Ronco C, Brendolan A, Feriani M, Milan M, Conz P, Lupi A, Berto P, Bettini M, La Greca G
Department of Nephrology, St. Bortolo Hospital, Vicenza, Italy.
Kidney Int. 1992 May;41(5):1383-93. doi: 10.1038/ki.1992.203.
Ultrafiltration and pressure profiles in hollow fiber dialyzers with different hydraulic permeabilities have been investigated with a new scintigraphic method. Radiolabelled albumin macroaggregates, used as a nondiffusible marker molecule, were added to the blood in an in vitro circuit and circulated through cuprophan and polysulphon dialyzers. Since the marker molecule was too big to cross the dialysis membrane, its changes in concentration were assumed to occur in response to the variation of the blood water content (filtration or back-filtration). These changes in concentration, recorded by a gamma camera, were evaluated to establish the cumulative values of filtration and back-filtration and their relevant profiles along the length of the dialyzer. The achieved data were compared with the experimental values of ultrafiltration empirically measured and with the theoretical values predicted by a classic linear method. Two conditions were analyzed: A) the minimal filtration rate necessary to avoid back-filtration (critical filtration); and B) the condition of zero net filtration in which filtration equals back-filtration. The nuclear method proved to be extremely precise in predicting the ultrafiltration values and significantly more precise than the linear method, especially for the highly permeable dialyzer. The reason for that probably depends on the non-linear pressure and ultrafiltration profile observed with the scintigraphic pattern of the dialyzer. Viscosity changes and local variations in blood flow may in fact interfere with the pressure drop inside the hollow fibers and result in such a complex behavior. The other interesting aspect of this method is the possibility of accurate measurement of the amount of back-filtration that wouldn't be possible with simple calculations. In conclusion, the complex nature of the phenomena regulating the water fluxes in hollow fiber dialyzers requires more complex calculation than a simple linear model to achieve an accurate range of predictability.
采用一种新的闪烁扫描法研究了具有不同水力渗透性的中空纤维透析器中的超滤和压力分布情况。将用作非扩散性标记分子的放射性标记白蛋白大聚体添加到体外循环的血液中，并使其通过铜仿膜和聚砜膜透析器循环。由于标记分子太大无法穿过透析膜，因此假定其浓度变化是对血液含水量变化（超滤或反超滤）的响应。通过γ相机记录的这些浓度变化经过评估，以确定超滤和反超滤的累积值及其沿透析器长度的相关分布。将获得的数据与经验测量的超滤实验值以及经典线性方法预测的理论值进行比较。分析了两种情况：A）避免反超滤所需的最小过滤速率（临界过滤）；B）净过滤为零的情况，即过滤等于反过滤。事实证明，核方法在预测超滤值方面极其精确，并且比线性方法精确得多，尤其是对于高渗透性透析器。其原因可能取决于通过透析器的闪烁扫描模式观察到的非线性压力和超滤分布。实际上，粘度变化和血流的局部变化可能会干扰中空纤维内部的压降，并导致这种复杂的行为。该方法的另一个有趣之处在于能够精确测量反超滤量，而这通过简单计算是无法实现的。总之，调节中空纤维透析器中水通量的现象具有复杂性，需要比简单线性模型更复杂的计算才能实现准确的预测范围。
