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

Abstract

The purpose of this study was to devise a means to use laser-Doppler flowmetry to measure cerebral perfusion before birth. The method has not been used previously, largely because of intrauterine movement artifacts. To minimize movement artifacts, a probe holder was molded from epoxy putty to the contour of the fetal skull. A curved 18-gauge needle was embedded in the holder. At surgery, the holder, probe, and skull were fixed together with tissue glue. Residual signals were recorded after fetal death and after maternal death 1 h later. These averaged <5% of baseline flow signals, indicating minimal movement artifact. To test the usefulness of the method, cerebral flow responses were measured during moderate fetal hypoxia induced by giving the ewes approximately 10% oxygen in nitrogen to breathe. As fetal arterial PO(2) 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. Perfusion then returned to baseline levels during a 30-min recovery period. These responses are quantitatively similar to those spot observations that have been recorded earlier using labeled microspheres. We conclude that cerebral perfusion can be successfully measured by using laser-Doppler flowmetry with the unanesthetized, chronically prepared fetal sheep as an experimental model. With this method, relative changes of perfusion from a small volume of the ovine fetal brain can be measured on a continuous basis, and movement artifacts can be reduced to 5% of measured flow values.

Effect of Mild Hypothermia and Hypoxia on Blood Flow and Oxygen Consumption of the Fetal Sheep Brain

“…In the present study, hypoxia resulted in an approximately 25% increase in cerebral blood flow compared with 40 to 50% increases of flow observed in similar aged fetuses using identical laser Doppler methods (12,19). Thus, there are some indications of preconditioning effects of hypothermia on flow responses 3 to 6 d later, but further studies are clearly needed to explore such a phenomenon.…”

“…For measurement of cerebral perfusion, laser Doppler flowmetry probes (type LDF100A; Biopac Systems, Santa Barbara, CA, U.S.A.) were inserted to a depth of 5 mm below the dura into the parasagittal parietal cortex through 0.5-mm burr holes drilled 5 mm lateral to the midline and 20 mm posterior to the coronal suture. Details of this method have been described previously (12). Thermocouples (type IT-23; Physitemp), for measurement of brain temperature, were inserted to the same depth through burr holes in the cerebral cortex 15 mm anterior to the laser Doppler flow probe.…”

“…The cooling with hypoxia protocol (n ϭ 13) consisted of an initial 30-min baseline period and then a 2-h period of cooling as described above for the cooling control protocol with the addition of a superimposed 30-min period of hypoxia beginning 1 h after the start of cooling. Hypoxia was administered by having the ewe breathe 10 to 11% O 2 in a balance of N 2 passing rapidly (30 L/min) through a plastic bag placed over her head as previously described (12). The hypoxic interval was followed by a 30-min recovery period while cooling was continued and then a 1-h recovery period without cooling.…”

Key Neuroprotective Role for Endogenous Adenosine A 1 Receptor Activation During Asphyxia in the Fetal Sheep

“…21,22 Through a midline abdominal incision, the uterus was opened. ECG electrodes were placed to record heart rate.…”

Absence of Robust Ischemic preconditioning by Five 1-minute total Umbilical Cord Occlusions in Fetal Sheep

“…We inserted the LDF probes, embedded in an epoxy holder, through 0.5-mm burr holes 5 mm right and left of the midline and 20 mm anterior to the lambda, at a depth of 5 mm below the dura, and fixed the holder in place with tissue glue, as previously reported. 17 We inserted the thermocouples through drill holes 5 mm right and left of the midline, 25 mm anterior to the lambda, at a depth of 5 mm below the dura, and fixed them in place with tissue glue, as previously reported. '8 We inserted an 18-gauge polyvinyl catheter and a thermocouple in the fetal brachial artery and a catheter in the amniotic fluid compartment.…”