Solway J, Rossing T H, Saari A F, Drazen J M
J Appl Physiol (1985). 1986 Jun;60(6):2071-8. doi: 10.1152/jappl.1986.60.6.2071.
Dynamic hyperinflation of the lungs occurs during high-frequency oscillatory ventilation (HFOV) and has been attributed to asymmetry of inspiratory and expiratory impedances. To identify the nature of this asymmetry, we compared changes in lung volume (VL) observed during HFOV in ventilator-dependent patients with predictions of VL changes from electrical analogs of three potential modes of impedance asymmetry. In the patients, when a fixed oscillatory tidal volume was applied at a low mean airway opening pressure (Pao), which resulted in little increase in functional residual capacity, progressively greater dynamic hyperinflation was observed as HFOV frequency, (f) was increased. When mean Pao was raised so that resting VL increased, VL remained at this level during HFOV as f was increased until a critical f was reached; above this value, VL increased further with f in a fashion nearly parallel to that observed when low mean Pao was used. Three modes of asymmetric inspiratory and expiratory impedance were modeled as electrical circuits: 1) fixed asymmetric resistance [Rexp greater than Rinsp]; 2) variable asymmetric resistance [Rexp(VL) greater than Rinsp, with Rexp(VL) decreasing as VL increased]; and 3) equal Rinsp and Rexp, but with superimposed expiratory flow limitation, the latter simulated using a bipolar transistor as a descriptive model of this phenomenon. The fixed and the variable asymmetric resistance models displayed a progressive increase of mean VL with f at either low or high mean Pao. Only the expiratory flow limitation model displayed a dependence of dynamic hyperinflation on mean Pao and f similar to that observed in our patients. We conclude that expiratory flow limitation can account for dynamic pulmonary hyperinflation during HFOV.
肺动态过度充气发生在高频振荡通气（HFOV）期间，其原因被认为是吸气和呼气阻抗的不对称。为了确定这种不对称的本质，我们比较了依赖呼吸机的患者在HFOV期间观察到的肺容积（VL）变化与三种潜在阻抗不对称模式的电模拟对VL变化的预测。在患者中，当在低平均气道开口压力（Pao）下施加固定的振荡潮气量时，功能残气量几乎没有增加，随着HFOV频率（f）增加，观察到动态过度充气逐渐加重。当平均Pao升高以使静息VL增加时，在HFOV期间随着f增加，VL保持在该水平，直到达到临界f；高于该值时，VL随着f进一步增加，其方式几乎与使用低平均Pao时观察到的平行。将三种吸气和呼气阻抗不对称模式建模为电路：1）固定不对称电阻[Rexp大于Rinsp]；2）可变不对称电阻[Rexp（VL）大于Rinsp，且Rexp（VL）随着VL增加而减小]；3）Rinsp和Rexp相等，但有叠加的呼气流量限制，后者使用双极晶体管作为该现象的描述模型进行模拟。固定和可变不对称电阻模型在低或高平均Pao时均显示平均VL随着f逐渐增加。只有呼气流量限制模型显示动态过度充气对平均Pao和f的依赖性与我们在患者中观察到的相似。我们得出结论，呼气流量限制可以解释HFOV期间的动态肺过度充气。
