During our experiences with total body perfusion, using extracorporeal heart-lung bypass, we noted unexplained variations in the response of peripheral vascular resistance to standard test doses of vasomotor drugs. Further experimentation was performed using the mature dog and our heart-lung bypass apparatus designed previously for the study of the role of the pulse in maintenance of the systemic circulation.12 The arterial inflow to the animal was a continuous, pulseless, gravity perfusion at an essentially constant blood pressure. The present experiments are predicated on the following concepts: (1) Peripheral vascular tone is defined as the effective state of constriction or dilation of the peripheral vascular tree during a given steady state perfusion; it can be described by the ratio of the measured blood pressure and flow. (2) Peripheral vascular reactivity is defined as the change in the pressure-flow ratio following the introduction of some stimulus, such as a vasomotor drug.
FRIES CC, FRIES AM, WESOLOWSKI SA. Peripheral Vascular Tonus and ReactivityIndependent Variables. Arch Surg. 1963;86(1):13-21. doi:10.1001/archsurg.1963.01310070015003