Smolich Joseph J, Cheung Michael M H, Mynard Jonathan P
Heart Research, Murdoch Children's Research Institute, Parkville, VIC, Australia.
Department of Paediatrics, University of Melbourne, Parkville, VIC, Australia.
Pediatr Res. 2021 Oct;90(4):795-800. doi: 10.1038/s41390-020-01352-y. Epub 2021 Jan 27.
This study evaluated whether an increased left ventricular (LV) pump function accompanying reduction of lung liquid volume in fetal lambs was related to increased LV preload, augmented LV contractility, or both.
Eleven anesthetized preterm fetal lambs (gestation 128 ± 2 days) were instrumented with (1) an LV micromanometer-conductance catheter to obtain LV end-diastolic volume (EDV) and end-diastolic pressure (EDP), the maximal rate of rise of LV pressure (dP/dt), LV output, LV stroke work, and LV end-systolic elastance (E), a relatively load-independent measure of contractility; (2) an endotracheal tube to measure mean tracheal pressure and to reduce lung liquid volume. LV transmural pressure was calculated as LV EDP minus tracheal pressure.
Reducing lung liquid volume by 16 ± 4 ml kg (1) augmented LV output (by 16%, P = 0.001) and stroke work (29%, P < 0.001), (2) increased LV EDV (12%, P < 0.001), (3) increased LV transmural pressure (2.2 mmHg, P < 0.001), (4) did not change LV dP/dt normalized for EDV (P > 0.7), and (5) decreased LV E (20%, P < 0.01).
These findings suggest a rise in LV pump function evident after reduction of lung liquid volume in fetal lambs was related to increased LV preload secondary to lessening of external LV constraint, without any associated rise in LV contractility.
This study has shown that reducing the volume of liquid filling the fetal lungs lessens the degree of external constraint on the heart. This lesser constraint permits a rise in left ventricular dimensions and thus greater cardiac filling that leads to increased left ventricular pumping performance. This study has defined a mechanism whereby a reduction in lung liquid volume results in enhanced pumping performance of the fetal heart. These findings suggest that a reduction in lung liquid volume which occurs during the birth transition contributes to increases in left ventricular dimensions and pumping performance known to occur with birth.
本研究评估了胎羊肺液体积减少时左心室（LV）泵功能增强是否与左心室前负荷增加、左心室收缩力增强或两者均有关。
对11只麻醉的早产胎羊（妊娠128±2天）进行如下仪器植入：（1）一根左心室微测压-电导导管，以获取左心室舒张末期容积（EDV）和舒张末期压力（EDP）、左心室压力最大上升速率（dP/dt）、左心室输出量、左心室搏功以及左心室收缩末期弹性（E），E是一种相对独立于负荷的收缩力测量指标；（2）一根气管内导管，用于测量平均气管压力并减少肺液体积。左心室跨壁压计算为左心室EDP减去气管压力。
将肺液体积减少16±4 ml/kg可导致：（1）左心室输出量增加（16%，P = 0.001）和搏功增加（29%，P < 0.001）；（2）左心室EDV增加（12%，P < 0.001）；（3）左心室跨壁压增加（2.2 mmHg，P < 0.001）；（4）经EDV标准化的左心室dP/dt无变化（P > 0.7）；（5）左心室E降低（20%，P < 0.01）。
这些发现表明，胎羊肺液体积减少后左心室泵功能的明显增强与左心室前负荷增加有关，这是由于左心室外部约束减轻所致，而左心室收缩力并无相应增加。
本研究表明，减少填充胎肺的液体量可减轻心脏的外部约束程度。这种较小的约束允许左心室尺寸增加，从而使心脏充盈增加，进而导致左心室泵血性能增强。本研究确定了一种机制，即肺液体积减少会导致胎儿心脏泵血性能增强。这些发现表明，出生过渡期间发生的肺液体积减少有助于左心室尺寸和泵血性能的增加，这是已知的出生时会出现的情况。
