Jason Cordell Birnholz MD, Presenter: Nothing to Disclose

Cardiac generated arterial pressure is the sole motive source for placental blood flow. A consequence of this model is the potential for noninvasive, in vivo estimation of combined cardiac output, stroke volume, and other indicators of cardiac function in the third trimester fetus from umbilical vein flow velocity, vein area, and heart rate.

Heart rate and cross sectional area and mean flow velocityof the umbilical vein (UV) are recorded in 524 fetuses at or beyond 24 weeks gestational age. Maximum mean flow velocity and minimal spectral broadening are sought with range gated pulsed Doppler at/or above 3.5 MHz and less than 10 degrees' incidence and vein area are determined from a free floating mid segment of the cord during apnea. Additional data include conventional fetal measurements. Patients were referred for clinical examination and had well established dating. Excluded from analysis were cases of aneuploidy, cardiac defects, major anomalies, and arrhythmias. Volume flow per unit time is calculated from the product of UV cross sectional area and mean velocity; stroke volume (SV) from 1/2 UVflow/HR; combined cardiac output (CO) from UVflow/min/0.22, and kinetic energy is estimated from 1/2 (UV mean velocity)².

UV cross sectional area and flow velocity could be measured in every case. Average calculated combined CO was 480 ml at 24 weeks, 1200ml @32 weeks, 1514ml @36 weeks, and 1770 ml @40 weeks. SV and CO and GA and KE estimates were not correlated. Idealized ventricular SV was 2.27 ml at 24 weeks, 4.38 ml at 32 weeks and 6.75 ml at 40.0 weeks GA.Descriptive equations and confidence limits are developed, and correlations are explored between CO, SV, GA, fetal weight, and KE.

UV area, flow velocity, and heart rate are readily and precisely determined under clinical practice conditions enabling several parameters of cardiac function for potential diagnostic study. Calculated values for CO and SV are in close accord with measured animal values and with published human estimates from Doppler calculations from both outflow tracts.

Birnholz, J, Noninvasive Estimation of Combined Cardiac Output and Stroke Volume in the Third Trimester Fetus from Technically Simple Ultrasonic Measurements.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4403949.html