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BACKGROUND: The hemodynamic variations of cardiac and cerebral blood monitoring during pneumoperitoneum and head-down tilt position in general anesthetized elderly patients remain unresolved. We evaluated the time course of cerebral tissue oxygen saturation (SctO2) and cardiac output (CO) and investigated how the changes in hemodynamic values during the surgery would affect cerebral perfusion in elderly patients. METHODS: In this prospective observational study of 47 elderly patients (≥65 years old, American Society of Anesthesiologists Physical status I to III) undergoing laparoscopic colorectal radical resection with head-down position, SctO2 by near-infrared spectroscopy and arterial pressure-based cardiac output (APCO), Cardiac index (CI), stroke volume (SV), and SV index (SVI) according to FloTrac/Vigileo were measured at 9 time points. Heart rate (HR), mean arterial blood pressure (MAP), end-tidal carbon dioxide (ETCO2), bispectral index (BIS), central venous pressure (CVP), and ventilator settings were recorded. Results are reported as medians [95% confidence interval (CI)]. RESULTS: Heart Rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), MAP, CO, CI, SV, SVI, and SctO2 before incision decreased significantly compared with the waking state (P<0.05). SBP, CO, CI, SV, and SVI before incision decreased significantly compared with induction and intubation (P<0.05). SBP, DBP, MAP, and CVP increased significantly after pneumoperitoneum and head-down tilt, and then decreased during the following hour. CO and SVI decreased, while CI and SV increased after pneumoperitoneum and head-down tilt. CO, CI, SV and SVI decreased at the following 20, 40, and 60 minutes respectively. SctO2 increased after pneumoperitoneum and head-down tilt and remained stable during the following hour. CVP decreased while CO, CI, SV, and SVI increased significantly at the end of pneumoperitoneum and head-down tilt (P<0.05). HR and MAP increased significantly at the end of surgery compared to at the end of pneumoperitoneum and head-down tilt (P<0.05). CI was associated with SctO2 as indicated by a Pearson r of 0.035 (P<0.05). CONCLUSIONS: Anesthesia, pneumoperitoneum, and head-down tilt affect cardiac function and cerebral perfusion in elderly patients. cardiac index independently affects elderly patients' cerebral blood flow.

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BACKGROUND: Modified ultrafiltration (MUF) can be performed in infants with ventricular septal defects (VSDs) after cardiopulmonary bypass (CPB) to reduce haemodilution and its potential adverse effects. High-flow MUF might reduce ultrafiltration duration and hasten the necessary correction of haemodilution during CPB. However, its influence on brain oxygenation remains controversial. OBJECTIVE: This non-randomized, prospective, pilot study aimed to investigate the influence of high-flow MUF on brain oxygenation in infants with VSDs. METHODS: High-flow MUF (≥20 mL/kg/min) was performed in twenty infants. Brain oxygen saturation (rSO2) and tissue haemoglobin index (tHI) were non-invasively and continuously measured intraoperatively using near-infrared spectroscopy (NIRS). Transcranial Doppler non-invasively detected the mean flow velocity of the middle cerebral artery (Vmean). RESULTS: rSO2 increased significantly during MUF, as did tHI, Vmean, mean arterial pressure and haematocrit (all p<0.05). No correlation was found between changes in rSO2 and changes in other parameters (all p≥0.05). CONCLUSION: In infants with ventricular septal defects managed with CPB during VSDs repair, high-flow MUF did not reduce brain oxygenation.

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Near-infrared spectroscopy (NIRS) was used to investigate the cerebral oxygenation of Moyamoya and healthy subjects. Continuous recordings of NIRS signals for 20 min (20 min signals) were obtained from 17 healthy subjects (age: 37.4 ± 11.3) and 17 Moyamoya subjects (age: 40.1 ± 11.2). Spectral analysis based on wavelet transformation identified five frequency intervals (I, 0.0095 Hz to 0.02 Hz; II, 0.02 Hz to 0.06 Hz; III, 0.06 Hz to 0.15 Hz; IV, 0.15 Hz to 0.40 Hz; and V, 0.40 Hz to 2.00 Hz) in the 20 min signals and three frequency intervals (III, 0.06 Hz to 0.15 Hz; IV, 0.15 Hz to 0.40 Hz; and V, 0.40 Hz to 2.00 Hz) in the 3 min signals (the first 3 min signals were continuously extracted from the 20 min signals). Significant differences (p < 0.05) were found in frequency intervals III and V. The former exhibited the myogenic activity of smooth muscle inside the blood vessels in both 20 min and 3 min signal analyses; the latter showed hemodynamic oscillation caused by heart pumping. This finding agrees with the vascular pathological changes in Moyamoya disease. As a potential screening method for Moyamoya disease, the simple threshold method exhibited 73.5% accuracy.

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To study the changes of cerebral oxygenation and hemodynamics in normal neonates at 2-5 min post-birth and understand the effects of pregnancy-induced hypertension (PIH) upon cerebral oxygenation and hemodynamics in newborn neonates. The near infrared spectroscopy (NIRS) was employed to measure the absolute quantity of brain tissue oxygen saturation (rSO2) in newborn neonates and the changes of concentrations of deoxyhemoglobin (Hb) and oxygenation hemoglobin (HbO2) with time relative to initial values to further obtain the changes of total hemoglobin (tHb) and cerebral perfusion (denoted by HbD). In normal neonates at 2-5 min post-birth, rSO2 increased while tHb remained relatively stable and HbD increased. In neonates born of PIH mothers at 3-5 min post-birth, the changes of tHb were markedly higher than those in the normal infants, p<0.05; at 2-5 min post-birth, the changes were markedly lower than the normal term infants. We concluded that NIRS can detect the changes of cerebral oxygenation and blood flow in a non-invasive and effective way.

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Based on the principles of organizational optics, the noninvasive tissue oxygenation saturation monitor was developed. The monitor was used to continuously monitor the changes in regional oxygen index of the thigh vastus lateralis in 101 volunteers, who performed an incremental intensity exercise on bicycle ergometer. Among the volunteers, 42 are athletes, 25 are patients whose spleens are asthenic, and the other 34 are controls. Hemoglobin concentration (CtHb) measured was heavily influenced by the thickness of fattiness; however, regional oxygen saturation (rSO2) was influenced much lightly. In the experiment, following increasing exercise intensity of the volunteers, their CtHb increased, while their rSO2 decreased. When the volunteers stopped the exercise, both of their C1Hb and rSO2 increased quickly. The results showed that the regional saturation of oxygen of muscle was closely correlated with physical performance. The changes of regional saturation of oxygen of muscle can be used to evaluate the balance between supply and consumption of oxygen, and quantitatively assess the capability of oxidative metabolism in muscles.

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Based on the absorption spectra of hemoglobin and myoglobin in the near infrared band, the concentrations of these pigments in the biological tissues can be obtained using near infrared spectroscopy (NIRS) by detecting the intensity attenuation of the emitted light compared with the incident light. Based on the steady-state spatially resolved NIRS, the prototype for detecting the concentrations of tissue hemoglobin and myoglobin was independently developed by our group. The probe consisted of an LED light source which could emit three different wavelengths in the near infrared band, and two detectors which were placed on the same line with and at the distances of 30/40 mm to the LED. The pigment concentrations of two pieces of pork, one from the erector spinae and the other from the rectus femoris, were detected using this prototype. The total concentrations of hemoglobin and myoglobin (c(total)) were (6.42 + 1.51) micromol x L(-1) in the erector spinae, and (15.48 +/- 4.54) micromol x L(-1) in the rectus femoris, respectively. The myoglobin was dominant in both of the results. These were consistent with the recent empirical reports. In summary, the NIRS method and prototype are authentic in detecting the pigment concentrations of pork tissue non-invasively, real-time, directly and conveniently.

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An infrared thermogram which reflects the human body surface temperature distribution can be obtained through detecting the infrared thermal radiation from each point on the human body surface. When a malignant tumor occurs in a breast, it will cause an increase in the prominent temperature in the breast surface focus region due to the abnormal blood transmission state of local focus tissue. Breast cancer can be detected through the visual analysis of the focus regions by physicians. In order to help physicians better find these focus regions, the present paper improved the traditional pseudo color display method by introducing visual effect factor and made the focus regions have a better display effect. The efficacy of this method was verified in the breast infrared thermograms of 47 breast cancer patients. The result from visual analysis of the focus region in infrared thermogram by this method can also be compared with the tissue blood transmission state from near infrared spectroscopy (NIRS) and other methods. It will be helpful to obtain more accurate diagnostic information.

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Human tissue oxygen saturation (rSO2) can be monitored non-invasively and in real time by near infrared spectroscopy (NIRS) based on spatially-resolved spectroscopy. To expand the clinical applications of the NIRS oximeter developed by our group based on the above principle, the accuracy of rSO2 must be ensured and enhanced as far as possible. In the present paper, the influences of the probe configuration, especially the distance between the detectors and the wavelength discreteness of the light source, on the accuracy of rSO2 were discussed. The results indicate that (1) to obtain rSOz accurately, two detectors need to be used, where the distance between them should be in the range of 5-20 mm and they should be both at least 20 mm apart from the light source; (2) there can be significant error in rSO2 (> 10%) induced by the discreteness of the two emission wavelengths especially the shorter one of the light source, so the real emission wavelengths must be accurately measured and the corresponding extinction coefficients of deoxygenated and oxygenated hemoglobin (Hb and HbO2) must be used in order to avoid this error. The above conclusions can be the guidance to optimally design the probe, which has been achieved in our NIRS oximeter.

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As a non-invasive technique for measuring tissue oxygenation, near-infrared spectroscopy (NIRS) has increasing applications in detecting cerebral hypoxia-ischemia. The authors, introduced the basic principle of the NIRS oximeter developed independently by our group (TSAH-100). The authors achieved the optimal coupling between the probe and the detected cerebral tissue. The present study investigated different regional oxygen saturations of brain (rSO2) measured non-invasively by NIRS, arterial blood oxygen saturation (SaO2) measured invasively by blood gas analysis and physiological parameters in newborn pigs with different hypoxia, in order to prove if the non-invasively cerebral rSO2 can indicate cerebral oxygenation status in clinical practice. Using this oximeter, cerebral rSO2 of 28 newborn piglets under different oxygenation status was detected. After mechanical ventilation and inhalation of 8%-17% oxygen for 30 min in the newborn pigs, the pigs were grouped according to the inhalation of oxygen. With the inhalation of 13%-17% oxygen was mild hypoxia group, with 10%-13% was moderate hypoxia group, and with 8%-10% was severe hypoxia group. There were 4 animals in mild hypoxia group, 8 animals in moderate hypoxia group, 12 animals in severe hypoxia group and 4 animals were in the normal control group. The physiological parameters were monitored during the experiment. The SaO2 were invasively measured by blood gas analysis after the experiment. The results indicate that both rSO2 and SaO2 decreased after different degree of hypoxia and there was a good correlation between cerebral rSO2 non-invasively measured by NIRS and SaO2 invasively measured by blood gas analysis (p<0.001). Cerebral rSO2 was also consistent with the degree of hypoxia and the changes in physiological parameters after hypoxia. The arterial pH and the mean arterial pressure (MAP) in the severe hypoxia group was lower than that in the control group (p<0.05). The blood lactic acid in the severe hypoxia group was higher than that in the control group (p<0.05). Thus, the rSO2 can accurately and directly indicate cerebral oxygenation status and can also replace the SaO2 invasively measured by blood gas analysis. Cerebral hypoxia-ischemia can be non-invasively and conveniently diagnosed using NIRS.

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OBJECTIVE: To study correlation of brain hypoxia of different degrees with brain function and damage. METHODS: The brain regional oxygen saturation (rSO2) was determined by using a non-invasive near infrared spectroscopy (NIRS) technique in 15 piglets; the piglets were subjected to inhale 3% - 11% oxygen-nitrogen mixed gas through mechanical ventilation for 30 min. The piglets were divided into groups according to the level of brain rSO2 (i.e. < 30%, 30% - 35%, 35% - 40%, and 40% - 50%), and the data were compared with those of the control group (rSO2 > 60%). Changes of brain function were detected through amplitude and frequency of EEG waves and signal complexity. The piglets were sacrificed via decapitation 72 h after brain damage, and then histopathological and ultrastructural examinations were performed on cerebral cortex and hippocampal CA1 area. RESULTS: In the group with rSO2 > 40%, the mean arterial pressure (MAP) after hypoxia was (56 +/- 0.00) mm Hg (1 mm Hg = 0.133 kPa), the blood lactic acid (LA) was (2.3 +/- 1.2) mmol/L, the EEG findings were within normal range, and there was no change in brain tissue ultrastructure. In the group with brain rSO2 = 30% approximately 40%, the MAP was (73 +/- 8) mm Hg, the LA was (8.2 +/- 3.9) mmol/L, the EEG waves showed decreased amplitude, frequency and complexity, but restored to some extent after hypoxia. The brain tissue ultrastructure showed damages to the cerebral cortex and neuron mitochondria at hippocampal CA1 area. In the group with brain rSO2 < 30%, the MAP was (35 +/- 0) mm Hg, the LA was (12 +/- 2) mmol/L, the EEG showed decreased amplitude, frequency, and complexity of signals compared with those of the normal control group, and was difficult to restore after hypoxia in some of the piglets; the brain tissue ultrastructure appeared to be similar to the changes seen with high-degree swollen cerebral cortex and neuron mitochondria at hippocampal CA1 area. CONCLUSION: Different degrees of hypoxia had different influence on brain function and brain damage. The lower the brain rSO2, the more severe the damages to the brain and its function. The rSO2 of brain tissues detected with noninvasive NIRS can reflect brain injury and its severity during cerebral anoxia.

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The objective of this paper is to investigate the difference in physiological parameters, EEG and morphology of brain tissues in newborn pigs with different regional oxygen saturations of brain (rSO(2)) and provide a basis for the determination of brain injury and degree of injury with the rSO(2) in clinical practice. A noninvasive near-infrared spectroscopy (NIRS) technique was used to monitor the rSO(2) of 27 newborn pigs. After mechanical ventilation and inhalation of 3-11% oxygen for 30 min by the newborn pigs, the pigs were grouped according to the rSO(2) in the brain caused by inhalation of different concentrations of oxygen. There were six animals each in rSO(2) < 30%, 30-35%, 35-40%, 40-50% groups and three animals in the rSO(2) > 60% group (normal control). The physiological parameters and the EEG were monitored during the experiment. The animals were sacrificed by decollation at 72 hours after brain injury, and light microscope examination and pathological analysis of the ultrastructure were conducted on the brain tissues in the CA1 zone of hippocampi. In rSO(2) > 40% groups, the mean arterial pressure (MAP) was stable and there were no significant changes in blood lactic acid, amplitudes of the EEG, light microscopic findings and ultrastructure after hypoxia. When the rSO(2) was between 30% and 40%, the MAP was stable, the level of blood lactic acid increased, metabolic acidosis occurred, there was no significant change in the amplitudes of the EEG, there were ischemic changes in brain tissues under a light microscope and there was an injury of mitochondria in the neurons in the CA1 zone of hippocampi. When the rSO(2) was less than 30%, circulatory failure occurred, the level of blood lactic acid increased, there was serious metabolic acidosis, the amplitudes of the EEG significantly decreased, there were vacuolization and broken fragments of cells under the light microscope and the mitochondria in the neurons in the CA1 zone of hippocampi were seriously injured. Under varying degrees of hypoxia, when the rSO(2) is between 30% and 40%, brain injury occurs and the functional zones of mitochondria are injured in newborn pigs. When the rSO(2) is less than 30%, the brain functions are seriously abnormal, and the serious morphological impairment in the functional zones of mitochondria is the basis for the disturbance of energy metabolism in brain neurocytes after hypoxia and the sequelae of the nervous system.

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To avoid cerebral hypoxia caused by the imbalance between cerebral oxygen supply and consumption, regional cerebral oxygenation of patients need to be monitored at real time during cardiopulmonary bypass (CPB) surgery, and the physiological parameters can be regulated and emergent treatment can be used according to it. Using the near infrared (NIR) instrument developed by our group, cerebral oxygenation of the patients under cardiac surgery was monitored. The instrument consists of a two-wavelength near infrared light source and two near infrared detectors. Hemoglobin concentration changes of regional cerebral tissue were calculated, and by steady-state spatially resolved spectroscopy (SRS) algorithm, regional cerebral oxygen saturation (rSO2) was also calculated. Physiological parameters of patients, such as mixed venous oxygen saturation (SvO2), were measured by another monitor during CPB. Hemoglobin concentration changes were easily disturbed, but the anti-disturbance ability of rSO2 was good. The value of rSO2 could be detected all over the surgeries, but SvO2 could be detected only during CPB. There were positive correlations between rSO2 and SvO2 in most of the patients, but the correlation coefficients were not very high. This was because SvO2 reflects the saturation of the main venous, but rSO2 reflects regional cerebral oxygenation. So the physiological meaning of rSO2 and SvO2 is different. The results indicate that cerebral oxygenation of patients can be reflected by rSO2 during CPB, while only monitoring SvO2 is not enough.

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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 (C(tHb)) compared with its original value is also monitored. It is shown that C(tHb) 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.

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To enhance the student training and scientific research of biomedical engineering (BME) department of Tsinghua University, we investigated the top three universities on BME in US, which are John Hopkins University (JHU), Georgia Tech and Emory University (GTEU) and the Harvard & MIT Division of Health Science and Technology (HST). We also investigated the department of medical physics and bioengineering of University College London (UCL) in UK. According to the investigations, many useful experiences are obtained. In this paper, the following four aspects are specified: first, the research fields being concerned in biomedical engineering in the above universities; second, the characteristics of the training programs to the undergraduate and graduate students of BME in these universities; third, the experiences of these universities; fourth, the suggestions to us.

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Cerebral oxygenation especially regional cerebral oxygen saturation (rSO2) needs to be monitored to avoid irreversible damages induced by hypoxia. Based on steady-state spatially resolved spectroscopy (SRS), rSO2was obtained by the NIRS oximeter developed by our group. The oximeter was calibrated by blood gas analyzer using the liquid tissue model made up by our group. The results indicate that the correlation between rSO2and the real oxygen saturation of the model is excellent (R>0.99), and the influences by the background absorption and overlaying tissues are little. The rSO2of 14 patients were monitored during cardiopulmonary bypass (CPB) non-invasively by our oximeter. The results indicate that first, NIRS is almost the only available method to monitor rSO2non-invasively during CPB; second, rSO2is negatively correlated with body temperature and positively with blood perfusion rate, so it reflects the balance between cerebral oxygen supply and consumption; third, the low perfusion rate stage and the rewarming stage are relatively critical because rSO2decreases significantly and may be relatively low.