In a recent issue of The Journal of Physiology, Averina et al. (2012) present a new model of circulatory control. The model as presented appears to be founded on an unsupported assumption - namely that sodium balance can be described as a first-order control system with fixed parameters regardless of the level of circulating angiotensin II. The model assumes (their eqn (6)) that the rate of excretion of sodium, FSe> and the rate of intake, .FSI, have the fixed relationship:
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