Search

Liquid nitrogen (LN2), which can greatly improve the efficiency of hot dry rock (HDR) mining, is commonly used as a cooling material in the enhanced geothermal system (EGS). Physical property, triaxial compression, and permeability tests were undertaken on treated granite samples, for a better scientific understanding of the effect of the LN2 cooling method on the mechanical and permeability properties of the rocks after heat treatment. The experimental results indicated that the physical properties of the treated granite change significantly, such as the density and wave velocity are substantially reduced. Meanwhile, with the increase of treatment temperature, the macroscopic cracks on its surface are gradually generated and the volume is expanded clearly. In addition, the surface wettability of granite gradually increases with increasing temperature. Compared with the air/water cooling methods, under LN2 cooling condition, the mechanical properties decrease markedly. When the temperature exceeds 600°C, the granite strength decreases significantly to only 56.16% of the reference value. The deformation properties also change significantly, with a final strain of about 3% at failure for a sample at 800°C, showing an obvious ductile deformation characteristic. Further, an appreciable correlation also exists between the initial permeability of granite and temperature. Once the temperature exceeds 200°C, the increase in temperature contributes to the increase in initial permeability. In addition to the effect of temperature, the increase in load also leads to a change in the permeability coefficient. When the temperature reaches 600°C, the permeability of granite first decreases and then increases with the increases in axial stress. The results of this paper are valuable in understanding the effect of thermal shock by LN2 on the fracturing efficiency and permeability characteristics of dry hot rocks.

Objectives: To establish an optimized airway management process to improve preoperative lung dysfunction in obstructive sleep apnea (OSA). Design: A retrospective case series study Setting: Tertiary university hospital in China Participants: The study included 483 children (319 males and 164 females; 6y to14y years) with OSA who underwent an adenotonsillectomy from November 2017 to December 2018. Main outcome measures: Children with OSA and who had abnormal airway function were identified by lung function test, and the risk factors for abnormal lung function were assessed. Next, the children received individualized atomization intervention based on the severity of their abnormal lung function, and the improvement in lung function was evaluated. Results: Lung function tests revealed that 45 patients had obstructive ventilation dysfunction, and histories of chronic cough or asthma were identified as risk factors for perioperative abnormal lung function. The FEV1% pre exceeded 80% after 2 days of atomization intervention in 27 of 28 mild cases, 4 of 13 moderate cases, but in none of the 4 moderate-severe cases. After 4 days of atomization intervention, the FEV1%pre of the remaining 14 patients in the three groups all increased up to 80%. Other indicators of lung function (e.g., FEV1/FVC% pre, MEF50% pre, MEF25% pre, and MMEF% pre) were also greatly improved following the improvement of FEV1% pre. No perioperative airway complications occurred. Conclusion: Prior to performing surgery on children with OSA and who have risk factors associated with abnormal lung function, it is potentially beneficial to establish an optimized airway management process to improve lung function before adenotonsillectomy. Keywords: Children, obstructive sleep apnea, airway management, lung function, surgical risk

Objectives To establish an optimized airway management process to improve preoperative lung dysfunction in obstructive sleep apnea (OSA). Methods The study included 483 children (319 males and 164 females; 6y to14y years) with OSA who underwent an adenotonsillectomy from November 2017 to December 2018. Children with OSA and who had abnormal airway function were identified by lung function test, and the risk factors for abnormal lung function were assessed. Next, the children received individualized atomization intervention based on the severity of their abnormal lung function, and the improvement in lung function was evaluated. Results Lung function tests revealed that 45 patients had obstructive ventilation dysfunction, and histories of chronic cough or asthma were identified as risk factors for perioperative abnormal lung function. The FEV1% pre exceeded 80% after 2 days of atomization intervention in 27 of 28 mild cases, 4 of 13 moderate cases, but in none of the 4 moderate-severe cases. After 4 days of atomization intervention, the FEV1%pre of the remaining 14 patients in the three groups all increased up to 80%. Other indicators of lung function (e.g., FEV1/FVC% pre, MEF50% pre, MEF25% pre, and MMEF% pre) were also greatly improved following the improvement of FEV1% pre. No perioperative airway complications occurred. Conclusions Prior to performing surgery on children with OSA and who have risk factors associated with abnormal lung function, it is potentially beneficial to establish an optimized airway management process to improve lung function before adenotonsillectomy.