Breen P H
Department of Anesthesiology, University of California-Irvine, UCI Medical Center, Orange 92868, USA.
J Clin Monit Comput. 1998 May;14(4):265-70. doi: 10.1023/a:1009923904917.
We have previously shown in a mechanical lung model [1] that bronchial flap-valve expiratory obstruction results in sequential lung expiration, best detected by prolonged and low magnitude tracheal expired flow (V) from the obstructed lung. However, the normal expiratory resistance of clinical ventilation circuits might also generate prolonged, low value exhaled V, that could be confused with bronchial flap-valve obstruction. We reasoned that bronchial flap-valve obstruction would also cause sequential CO2 unloading from each lung and result in a biphasic tracheal capnogram.
To test this hypothesis, we ventilated (VT, 650 ml; f, 10 br/min) a dual mechanical test lung, with each side connected to a separate alcohol-burning chamber. An airway adapter-monitor system measured airway V, P, PCO2, and FO2. The circumference of the diaphragm in a respiratory one-way valve was trimmed to generate unidirectional resistance to expiratory V. Measurement sequences were repeated after this flap-valve was interposed in the left "main-stem bronchus."
During moderate or severe left bronchial flap-valve obstruction, left bronchial V was delayed so that the left lung anatomical dead space (devoid of CO2) mixed with normal right exhalate to depress the expiratory upstroke or early plateau of the tracheal capnogram. During severe obstruction, decreased perfusion of the left lung caused lower alveolar PCO2. Then, prolonged low V from the left bronchus also resulted in depression of the end of the tracheal alveolar plateau. In general, the low magnitude of bronchial V from the obstructed lung limited its effect on the tracheal capnogram and the best marker of sequential lung emptying during bronchial flap-valve obstruction may be late exhaled V without reduction in total tidal volume.
我们之前在一个机械肺模型中表明[1]，支气管瓣阀呼气阻塞会导致肺的顺序性呼气，这通过阻塞肺延长且幅度较小的气管呼气流量（V）最易检测到。然而，临床通气回路的正常呼气阻力也可能产生延长的、低值的呼出V，这可能与支气管瓣阀阻塞相混淆。我们推断支气管瓣阀阻塞也会导致每个肺的顺序性二氧化碳排出，并导致双相气管二氧化碳图。
为了验证这一假设，我们对一个双机械测试肺进行通气（潮气量，650毫升；频率，10次/分钟），每一侧连接到一个单独的酒精燃烧室。一个气道适配器监测系统测量气道V、压力、二氧化碳分压和氧分压。呼吸单向阀中隔膜的周长被修剪以产生对呼气V的单向阻力。在这个瓣阀插入左“主支气管”后重复测量序列。
在中度或重度左支气管瓣阀阻塞期间，左支气管V延迟，使得左肺解剖死腔（不含二氧化碳）与正常的右呼出物混合，从而压低气管二氧化碳图的呼气上升支或早期平台。在严重阻塞期间，左肺灌注减少导致肺泡二氧化碳分压降低。然后，来自左支气管的延长的低V也导致气管肺泡平台末期压低。一般来说，阻塞肺的支气管V幅度较低，限制了其对气管二氧化碳图的影响，支气管瓣阀阻塞期间肺顺序排空的最佳标志可能是呼出后期的V，而总潮气量不减少。
