Cerebral tissue oxygenation during hypoxia and hyperoxia using artificial placentation in lamb

Differential gene expression of aldolase C (ALDOC) and hypoxic adaptation in chickens

Two sequence variants of the aldolase C (ALDOC) gene were discovered based on comparison of the sequences from an altiplano chicken breed (Tibetan chicken) and two lowland breeds (White Leghorn and ShouGuang). Gel-shift results indicated that one of these variants, L25375:c.310-258G>A, was able to bind hypoxia-induced factor-l (HIF1A), therefore, functioning as a hypoxia response element (HRE). The combined activity of the HRE and HIF1A could increase under the influence of a hypoxic stimulus. Hypoxia leads to increased death rates of chicken embryos, while the L25375:c.310-258G>A described herein is prevalent in healthy embryos grown under hypoxic conditions. Fluorescence quantitative real-time PCR results revealed that HIF1A upregulated the transcript level of the glycolytic enzyme ALDOC in the brain and skeletal muscle of animals subjected to hypoxia. Thus, a large amount of ATP is produced by increased glycolysis, allowing the organism to meet energy metabolism demands. As such, we believe this sequence variant is an adaptation to external anoxic environment.

Laserspectroscopy in the fetus during labour

The newly available modified laserspectroscopy for fetal physiologic measurements provides information about biochemical parameters and is potentially an additional technique for fetal surveillance.

METHOD

Using laserspectroscopy it was possible to trace changes in absorbances at four different wavelengths and to calculate relative changes of HbO2, desaturated haemoglobin, total haemoglobin, and cytochrome aa3. Using an experimental set-up with fetal lamb during intermittend cord occlusion, we were able to study tissue oxygenation of the fetal brain (tpO2) under defined conditions. Furthermore, the NIR sensor was used during physiologic measurements in the human fetus.

RESULTS

As had been proposed earlier, it is obvious that the tolerance to hypoxia is increased after cord compression is repeated, as is indicated by the shifting of the cytochrome dissociation curve to the left. In the human fetus without fetal distress we observed stable values with only minor fluctuations related to changes of intrauterine pressure. On the other hand, in cases where there was an intrauterine complication the deterioration of oxygenation was detected form a decrease in HbO2 and cytochrome aa3.

DISCUSSION AND CONCLUSION

The routinely used CTG has been criticised for the effect of leading to an unacceptably high number of cesarean sections. Information on biochemical variables leads to better identification of fetal distress. In comparison to fetal blood sampling NIR laserspectroscopy holds the promise of a non-invasive tool providing continues monitoring.

In vivo near-infrared spectroscopy

Interrogation of tissue with light offers the potential for noninvasive chemical measurement, and penetration with near-infrared wavelengths (750-1000 nm) is greater than with visible light. Specific absorption by clinically relevant compounds such as oxy- and deoxyhemoglobin and the intracellular respiratory enzyme cytochrome oxidase enable in vivo measurement of these to be performed safely and conveniently. This is the basis of in vivo near-infrared spectroscopy (ivNIRS). Multiple scattering of the interrogating beam by tissues leads to an optical path that is considerably longer than the simple physical pathlength and this complicates the analysis. Modeling of photon propagation through tissues with, for example, finite element and Monte Carlo methods, is assisting in improving the ivNIRS methodology. Instrumentation has advanced from simple continuous wave approaches, through time-resolved methods based on either time-domain or frequency-domain approaches, to spatially resolved measurement based on diffuse reflectance. Initial clinical applications were for monitoring the brain in the neonate and fetus and muscle in adults. Currently, use in adults and children for neurological assessments are of growing interest.