ASSESSMENTS OF FETAL SWALLOWED VOLUME - TRACER DISAPPEARANCE VERSUS ESOPHAGEAL FLOW

OBJECTIVE: We sought to compare fetal swallowed volume determinations simultaneously by two techniques-amniotic fluid (AF) tracer disapperan ce and esophageal flow probe measurements. METHODS: Six ovine fetuses (129 +/- 1 days) were chronically prepared with a thoracic esophageal flow probe and vascular and two AF catheters. I-125-labeled albumin wa s injected into the AF cavity, and samples weve withdrawn at timed int euvals for 8 hours. The AF volume was calculated by time-0 extrapolati on of the semilog of I-125 disapearance. Tracer-determined swallowed v olume was calculated as the product of AF volume and the slope of isot ope disappearance. Flow probe measurement of swallowed volume was dete rmined by computer integration of calibrated flow probe velocity recor dings. RESULTS: The AF volume averaged 805 +/- 168 mL. The isotope dis appearance rate from the AF war 2.8 +/- 0.4%/hour. Average tracer-dete rmined swallowed volume (547 +/- 113 mL/day) was greater than flow pro be volume (366 +/- 81 mL/day), although these values weve not signific antly different. However, when corrected for estimated swallowed lung fluid, tracer-determined volume was significantly greater than flow pr obe volume (P < .05). CONCLUSION: Ovine fetal swallowed volume determi nations by AF tracer techniques ave greater than those determined by e sophageal flow probe measurements.