Mechanism of gravity-depend atelectasis : Analysis by nouradioactive xenon-euhance dynamic CT

肺容量减少和浅呼吸导致肺背侧进行性肺不张（重力依赖性肺不张：GDA）。我们建立了GDA动物模型（Invest Radiol 24: 522, 1989）。本研究的目的是确定气道阻塞是否是GDA的关键因素。方法：对10只家兔进行高频振荡通气（HFOV）下50%离子放射性氙氧动态吸入CT扫描。时间- ct值曲线为。-假设描述为指数函数，C=C_o(1-e^<-Kt>)（Kety模型）。K值等于肺泡通气量/肺泡容积，用re. gres计算。锡安的分析。1 .实验组（n=5）采用10 cmH_2人工气腹缩小肺容量，对照组（n=5）不采用气腹。两组均放置HFOV 6小时，每1小时计算K值。结果：实验组均形成GDA。在多尔地区。氙的清洗。在GDA出现前K值升高，而腹侧区K值变化不明显。对照组没有发现——gda’和K值在两个区域都没有变化。结论：GDA为。与肺泡通气量/肺泡容积比增加有关。这一结果表明GDA不是由其引起的。通过气道阻塞。通过这个程序，我们可以。在动脉氧压下降或降低前诊断GDA。CT图像检测。

Reduction, in lung volume and shallow breathing produce progressive atelectasis in the dorsal lung(gravity-dependent atelectasis : GDA). We have developed an animal model of GDA(Invest Radiol 24 : 522, 1'989). The purpose of this study is to determine whether airway occlusion is a key factor for GDA.Methods : Dynamic inhalation CT was performed in ten rabbits, using 50%'iionradioactive xenon in oxygen on high frequency oscillatory ventilation(HFOV). Time-CT value curves were. -assumed to be described as exponential function, C=C_o(1-e^<-Kt>)(Kety's model). K value, which is equal to alveolar ventilation /alveolar volume, was calculated with re. gres. sion analysis. I. n experimental group(n=5)lung volume was reduced with artificial pneumoperitoneus of 10 cmH_2, while control group(n=5)did not have pneuxoperitoneum. Both groups were placed on HFOV for six hours and K values were calculated every one hour.Results : In all of the experimental group GDA was formed. In the dorial regions. wash-in of xenon. was observed and' K values increased just before GDA appeared'' Meanwhile K values in the ventral regions did not change significantly. The control group did not reveal-GDA'and K values did not change in either region.Conclusions : GDA is. related to the increase in alveolar ventilation /alveolar volume ratio. This result suggests that GDA is not caused. by airway occlusion. By means of this procedure-we can. diagnose GDA before"' the decrease in arterial oxygen pressure or. detection on CT images.