Ravenscraft S A, Burke W C, Marini J J
University of Minnesota, Minneapolis.
Chest. 1992 May;101(5):1342-51. doi: 10.1378/chest.101.5.1342.
The linearly decelerating flow waveform for volume-cycled mechanical ventilation is an option on many modern ventilators. We have developed mathematical models for two available forms of volume-cycled decelerating-flow ventilation (VCDF). These equations use clinician-chosen ventilator settings as inputs (frequency, tidal volume, peak inspiratory flow or inspiratory time fraction, and end-inspiratory pause), and patient-determined inputs which describe the patient's ventilatory impedance (inspiratory [RI] and expiratory [RE] resistance and respiratory system compliance [C]. The equations predict key outcome variables: mean airway pressure; and peak, mean, and end-expiratory alveolar pressures. The mathematical expressions were validated in a mechanical lung analog. Values observed in the test lung were compared to values predicted by the mathematical models for a wide range of ventilator settings and impedance combinations (RI and RE, 5 to 40 cm H2O.s/L; C, 0.02 to 0.10 L/cm H2O). The correspondence between observed and predicted values was generally excellent across the broad range of inputs tested (r greater than or equal to 0.98). Outcome variables were quite sensitive to clinician-chosen inputs over certain critical ranges. Carefully applied, VCDF offers several theoretic advantages for the clinical setting; however, appropriate caution must be exercised to avoid the application of tissue-injuring pressure.
容量控制机械通气的线性减速气流波形是许多现代呼吸机的一种选择。我们已经为两种可用形式的容量控制减速气流通气（VCDF）开发了数学模型。这些方程将临床医生选择的呼吸机设置作为输入（频率、潮气量、吸气峰流速或吸气时间分数以及吸气末暂停），以及描述患者通气阻抗的患者确定输入（吸气[RI]和呼气[RE]阻力以及呼吸系统顺应性[C]）。这些方程预测关键结果变量：平均气道压；以及峰压、平均压和呼气末肺泡压。这些数学表达式在机械肺模拟器中得到了验证。将测试肺中观察到的值与数学模型针对广泛的呼吸机设置和阻抗组合（RI和RE，5至40 cm H2O·s/L；C，0.02至0.10 L/cm H2O）预测的值进行比较。在广泛测试的输入范围内，观察值与预测值之间的对应关系总体上非常好（r大于或等于0.98）。在某些关键范围内，结果变量对临床医生选择的输入非常敏感。谨慎应用时，VCDF在临床环境中具有一些理论优势；然而，必须谨慎行事以避免施加造成组织损伤的压力。
