Morin F C, Egan E A
Department of Pediatrics, School of Medicine and Biomedical Sciences, State University of New York, Buffalo 14214.
J Appl Physiol (1985). 1992 Jul;73(1):213-8. doi: 10.1152/jappl.1992.73.1.213.
During the latter third of gestation, the number of resistance vessels in the lungs of the fetal sheep increases by 10-fold even after correction for lung growth. We measured pulmonary arterial pressure and blood flow directly and calculated total pulmonary resistance (pressure divided by flow) in intrauterine fetal lambs at 93-95 days and at 136 days of gestation (term is 145-148 days). In addition, we used a hyperbaric chamber to increase oxygen tension in the fetuses and measured the effect on the pulmonary circulation. When corrected for wet weight of the lungs, pulmonary blood flow did not change with advancing gestation (139 +/- 42 to 103 +/- 45 ml.100 g-1.min-1). Pulmonary arterial pressure increased (42 +/- 5 to 49 +/- 3 mmHg); thus total pulmonary resistance increased with advancing gestation from 0.32 +/- 0.12 to 0.55 +/- 0.21 mmHg.100 g.min.ml-1. If the blood flow is corrected for dry weight of the lungs, neither pulmonary blood flow nor total pulmonary resistance changed with advancing gestation. Increasing oxygen tension increased pulmonary blood flow 10-fold in the more mature fetuses but only 0.2-fold in the less mature fetuses. At the normal low oxygen tension of the fetus, pulmonary blood flow does not increase between these two points of gestation in the fetal lamb despite the increase in vessel density in the lungs. However, during elevated oxygen tension, pulmonary blood flow does increase in proportion to the increase in vessel density.
在妊娠后期的三分之一阶段，即使校正了肺生长因素，胎羊肺中阻力血管的数量仍增加了10倍。我们直接测量了宫内胎羊在妊娠93 - 95天和136天（足月为145 - 148天）时的肺动脉压和血流量，并计算了总肺阻力（压力除以流量）。此外，我们使用高压舱提高胎儿的氧张力，并测量其对肺循环的影响。校正肺湿重后，肺血流量并不随妊娠进展而变化（从139±42降至103±45 ml·100 g⁻¹·min⁻¹）。肺动脉压升高（从42±5升至49±3 mmHg）；因此，总肺阻力随妊娠进展而增加，从0.32±0.12升至0.55±0.21 mmHg·100 g·min·ml⁻¹。如果以肺干重校正血流量，肺血流量和总肺阻力均不随妊娠进展而变化。提高氧张力使较成熟胎儿的肺血流量增加了10倍，但使较不成熟胎儿的肺血流量仅增加了0.2倍。在胎儿正常的低氧张力状态下，尽管肺血管密度增加，但胎羊在这两个妊娠阶段之间肺血流量并未增加。然而，在氧张力升高期间，肺血流量确实会与血管密度的增加成比例增加。
