RENAL HEMODYNAMICS - LONGITUDINAL-STUDY FROM THE LATE FETAL LIFE TO ONE-YEAR OF AGE

Objective: To evaluate longitudinally the renal circulation from late gestation to the first year of life in order to understand fundamental changes within this vascular bed as the fetus adapts to major circula tory changes occurring during this time period. Methods: Sixteen healt hy human fetuses were studied during the last trimester of the pregnan cy, within 2 days of birth, at 6 weeks, at 6 months, and at 1 year. Us ing noninvasive color pulsed Doppler, blood flow velocities of the ren al artery, the tricuspid and mitral valves In the fetus, and in the as cending aorta in the newborn/infants were obtained at each study, Diam eters of these respective areas were also obtained. Total cardiac outp ut and renal blood flow were calculated using the time velocity integr al, the area of the structure of interest, and heart rate. Results: 1) Renal artery dimensions, time velocity integral, peak flow velocity, systolic to diastolic ratio, absolute volume blood flow (RVBF) were al l significantly correlated with advancing gestational age; 2) RVBF rel ative to body weight and percent RVBF were not. Conclusions: In spite of an over-all increase in renal blood flow, flow to the kidney appear s to be constant during the time period of this study. Most of the ''m aturational'' changes that occur within this vascular bed appear to be related to changes within the vascular resistance and the renal arter y diameter.