| Lactate is a key metabolite of glycolytic activity and as such, can be used as an indicator of the energy production of the whole organism, for the assessment of tissue perfusion and oxidative capacity. Estimating lactate levels in biological fluids allows the determination of anaerobic threshold during physical exercise. Likewise, lactate is of significant importance in several clinical situations, where a rapid and easy method is needed for diagnostic assessment and survival rate increase of the patient.; To achieve this objective, the potential of Near Infrared Spectroscopy (NIRS) to quantify lactate in biological fluids and tissues was evaluated. Initially, the project focused on quantifying of lactate in plasma samples taken from exercising humans. Using Partial Least Squares (PLS) and a leave-N-out cross validation routine, it was found that lactate concentration in human plasma could be estimated with a standard error of cross validation of 0.51 mmol/L.; To minimize sample preparation and reduce the time of analysis, NIRS was then evaluated as a technique for rapid analysis of lactate in whole blood from exercising rats and humans. Furthermore, standard addition method was used to expand the lactate concentration range and therefore cover a greater part of the physiological lactate concentration range. Regression analysis provided standard errors of cross validation of 0.29 mmol/L and 0.65 mmol/L for rats and humans respectively.; To improve precision, referenced lactate measurements were calculated. In this method, baseline spectra of subjects were subtracted from all collected spectra before chemometric routines were used. An improvement of the standard error of cross validation to 0.21 mmol/L was found by applying this procedure.; In vivo measurement of lactate during exercise in humans by NIRS was also evaluated. Using diffuse reflectance and 2D correlation spectroscopy, lactate was identified as the primary constituent monitored by in vivo measurements. Regression analysis resulted in a substantial error of 2.21 mmol/L for absolute measurements. However, results for referenced lactate measurements provided a significant improvement of the standard error of cross validation to 0.76 mmol/L. This finding suggests that NIRS may provide a valuable tool to assess in vivo physiological status for both research and clinical needs. |
