Institutionen för klinisk vetenskap / Department of Clinical Sciences
Abstract
Optimization of peritoneal dialysis schedule and dialysis fluid
composition needs, among others, methods for quantitative assessment of
fluid and solute transport. Furthermore, an integrative quantitative
description of physiological processes within the tissue, which
contribute to the net transfer of fluid and solutes, is necessary for
interpretation of the data and for predictions of the outcome of possible
intervention into the peritoneal transport system. The current project
includes the investigations of 1) the effectiveness of crystalloid
osmotic agents in evoking ultrafiltration from blood, 2) the impact of
ultrafiltration on protein transport, 3) the evaluation of the role of
perfusion in the peritoneal transport, and 4) the integration of the
physiological data about transport characteristics of the capillary wall,
the tissue, and lymphatic absorption for the description of the net
peritoneal transport, using the methods of mathematical modeling.
Three different methods were tested for the estimation of fluid transport
parameters. All three provided good description of the data, however some
differences were found, especially in time dependence of the parameters
during a single dwell study. The effectiveness of glucose as an osmotic
agent, evaluated as osmotic conductance, were much lower in the patients
with permanent ultrafiltration capacity (UFC) loss related to the
increased transport of small solutes than in stable patients on
continuous ambulatory peritoneal dialysis (CAPD). In contrast, patients
with permanent UFC loss related to the increased absorption of fluid from
the peritoneal cavity bad similar osmotic conductance as stable patients.
A discriminative impact of ultrafiltration on peritoneal transport of
albumin, [beta]2-microglobulin, and total protein, was found in stable
patients on CAPD: in some patients sieving coefficients for the proteins
were high and the initial increase of the protein concentration in
dialysate was fast; in another group, with low sieving coefficients for
the proteins, and the increase of the protein concentration in dialysate
was slow. No difference in the diffusive mass transport coefficients for
the proteins and small solutes, neither for fluid transport, between
these two groups of patients was found.
The perfusion rate of the tissue with blood was included into the
distributed model of peritoneal transport. It was shown that changes of
perfusion rate during a single dwell study, which might be induced by
vasodilatory effect of dialysate, could explain the time - dependence of
the diffusive mass transport coefficients (described previously). The
model could also explain why the estimations of the effective peritoneal
blood flow yielded much different values for gases and than for small
solutes.
Transport characteristics for the capillary wall, the tissue, and the
rate of lymphatic absorption from the tissue, were incorporated into the
distributed model, to provide an integrated mathematical description of
diffusive and convective transport of solutes of any size. The
phenomenological transport parameters, diffusive mass transport parameter
and sieving coefficient, the solute penetration depth, and effective
peritoneal blood flow, were described as functions of the local,
physiological parameters of the peritoneal transport system