Microcirculation plays an important role in maintaining our lives. Observing the microcirculation has been considered important in understanding the disease mechanisms and diagnosing diseases. Sidestream dark-field (SDF) imaging is one of the methods to observe the microcirculation. However, the SDF imaging has several problems for instance artifacts caused by pressure and heat. Measurement points is under pressure because SDF imaging requires direct contact with measurement points, which may affect hemodynamics. Therefore, we construct a non-contact setup. Furthermore, at the early stage of sepsis, it is known that the microcirculation is impaired. To investigate the relationship between the flow of red blood cells (RBCs) and septic shock, we conducted an experiment using the setup to observe septic model rats and sham rats. Moreover, we calculated the blood velocity to estimate the flow of RBCs by using acquired motion pictures. We confirmed that the sham rats showed slight change in lactate value during the observation and improved the blood velocity compared with just after abdominal closure. However, lactate value of the septic model rats increased and the blood velocity of septic model rats decreased. This finding suggests that microcirculatory alteration may be a sign of sepsis and septic shock progression.
Near-infrared spectroscopy (NIRS) is a noninvasive method for monitoring tissue oxygen saturation (StO<sub>2</sub>). Many commercial NIRS devices are presently available. However, the precision of those devices is relatively poor because they are using the reflectance-model with which it is difficult to obtain the blood volume and other unchanged components of the tissue. Human webbing is a thin part of the hand and suitable to measure spectral transmittance. In this paper, we present a method for measuring StO<sub>2</sub> of human webbing from a transmissive continuous-wave nearinfrared spectroscopy (CW-NIRS) data. The method is based on the modified Beer-Lambert law (MBL) and it consists of two steps. In the first step, we give a pressure to the upstream region of the measurement point to perturb the concentration of deoxy- and oxy-hemoglobin as remaining the other components and measure the spectral signals. From the measured data, spectral absorbance due to the components other than hemoglobin is calculated. In the second step, spectral measurement is performed at arbitrary time instance and the spectral absorbance obtained in the step 1 is subtracted from the measured absorbance. The tissue oxygen saturation (StO<sub>2</sub>) is estimated from the remained data. The method was evaluated on an arterial occlusion test (AOT) and a venous occlusion test (VOT). In the evaluation experiment, we confirmed that reasonable values of StO<sub>2</sub> were obtained by the proposed method.
The sidestream dark-field (SDF) imaging allows direct visualization of red blood cells in microvessels near tissue surfaces. We have developed an image-based oximetry method using two-band images obtained by SDF imaging (SDF oximetry) and a trial SDF device with light-emitting diodes to obtain band images. In this study, we propose a technique of producing oxygen saturation (SO<sub>2</sub>) maps from SDF images and perform animal experiments in vivo. To produce SO<sub>2</sub> maps, we use spectral analysis using two band images obtained with our SDF device. As an image processing, the combination of both the Hessian-based and pixel value-based techniques as blood vessel extraction from an SDF image is used. From the experiment with the surface of rat small intestines, we can produce SO<sub>2</sub> maps and find that the map represents arterioles and venules those were determined based on the blood ow from SDF images. Moreover, we find the variation of SO<sub>2</sub> along a blood vessel running direction.