Chemometric determination of blood parameters using visible-near-infrared spectra.

Visible and near-infrared (NIR) integrating sphere spectroscopy and chemometric multivariate linear regression were applied to determine hematocrit (HCT) and oxygen saturation (SatO2) of circulating human blood. Diffuse transmission, total transmission, and diffuse reflectance were measured and the partial least squares method (PLS) was used for calibration considering different wavelength ranges and selected optical measurement parameters. HCT and SatO2 were changed independently. Each parameter was adjusted to different levels and four designs with blood from different donors were carried out for the calibration with PLS. The calibration included the changes in hemolysis as well as inter-individual differences in cell dimensions and hemoglobin content. At a sample thickness of 0.1 mm the HCT and SatO2 were predicted with a root mean square error (PRMSE) of 1.4% and 2.5%, respectively, using transmission and reflectance spectra and the full Vis-NIR range. Using only diffuse NIR reflectance spectroscopy and a sample thickness of 1 mm, HCT and SatO2 could be predicted with a PRMSE of 1.9% and 2.8%, respectively. Prediction of hemolysis was also possible for one blood sample with a PRMSE of 0.8% and keeping HCT and SatO2 stable with a PRMSE of 0.03%.

A novel device for the non-invasive measurement of free hemoglobin in blood bags.

The production of red blood cell concentrates from human donors is a very expensive procedure and human resources are in short supply. Under perfect storage conditions at a temperature of 2-6 degrees C, a blood bag must be used within 35-49 days (in Germany). Visual inspection of the bag for apparent hemolysis by a blood bank physician is a crucial but subjective quality control assessment. Since an interruption of the cold chain cannot be definitely ruled out, bags are often disposed of prematurely for safety reasons. There is currently no method of testing a closed blood bag with respect to hemolysis for its suitability to be used in a transfusion. The proposed optical measuring device is a hemoglobin sensor which determines the free hemoglobin in standard erythrocyte concentrates without opening the bag. The optical measurements are done on the flexible tube connected to the main bag. The optical measurements were evaluated using standard hemoglobin solutions with an accuracy of 0.005 g/dL. These investigations show that in the future each blood bag can be tested non-invasively for its content of free hemoglobin. This will contribute to decreasing the wastage rate of red blood cell concentrates.

Optical Properties of Circulating Human Blood in the Wavelength Range 400-2500 nm.

Knowledge about the optical properties µa,µs, and g of human blood plays an important role for many diagnostic and therapeutic applications in laser medicine and medical diagnostics. They strongly depend on physiological parameters such as oxygen saturation, osmolarity, flow conditions, haematocrit, etc. The integrating sphere technique and inverse Monte Carlo simulations were applied to measure µa,µs, and g of circulating human blood. At 633 nm the optical properties of human blood with a haematocrit of 10% and an oxygen saturation of 98% were found to be 0.210±0.002 mm-1 for µa,77.3±0.5 mm-1 for µs, and 0.994±0.001 for the g factor. An increase of the haematocrit up to 50% lead to a linear increase of absorption and reduced scattering. Variations in osmolarity and wall shear rate led to changes of all three parameters while variations in the oxygen saturation only led to a significant change of the absorption coefficient. A spectrum of all three parameters was measured in the wavelength range 400-2500 nm for oxygenated and deoxygenated blood, showing that blood absorption followed the absorption behavior of haemoglobin and water. The scattering coefficient decreased for wavelengths above 500 nm with approximately λ-1.7; the g factor was higher than 0.9 over the whole wavelength range. © 1999 Society of Photo-Optical Instrumentation Engineers.

Flow-dependent regulation of arteriolar diameter in rat skeletal muscle in situ: role of endothelium-derived relaxing factor and prostanoids.

1. Arteriolar diameter in the resting rat spinotrapezius muscle was studied by intravital video microscopy before and after blockade of the L-arginine-EDRF (NG-nitro-L-arginine, L-NNA) or the cyclo-oxygenase-prostacyclin (indomethacin) pathway. Blockade of either pathway leads to a decrease of arteriolar diameter of 25-40%, while the combined blockade of both results in vasoconstriction of 50-60%. 2. Alteration of blood flow velocity elicited by partial micropipette occlusion induces corresponding changes of vessel diameter. The flow-dependent diameter response is reduced by about 80% by L-NNA. By contrast, blockade of prostanoid production shows no significant influence on vessel response to blood flow alteration in the range tested. 3. Transient overshooting vasodilatation is seen for about 1 min following the sudden restoration of flow velocity subsequent to occlusion. In contrast to the initial phase of this response, the late phase is blocked by L-NNA. 4. The findings suggest that basal release of endothelium-derived relaxing factor (EDRF) and prostanoids leads to additive and independent dilator effects, and that flow-dependent diameter changes are primarily mediated by EDRF. 5. If present data are compared with literature reports, it appears that arterial flow sensitivity is most pronounced in the smallest vessels. In such vessels, flow-dependent dilatation will amplify even small changes of volume flow by more than four times.