呼吸中枢驱动增加时呼吸力学改变以及对吸气开始信号的影响

目的探讨呼吸中枢增加所造成的呼吸力学改变及其对吸气开始信号的影响。方法以10例正常志愿者为研究对象,采用CO2重复呼吸的方法,使呼气末CO2分压(PCO2-ET)增高到最大耐受水平,观察呼吸中枢驱动增加时的呼吸力学和吸气开始时相关信号的动态变化。结果正常志愿者重复呼吸试验最大可以耐受的PCO2-ET值为(81.2±6.6)mm Hg。随着PCO2-ET逐渐升高,膈肌肌电图的均方根(RMSdi)、跨膈压(Pdi)和潮气量(VT)进行性增高,而呼吸周期(Ttot)逐渐缩短,PCO2-ET水平从基础值PCO2-ET(level-0)]到最大值PCO2-ET(level-4)],RMSdi从(17.17±12.41)μV增加到(147.99±161.64)μV,Pdi和VT分别由(7.5±1.7)cm H2O和(0.68±0.27)L增加到(26.13±11.51)cm H2O和(2.21±0.37)L,而Ttot从(2.91±0.85)s减少到(1.92±0.39)s,RMSdi、Pdi、VT和Ttot与PCO2-ET的动态变化呈高度线性相关(r值分别为0.956、0.973、0.956和0.89,P均<0.001)。吸气开始时,最早出现吸气信号改变为RMSdi,其次为口腔压(Pm),再次为吸气流量(Flow);随着PCO2-ET增加,Pm和Flow滞后于RMSdi的时间逐渐延长,而Flow滞后于Pm的时间不变。结论膈肌肌电图信号的出现先于其他吸气相关信号,随着呼吸中枢驱动的增加,传统的吸气同步信号口腔压和吸气流量滞后于膈肌肌电图时间延长,提示膈肌肌电图可作为更加敏感的吸气开始的信号,可以用于呼吸机的人机同步触发,改善同步性,尤其是适合在中枢驱动异常增高的条件下。

Changes of Respiratory Mechanics in Response to Elevated Respiratory Central Drive and their Impact on Initiation Signal of Inspiration in Normal Adult Volunteers

Objective To investigate the changes of respiratory mechanics in response to elevated respiratory central drive and their impacts on the inspiratory signals detection. Methods 10 normal volunteers were recruited for the study from the colleagues of the State Key Laboratory of Respiratory Disease. Rebreathing method was used to increase the end expiratory PCO2 （PCO2-ET） to the subject＇s maximal tolerance in order to stimulate the increase of respiratory central drive. The changes of respiratory mechanics in response to elevated respiratory central drive and their impacts on the initiation signals of inspiration were observed. Results After re-breathing, the average maximal tolerated PCO2-ET was （81.2 ± 6. 6 ） mm Hg. As the PCO2-ET rising, electromyogram of diaphragmatic muscle （ RMSdi ） , transdiaphragmatic pressure （Pdi） and tidal volume （V_T ） increased progressively while the time of respiratory cycle （T_tot ） shorten gradually. As the PCO2-ET level increased from baseline PCO2-ET_（level-0）] to the maximal level PCO2-ET（level-4）], RMSdi increased from（ 17.17 ± 12. 41 ）μV to （ 147.99± 161.64） μV, Pdiand V_T increased from （7.5±1.7） cmH2O and （0.68_＋0.27）L to （26. 13 ±11.51）cm H2O and （2.21±0.37） L respectively, while T_tot shorten from （2.91±0.85）sto （1.92±0.39）s. Thesefourparameters of respiratory mechanics, RMSdi, Pdi, V_T and T_tot were highly correlated linearly with PCO2-ET （ r value was 0. 956,0. 973,0. 956 and 0. 89 respectively, all P 〈 0. 001 ）. At the start of inspiration, the first detectable signal was electromyogram of diaphragmatic muscle （RMSdi） ,followed by mouth pressure （Pm） and inspiratory flow （Flow） on time sequence. As the rising of PCO2-ET,the time lag of Pm and Flow from RMSdi after the initiation of inspiration increased gradually. However, the time lag between Flow and Pm remained constant. Conclusions At the siart of inspiration, the signal of RMSdi appears first as compared with Pm and Flow. As the rising of PCO2-ET, the time lag of Pm and Flow from RMSdi after the initiation of inspiration increased gradually, suggesting RMSdi is more sensitive inspiratory signal, which might be used for triggering of ventilator in order to improve the synchronization, especially in the situation of elevated respiratory central drive.