Respiratory mechanics during initial lung aeration at birth in the preterm lamb

Abstract

Despite recent insights into the dynamic processes during lung aeration at birth, several aspects remain poorly understood. We aimed to characterize changes in lung mechanics during the first inflation at birth and their relationship to changes in lung volume. Intubated preterm lambs (gestational age, 124–127 days; n = 17) were studied at birth. Lung volume changes were measured by electrical impedance tomography (VL EIT). Respiratory system resistance (R5) and oscillatory compliance (Cx5) were monitored with the forced oscillation technique at 5 Hz. Lambs received 3–7 s of 8 cmH2O of continuous distending pressure (CDP) before delivery of a sustained inflation (SI) of 40 cmH2O. The SI was then applied until either Cx5 or the VL EIT or the airway opening volume was stable. CDP was resumed for 3–7 s before commencement of mechanical ventilation. The exponential increases with time of Cx5 and VL EIT from commencement of the SI were characterized by estimating their time constants (τCx5 and τVL EIT, respectively). During SI, a fast decrease in R5 and an exponential increase in Cx5 and VL EIT were observed. Cx5 and VL EIT provided comparable information on the dynamics of lung aeration in all lambs, with τCx5 and τVL EIT being highly linearly correlated ( r2 = 0.87, P < 0.001). Cx5 and VL EIT decreased immediately after SI. Despite the standardization of the animal model, changes in Cx5 and R5 both during and after SI were highly variable. Lung aeration at birth is characterized by a fast reduction in resistance and a slower increase in oscillatory compliance, the latter being a direct reflection of the amount of lung aeration.

Imaging the Respiratory Transition at Birth: Unraveling the Complexities of the First Breaths of Life

“…At birth the lung is fluid filled, and airways (and tissue) have a high resistance. (34) The left main bronchus exits the carina acutely, and is encumbered by the heart.…”

“…Crying created different flow characteristics than tidal breathing, quickly inflating the lung with faster Ti and PIF. This is advantageous within the highly resistive fluid-filled lung at birth, (34) but once aerated provides little mechanical or gas exchange benefit. We postulate that crying has a de novo physiological purpose, and not simply due to the noxious stress response of birth.…”

Changes in respiratory mechanics at birth in preterm infants: A pilot study

“…X 5 changes during SI at birth in preterm lambs, although of variable magnitude, present the same pattern for all lambs: X 5 increases like an exponential function during SI and after-SI X 5 improved compared with before-SI X 5 . 16 In infants, we found that the increase of X 5…”

Unravelling the complexities of the first breaths of life

“…7 The lung is in a state of flux in early ex-utero life; the alveoli maybe air-filled but fetal lung fluid remains in the interstitium, and fluid can influx back into alveoli if the intrathoracic pressure gradient falls, compromising FRC. 4,8,25 It has been proposed that 'expiratory braking' is essential during this period, 1,[5][6][7]15,16 and flow patterns measured at the airway opening support this, but have not been correlated to temporal FRC change. 14…”

“…At birth the lung is fluid filled, and airways (and tissue) have a high resistance. (34) The left main bronchus exits the carina acutely, and is encumbered by the heart. This may create preferential flow states towards the right lung, especially during the higher inspiratory flows of crying.…”