Energy transfer is the single most important factor for the difference in vascular response between isolated ultrafiltration and hemodialysis.

Differences in vascular reactivity between isolated ultrafiltration (i-UF) and hemodialysis (UF + HD) have been attributed to various factors, including differences in core temperature (CT) and energy transfer (ET). However, the relative importance of these thermal factors is not known. The aim of this study was to elucidate to what extent differences in ET are responsible for the divergent vascular response between i-UF and UF + HD. During four different dialysis treatments in 15 patients, four measurements were performed that consisted of 1 h of i-UF, UF + HD at a dialysate temperature (T(d)) of 37.5 degrees C (UF + HD(37.5)), UF + HD at T(d) 35.5 degrees C (UF + HD(35.5)), and UF + HD with a similar ET as during i-UF(UF + HD(ET-set)). The UF rate in all sessions was 1 L/h. CT ( degrees C) decreased significantly during i-UF and UF + HD(ET-set) (P < 0.05), increased significantly during UF + HD(37.5) (P < 0.05), and remained unchanged during UF + HD(35. 5) (NS). Forearm vascular reactivity increased significantly during i-UF, UF + HD(ET-set), and UF + HD(35.5) (P < 0.05), but not during UF + HD(37.5) (NS). Venous tone increased significantly during i-UF, UF + HD(35.5), and UF + HD(ET-set) (P < 0.05), and decreased significantly during UF + HD(37.5) (P < 0.05). When i-UF and UF + HD are matched for ET, all differences in vascular response disappear, showing that differences in ET are the single most important factor for the observed difference in vascular response between i-UF and UF + HD. In contrast to UF + HD(37.5), vascular reactivity was improved when the increase in CT was prevented during UF + HD(35.5) and appeared to increase more when CT was lowered. Preventing the increase in CT during UF + HD appears to be mandatory for optimization of hemodynamic stability during dialysis.