During cardiopulmonary bypass (CPB) because of weak arterial pulsation, near-IR spectroscopy (NIRS) is almost the only available method to monitor cerebral oxygenation noninvasively. Our group develops a NIRS oximeter to monitor regional cerebral oxygenation especially its oxygen saturation (rScO2). To achieve optimal coupling between the sensor and human brain, the distances between the light source and the detectors on it are properly chosen. The oximeter is calibrated by blood gas analysis, and the results indicate that its algorithm is little influenced by either background absorption or overlying tissue. We used it to measure the rScO2 of 15 patients during CPB. It is shown that rScO2 is negatively correlated with body temperature and positively with perfusion rate. There are two critical stages during CPB when rScO2 might be relatively low: one is the low-perfusion-rate stage, the other is the early rewarming stage. During cooling, the changes of total hemoglobin concentration (CtHb) compared with its original value is also monitored. It is shown that CtHb decreases to a small extent, which may mainly reflect cerebral vasoconstriction induced by cooling. All these results indicate that NIRS can be used to monitor cerebral oxygenation to protect cerebral tissue during CPB.
We investigate the optical properties of the brain in 23 neonates in vivo using a frequency domain near-infrared spectroscopy (NIRS). In this study, a calibration procedure is employed to determine the absorption and reduced scattering coefficients with single source-detector separation. The absorption coefficients of the infant foreheads are lower than the values reported in adults. A large intersubject variation in the reduced scattering coefficients is also demonstrated. Furthermore, physiological parameters are derived from the absorption coefficients at two wavelengths (788 and 832 nm). The mean total hemoglobin concentration (THC) is 39.7±9.8 µM and the mean cerebral blood oxygen saturation (StO2) is 58.7±11.2%. Our preliminary results show that this bedside frequent domain NIRS could provide quantitative optical measurement of the infant brain.
The value of cerebral oxygenation saturation is important for optimal treatment and prognosis in neonates during perinatal period. The purpose of this study was to investigate the cerebral oxygen in newborn infants and obtain clinical characteristic parameters by using steady state spatially resolved near infrared spectroscopy. The subjects consist of 239 infants selected from two hospital. The results show that the values of regional cerebral oxygen saturation (rSO2) for preterm infants with gestational ages of 27 - 32 weeks were different from term infants and the value of rSO2 for sick term infants after treatment were better than that of before treatment. Above results suggest that the value of rSO2 may be used as a clinical parameter to assess cerebral oxygen for preterm and sick infants avoiding hypoxia.
The physiological meaning of cerebral oxygen saturation absolute values and the oxygen metabolism of piglet with hypoxia-ischemia (HIE) were researched. The subjects were two piglets. During the total experiment of hypoxia then recovery, the regional cerebral tissue oxygen (rScO2), pulse oxygen saturation (SpO2) were detected non-invasively and the jugular oxygen saturation (SjO2), arterial oxygen saturation (SaO2) were given invasively. The results show that because SjO2 was equal to or larger than rScO2 and SaO2 > ScO2, rScO2 cannot be determined by the weighted sum of SjO2 and SaO2 which had been presented in some papers. According to above-mentioned analysis, the ecchymoma and pathological changes of the vessels due to HIE may be another contribution of rScO2. SjO2 was correlated with SaO2 (R=0.996 and 0.962 for two piglets) and the values of (SaO2-SjO2) are close to constants (29.3±8% and 30.3±8%).It means that because the subjects were under anesthesia, the oxygen consumption of cerebral tissue kept constants.
Linear CCDs three-dimensional measurement system is constituted with three one dimensional imaging units (ODIUs) composed of charge-couple device (CCD) linear image sensor paired with equivalent cylindrical lens cells. The cylindrical lens is needed for optical transformation from object point to its realistic image line in the ODIU, and the imaging quality of equivalent cylindrical lens (width and distortion aberration of the image line) directly affected the reconstruction precision of three dimension coordinates. At present, the methods of how to design an equivalent cylindrical lens with both high precision and wide field of view were not reported in literatures. An improved Double Gauss structured lenses by replacing the first spherical lens in the traditional Double Gauss lenses with a cylindrical lens is introduced to realize the point to line optical transformation and aberration adjustment. The coma aberration and distortion can be automatically adjusted due to the structure symmetry of composite lenses, and the spherical aberration, astigmatism and curvature of field can also be largely adjusted by appropriately selecting material, luminous flux, curvature, thickness, and distance of lenses. Under the computer simulating by Zemax (an optical systems design software), the composite cylindrical lens was designed and fabricated. Finally, the three-dimensional positioning system made up of above-mentioned composite cylindrical lens and corresponding circuits is constructed, and the direct linear transformation (DLT) is adopted to three dimension coordinated reconstruction. The result of reconstruction error of X, Y, Z axis with in the view field of 700x760x500 mm less than 1mm are obtained.
In recent studies, near-infrared spectroscopy (NIRS) has been considered as a potentially ideal noninvasive technique for the postoperative monitoring of plastic surgery. In this study, free flaps were raised on rhesus monkeys' forearms and oxygen delivery to these flaps was monitored following vascular occlusions and inhalation of pure oxygen. Optical fibers were adopted in the probe of the oximeter so that the detection could be performed in reflectance mode. The distance between emitter and detector can be adjusted easily to achieve the best efficacy. Different and repeatable patterns of changes were measured following vascular occlusions (arterial occlusion, venous occlusion and total occlusion) on flaps. It is clear that the near-infrared spectroscopy is capable of postoperatively monitoring vascular problems in flaps. NIRS showed high sensitivity to detect the dynamic changes in flaps induced by inhalation of pure oxygen in this study. The experimental results indicated that it was potential to assess tissue viability utilizing the dynamic changes induced by a noninvasive stimulation. It may be a new assessing method that is rapid, little influenced by other factors and brings less discomfort to patients.
Various NIRS studies have evaluated brain activity with intriguing and promising results. In this paper, results of an experiment using NIRS to evaluate brain activation induced by mental subtraction are discussed. The investigation evaluates activation responses of three NIR parameters, oxygenated- hemoglobin (Oxy-Hb), deoxygenated-Hb (Deoxy-Hb), and total-Hb (Tot-Hb). NIRS parameters were sensitive to mental subtraction; however, they were not sensitive to subtle variations in task difficulty. An important result was that order of presentation was significant, with activity during the first task being far greater than during the second task. Such findings raise questions about how to design cognitive studies using multiple task approaches commonly applied in brain activation research. A second topic addresses in this research was how to reduce brain activity during recovery. During nontask interval, subjects either rested or counted, which was used to reduce post-task mental activity. The nontask interval before mental subtraction (interval #1) was always lower than that of the two nontask intervals that followed cognitive performance (intervals #2 and 3). Recovery after activation was incomplete, regardless of type of nontask procedure. This suggests that recovery is still an issue needing elucidation and consideration in future designs.
Its very important to improve the sensitivity of the near- infrared tissue oximeter during practical non-invasive measurement on human muscle. It has been thought that this sensitivity is influenced by the existence of overlying tissues such as skin and fat because only those photons which have passed through the muscle bring back useful information. In this paper, the influences of fat layer, detecting distance, wavelength, and the oxygenation in muscle on photon partial path length in muscle layer are discussed based on Monte-Carlo simulation results. Also examined are the statistical error in simulation and the noise in detector. Finally, the experimental results of the cuff occlusion on forearm are given. The results show the relationship between the sensitivity of the tissue oximeter and the detecting distance, which has the same tendency as the simulation predicted.
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