title: Control of fetal cardiac output during changes in blood volume.
abstract: Changes in cardiac output (Qco), heart rate, right atrial pressure, (Pra), and mean systemic pressure (Pms) in response to blood volume changes were measured in chronically prepared fetal sheep. With a 10% decrease in blood volume, fetal cardiac output, measured with the microsphere technique, decreased significantly from 592 +/- 28 to 471 +/- 32 ml . min-1 . kg-1. Heart rate changed little from control animals (163 +/- 5) to those with decreased volume (161 +/- 10 beats/min). Right atrial pressure decreased significantly from 5.4 +/- 0.4 to 4.2 +/- 0.6 mmHg. Mean systemic pressure decreased from 13.8 +/- 0.3 to 10.5 +/- 0.6 mmHg. With a 10% increase in fetal blood volume, cardiac output rose insignificantly to 632 +/- 38 ml . min-1 . kg-1. However, right atrial pressure increased significantly to 8.9 +/- 0.6 mmHg and mean systemic pressure increased significantly to 16.5 +/- 0.8 mmHg with the increased volume. Heart rate again changed little (153 +/- 9 beats/min). The fact that cardiac output rose only a small amount, whereas right atrial pressure rose sharply with an increased blood volume, suggests that the fetal heart is operating near the upper limit of its Starling function curve. As a result, there is very limited cardiac reserve for increases in fetal cardiac output.
mesh_terms: D000818:Animals; D001794:Blood Pressure; D001810:Blood Volume; D002302:Cardiac Output; D005260:Female; D005318:Fetal Heart / Q000502:physiology*; D006339:Heart Rate; D011247:Pregnancy; D012756:Sheep / Q000502:physiology*