High-flow nasal cannula versus noninvasive ventilation after extubation in hypercapnic patients with COPD:A retrospective analysis

To the Editor:Invasive ventilation is a necessary form of respiratory support in the intensive care unit.Noninvasive ventilation(NIV)is frequently used as a sequential respiratory support following extubation in patients with acute exacerbation of chronic obstructive pulmonary disease(AECOPD)to prevent the recurrence of respiratory failure,avoid reintubation,and improve the prognosis.[1]However,some patients may have a poor tolerance to NIV.

重载机车与102车钩系统的相互作用关系

针对某型重载机车与102型车钩,对102型车钩在直线与曲线上的稳钩机理及其与重载机车的相互作用关系进行了理论分析,并运用建立的双机重联动力学模型,计算分析了重载机车与102车钩系统在直线、曲线上的动态运行性能.结果表明:在直线上,当纵向压钩力增加时,车钩挡肩能够限制车钩偏转,维持机车-车钩系统的稳定,使得机车车体与转向架相对位移以及轮轴横向力基本保持不变;在曲线上,连挂车钩后端处车体与车钩的相对转角大于前端,将造成连挂车钩后端挡肩先与前从板发生接触,而前端仍处在自由角范围内,且曲线半径越小,使连挂车钩后端前从板达到临界转动状态的纵向压钩力越大.机车通过400, 800 m半径曲线时,随着纵向压钩力的增加,连挂车钩后端处轮轴横向力随之增大,而前端处轮轴横向力随之减小;机车通过300 m半径曲线时,机车车体与前转向架二系止挡发生刚性接触,随着纵向压钩力的增加,连挂车钩后端处轮轴横向力明显增大,而前端处轮轴横向力基本保持不变.