Photoinduced Electron Spin Resonance Phenomenon in α

The photoinduced phenomenon in α-Cr2O3 nanoscaled spherical particles was investigated in the temperature range of 150 up to 315 K. An X-band electron-spin resonance spectrometry was employed to probe the magnetic behavior in α-Cr2O3 under an IR illumination in the nanosecond regime. The photoinduced effect on both low and high field ESR signals appears above 280 K and is remarkably enhanced just below Néel temperature TN. Such a photoinduced ESR phenomenon disappears in a reproducible way in the paramagnetic insulating state which occurs above TN of crystalline α-Cr2O3. In the antiferromagnetic phase, that is, below TN, the shift of the low field absorption could be attributed to the interaction of the light with specific Cr3+ ions located in strongly distorted sites correlated to strong ligand-field effect

Application of fiberoptic sensors for the study of hepatic dysoxia in swine hemorrhagic shock

OBJECTIVES: To determine whether the simultaneous measurement of tissue pH, Pco2, and Po2 with a multiple-parameter fiberoptic sensor can be used to indicate the onset of hepatic dysoxia, to determine critical values, and to assess their use in predicting negative outcomes. DESIGN: Prospective animal study. SETTING: University research laboratory. SUBJECTS: Fourteen Yorkshire swine. INTERVENTIONS: Hemorrhagic shock (n = 11) was induced over 15 mins to lower systolic blood pressure to 40 mm Hg and was maintained for 30, 60, or 90 mins. Resuscitation was achieved with shed blood and warm saline to maintain mean pressure \u3e60 mm Hg for 120 mins. Sham animals (n = 3) were subjected to 90 mins of sham shock, followed by a 120-min recovery period. MEASUREMENTS AND MAIN RESULTS: The multiple-parameter sensor continuously measured tissue pH, Pco2, and Po2. pH and Pco2, indicators of anaerobic metabolism, were plotted against tissue Po2. All shocked animals, but no sham animals, showed a biphasic relationship between Po2 and both pH and Pco2. Curves were fit to both an exponential and a dual-line linear function to determine critical values for Po2, pH, and Pco2. The length of time the animal was dysoxic was evaluated as a predictor of negative outcome. Critical values determined from the exponential models were more sensitive indicators of negative outcome than values determined from the linear model and more sensitive than arterial lactate and tonometric intramucosal pH and Pco2. CONCLUSIONS: The multiple-parameter sensor offers the unique opportunity to study solid as well as hollow organ dysoxia through the simultaneous measurement of interstitial pH, Pco2, and Po2 in a small tissue region. The gradual transition from sufficient oxygen availability to dysoxia as a result of hemorrhage was better described by an exponential equation. The length of time that pH was below or Pco2 was above the critical value determined from the exponential model was predictive of a negative outcome

Simultaneous measurement of hepatic tissue pH, venous oxygen saturation and hemoglobin by near infrared spectroscopy

The purpose of this study was to investigate the feasibility of using near infrared (NIR) spectroscopy of the liver to simultaneously assess oxygen content in combination with tissue pH, an indicator of anaerobic metabolism. Six anesthetized swine were subjected to 45 min of hemorrhagic shock followed by resuscitation with blood and crystalloid. Calibration models between NIR spectra and reference measurements of tissue pH, hepatic venous oxygen saturation (S(V)O2), and blood hemoglobin concentration (Hb) were developed using partial least-squares regression. Model accuracy was assessed using cross validation. The average correlation (R2) between NIR and reference measurements was 0.87, 0.68, and 0.93, respectively for pH, Hb, and S(V)O2. Estimated accuracy, the root mean squared deviation between spectral, and reference measurements was 0.03 pH units, 0.3 g/dL, and 6%. NIR determination of hepatic oxygen content and tissue pH during shock and resuscitation demonstrated that there can be a variance between hepatic venous oxygenation and regional tissue acidosis. NIR spectroscopy provides a technique to explore the implications of post-shock depression of tissue pH and evaluate new methods of resuscitation