Konyukov Y, Takahashi T, Kuwayama N, Hotta T, Takezawa J, Shimada Y
Intensive Care Unit, Nagoya University Hospital, Japan.
Chest. 1994 Jun;105(6):1836-41. doi: 10.1378/chest.105.6.1836.
Work of breathing necessary to trigger a ventilator (WOBtr) was calculated during pressure support ventilation (PSV), and the effect of bias flow on WOBtr was evaluated. A spring-loaded bellows type lung model with two bellows placed in series was used to simulate spontaneous breathing. A Venturi mechanism of jet flow generated subatmospheric pressure inside the diaphragm bellows simulated inspiratory effort. The lung compliance (CL) was set at 0.3 L/cm H2O or 0.05 L/cm H2O. The airway resistance (Raw) was set at 5, 20, or 50 cm H2O/L/s. Pressure support levels were increased from 0 to 45 cm H2O. Sensitivity was set at 2 cm H2O. No bias flow was used at first. The WOBtr was calculated using a pressure-volume (P-V) loop derived from the diaphragm bellows movement during the triggering period. We determined WOBtr and its dependence on the various pressure support (PS) levels, CL and Raw. To evaluate the effects of bias flow on WOBtr and triggering delay, a ventilator was put in the PSV mode, with various bias flow rates (from 0 to 20 L/min) at a sensitivity of 2 cm H2O. We found that when no bias flow was used, WOBtr increased with an increase in both Raw and end-expiratory lung bellows pressure which was considered as auto-PEEP. With bias flow, both triggering delay and WOBtr increased. An increase in bias flow at a given PS level resulted in both decreased pressure support time and tidal volume (VT). It is concluded that the bias flow system is not desirable for use during PSV.
在压力支持通气（PSV）期间计算触发呼吸机所需的呼吸功（WOBtr），并评估偏流对WOBtr的影响。使用两个串联波纹管的弹簧加载波纹管式肺模型来模拟自主呼吸。射流的文丘里机制在隔膜波纹管内产生低于大气压的压力，模拟吸气努力。肺顺应性（CL）设定为0.3 L/cm H2O或0.05 L/cm H2O。气道阻力（Raw）设定为5、20或50 cm H2O/L/s。压力支持水平从0增加到45 cm H2O。灵敏度设定为2 cm H2O。起初不使用偏流。使用触发期间隔膜波纹管运动得出的压力-容积（P-V）环计算WOBtr。我们确定了WOBtr及其对各种压力支持（PS）水平、CL和Raw的依赖性。为了评估偏流对WOBtr和触发延迟的影响，将呼吸机置于PSV模式，在灵敏度为2 cm H2O时设置各种偏流率（从0到20 L/min）。我们发现，当不使用偏流时，WOBtr随着Raw和呼气末肺波纹管压力（被视为内源性呼气末正压）的增加而增加。使用偏流时，触发延迟和WOBtr均增加。在给定的PS水平下，偏流增加导致压力支持时间和潮气量（VT）均降低。得出的结论是，在PSV期间使用偏流系统是不可取的。
