Kg. Schmidt et al., ASSESSMENT OF FLOW EVENTS AT THE DUCTUS VENOSUS INFERIOR VENA-CAVA JUNCTION AND AT THE FORAMEN OVALE IN FETAL SHEEP BY USE OF MULTIMODAL ULTRASOUND, Circulation, 93(4), 1996, pp. 826-833
Background Previous techniques for the study of the fetal circulation
did not permit assessment of phasic events associated with the cardiac
cycle. We used multimodal ultrasound techniques to examine flow event
s that occur in the major veins and across the foramen ovale in the ci
rculation of the fetal lamb. Methods and Results We studied eight feta
l lambs instrumented with catheters in the superior and inferior venae
cavae and a peripheral umbilical vein and performed ultrasound studie
s that included M-mode and two-dimensional imaging, pulsed and Doppler
color flow ultrasound, and contrast echocardiography to evaluate flow
in the ductus venosus, in both venae cavae, and through the foramen o
vale. Two blood streams of different flow velocities were identified w
ithin the cephalic portion of the inferior vena cava. The stream that
originated from the narrowed ductus venosus had a higher velocity than
that from the caudal inferior vena cava (mean velocity, 57 +/- 13 ver
sus 16 +/- 3 cm/s; P<.0002). Facilitated by the eustachian valve and t
he septum primum, the ductus venosus stream preferentially passed thro
ugh the foramen ovale to the left atrium. This flow occurred Juring mo
st of the cardiac cycle, except for 19.6 +/- 2.3% of the cycle when th
e foramen ovale was closed during atrial contraction. Superior vena ca
va flow passed almost exclusively into the right atrium and tricuspid
valve; a small amount that was refluxed from the right atrium into the
inferior vena cava subsequently passed through the foramen into the l
eft atrium. Conclusions Visualization of fetal circulatory streaming a
t the venous sites by ultrasound techniques aids in understanding the
function of the fetal circulation and may be helpful in detecting the
human fetus that is hemodynamically compromised.