Hotchkiss John R, Adams Alexander B, Stone Mary K, Dries David J, Marini John J, Crooke Philip S
Section of Pulmonary and Critical Care and Section of Surgery, Regions Hospital and University of Minnesota, St. Paul, Minnesota 55101, USA.
Am J Respir Crit Care Med. 2002 Jan 1;165(1):47-53. doi: 10.1164/ajrccm.165.1.2101025.
Pressure support ventilation (PSV) is almost universally employed in the management of actively breathing ventilated patients with acute respiratory failure. In this partial support mode of ventilation, a fixed pressure is applied to the airway opening, and flow delivery is monitored by the ventilator. Inspiration is terminated when measured inspiratory flow falls below a set fraction of the peak flow rate (flow cutoff); the ventilator then cycles to a lower pressure and expiration commences. We used linear and nonlinear mathematical models to investigate the dynamic behavior of pressure support ventilation and confirmed the predicted behavior using a test lung. Our mathematical and laboratory analyses indicate that pressure support ventilation in the setting of airflow obstruction can be accompanied by marked variations in tidal volume and end-expiratory alveolar pressure, even when subject effort is unvarying. Unstable behavior was observed in the simplest plausible linear mathematical model and is an inherent consequence of the underlying dynamics of this mode of ventilation. The mechanism underlying the observed instability is "feed forward" behavior mediated by oscillatory elevation in end-expiratory pressure. In both mathematical and mechanical models, unstable behavior occurred at impedance values and ventilator settings that are clinically realistic.
压力支持通气（PSV）几乎普遍应用于急性呼吸衰竭且正在接受通气治疗的自主呼吸患者的管理。在这种部分支持通气模式中，向气道开口施加固定压力，呼吸机监测气流输送情况。当测得的吸气气流低于峰值流速的设定比例（气流截断）时，吸气终止；然后呼吸机切换到较低压力，呼气开始。我们使用线性和非线性数学模型研究压力支持通气的动态行为，并使用测试肺证实了预测行为。我们的数学和实验室分析表明，即使患者用力不变，在气流阻塞情况下进行压力支持通气时，潮气量和呼气末肺泡压力也可能出现显著变化。在最简单的合理线性数学模型中观察到了不稳定行为，这是这种通气模式潜在动力学的固有结果。观察到的不稳定现象的潜在机制是由呼气末压力的振荡升高介导的“前馈”行为。在数学模型和机械模型中，不稳定行为均出现在临床实际的阻抗值和呼吸机设置下。
