Department of Physiology, University of Toronto, Toronto, Ontario, Canada Thornhill Research Inc., Toronto, Ontario, Canada.
Department of Anaesthesia, University Health Network, Toronto, Ontario, Canada.
Br J Anaesth. 2015 Mar;114(3):406-13. doi: 10.1093/bja/aeu377. Epub 2014 Dec 8.
Current non-invasive respiratory-based methods of measuring cardiac output [Formula: see text] make doubtful assumptions and encounter significant technical difficulties. We present a new method using an iterative approach [Formula: see text], which overcomes limitations of previous methods.
Sequential gas delivery (SGD) is used to control alveolar ventilation [Formula: see text] and CO2 elimination [Formula: see text] during a continuous series of iterative tests. Each test consists of four breaths where inspired CO2 [Formula: see text] is controlled; raising end-tidal Pco2 [Formula: see text] by about 1.33 kPa (10 mm Hg) for the first breath, and then maintaining [Formula: see text] constant for the next three breaths. The [Formula: see text] required to maintain [Formula: see text] constant is calculated using the differential Fick equation (DFE), where [Formula: see text] is the only unknown and is arbitrarily assumed for the first iteration. Each subsequent iteration generates measures used for calculating [Formula: see text] by the DFE, refining the assumption of [Formula: see text] for the next test and converging it to the true [Formula: see text] when [Formula: see text] remains constant during the four test breaths. We compared [Formula: see text] with [Formula: see text] measured by bolus pulmonary artery thermodilution [Formula: see text] in seven pigs undergoing liver transplantation.
[Formula: see text] implementation and analysis was fully automated, and [Formula: see text] varied from 0.6 to 5.4 litre min(-1) through the experiments. The bias (between [Formula: see text] and [Formula: see text]) was 0.2 litre min(-1) with 95% limit of agreement from -1.1 to 0.7 litre min(-1) and percentage of error of 32%. During acute changes of [Formula: see text], convergence of [Formula: see text] to actual [Formula: see text] required only three subsequent iterations.
[Formula: see text] measurement is capable of providing an automated semi-continuous non-invasive measure of [Formula: see text].
目前基于呼吸的无创心输出量测量方法[公式：见文本]存在可疑假设，并遇到重大技术困难。我们提出了一种新的方法，采用迭代方法[公式：见文本]，克服了以前方法的局限性。
顺序气体输送（SGD）用于控制肺泡通气[公式：见文本]和 CO2 消除[公式：见文本]在连续的一系列迭代测试中。每次测试包括四个呼吸，其中控制吸入 CO2[公式：见文本]；第一个呼吸时将呼气末 Pco2[公式：见文本]升高约 1.33 kPa（10 mmHg），然后在接下来的三个呼吸中保持[公式：见文本]恒定。使用差分式 Fick 方程（DFE）计算维持[公式：见文本]恒定所需的[公式：见文本]，其中[公式：见文本]是唯一的未知数，在第一次迭代时任意假设。每个后续迭代都会生成用于通过 DFE 计算[公式：见文本]的测量值，从而细化下一次测试中[公式：见文本]的假设，并在四次测试呼吸期间[公式：见文本]保持恒定时收敛到真实[公式：见文本]。我们比较了[公式：见文本]与通过肺动脉热稀释[公式：见文本]测量的[Formula: see text]在七只接受肝移植的猪中。
[公式：见文本]的实施和分析完全自动化，[公式：见文本]在实验过程中从 0.6 到 5.4 升/分钟变化。偏差（在[公式：见文本]和[公式：见文本]之间）为 0.2 升/分钟，95%一致性界限为-1.1 至 0.7 升/分钟，误差百分比为 32%。在[公式：见文本]的急性变化期间，只需三个后续迭代即可使[公式：见文本]收敛到实际[公式：见文本]。
[公式：见文本]测量能够提供一种自动化的半连续无创心输出量测量方法。
