Gluocose monitoring in whole blood by measuring laser-induced acoustic profiles

Time-resolved optoacoustic (OA) method was employed to measure changes in glucose concentration in the whole and diluted blood. An increase of the glucose level in tissue results in a corresponding decrease of optical scattering. Relative changes in tissue optical scattering can be obtained by measuring the effective optical attenuation coefficient, μ eff by exponential fitting of the time-resolved optoacoustic profiles. Glucose effects in blood have been investigated using the forward mode of OA detection performed in the visible (at the wavelength, λ=532 nm) and near infrared (λ=1064 nm) spectral ranges. In our previous set of experiments, the OA studies performed in model media in vitro and biological tissue (sclera) in vivo demonstrated gradual reduction of optical scattering with the increase in glucose level. The present study has supported our previous observations. However, one novel effect was observed comprised of a transient increase in μ eff during the first 5-10 minutes after injection of glucose. This phenomenon may be explained by changes in erythrocytes shape and size as a result of their adaptation to hyperglycemic conditions. Our observation was supported by light microscopy images of red blood cells under normal and hyperglycemic conditions. With glucose concentration changing rapidly (osmotic shock), any small reduction in µeff due to the glucose-induced decrease of relative refraction index of blood, can be compensated or even overwhelmed by the increase in µeff due to erythrocyte shrinkage and/or spherulation. Further cellular adaptation to glucose make erythrocytes return to their normal shape of biconcave disks about 7-μm in diameter. The kinetics of the effective optical attenuation was studies in response to glucose injection in order to better understand the mechanisms of erythrocyte adaptation to osmotic shock and to determine the time course of RBCs adaptation to various glucose concentrations. Finally, Mannitol as alternative osmolyte, which cannot penetrate through the RBC membrane, was used in the study. The effect of Mannitol on optical properties of blood was found to be even more pronounced compared to the effect of glucose. In this study, blood was chosen as an experimental medium with perspective of using the optoacoustic monitoring of glucose concentration either inside veins or in tissues that are well supplied with blood. The results of this study help in designing an optoacoustic measurement protocol for monitoring blood glucose in diabetic patients.