Breen P H, Serina E R, Barker S J
Department of Anesthesiology, University of California at Irvine Medical Center, Orange, CA 92613, USA.
Anesth Analg. 1995 Aug;81(2):292-6. doi: 10.1097/00000539-199508000-00014.
Flap-valve obstruction to expiratory flow (V) in a major bronchus can result from inspissated secretions, blood, or foreign body. During inhalation, increasing airway caliber preserves inspired V past the obstruction; during exhalation, decreasing airway diameter causes airflow obstruction and even frank gas trapping. We reasoned that the resultant sequential, biphasic exhalation of the lungs would be best detected by measuring exhaled V versus time. Accordingly, we designed an airway obstruction element in a mechanical lung model to examine flap-valve bronchial obstruction. A mechanical lung simulator was ventilated with a pressure-limited flow generator, where f = 10/min, tidal volume = 850 mL, and respiratory compliance = 40 mL/cm H2O. Airway V (pneumotachometer) and pressure (P) were digitally sampled for 1 min. Then, 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 right "main-stem bronchus." Integration of airway V versus time generated changes in lung volume. During flap-valve obstruction of the right bronchus, the V-time plot revealed preservation of peak expired flow from the normal lung, followed by retarded and decreased flow from the obstructed right lung. Gas trapping of the obstructed lung occurred during conditions of decreased expiratory time and increased expiratory resistance. Airway P could not differentiate between bronchial and tracheal flap-valve obstruction because P decreased abruptly in both conditions. The flow-volume loop displayed less distinctive changes than the flow-time plot, in part because the flow-volume loop was data (flow) plotted against its time integral (volume), with loss of temporal data. In this mechanical lung model, we conclude that bronchial flap-valve obstruction was best detected by the flow-time plot, which could measure the sequential emptying of the lungs.
主支气管中瓣状瓣膜导致的呼气气流（V）阻塞可由黏稠分泌物、血液或异物引起。在吸气过程中，气道管径增大可使吸入气流越过阻塞部位；而在呼气过程中，气道管径减小会导致气流阻塞，甚至出现明显的气体潴留。我们推测，通过测量呼气V随时间的变化，能够最好地检测出肺部由此产生的连续性双相呼气情况。因此，我们在机械肺模型中设计了一个气道阻塞元件，以研究瓣状瓣膜引起的支气管阻塞。使用压力限制型流量发生器对机械肺模拟器进行通气，其中f = 10次/分钟，潮气量 = 850毫升，呼吸顺应性 = 40毫升/厘米水柱。对气道V（呼吸流速计）和压力（P）进行1分钟的数字采样。然后，修剪呼吸单向阀中隔膜的周长，以产生对呼气V的单向阻力。在右“主支气管”中插入该瓣状瓣膜后，重复测量序列。对气道V随时间的积分产生肺容积变化。在右支气管瓣状瓣膜阻塞期间，V - 时间图显示正常肺的呼气峰值流速得以保留，随后阻塞的右肺流速延迟且降低。在呼气时间缩短和呼气阻力增加的情况下，阻塞肺出现气体潴留。气道P无法区分支气管和气管瓣状瓣膜阻塞，因为在这两种情况下P均会突然下降。流量 - 容积环显示的变化不如流量 - 时间图明显，部分原因是流量 - 容积环是将数据（流量）与其时间积分（容积）进行绘制，时间数据丢失。在这个机械肺模型中，我们得出结论，通过流量 - 时间图能最好地检测出支气管瓣状瓣膜阻塞，该图可测量肺部的顺序排空情况。
