Optical properties of whole bovine blood are examined under conditions of different glucose loadings. Partial least-squares (PLS) is used to compute calibration models for glucose from spectra collected over the combination spectral region (5000 - 4000 cm- 1) and first overtone - short wavelength spectral regions (9000 - 5400 cm-1). These models achieve a prediction accuracy of approximately 1mM. Calibration models built for specific glucose absorption regions perform better than models generated strictly from the short wavelength region in which light scattering effects dominate. Net analyte signal (NAS) analysis is employed to investigate the spectral information that forms the basis for the models. The NAS reveals the portion of the glucose spectrum that is orthogonal to the spectral variance induced by the blood matrix. To investigate the selectivity of the spectral measurements, the glucose NAS is compared to residual absorbance spectra formed after subtraction of the non-glucose variance (estimated by application of principal component analysis to a set of blood samples with endogenous glucose concentrations). A match between the NAS and the residual spectra reveals that direct information associated with absorption of light by the glucose molecule is present in the measured data. A similar comparison is made with the regression vector associated with the PLS model. A match between the NAS and regression vector confirms that the correlations encoded in the calibration model do, in fact, arise from glucose absorption information. The results obtained through this work demonstrate that NAS analysis is a valuable tool for use in investigating the selectivity of multivariate calibration models.
Optical properties of whole bovine blood are examined under conditions of different glucose loadings. A strong dependency is established between the scattering properties of the whole blood matrix and the concentration of glucose. This dependency is explained in terms of variations in the refractive index mismatch between the scattering bodies (predominately red blood cells) and the surrounding plasma, and also by variations in the size and shape of the red blood cells. Measurements in the presence of a well-known glucose transport inhibitor indicate that variations in refractive index mismatch are related to the penetration of glucose into the red blood cells. In addition, results measure the glucose dependent aggregation properties of red blood cells. In this experiment, pulsations in transmitted light intensity are explained by cycles of aggregation and disaggregation of red blood cells in response to a propagating pump wave through the blood matrix. Magnitude of these pulsations depends on the concentration of glucose in the sample. Results are also presented to characterize the time-dependent variation in light transmission in response to a step change in glucose concentration. Finally, multivariate calibration models are presented for the measurement of glucose in a whole blood matrix. These models are based on near infrared spectra and Kromoscopy data collected from eighty different samples prepared from a single whole blood matrix. The best model is generated for combination near infrared spectra, which provides a standard error of prediction is less than 1 mM over a concentration range of 3 to 30 mM.
Four-channel Kromoscopic analysis is demonstrated for in vitro measurement of glucose in cow blood in the spectral range of the first overtone of CH stretching vibrations and also the short wavelength near infrared region. The sample set included 48 blood samples with glucose concentration randomly distributed in the range 4.55 -37.60 mM. Solid glucose was added to each blood sample to create a wide range of glucose concentrations. During the measurement procedure blood was circulated through a 1 mm path length cell at a flow rate of 3 m:/min. Regular pulsations on the order of 1% were observed and corresponded to periodic aggregation and disaggregation of red blood cells under these flow conditions. Glucose can be quantified with a standard error of prediction of 1 mM over all blood samples. The impact of scattering and absorption proceses are also discussed.
The ability of Kromoscopy to measure glucose selectively is demonstrated in solutions composed glucose, urea, triacetin, bovine serum albumin (BSA), cholesterol, and hemoglobin (Hb). Kromoscopic measurements are made with a four-channel instrument designed for measuring light between 1500 and 1900 nm. The channels are configured to respond to four individual bands of near infrared light centered at 1600, 1700, 1750, and 1800 nm. An equation is proposed that describes the relative response for each channel as a function of relevant experimental parameters. This equation predicts the linear response observed for these types of measurements as a function of solute concentration. In addition, molar absorptivities are provided for glucose, urea, triacetin, BSA, Hb, and water. The non-negligible absorptivity of water demands the consideration of water displacement caused by solute dissolution. Channel responses are measured for a series of thirty-one samples. The chemical composition of these samples is designed to minimize the correlations between glucose concentration and the concentrations of all other solutes. Likewise, these samples provide negligible correlation between the concentration of glucose and the extent of water displacement. A calibration model is constructed for glucose by using a conventional P-matrix multiple linear regression analysis of the four-channel information. The resulting model demonstrates selectivity for glucose with values of 1.27 and 1.34 mM for the standard errors of calibration and prediction, respectively, over a glucose concentration range of 1.9 to 19 mM.
The selectivity of a four-channel Kromoscopic analysis is demonstrated for the measurement of glucose in separate binary and tertiary matrices. A novel virtual search procedure is used to identify three different sets of four, overlapping transmission filters. The first filter set includes filters centered at 900, 1300, 1410, and 1538 nm and is selected to differentiate glucose and urea in a series of binary mixtures. These binary mixtures were prepared with independent levels of 1-10 mM glucose and 9- 213 mM urea dissolved in an aqueous phosphate buffer solution. A second filter set contains filters centered at 1064, 1100, 1224, and 1290 nm and is used to measure glucose in a series of tertiary mixtures composed of glucose, urea and bovine serum albumin. This tertiary matrix consists of 2-13 mM glucose, 13-129 mM urea and 0.05-0.46 g/L bovine serum albumin dissolved in the same type of buffer. Multilinear regression is used to relate the relative Kromoscopic responses to the concentration of glucose in these sample solutions. In both cases, the prediction errors are on the order of 0.6-0.8 mM. The impact of solution temperature is also investigated by examining glucose responses obtained from solutions maintained at temperatures ranging from 35 to 39 degree(s)C. The filter set used in this experiment is composed of filters centered at 1100, 1150, 1254, and 1300 nm. Results from this particular filter set indicate that the directionality and magnitude of the glucose responses are independent of solution temperature. Finally, accurate glucose measurements are demonstrated when a same-temperature blank is used to generate the relative channel response.
The method and device for non-invasive measurement of blood glucose concentration based on the diffuse reflectance from the transcutaneous layers is proposed. Original normalizing ratio algorithm permitting to separate glucose absorption from absorption of other blood components is suggested. It was shown that the influence of water and some other components such as hemoglobin, albumin, globulin's and cholesterol concentration variations to the estimation of the glucose concentration can be compensated using spectral analysis of the reflection on several specially selected wavelengths and proposed algorithm. Device with optical geometry minimizing the effects of changes in the scattering background of biological tissues was developed. NIR spectral range 800 - 1800 nm was used because of its good transparency for biological tissue and presence of glucose absorption band. We used two kinds of light sources, namely LED array and Xe flash lamp. Tissue phantoms (different glucose concentration (0 - 1000 mg/dl) solutions with polystyrene beads or with milk) were used as samples. Scattering and absorption contribution to the dependence of diffuse reflection on glucose concentration was experimentally verified.
Investigations of correlation parameters of short and supershort pulse laser emission in near IR region (YAG:Nd, glass:Nd, HF lasers, and so on) collide with certain difficulties. The results of the investigation of correlation by means of nonlinear optics technique have been presented. The problems that have been solved theoretically and experimentally are: (1) temporal and spatial correlation functions; (2) pico- and femtosecond durations measurements; and (3) cross correlation functions for different frequency optical signals.
The new method of non invasive determination of blood components concentration -- bilirubin and hemoglobin -- was analyzed with the help of optic spectra of reflection from the skin surface and subcutaneous tissues. It is based on the registration of non-linear relation between optoelectronic characteristics of spectra of reflection, received and worked up for some wavelengths and concentration of studying components. This correlation is manifested most brightly and differs radically from a linear one in its sphere of relatively high concentrations with regard to patients.
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