Modarreszadeh M, Kump K S, Chizeck H J, Hudgel D W, Bruce E N
Department of Biomedical Engineering, Case Western Reserve University, Ohio 44106.
J Appl Physiol (1985). 1993 Nov;75(5):2003-12. doi: 10.1152/jappl.1993.75.5.2003.
We have designed and implemented a computer-controlled system that uses an adaptive control algorithm (generalized minimum variance) to buffer the breath-by-breath variations of the end-tidal CO2 fraction (FETCO2) that occur spontaneously or are exaggerated in certain experimental protocols (e.g., induced hypoxia, any type of induced variations in the ventilatory pattern). Near the end of each breath, FETCO2 of the following breath is predicted and the inspired CO2 fraction (FICO2) of the upcoming breath is adjusted to minimize the difference between the predicted and desired FETCO2 of the next breath. The one-breath-ahead prediction of FETCO2 is based on an adaptive autoregressive with exogenous inputs (ARX) model: FETCO2 of a given breath is related to FICO2, FETCO2 of the previous breath, and inspiratory ventilation. Adequacy of the prediction is demonstrated using data from experiments in which FICO2 was varied pseudorandomly in wakefulness and sleep. The algorithm for optimally buffering changes in FETCO2 is based on the coefficients of the ARX model. We have determined experimentally the frequency of FETCO2 variations that can be buffered adequately by our controller, testing both spontaneous variations in FETCO2 and variations induced by hypoxia in young awake human subjects. The controller is most effective in buffering variations of FETCO2 in the frequency range of <0.1 cycle/breath. Some potential applications are discussed.
我们设计并实现了一种计算机控制系统，该系统使用自适应控制算法（广义最小方差）来缓冲呼气末二氧化碳分数（FETCO2）的逐次呼吸变化，这些变化在某些实验方案中（例如，诱导性缺氧、任何类型的通气模式诱导变化）会自发出现或被放大。在每次呼吸接近尾声时，预测下一次呼吸的FETCO2，并调整即将到来的呼吸的吸入二氧化碳分数（FICO2），以最小化预测的下一次呼吸的FETCO2与期望的FETCO2之间的差异。FETCO2的提前一步预测基于带有外部输入的自适应自回归（ARX）模型：给定呼吸的FETCO2与FICO2、前一次呼吸的FETCO2和吸气通气量有关。使用清醒和睡眠状态下FICO2伪随机变化的实验数据证明了预测的充分性。用于最佳缓冲FETCO2变化的算法基于ARX模型的系数。我们通过实验确定了我们的控制器能够充分缓冲的FETCO2变化频率，对年轻清醒人类受试者中FETCO2的自发变化和缺氧诱导的变化都进行了测试。该控制器在缓冲频率范围小于0.1次呼吸/周期的FETCO2变化时最为有效。文中还讨论了一些潜在应用。
