Mathematical modelling of thermal and circulatory effects during hemodialysis

Intradialytic hypotension (IDH) is one of the most common complications of hemodialysis (HD) treatment. The initiating factor of IDH is a decrease in blood volume which is related to an imbalance between ultrafiltration (UF) and refilling rate. Impaired reactivity of resistance and capacitance vessels in reaction to hypovolemia plays possibly a major role in the occurrence of IDH. These vessels also fulfill an important function in body temperature regulation. UF induced cutaneous vasoconstriction would result in a reduced surface heat loss and an increase in core temperature. To release body heat, skin blood flow (SBF) is increased at a later stage of the HD treatment, whereby possibly IDH can occur. Aim of the study is to develop a mathematical model which can provide insight into the impact of thermoregulatory processes on the cardiovascular system during HD treatment. The mathematical procedure has been created by coupling a thermo-physiological (TP) model with a cardiovascular (CV) model to study regulation mechanisms in the human body during HD+UF. Model simulations for isothermal vs. thermoneutral HD+UF were compared to measurement data of patients on chronic intermittent HD (n=13). Core temperature during simulated HD+UF sessions increased within the range of measurement data (0.23ºC vs. 0.32±0.41ºC). The model showed a decline in mean arterial pressure (MAP) of -7% for thermoneutral HD+UF versus -4% for isothermal HD+UF after 200 minutes during which relative blood volume (RBV) changed by -13%. In conclusion, simulation results of the combined model show possibilities for predicting circulatory and thermal responses during HD+UF.