Estimating umbilical cord flow resistance from measurements of the whole cord.

Measuring umbilical blood pressure in utero is challenging and for this reason non-invasive methods are required. However, the total vessel blood pressure drop can be estimated using numerical and empirical results by studying the mechanics of fluids in coiled and straight tubes. Two key findings emerge from such an analysis.

Pressure and flow in the umbilical cord.

A fluid dynamic study of blood flow within the umbilical vessels of the human maternal-fetal circulatory system is considered. It is found that the umbilical coiling index (UCI) is unable to distinguish between cords of significantly varying pressure and flow characteristics, which are typically determined by the vessel curvature, torsion and length. Larger scale geometric non-uniformities superposed over the inherent coiling, including cords exhibiting width and/or local UCI variations as well as loose true knots, typically produce a small effect on the total pressure drop.

Impinging laminar jets at moderate Reynolds numbers and separation distances.

An experimental and numerical study of impinging, incompressible, axisymmetric, laminar jets is described, where the jet axis of symmetry is aligned normal to the wall. Particle streak velocimetry (PSV) is used to measure axial velocities along the centerline of the flow field. The jet-nozzle pressure drop is measured simultaneously and determines the Bernoulli velocity.