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.

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.

Photoacoustic spectroscopy provides information about both the amplitude and phase of the response of a system to an optical excitation process. This paper presents a theoretical model of photoacoustic processes in the frequency domain which includes the relaxation time of the radiationless deexcitations and a two-layer absorbing system. Emphasis is placed on the effect of these conditions on the phase of the photoacoustic signal and the utility of this measurement in evaluating material parameters. Circumstances under which the phase may be used to measure the optical absorption coefficient of the solid and the nonradiative relaxation times are defined. The value of the phase measurement in the study of surface films is discussed.

No abstract

No abstract