Impact of the nature of the capillary wall on plasma refilling during hemodialysis.

Objectives: Our aim was to clarify the impact of the nature of the capillary wall, defined by the contribution of large (LP), small (SP), and ultrasmall (UP) pores, on plasma refilling in a hemodialysis session.

Methods: This study included data from 78 patients. The relative blood volume change (ΔBV%) was monitored using a Crit-Line monitor. A bioimpedance device was used to measure extracellular and intracellular fluid volumes, and the excess fluid mass (M) was calculated. We simulated blood volume change (sΔBV%) based on a three-pore model. Hydraulic permeability of the capillary wall (LpS) and fractional contribution of LP to LpS (α) were determined by fitting sΔBV to ΔBV. The total refilling volume (TV) was calculated from the total ultrafiltration volume and total blood volume change. Values were standardized to a body surface area of 1.73 m and are denoted by the subscript BSA.

Results: LpS and α were 3.09 (2.32, 4.68) mL/mmHg/min and 0.069 (0.023, 0.109), respectively. The standardized regression coefficient (β) of the ultrafiltration rate (UFR) and initial excess fluid mass (M,) by multiple linear regression analysis of TV without (Model 1) and with (Model 2) α were as follows: UFR, 0.714/<0.001 (β/p); M,, 0.247/<0.001 (Model 1); UFR, 0.799/<0.001; M,, 0.066/0.237; and α, -0.327/<0.001 (Model 2).

Conclusions: The impact of volume overload (M,) on plasma refilling became insignificant with the addition of α in the model, suggesting that the nature of the capillary wall described by inter-endothelial gaps (LP) may have a greater impact on plasma refilling than volume overload.