Acquisition of Selected Physiological Parameters with Spectral Optical Sensors

According to the Word Health Organization (WHO) cardiovascular diseases (CVDs) are the number one cause of death globally, where CVD patients need an early detection and management. The field of optical and spectral biosensors contains a huge amount of highly promising methods and approaches, which could enable the measurement of these health indicators by spectral biosensor solutions. This master thesis summarizes and reviews the commonly used methods in the field of optical blood glucose, heart rate, and blood pressure measurement. It also gives a review of non-invasive and optical biosignal acquisition using spectral sensors. Moreover, for describing the complex optical behavior of human tissue, a summary of the most important optical parameters as well as a description of the interactions between light and matter is given, where care is taken to describe the basic ways of optical tissue characterization for biooptical applications and in-vivo measurements. Considering optical blood glucose determination, spectral methods, containing near- and mid-range infrared, and Raman spectroscopy are reviewed as well as other optical and non-optical methods are summarized. The results show that no optical method for non-invasive glucose level prediction is available on the market today, although some approaches have a huge potential for detecting trends of the glucose concentration. The described photoplethysmography (PPG) represents the origin of optical heart rate monitoring (HRM), where a focus is placed on choosing the best wavelength, resulting in a preference of green light, but a persisting dependency on the target application. Moreover, next to major influences as well as limitations of HRM, heart rate variability (HRV), and pulse oximetry are discussed. Based on the PPG signal, optical blood pressure estimation methods are evaluated, which are based on the measurement of the pulse wave velocity (PWV), the pulse transit time (PTT), and pulse arrival time (PAT) approaches, considering the physiological and biomechanical properties of vessels. The results are an indicator for the possibility of a fully optical blood pressure measurement, whereas several drawbacks must be overcome.