Developmental Physiology of the

Respiratory System

Mohammad Rezaei

Pediatric Pulmonologist

Lung Development

• Prenatal Development

• Postnatal Development and Growth

Prenatal Development of the Lung

Prenatal Development of the Lung

Prenatal Development of the Lung

Embryonic stage

Prenatal Development of the Lung

Pseudoglandular stage

Prenatal Development of the Lung

Canalicular stage

Prenatal Development of the Lung

Saccular stage

Prenatal Development of the Lung

Alveolar stage

Birth• Lung Fluid

• Pulmonary Blood Flow

Postnatal Development and Growth of the Lung

Postnatal Development of the Lung

Alveolarization Microvascular Maturation

Postnatal Growth of the Lung

Postnatal lung growth continue throughout infancy and childhood and into the adolescent years.

Chest Wall & Diaphragm

• Chest wall compliance

• Diaphragm and respiratory muscles (type of fibers)

Chest Wall Configuration

Chest Wall Configuration

Normal values for pulmonary function with age

• predicted values of pulmonary function depend upon age, height, gender, and race .

• Lung Capacities and flows continue to increase until late adolescence. (then decrease)

• Lung Volume, Gas exchange surface area, Diffusion capacity,…all increase in relation of body mass increase.

Normal values for pulmonary function with age

Compliance

• Chest wall

• Lung

Normal values for pulmonary function with age

Resistance• Airway diameter (r)

The diameter of airways in infants and children is much smaller than adults, resulting in increased Raw

• Number of airways• RR• Lung Volume

Site of Airway Resistance• In the infant lung, small peripheral airways may contribute as much

as 50% of the total airway resistance, and this proportion does not decrease until about 5 years of age. (Remember small airway diseases such as Bronchiolitis)

Normal values for pulmonary function with age

Total Lung Capacity

• Lung volume is linearly related to body length during childhood

Normal values for pulmonary function with age

Functional residual capacity

• in the infants predicts a supine FRC of only 10% of TLC, whereas in adults FRC accounts for approximately 50% of TLC in the upright position.

• In infants, the post inspiratory activity of the inspiratory muscles and the laryngeal control of expiratory flow ( “grunting” ) modify respiratory mechanics to maintain the patency of small airways and alveoli.

• Mean values for FRC range from 20-25 mL/kg in infants up to 18 months of age

Normal values for pulmonary function with age

Tidal Volume

Respiratory Rate

Normal values for pulmonary function with age

Minute Ventilation

Minute Ventilation = Tidal Volume x Respiratory Rate

Normal valuesfor pulmonaryfunction with age

Thank you