Faridy E E
Respir Physiol. 1987 Jun;68(3):293-300. doi: 10.1016/s0034-5687(87)80014-2.
The volume of pulmonary fluid (PF) in fetus decreases at late gestation and with initiation of labor. In addition there is a massive release of surfactant in PF during labor. In postmaturity the reduction in PF continues till the lungs become virtually fluid-free. Furthermore there is a loss of surface activity with prolongation of gestation. The present study was conducted to determine the role of the volume and surface activity of pulmonary fluid on the opening pressure (OP) in fetal lungs. Fetal (term and post term) and degassed newborn lungs were inflated with air and OP recorded. The lowest OP was noted in lungs of term fetuses delivered after labor. As the lung became dryer, either after birth or during postmaturity, the OP increased. The OP was greater in postmature compared to degassed postnatal lungs. Instillation of minute volumes of isotonic saline in post term to restore the volume of pulmonary fluid to that of term lungs decreased the OP. Thereafter as the volume of intrapulmonary fluid was increased beyond that of term, either in term or post term lungs, the OP was also increased. The angle of deflection from fluid-removed to fluid-instilled segments of the OP-volume curve was more acute in the fetal lung that in the adult. These studies suggest that a reduction in the volume of pulmonary fluid at birth beyond that of term fetus (FRC) may not be beneficial for newborn and that massive release of surfactant in PF during labor serves to enhance opening of air saccules.
胎儿肺液（PF）的体积在妊娠晚期及分娩开始时会减少。此外，分娩过程中肺液中会大量释放表面活性剂。过期妊娠时，肺液的减少会持续到肺部几乎没有液体。此外，随着妊娠时间延长，表面活性会丧失。本研究旨在确定肺液的体积和表面活性对胎儿肺开放压（OP）的作用。用空气使胎儿（足月和过期）及已排气的新生肺膨胀，并记录开放压。在分娩后娩出的足月胎儿的肺中观察到最低的开放压。随着肺变干，无论是在出生后还是过期妊娠期间，开放压都会升高。过期妊娠时的开放压比已排气的产后肺更高。向过期胎儿肺内滴注少量等渗盐水以将肺液体积恢复到足月肺的水平会降低开放压。此后，无论是足月还是过期胎儿肺，当肺内液体体积增加超过足月水平时，开放压也会升高。胎儿肺的开放压 - 体积曲线从液体去除段到液体注入段的偏转角度比成人肺更陡峭。这些研究表明，出生时肺液体积减少至低于足月胎儿的功能残气量（FRC）可能对新生儿无益，且分娩过程中肺液中表面活性剂的大量释放有助于增强肺泡的开放。
