Mason G R, Peters A M, Myers M J, Hughes J M
Department of Medicine, Royal Postgraduate Medical School, Hammersmith Hospital, London W12 ONN, United Kingdom.
J Appl Physiol (1985). 1998 Mar;84(3):1103-7. doi: 10.1152/jappl.1998.84.3.1103.
Measurement of the clearance rate of inhaled aerosols of 99mTc-diethylenetriamine pentaacetic acid (DTPA) from distal airway to pulmonary capillary is a sensitive technique for the detection of lung injury. As the solute diffuses across the blood-gas barrier, the concentration in circulating blood increases, giving rise to a background signal superimposed on the signal from residual DTPA in the airway. Background subtraction is conventionally based on the thigh, but this tissue has the disadvantage in that its composition, in terms of the relative volumes of its extracellular extravascular and intravascular compartments (a ratio of approximately 4:1), is quite different from that of the lung (<1:6). With comparison to the thigh, we examined alternative regions for background, liver, and cranium, which have extravascular-to-intravascular compartment ratios much closer to these for the lung, to determine the most appropriate background for correction of the pulmonary signal. From 1 min after intravenous injection of 99mTc-DTPA, the time-activity curves recorded by a gamma camera over the liver and lung in a group of otherwise normal cigarette smokers decreased up to 30 min after injection, with time courses that could essentially be superimposed on each other; the curve recorded over the thigh with a separate scintillation probe continued to increase. The curve recorded over the cranium had a time course similar to that for the liver and lung. Following aerosol inhalation, the lung clearance rates over the initial 7 min when background subtraction was used, based on the liver, cranium, and thigh were, respectively, 4.9 +/- 2.9, 4.7 +/- 2. 6, and 5.4 +/- 3.4 (SD) %/min, compared with 4.1 +/- 2.2%/min without subtraction. The corresponding values based on 30 min of data were 3.3 +/- 1.4, 3.4 +/- 1.4, 4.2 +/- 2.3, and 2.8 +/- 1. 0%/min. When the liver was used for background, the lung clearance curves were clearly multiexponential, whereas thigh correction tended to give curves that were monoexponential or even convex upward on semilogarithmic axes. With an appropriate region for background, the true shape of a lung curve can be identified, which permits the study of an intervention on the clearance while it is in progress. The intravenous DTPA, required for calibrating the background regions, can be given before inhalation of the tracer.
测量99mTc-二乙烯三胺五乙酸（DTPA）吸入气雾剂从远端气道到肺毛细血管的清除率是检测肺损伤的一种敏感技术。当溶质扩散穿过血气屏障时，循环血液中的浓度会增加，从而在气道中残留DTPA的信号上叠加一个背景信号。传统上背景扣除是基于大腿，但该组织存在缺点，即其细胞外血管外和血管内隔室的相对体积组成（比例约为4:1）与肺（<1:6）有很大不同。与大腿相比，我们研究了替代的背景区域，肝脏和颅骨，它们的血管外与血管内隔室比例与肺的比例更接近，以确定校正肺部信号的最合适背景。在静脉注射99mTc-DTPA后1分钟，一组原本正常的吸烟者中，γ相机记录的肝脏和肺部的时间-活性曲线在注射后30分钟内下降，其时间进程基本可以相互叠加；用单独的闪烁探头记录的大腿曲线持续上升。颅骨上记录的曲线时间进程与肝脏和肺部相似。吸入气雾剂后，当基于肝脏、颅骨和大腿进行背景扣除时，最初7分钟内的肺清除率分别为4.9±2.9、4.7±2.6和5.4±3.4（标准差）%/分钟，而不进行扣除时为4.1±2.2%/分钟。基于30分钟数据的相应值分别为3.3±1.4、3.4±1.4、4. ±2.3和2.8±1.0%/分钟。当使用肝脏作为背景时，肺清除曲线明显呈多指数形式，而用大腿校正往往会得到单指数曲线，甚至在半对数轴上向上凸出的曲线。有了合适的背景区域，可以识别肺曲线的真实形状，这使得在清除过程中研究干预措施成为可能。校准背景区域所需的静脉注射DTPA可以在吸入示踪剂之前给予。
