Abstract

The normal range for pH in the human body is 7.35-7.45. When pH falls below 7.3, it is considered as severe acidemia. Acidemia, together with increased blood lactate concentrations (hyperlactatemia) constitute a severe threat to life, which is often referred to as lactic acidosis. The feasibility of near infrared transmission/reflectance spectroscopy as a tool to determine lactate concentration levels and pH, independently, has been well established. However, the effects on spectral features arising from simultaneous variations in pH and lactate are not fully understood. Hence, this paper reports on a spectroscopic study of 37 different lactate concentrations that were prepared at three different pH levels (7.4, 7.0 and 6.5). Near infrared spectra were acquired in the range 800-2500 nm, and were later divided into four spectral ranges. Further investigations were carried out on various wavelengths within each spectral range and sample set. Furthermore, partial least squares regression with cross-validation was performed on all data sets. The results showed a clear interdependence and overlapping spectral behavior between blood lactate concentrations and pH. The findings from this study suggest that for an accurate estimation of blood lactate using this technique, the pH of the sample must be previously known.

© 2020 The Author(s)

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