Adaptation of laser-Doppler flowmetry to measure cerebral blood flow in the fetal sheep

The purpose of this study was to devise a means to use laser-Doppler flowme try to measure cerebral perfusion before birth. The method has not been use d previously, largely because of intrauterine movement artifacts. To minimi ze movement artifacts, a probe holder was molded from epoxy putty to the co ntour of the fetal skull. A curved 18-gauge needle was embedded in the hold er. At surgery, the holder, probe, and skull were fixed together with tissu e glue. Residual signals were recorded after fetal death and after maternal death 1 h later. These averaged <5% of baseline flow signals, indicating m inimal movement artifact. To test the usefulness of the method, cerebral fl ow responses were measured during moderate fetal hypoxia induced by giving the ewes similar to 10% oxygen in nitrogen to breathe. As fetal arterial Po , decreased from 21.1 +/- 0.5 to 10.7 +/- 0.4 Torr during a 30-min period, cerebral perfusion increased progressively to 56 +/- 8% above baseline. Per fusion then returned to baseline levels during a 30-min recovery period. Th ese responses are quantitatively similar to those spot observations that ha ve been recorded earlier using labeled microspheres. We conclude that cereb ral perfusion can be successfully measured by using laser-Doppler flowmetry with the unanesthetized, chronically prepared fetal sheep as an experiment al model. With this method, relative changes of perfusion from a small volu me of the ovine fetal brain can be measured on a continuous basis, and move ment artifacts can be reduced to 5% of measured flow values.