Department of Respiratory and Critical Care Medicine, Zhoupu Hospital, Shanghai University of Medicine and Health Sciences, 1500 Zhouyuan Road, Pudong New Area, Shanghai, 201318, China.
Laboratory Department, Zhoupu Hospital, Shanghai University of Medicine and Health Sciences, 1500 Zhouyuan Road, Pudong New Area, Shanghai, 201318, China.
BMC Pulm Med. 2024 Oct 9;24(1):498. doi: 10.1186/s12890-024-03294-1.
Large variations in respiratory system compliance and resistance may cause the accuracy of tidal volume (VT) delivery beyond the declared range. This study aimed at evaluating the accuracy of VT delivery using a test lung model to simulate pulmonary mechanics under normal or disease conditions.
In vitro assessment of the VT delivery accuracy was carried out on two commercial ventilators. Measurements of the inspired and expired VT from the ventilator and FlowAnalyser were compared to evaluate the separated and combined influences of compliance and resistance on the delivered VT accuracy. To do this, the errors of five delivered volumes (30 ml, 50 ml, 100 ml, 300 ml, and 500 ml) were checked under 29 test conditions involving a total of 27 combinations of resistance and compliance.
For the tested ventilator S1 with a flow sensor near the expiratory valve, the average of expired VT errors (ΔVTexp) in three measurements (4 test conditions for each measurement) correlated to test lung compliance (r=-0.96, p = 0.044), and the average of inspired VT errors (ΔVTins) correlated to compliance (r = 0.89, p = 0.106); for the tested ventilator S2 with a flow sensor located at the Y piece, no clear relationship between compliance and ΔVTexp or ΔVTins was found. Furthermore, on two ventilators tested, the current measurements revealed a poor correlation between test lung resistance and ΔVTins or ΔVTexp, and the maximum values of ΔVTexp and ΔVTins correspond to the maximum resistance of 200 cmHO/(L/s), at which the phenomenon of the flap fluttering in the variable orifice flow senor was observed, and the recorded peak inspiratory pressure (Ppeak) was much higher than the Ppeak estimated by the classical equation of motion. In contrast, at the lower resistance values of 5, 20, 50 and 100 cmHO/(L/s), the recorded Ppeak was very close to the estimated Ppeak. Overall, the delivered VT errors were in the range of ± 14% on two ventilators studied.
Depending on the placement site of the flow sensor in the ventilator circuit, the compliance and resistance of the test lung have different influences on the accuracy of VT delivery, which is further attributed to different fluid dynamics effects of the compliance and resistance. The main influence of compliance is to raise the peak inspiratory pressure Ppeak, thereby increasing the compression volume within the ventilator circuit; whereas a high resistance not only contributes to elevating Ppeak, but more importantly, it governs the gas flow conditions. Ppeak is a critical predictive indicator for the accuracy of the VT delivered by a ventilator.
呼吸系统顺应性和阻力的较大变化可能导致潮气量（VT）输送的准确性超出声明范围。本研究旨在使用测试肺模型评估 VT 输送的准确性，以模拟正常或疾病条件下的肺力学。
对两种商业呼吸机进行了 VT 输送准确性的体外评估。比较了呼吸机和 FlowAnalyser 测量的吸气和呼气 VT，以评估顺应性和阻力对输送 VT 准确性的单独和组合影响。为此，在总共 27 种顺应性和阻力组合的 29 种测试条件下，检查了五个输送量（30ml、50ml、100ml、300ml 和 500ml）的输送误差。
对于在呼气阀附近具有流量传感器的测试呼吸机 S1，在三个测量（每个测量四个测试条件）中，呼气 VT 误差（ΔVTexp）的平均值与测试肺顺应性相关（r=-0.96，p=0.044），并且吸气 VT 误差（ΔVTins）的平均值与顺应性相关（r=0.89，p=0.106）；对于在 Y 型件处具有流量传感器的测试呼吸机 S2，发现顺应性与 ΔVTexp 或 ΔVTins 之间没有明显关系。此外，在测试的两台呼吸机上，当前测量结果显示测试肺阻力与 ΔVTins 或 ΔVTexp 之间的相关性较差，并且 ΔVTexp 和 ΔVTins 的最大值对应于 200cmHO/（L/s）的最大阻力，在此观察到可变孔流量传感器中的瓣片飘动现象，并且记录的峰吸气压（Ppeak）远高于经典运动方程估计的 Ppeak。相比之下，在 5、20、50 和 100cmHO/（L/s）的较低阻力值下，记录的 Ppeak 非常接近估计的 Ppeak。总体而言，在研究的两台呼吸机上，输送的 VT 误差在±14%范围内。
根据呼吸机回路中流量传感器的放置位置，测试肺的顺应性和阻力对 VT 输送的准确性有不同的影响，这进一步归因于顺应性和阻力的不同流体动力学效应。顺应性的主要影响是提高峰吸气压 Ppeak，从而增加呼吸机回路内的压缩体积；而高阻力不仅有助于提高 Ppeak，更重要的是，它控制着气体流动条件。Ppeak 是预测呼吸机输送 VT 准确性的关键指标。
