Role of whole body autoregulation in the control of blood pressure and sodium balance: insights from computer simulations with Guyton's model

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The concept of whole body blood flow autoregulation (WBFAR) has often been used to explain the increase in blood pressure (BP) in various models of salt‐loading hypertension. Computer simulations offer a unique way to test the role of WBFAR in achieving salt balance and BP control during salt‐loading since it is not possible to block WBFAR experimentally. Using Guyton's large circulatory model, we tested, in the presence or absence of WBFAR, the hemodynamic and fluid volume changes that occur after a 10‐fold increase in salt intake in three different situations: (A) normal neurohormonal modulation; (B) fixed circulating angiotensin II at a normal level; (C) full neurohormonal blockade (fixed angiotensin, aldosterone and ANP, and fixed autonomic output). In the presence of WBFAR, BP after salt‐loading remained stable in situation A, but increased by ~10 mmHg in situation B, and by ~30 mmHg in situation C. Even then, changes in cardiac output (CO) and blood volume (BV) were minimal (less than 4% and 2%, respectively). In the absence of WBFAR, the same simulations led to similar changes in BP. However, a nearly twofold increase in CO and an increase in BV by more than 20% were required to achieve salt‐balance in situation C. From the simulations one may conclude that autoregulation limits the amount of fluid retention required to increase BP in order to achieve salt balance during salt‐loading, but does not affect the final level of BP.