摘要:
The purpose of this lesson is to review the normal process in the development of the pediatric airway and the effects of disease upon its structures in infancy and childhood.The growth of the airway is a dynamic process throughout fetal development and for several years after birth. However, by the 16th week of gestation, complete development of bronchial generations through the level of the terminal bronchioles has occurred. Between the 16th and 24th weeks of gestation, the first respiratory bronchioles appear, with alveolar development beginning around 24 wveeks of gestation. The number of alveoli continues to increase rapidly for the first 3 years after birth and then slows, with multiplication ceasing by approximately 3 to 8 years of age.From birth to adulthood, tracheal diameter approximately quadruples. Cross-sectional area increases by a factor of 8 to 10. Alveolar dimension increases approximately 4-fold and alveolar numbers approximately 10 fold. During gestation, the fetal lung is jiYled with a substance, referred to as fetal lung liquid, that is a secretory product of the lung itself Respiratory-type (diaphragmatic) activity also is present during gestation.At birth, the tracheal cartilages are developed with a normal adult distribution; however, the cartilages are less rigid than in older children or adults. In addition, the posterior noncartilaginous aspect of the trachea, the pars membranaceu, comprises a relatively greater portion of the circumference of the trachea. These two factors account for a signqicantly greater compliance of the airway in infants. As a result, a dramatic change in the anterior/posterior (AP) diameter of the intrathorucic trachea niay be evident from inspiration to expiration. In a crying infiint, at the end of expiration, nearly complete collapse of the AP diameter of the trachea is normal (Figure IA). On inspiration, the trachea should assume a much larger diameter, as usually is recognized on chest radiogrciphy (Figure 1 B). The cervical tracheal size is determined bv pressure within its lumen. This is demonstrated most dramatically in situations where obstruction at the laryngeal level, such as in croup, exists. With vigorous inspiration, collapse of the entire upper trachea may appear in the presence of a higher level o f obstruction. With vocal cord closure and increased pressure within the chest, the cervical trachea may increase significantlv in size.The course of the trachea is altered by the phase of respiration in infants. With expiration, the trachea is expected to have a buckled configuration, with an angular deviation awav from the side of the aortic arch at the level of the thorucic inlet (Figure 2A) and a similarly angular buckling posteriorly and then inferiorly at the thorucic inlet on expirution (Figure 2B).
ISSN:0149-9009
出版商:OVID
年代:1996
数据来源: OVID