MEASUREMENT OF INTERNAL FILTRATION (IF) FLOW RATE IN HIGH FLUX DIALYZERS BY DOPPLER ULTRASONOGRAPHY

Abstract

In an effort to improve solute removal efficiency, several types of dialyzers with enhanced IF were developed and introduced for clinical applications. In these dialyzers, enhanced IF increased convective transport of the solute in addition to diffusive transport. In a paper published in the ASAIO Journal 2000(46:456–460), we reported the effects of IF on solute removal efficiency of the dialyzer during an analytical and an experimental study. The IF flow rate (QIF) was not, however, measured in the experimental study. Instead it was estimated in the analytical simulation. Herein, the QIF value was measured by doppler ultrasonography. Average blood flow rate (QBav) at a cross-sectional plane was measured by pulse doppler and the longitudinal QBav profile along the dialyzer was obtained using a probe slider that can move the probe in parallel along the dialyzer. Two types of cellulosic triacetate membrane dialyzers (FB-150F and FB150IF) with the same surface area of 1.5 m2 were produced by Nissho Corp., Japan and used in the experimental study. In order to enhance IF, the FB-150IF dialyzer has a smaller inner diameter (ID) (135 μn) than the FB-150F dialyzer (200 μm). Dialysis experiments using bovine blood at 41 % of hematocrit were carried out to measure the QIF values in these dialyzers. Moderate IF was observed at the halfway point of the dialyzer in FB-150F; Qif of 14.3 and 16.7 ml/mm were obtained under inlet blood flow rates (QBI) of 200 and 400 ml/min, respectively. These values were nearly equal to the values reported by Dr. Ronco's group using gamma camera detection. On the other hand, the FB-150IF as relatively high QIF values, 50.0 and 63.2 ml/min at Qbi of 200 and 400 ml/min, respectively. The IF in FB-150IF was induced by a steeply increasing pressure drop on the blood side. The doppler ultrasonography is useful for measuring IF in several dialyzers because it is noninvasive for the patient and produces reliable data with higher reappearance.