The Scaling of Blood Pressure and Volume

The cardiovascular system is an apparatus of mass convection, and changes in organismic size impart changes in variables of this system, namely scaling effects. Blood flow depends on pressure and conductance, and the maintenance of flow results in entropy production, that is, loss of available work. In terms of scaling, it is well known that blood pressure is kept constant while blood volume varies linearly with body mass. Yet, such expected rules have never been proven. The present study shows that these scaling rules derive from the simultaneous optimization of blood flow and entropy production in circulation and how these impact the transition from ecto- to endotermy. Thus, for the first time in almost a century of data collection, these observed relationships are explained from a theoretical standpoint. The demonstration presented herein is a building block to form a solid basis for the other scaling rules of the cardiovascular system as well as of other organic systems. The approach is of wide interest in any area where generalized flow is analyzed in terms of system optimization, giving a broad perspective on change in either engineered or naturally evolving systems.