Chinard F P, Cua W O
Am J Physiol. 1987 Feb;252(2 Pt 2):H340-8. doi: 10.1152/ajpheart.1987.252.2.H340.
In multiple indicator-dilution experiments, transvascular passage of a permeating indicator is conventionally derived from the up-slope separation of the curve of the permeating indicator from that of a vascular reference and is expressed as the extraction (Ec). Extraction may be limited by the barrier (barrier-limited distribution). It may be limited by the volume of distribution accessible to it; in the time domain of an indicator-dilution experiment, the passage to and distribution in the extravascular volume are rapid relative to the velocity of blood in the exchange vessels. We examine here the relations of the extraction of tracer water as tritium oxide (THO) [Ec(THO)] and of the extraction of tracer sodium as 22Na [Ec(22Na)] to extravascular lung water, delta V wev, by adding isotonic fluid to the gas phase of the lungs. The net convective transvascular passage of water is negligible relative to the transendothelial molecular exchange. In 10 experiments in vivo and in 10 experiments in isolated perfused lungs, Ec(THO) increases as delta V wev increases. Ec(22Na) and the permeability-surface area product (PS) for 22Na do not change as delta V wev increases. We conclude that the extraction of THO is determined mainly by the volume accessible to it (flow- or volume-limited distribution) and that the extraction of 22Na is determined mainly by the resistance of the endothelium (barrier-limited distribution). A diffusion limitation in the added alveolar fluid rather than a barrier limitation at the endothelium may moderate Ec(THO).
在多个指示剂稀释实验中，渗透指示剂的跨血管转运通常从渗透指示剂曲线与血管参考曲线的上坡分离中得出，并表示为提取率（Ec）。提取可能受屏障限制（屏障限制分布）。它可能受其可及分布容积的限制；在指示剂稀释实验的时域中，相对于交换血管中的血流速度，向血管外容积的转运和分布是快速的。我们在此通过向肺气相中添加等渗液体，研究作为氧化氚（THO）的示踪水的提取率[Ec(THO)]和作为22Na的示踪钠的提取率[Ec(22Na)]与血管外肺水（ΔVwev）的关系。相对于跨内皮分子交换，水的净对流跨血管转运可忽略不计。在10个体内实验和10个离体灌注肺实验中，Ec(THO)随ΔVwev增加而增加。Ec(22Na)和22Na的通透表面积乘积（PS）不随ΔVwev增加而变化。我们得出结论，THO的提取主要由其可及容积决定（流量或容积限制分布），而22Na的提取主要由内皮的阻力决定（屏障限制分布）。添加的肺泡液中的扩散限制而非内皮处的屏障限制可能会调节Ec(THO)。
