1149 Umbilical vein blood flow determination in the ovine fetus: Comparison of Doppler ultrasonographic and steady-state diffusion techniques Henry L. Galan, MD, a Maciej Jozwik, MD, PhD, c Serena Rigano, MD, d Timothy R.H. Regnault, PhD, b John C. Hobbins, MD, a Frederick C. Battaglia, MD, b and Enrico Ferrazzi, MD d Denver, Colorado, Bialystok, Poland, and Milan, Italy OBJECTIVE: This study was undertaken to assess the accuracy of triplex ultrasonographic measurement of venous umbilical blood flow in comparison with the steady-state diffusion technique and to determine the im- pact of cotyledon weight and number on umbilical blood flow. STUDY DESIGN: Six late-gestation ewes with long-term catheter placement were studied for venous umbili- cal blood flow with the ethanol steady-state diffusion technique and with triplex-mode ultrasonography (color Doppler, pulsed-wave Doppler, and real-time ultrasonography).At necropsy the number and weight of the cotyledons serving each umbilical vein were recorded. RESULTS: Umbilical blood flow determined by triplex-mode ultrasonography (207.5 ± 8.6 mL · kg –1 fetus · min –1 ) was virtually identical to that determined with the steady-state diffusion technique (208.1 ± 7.3 mL · kg –1 fetus · min –1 ; P = .9). When values were normalized for the weight or number of cotyledons serving each vein, there was no difference in umbilical blood flow between small and large umbilical veins in all the sheep. CONCLUSIONS: Our study validates the accuracy of the triplex ultrasonographic method and provides justi- fication for its use in future human investigations. In absolute terms umbilical blood flow frequently differs be- tween the 2 veins.When expressed per number or mass of cotyledons, however, the umbilical blood flows are similar. (Am J Obstet Gynecol 1999;181:1149-53.) Key words: Fetus, ovine, placenta, ultrasonography, umbilical blood flow, umbilical vein Umbilical blood flow is a basic and important physio- logic determinant that has been studied extensively in animal models. 1-10 A smaller number of investigations have focused specifically on the venous side of the circu- lation. 4-7, 9, 10 A commonly used technique in these ani- mal studies to determine blood flow has been the steady- state diffusion technique, which is based on the Fick principle and uses several available blood flow indicators, such as tritiated water, ethanol, or antipyrine. 4, 11, 12 Other methods for measuring umbilical blood flow have included the umbilical venoarterial oxygen difference according to the Bohr principle, electromagnetic trans- ducers, microspheres, thermodilution, and d ye dilution. 4-7, 10 These techniques for measuring blood flow have largely used invasive approaches that involve la- parotomy and catheter or flow probe placement with the subject under regional anesthesia. As a result these ap- proaches are laborious and time-consuming. Noninvasive determination of blood flow became available with the advent of ultrasonography. B-mode imaging and continuous Doppler ultrasonography were first to arrive in the late 1970s. 13-15 However, these tech- niques were complicated by the complex equipment and the time needed to obtain necessary measurements. For blood flow calculations to be accurate, precise measure- ments of the vessel radius and the mean velocity are re- quired. However, the precisions of the diameter and ve- locity measurements in these early studies were limited by technology. Because the radius is squared in the cal- culation of blood flow, the vessel area calculation is ex- tremely sensitive to error. As a result the limited imaging resolution of the 1970s may have introduced major error. 16 Another source of error comes from the fact that accurate velocity estimates require that the angle be- tween Doppler beam and direction of blood flow be <20 From the Division of Perinatal Medicine, Departments of Obstetrics and Gyn ecology a and Pediatrics, b University of Colorado, the Department of Gynecology, Bialystok Medical University, c and the Department of Obstetrics and Gynecology, University of Milan. d Supported by National Institutes of Health Program Project Grants PO1 HD20761 and 1RO1 HD34837, March of Dimes Grant 6-F497-0174, and the American Association of Obstetricians and Gynecologists Foundation. Presented at the Nineteenth Annual Meeting of the Society for Maternal- Fetal Medicine, San Francisco, California, January 18-23, 1999. Reprint requests: Henry L. Galan, MD, Assistant Professor, Department of Obstetrics and Gynecology, University of Colorado Health Sciences Center, 4200 E 9th Ave, Campus Box B-198, Denver, CO 80262. Copyright © 1999 by Mosby, Inc. 0002-9378/99 $8.00 + 0 6/ 6/ 102316