无创通气下应用强迫振荡技术检测呼吸阻力

目的 构建强迫振荡测量系统,在无创正压通气(NPPV)条件下检测人呼吸系统阻抗(Rrs)和电抗(Xrs),用于评估肺阻力(RL)和弹件阻力(EL).方法 基于现有的强迫振荡技术,构建包括振荡发生器和信号分析软件在内的新强迫振荡测量系统,采用呼吸系统一阶线性力学模型(R-I-E模型)验证新系统测量的准确性和可靠性.8例健康正常人为研究对象,分别经鼻罩给予不同水平的双水平气道止压(BiPAP)和持续气道正压(CPAP)通气,探讨在不同通气模式和压力水平下利用Rrs无创评价R,的可行性.结果 (1)振荡压力和振荡流量的相干函数系数值r2=0.98,强迫振荡测量可靠.5 Hz强迫振荡测定的模型阻抗与模型的粘性阻力接近,两者平均相差(1.26±0.44)cm H2O·s·L-1,一敛性范嗣在(0.36～2.14)cm H2O·s·L-1.(2)8例在不同通气模式及压力条件下测定的Rrs值大小接近,与RL平均相差(0.16±1.58)cm H2O·s·L-1.RL的预计方程式为RL=1.40+0.77Rrs,[决定系数(r2)=0.43,P<0.01].(3)强迫振荡弹性阻力EFOT(EFOT=-2πfXrs)显著大于实际值EL,(P<0.01).两者存在低水平的相关(r=0.40,P<0.01).结论 新强迫振荡系统测量准确、可靠.Rrs近似地反映了RL的大小,RL预测值可用于优化NPPV的压力支持水平,使呼吸机提供的压力支持能有效地克服肺阻力.

Application of the forced oscillation technique for assessment of respiratory mechanical properties during noninvasive ventilation

Objective To construct a new forced oscillatory measuring system to detect resistance (Rrs) and reactance (Xrs) of patients'respiratory system for evaluation of lung resistance(RL) and elastance (EL) during noninvasive positive pressure ventilation (NPPV). Methods A new forced oscillatory measuring system including an oscillatory generator and a signal analysis procedure based on established forced oscillatory technique (FOT) and algorithm was constructed for measurement of oscillatory Rrs and Xrs. A resistance-inertance-elastance (R-I-E) model mimicing normal respiratory system was adopt to test measuring accuracy and reliability of the FOT measuring system. In addition, 8 healthy volunteers were enrolled and subjected to a bi-level positive airway pressure(BiPAP) and continuous positive airway pressure (CPAP) ventilator through a nasal mask respectively. 5 Hz forced oscillation was imposed and the feasibility was approached using Rrs at different NPPV modes and pressure levels for each subject to evaluate RL noninvasively. Results (1) The coherence function r2 of oscillatory pressure and flow was 0.98 which confirmed the reliability of FOT measuring system. The mean values of 5 Hz forced oscillatory resistance of the R-I-E model was close to its true viscous resistance value, with a mean difference of (1.26 ± 0. 44) cm H2O·s·L-1,the limits of agreement was (0.36-2.14)cm H2O·s·L-1.(2)The mean value of Res (8 cases) measured by FOT at different NPPV pressure level was proximal,the mean difference between Rrs and RL was (0.16+1.58)cm H2O·s·L-1.The linear regression equation of RL from Rrs was Rl=1.40 + 0.77Rrs(r2 =0.43, P<0.01). (3)The mean value of elastance measured by FOT (EFOT = -2πfXrs) was significantly higher than EL (P < 0. 01) , the degree of correlation between them was low (r =0. 40, P < 0. 01). Conclusion The newly constructed FOT measuring system is of accuracy and reliability for assessment of respiratory mechanical properties during NPPV, Rrs can approximately reflect the size of RL, and therefore, helpful for optimization of NPPV pressure support, then, eliminating RL of pressure support from ventilator effectively.