less reserve more rapid drop in SpO 2 with hypoventilation
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Pediatric Respiratory Physiology Neonate Lung compliance high elastic fiber development occurs postnatally static elastic recoil pressure is low Chest wall compliance is high cartilaginous ribs limited thoracic muscle mass More prone to atalectasis and respiratory insufficiency especially under general anesthesia Infancy and childhood static recoil pressure steadily increases compliance, normalized for size, decreases
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Pediatric Respiratory Physiology Infant and toddler more prone to severe obstruction of upper and lower airways
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pedsRespPhys - Pediatric Respiratory Physiology Drs. Greg...

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