Spectrometric measurements in the anterior eye vasculature of the albino rabbit--a study with the EMPHO I

Anaemia and Haemoglobin Status: A New Concept and a New Method of Assessment

Traditionally, anaemia has been determined and interpreted by the magnitude and severity of iron deficiency and the impact of intervention strategies. Internationally, it is defined as a state in which the quality and/or quantity of circulating red cells are reduced below a normal level The body employs several mechanisms during the development of anaemia to maintain the oxygen supply to the tissues. Thus, applying any quantitative cut-off point as an indicator for anaemia may lead to misclassification, since haemoglobin concentration does not necessarily reflect the level of tissue oxygen supply. Ideally, an assessment strategy should be able to determine both the degree of haemoglobin oxygenation and the haemoglobin concentration at a tissue level. The Erlangen microlight-guide spectrophotometer is a non-invasive instrument that can assess both capillary blood oxygenation and relative haemoglobin concentration.

A scanning technique to measure regional cerebral blood flow and oxyhemoglobin level

OBJECTIVE

The application of a laser scanning technique to measure regional cerebral blood flow (CBF) and tissue hemoglobin oxygenation (HbO2) using the rat closed cranial window preparation is described.

METHODS

Twenty-nine male Wistar rats were used to consecutively measure local CBF by laser Doppler flowmetry and tissue HbO2 by a microspectrophotometric method at multiple corresponding cortical locations. The scanning technique used a computer-controlled micromanipulator. Data from three experimental models are presented: the whisker stimulation model, the ischemia-reperfusion model, and the sinus-vein thrombosis model. Sequential changes in local CBF and HbO2 data before, during, and after stimulation, ischemia, and sinus thrombosis were examined. Data from predefined locations within the same region were correlated with the topographical location and then arranged in a three-dimensional image.

RESULTS

In the whisker stimulation model, we found a disproportionate increase in CBF (32 +/- 12%) as compared with that of HbO2 (9 +/- 4%) during stimulation. In the ischemia-reperfusion model, the three-dimensional image showed heterogeneous low CBF (depending on the area) and homogeneous HbO2 at a reduced level during ischemia and postischemic hyperperfusion. However, the range of oxygenation was normal after reperfusion. In the sinus-vein thrombosis model, drainage of the unsaturated blood via the collateral pathways was noted.

CONCLUSION

The laser scanning technique is useful for visualizing sequential changes in hemodynamic-metabolic interactions of cortical brain tissue. This technique can reveal phenomena not detected by traditional monitoring procedures.

Effects of elevated intraocular pressure on haemoglobin oxygenation in the rabbit optic nerve head: a microendoscopical study

Intraocular pressure dependent reactions of optic nerve head vasculature and intracapillary haemoglobin oxygenation (HbO(2); oxygen saturation) were studied in the center and at the rim of the rabbit optic nerve head (ONH) as well as in the choroid, by a new combination of microendoscopy and simultaneous haemoglobin spectrophotometry. In 13 anesthetized albino rabbits the vasculature and the intracapillary Hb-oxygenation were studied by a microendoscope which was introduced into the eye bulb. Photometric measurements were performed via a beam splitter with the Erlangen micro-lightguide spectrophotometer (EMPHO) from the center of the endoscopic picture. The haemoglobin oxygenation was calculated by real time analysis of the spectral curves. Intraocular pressure was elevated stepwise from 20-80 mmHg. At the rim of the optic nerve head the vascular diameters as well as the intracapillary HbO(2)-values were stable till an intraocular pressure of 60 mmHg and decrease after IOP elevation to 70 and 80 mmHg. In contrast, in the center of the optic nerve head and in the choroid these parameters decline already from 40-50 mmHg on. At an IOP of 60 mmHg (P<0.01) and 70 mmHg (P<0.05) HbO(2)is significantly lower in the ONH center than at the rim. In the center and the choroid HbO(2)is well maintained between 20 and 40 mmHg. After pressure release at the end of the experiment HbO(2)increased to 94.3+/-4.6% (rim) and 98.8+/-1.5% (center) of the initial value at 20 mmHg (difference not significant).By the high spatial resolution of this new optical method we were able to demonstrate that the center of the optic nerve head is more sensitive to changes in intraocular pressure than the optic nerve head rim. Thus, tissue damage after critical haemodynamic and oxygenation parameters seems more probable in the relatively poor perfused center of the ONH than in the overperfused rim.

Electronic light microscopy combined with spectrophotometry allows real-time analysis of structures at the subcellular level

A combination of microscopy (video-enhanced contrast microscopy) and spectrophotometry (which analyses online the spectra from the microscopic picture) is presented. This set-up allows the in vivo microscopic observation of cellular and subcellular structures as well as simultaneous online determination of cellular chromophores. To test our equipment we measured spectra of isolated red blood cells and NG 108-15 cells and correlated these spectra with the corresponding video-enhanced microscopic picture. By labelling specific cell organelles of astrocytes with in vivo fluorescent dyes, we visualized mitochondria and captured the corresponding spectra.

A combination of microendoscopy and spectrophotometry allowing real-time analysis of microcirculatory parameters during in vivo observations

A combination of microendoscopy (which is a modification of endoscopy with fine rigid endoscopes) and spectrophotometry (which analyses on line the remission spectra from the endoscopic picture) is presented. This setup allows the endoscopic in vivo observation of haemodynamics as well as simultaneous on line determination of intravascular haemoglobin oxygenation. Furthermore, the clearance of intravasally applied tracers can be analysed. Application, results and further evaluation of this new technique are demonstrated in the retinal vessels of the albino rabbit.