Second, we found that approximately one in three individuals have relatively low tolerance to reduced central blood volume [19]. These ‘low tolerant’ individuals demonstrated a physiology that was characterized by attenuated responses in tachycardia, peripheral vasoconstriction, sympathetic nerve activity, cardiac vagal withdrawal, and oscillations in blood pressure and cerebral blood flow [20, 21]. The identification of specific physiological signals that distinguish those patients at highest risk for early development of shock is one of the most fundamental observations that need to be considered in any assessment of advanced decision support and care for acute emergency settings.