Effect of ventilation on pulmonary blood volume of the fetal lamb

Abstract

Blood volume changes in the fetal lung following the onset of ventilation were studied by isotopic measurement of red blood cell and plasma volume in rapidly frozen lungs of ten near term fetal lambs. Total pulmonary blood volumes of fetal lambs ventilated with 3% O2 and 7% CO2 in nitrogen (so that blood gas levels were little changed from fetal values), or with air, were compared with measurements in unventilated lambs. Regional correlations of blood volume and blood flow (measured with isotope-labeled microemboli) within the lungs were also examined. Total pulmonary blood volume averaged 5.6 ml/kg body weight in unventilated fetal lambs and was approximately 43% greated in fetal lambs after 5-20 min of air ventilation, but not significantly different in lambs ventilated with 3% O2 and 7% CO2 in nitrogen. Thus it is ventilation with air, rather than the introduction of gas into the alveoli, which enlarges the fetal pulmonary vascular bed. Regional pulmonary blood volume and blood flow were correlated, though poorly, in air-ventilated lungs, but not in lungs ventilated with 3% O2 and 7% CO2 in nitrogen; this suggests that a common factor may operate to increase both blood flow and blood volume in the fetal lung following the introduction of air.

Haemodynamic effects of umbilical cord milking in premature sheep during the neonatal transition

“…Furthermore, our inability to detect placental transfusion, despite a 10-fold increase in PBF in PBCC lambs, demonstrates that an increase in pulmonary blood volume associated with an increase in PBF is not responsible for placental transfusion. This is consistent with the previous finding that the increase in pulmonary blood volume, associated with pulmonary vascular dilation, is small and can only account for a total increase in blood volume of ~2% 36. Mathematically, this can be explained by the fact that the volume of a tube increases with the increasing radius squared, whereas flow increases with increasing radius to the fourth power.…”

Transfusion or Timing: The Role of Blood Volume in Delayed Cord Clamping During the Cardiovascular Transition at Birth

“…It has been hypothesized that the increase in PBF after birth increases pulmonary blood volume by drawing blood into the dilated pulmonary vasculature, thereby accounting for the need of the newborn to increase blood volume during DCC (20). However, the increase in pulmonary blood volume associated with the increased PBF at birth is only 2–3 mL/kg (21). This is explained by the fact that when blood vessels dilate, the volume contained within them increases with the radius squared but the resistance decreases with the radius to the 4th power.…”

Blood Volume in Newborn Piglets: Effects of Time of Natural Cord Rupture, Intra-Uterine Growth Retardation, Asphyxia, and Prostaglandin-Induced Prematurity

“…Acute asphyxia increases fetal arterial pressure and umbilical blood flow (14). Moreover, lack of respiratory efforts in the newborn has been shown to impede placental transfusion ( 19,30).…”