In order to clarify the relationship between the blood flow rate (QB) and transmembrane pressure (TMP) during hemodialysis (HD) or pre-dilution on-line hemodiafiltration (OHDF), blood pressure was measured at the blood inlet (PBi), blood outlet (PBo), dialysate inlet (PDi), and dialysate outlet (PDo) of dialysis membranes. The QB was gradually increased from 100 mL/min to 250 mL/min, while the dialysate flow rate was kept at 500 mL/min. During pre-dilution OHDF, the substitution flow rate was 18 L/hour. TMP was calculated from PBi, PBo (or its mean) and PDi, or PDo (or its mean) using 5 different formulas. The calculated TMP values varied according to the formula used. In HD, TMP decreased as the QB increased, regardless of which formula was used. In pre-dilution OHDF, TMP increased in parallel with the QB when the PBi-based TMP formula was used, while it decreased as the QB increased when the other formulas were employed. Our findings suggest that the inclusion of PBi in formulas for calculating TMP could be essential for estimating the effect of QB on TMP, as increasing the QB caused a pressure loss across the blood side of the filter. In HD, increasing the QB might result in a greater shear rate, which could account for the observed reduction in TMP. In pre-dilution OHDF, the concentration of the cells and protein in blood might increase the TMP.

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【Introduction】Matrix stones are a rare form of urinary tract calculi, and they are very difficult to definitively diagnose using conventional diagnostic imaging techniques. We report a case in which urinary tract matrix stones led to a suspicion of urinary tract tumors in a patient on maintenance hemodialysis. 【Case report】A 63-year-old man had been on maintenance hemodialysis for 34 months because of end-stage chronic kidney disease caused by diabetes mellitus nephropathy. He developed asymptomatic gross hematuria. Computed tomography detected hydronephrosis due to a tumor in the right upper ureter. Magnetic resonance imaging demonstrated tumors in the right renal pelvis and right upper ureter. Retroperitoneoscopic right nephroureterectomy was performed. However, instead of tumorous lesions, black-colored calculi were observed in the renal pelvis and ureter. Histopathologically, the resected specimen showed regenerative and hyperplastic epithelial changes without malignancy. An analysis of the calculi indicated that the matrix stones were entirely composed of protein. 【Conclusion】Clinicians should consider the possibility of matrix stones when a ureteral tumor is suspected on conventional diagnostic images in patients on maintenance hemodialysis.

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